Materiały źródłowe

• #1 Lactose Intolerance – StatPearls – NCBI Bookshelf

  https://www.ncbi.nlm.nih.gov/books/NBK532285/

  Lactose intolerance is a clinical syndrome that manifests with characteristic signs and symptoms upon consuming food substances containing lactose, a disaccharide. Normally upon lactose consumption, it is hydrolyzed into glucose and galactose by the lactase enzyme, which is found in the small intestinal brush border. Deficiency of lactase due to primary or secondary causes results in clinical symptoms. […] Lactase enzyme deficiency can occur in individuals with lower levels of this enzyme, resulting in failure to hydrolyze lactose into absorbable glucose and galactose components. There are four leading causes of lactase deficiency. […] The lactase enzyme is located in the brush border of the small intestinal mucosa. Deficiency of lactase results in the presence of unabsorbed lactose within the bowel. This results in an influx of fluid into the bowel lumen resulting in osmotic diarrhea. Colonic bacteria ferment the unabsorbed lactose-producing gas (hydrogen, carbon dioxide, and methane), which hydrolyzes lactose into monosaccharides. This results in an additional influx of fluid within the lumen. The overall effect of these mechanisms results in various abdominal signs and symptoms.

• #2 Lactose Intolerance: Background, Pathophysiology, Etiology

  https://emedicine.medscape.com/article/187249-overview

  Lactose intolerance is a common disorder and is due to the inability to digest lactose into its constituents, glucose and galactose, secondary to low levels of lactase enzyme in the brush border of the duodenum. […] Lactase deficiency is the most common form of disaccharidase deficiency. […] A deficiency of intestinal lactase prevents hydrolysis of ingested lactose. The osmotic load of the unabsorbed lactose causes secretion of fluid and electrolytes until osmotic equilibrium is reached. Dilation of the intestine caused by the osmosis induces an acceleration of small intestinal transit, which increases the degree of maldigestion. Within the large intestine, free lactose is fermented by colonic bacteria to yield short-chain fatty acids and hydrogen gas. […] The combined increase in fecal water, intestinal transit, and generated hydrogen gas accounts for the wide range of gastrointestinal symptoms.

• #3 Lactose Intolerance in Adults: Biological Mechanism and Dietary Management

  https://pmc.ncbi.nlm.nih.gov/articles/PMC4586575/

  Lactose intolerance related to primary or secondary lactase deficiency is characterized by abdominal pain and distension, borborygmi, flatus, and diarrhea induced by lactose in dairy products. […] The biological mechanism and lactose malabsorption is established and several investigations are available, including genetic, endoscopic and physiological tests. […] Lactose intolerance depends not only on the expression of lactase but also on the dose of lactose, intestinal flora, gastrointestinal motility, small intestinal bacterial overgrowth and sensitivity of the gastrointestinal tract to the generation of gas and other fermentation products of lactose digestion. […] About two thirds of the Worlds population undergoes a genetically programmed decrease in lactase synthesis after weaning (primary lactase deficiency).

• #4

  https://link.springer.com/article/10.1007/s42399-021-00792-9

  Lactose intolerance is a pathology frequently encountered today. It occurs when the activity of lactase in the intestine is reduced or absent, with consequent failure to digest lactose. The absence of lactase determines both the excessive osmotic load in the small intestine and the fermentation of lactose by the bacterial flora with consequent production of short-chain fatty acids and gas. This latter process is responsible for the onset of symptoms associated with lactose intolerance (abdominal pain, bloating, flatulence, etc.) which arise after the intake of lactose. […] A deficiency of lactase leads to a reduction in the absorption of lactose present in the intestinal tract and this can cause the appearance of the symptoms. First, the excessive osmotic load increases the intestinal water content. Second, lactose is readily fermented by the colonic microbiome leading to production of short-chain fatty acids and gas (mainly hydrogen – H2 -, carbon dioxide – CO2 -, and methane – CH4 -).

• #5 Update on lactose malabsorption and intolerance: pathogenesis, diagnosis and clinical management | Gut

  https://gut.bmj.com/content/68/11/2080

  Lactase deficiency (LD) is the failure to express the enzyme that hydrolyses lactose into galactose and glucose in the small intestine. […] Lactose malabsorption (LM) refers to any cause of failure to digest and/or absorb lactose in the small intestine. This includes primary genetic and also secondary LD due to infection or other conditions that affect the mucosal integrity of the small bowel. […] Lactose intolerance (LI) is defined as the onset of abdominal symptoms such as abdominal pain, bloating and diarrhoea after lactose ingestion by an individual with LM. The likelihood of LI depends on the lactose dose, lactase expression and the intestinal microbiome. […] Independent of lactose digestion, patients with visceral hypersensitivity associated with anxiety or the Irritable Bowel Syndrome (IBS) are at increased risk of the condition.

• #6 Lactose Intolerance in Adults: Biological Mechanism and Dietary Management

  https://pmc.ncbi.nlm.nih.gov/articles/PMC4586575/

  Additionally, in individuals with lactase persistence the occurrence of gastrointestinal infection, inflammatory bowel disease, abdominal surgery and other health issues can also cause a decrease in lactase activity (secondary lactase deficiency). […] Whatever the cause, lactase deficiency results in unabsorbed lactose being present in the intestinal tract, which has effects that can lead to symptoms of lactose intolerance in susceptible individuals. […] First, the increased osmotic load increases the intestinal water content. Second, lactose is readily fermented by the colonic microbiome leading to production of short chain fatty acids and gas (mainly hydrogen (H2), carbon dioxide (CO2), and methane (CH4)). […] Malabsorption is a necessary precondition for lactose or FODMAP intolerance; however, the two are not synonymous and the causes of symptoms must be considered separately.

• #7 Lactose Sensitivity and Lactose Malabsorption: The 2 Faces of Lactose Intolerance

  https://www.jnmjournal.org/journal/view.html?doi=10.5056/jnm20094

  We hypothesized that lactose may trigger symptoms of LI in some patients without LM. We named lactose sensitivity (LS) this disorder of unknown mechanism. […] This study confirms the existence of a high frequency of digestive disorders induced by lactose ingestion (61%) in patients that report FBD and LI. This study also shows the 2 faces of LI: LM and LS. However, despite that LM or LS was found in 70% of the participants, there was no association between these 2 disorders. […] In humans, the physiopathology of digestive disorders associated with lactase deficiency is easy to understand. In the small intestine mucosa, lactase (-galactosidase), a disaccharidase present in the microvillar membrane of columnar epithelial cells hydrolyzed lactose into its component glucose and galactose. The lactase defect is responsible for the stagnation of undigested lactose in the small bowel that induces increased fluid into the caecum from the ileum by osmotic action.

• #8 Lactose intolerance – Wikipedia

  https://en.wikipedia.org/wiki/Lactose_intolerance

  Lactose intolerance is caused by a lessened ability or a complete inability to digest lactose, a sugar found in dairy products. […] Lactose intolerance is due to the lack of the enzyme lactase in the small intestines to break lactose down into glucose and galactose. […] Primary lactose intolerance occurs as the amount of lactase declines as people grow up. […] Secondary lactose intolerance is due to injury to the small intestine. Such injury could be the result of infection, celiac disease, inflammatory bowel disease, or other diseases. […] Lactose intolerance is classified according to its causes as: Primary hypolactasia, Secondary hypolactasia, Primary congenital alactasia. […] Lactose intolerance is a consequence of lactase deficiency, which may be genetic (primary hypolactasia and primary congenital alactasia) or environmentally induced (secondary or acquired hypolactasia).

• #9 Lactose Intolerance | Concise Medical Knowledge

  https://www.lecturio.com/concepts/lactose-intolerance/

  Lactose intolerance (LI) is a clinical condition presenting with gut symptoms after the ingestion of lactose. Malabsorption is not always present, but when it is, the most common cause is lactase deficiency due to enzyme nonpersistence. Lactose is a disaccharide in milk that requires lactase to break it down into its 2 absorbable constituents, glucose and galactose. […] The pathogenesis of LI symptoms: The likelihood of a person with primary LD developing symptoms after lactose ingestion depends on a number of factors. […] In secondary LD, the activity levels of other enzymes and transport processes also fall, secondary to infections and inflammation of the small bowel. […] Undigested lactose causes an osmotic load that pulls water and electrolytes into the bowel. […] Gas is produced by bacterial fermentation of lactose in the colon. […] The likelihood of developing symptoms after lactose ingestion depends on a number of factors.

• #10 Lactose Intolerance in Adults: Biological Mechanism and Dietary Management

  https://www.mdpi.com/2072-6643/7/9/5380

  Lactose intolerance related to primary or secondary lactase deficiency is characterized by abdominal pain and distension, borborygmi, flatus, and diarrhea induced by lactose in dairy products. […] The biological mechanism and lactose malabsorption is established and several investigations are available, including genetic, endoscopic and physiological tests. […] Lactose intolerance depends not only on the expression of lactase but also on the dose of lactose, intestinal flora, gastrointestinal motility, small intestinal bacterial overgrowth and sensitivity of the gastrointestinal tract to the generation of gas and other fermentation products of lactose digestion. […] About two thirds of the World’s population undergoes a genetically programmed decrease in lactase synthesis after weaning (primary lactase deficiency).

• #11 Lactose Intolerance in Adults: Biological Mechanism and Dietary Management

  https://www.mdpi.com/2072-6643/7/9/5380

  Additionally, in individuals with lactase persistence the occurrence of gastrointestinal infection, inflammatory bowel disease, abdominal surgery and other health issues can also cause a decrease in lactase activity (secondary lactase deficiency). […] Whatever the cause, lactase deficiency results in unabsorbed lactose being present in the intestinal tract, which has effects that can lead to symptoms of lactose intolerance in susceptible individuals. […] Symptoms of lactose intolerance generally do not occur until there is less than 50% of lactase activity. […] Regular lactose intake may also have an effect. […] Lactase expression is not up-regulated by lactose ingestion, tolerance could be induced by adaptation of the intestinal flora. […] Another condition that may play a role in food tolerance is small intestinal bacterial overgrowth (SIBO) caused by abnormally high bacterial counts in the small intestine, exceeding 10^5 organisms/mL.

• #12 Pediatric Lactose Intolerance: Background, Pathophysiology, Etiology

  https://emedicine.medscape.com/article/930971-overview

  Lactose intolerance in adulthood is very common and is the result of a genetically programmed progressive loss of the activity of the small intestinal enzyme lactase. […] Expression of the lactase enzyme starts to decline in most persons at age 2 years; almost 4 billion people worldwide have lactose malabsorption. […] The molecular bases of lactose intolerance have been reviewed. […] Human and animal studies suggest that numerous modulators result in variable expression of lactase at different ages. […] Improvement of lactose digestion in a previously intolerant child or adult is caused by growth of lactose-digesting bacteria rather than an induction in activity of the lactase enzyme because lactase is a noninducible enzyme. […] Congenital lactase deficiency is an extremely rare autosomal recessive disorder associated with a complete absence of lactase expression.

• #13 Lactose intolerance: MedlinePlus GeneticsLock

  https://medlineplus.gov/genetics/condition/lactose-intolerance/

  Lactose intolerance is a condition that makes it difficult to digest lactose, a sugar found in milk and several other dairy products. Lactose is normally broken down by an enzyme called lactase, which is produced by cells in the lining of the small intestine. Lack or loss of lactase has both genetic and non-genetic causes. […] Congenital lactase deficiency is caused by variants (also called mutations) in the LCT gene. The LCT gene provides instructions for making the lactase enzyme. Variants in the LCT gene that cause congenital lactase deficiency are believed to interfere with the processing and function of lactase, causing affected infants to have a severely impaired ability to digest the lactose in breast milk or formula. […] Lactase nonpersistence in adulthood is caused by the gradually decreasing activity (expression) of the LCT gene after infancy, which occurs in most humans. LCT gene expression is controlled by a DNA sequence called a regulatory element, which is located within a nearby gene called MCM6. Some individuals have inherited changes in this element that lead to sustained lactase production in the small intestine and the ability to digest lactose throughout life. People without these changes have a reduced ability to digest lactose as they get older, resulting in the signs and symptoms of lactase nonpersistence.

• #14 Lactose Intolerance in Adults: Biological Mechanism and Dietary Management

  https://pmc.ncbi.nlm.nih.gov/articles/PMC4586575/

  The threshold for dietary lactose tolerance is dependent on several factors including the dose consumed, residual lactase expression, ingestion with other dietary components, gut-transit time, small bowel bacterial overgrowth, and also composition of the enteric microbiome. […] Symptoms of lactose intolerance generally do not occur until there is less than 50% of lactase activity. […] Regular lactose intake may also have an effect. […] Although lactase expression is not up-regulated by lactose ingestion, tolerance could be induced by adaptation of the intestinal flora. […] Further, most people with lactase non-persistence can tolerate small amounts of lactose (less than 12 g, equivalent to one cup), especially when it is combined with other foods or spread throughout the day. […] Another condition that may play a role in food tolerance is small intestinal bacterial overgrowth (SIBO) caused by abnormally high bacterial counts in the small intestine, exceeding 105 organisms/mL.

• #15 Lactose intolerance pathophysiology – wikidoc

  https://www.wikidoc.org/index.php/Lactose_intolerance_pathophysiology

  It is thought that lactose intolerance is the result of lactose malabsorption caused by low levels of small intestinal lactase. […] The most important causes of low level of small intestinal lactase are: Mucosal injury, Reduced genetic expression of the enzyme lactase-phlorizin hydrolase. […] Lactose is metabolized by intestinal lactase to galactose and glucose in the villous enterocytes and then uptaken by Na+/glucose cotransporter (SGLT1). […] In the colon, unabsorbed lactose is converted to hydrogen and short chain fatty acids such as acetate, butyrate and propionate by intestinal bacteria and creates symptoms of lactose intolerance. […] Lactose intolerance is transmitted in an autosomal recessive pattern. […] Genes involved in the pathogenesis of lactose intolerance include polymorphism of the MCM6 (minichromosome maintenance complex component 6), gene located upstream from the gene lactase-phlorizin hydrolase (LPH) on the long arm (q) of chromosome 2 in region 21 (2q21). Lactase persistence is strongly related with the presence of the T allele of the single nucleotide polymorphisms (SNP) located at -13.9 kb upstream of the lactase gene. […] Acquired primary lactase deficiency is associated with a CC genotype at -13.9 kb and lactase persistence is related to TT genotype.

• #16 Lactose intolerance – Wikipedia

  https://en.wikipedia.org/wiki/Lactose_intolerance

  The accumulation of epigenetic factors, primarily DNA methylation, in the extended LCT region, including the gene enhancer located in the MCM6 gene near C/T-13910 SNP, may also contribute to the onset of lactose intolerance in adults. […] Lactose intolerance in infants (congenital lactase deficiency) is caused by mutations in the LCT gene. […] Lactose intolerance in adulthood is a result of gradually decreasing activity (expression) of the LCT gene after infancy, which occurs in most humans.

• #17 Lactose Intolerance: Background, Pathophysiology, Etiology

  https://emedicine.medscape.com/article/187249-overview

  An association between certain single nucleotide polymorphisms (CT-13910 and GA-22018) with lactose tolerance in a northeaster Brazilian population has been reported. […] In Indo-Europe, lactase deficiency is associated with rs4982235 SNP (or -13910CT), which may predispose affected individuals to lactose intolerance.

• #18 Update on lactose malabsorption and intolerance: pathogenesis, diagnosis and clinical management | Gut

  https://gut.bmj.com/content/68/11/2080

  Lactose malabsorption is typically caused by lactase downregulation after infancy due to lactase non-persistence which in Caucasians is mediated by the LCT 13910:C/C genotype. […] Lactase non-persistence is the genetic wildtype and not a disease. Both lactase persistence and non-persistence are common phenotypes in healthy humans. […] The lactase genetic region is among the genetic regions strongest shaped by human evolution within the last 10 000 years, with lactase persistence providing a selective advantage of up to 4%5% per generation. […] The LCT 13910 is the region within the human genome with the strongest interaction with the intestinal microbiota. […] Recent data point to interactions between human genes and the microbiota.

• #19

  https://link.springer.com/article/10.1007/s42399-021-00792-9

  In addition to gene mutations, other mechanisms may be responsible for lactose intolerance. In fact, epigenetic modifications in DNA and histone proteins can contribute to lactase non persistence. […] Typical symptoms of lactose intolerance are abdominal pain, bloating, flatulence, diarrhea, borborygmi, and in some cases, constipation, nausea, and vomiting. […] In subjects with lactose intolerance, gas is produced because lactose is not digested and absorbed in the small bowel, and it is fermented by intestinal flora. […] The formal test which is commonly used in patients suspected of having lactose intolerance is the H2 Breath Test (HBT). It has become widely available and it is often used for diagnosis of lactose intolerance. […] In response to the hypotheses put forward over time regarding the genetic predisposition to lactose intolerance, polymorphisms of the gene that codes for lactase predisposing to this intolerance have been identified.

• #20 Lactose Intolerance Genetics: Who Can Digest Diary and Why?

  https://www.healthline.com/health/lactose-intolerance-genetics

  LCT mutations are associated with congenital lactase deficiency, while both LCT and MCM6 gene variants contribute to lactase nonpersistence and persistence. […] The MCM6 gene variant that promotes the ability to digest lactose passes to the next generation in an autosomal dominant pattern. That means if you inherit the gene for lactase persistence from even one parent, you will also have lactase persistence and the ability to digest lactose. […] Lactose intolerance may develop from either dominant or recessive traits. Congenital lactase deficiency, the rarest form, is a recessive trait that develops when both parents have copies of LCT genetic variants. […] Since some of the genes for lactase deficiency are recessive, you can also develop the condition if you inherit the recessive gene variant from both of your parents, even though neither of them will have the condition. […] Some cases of secondary lactose intolerance caused by small intestine injuries are reversible after successful treatment of the injury. However, genetic forms of lactose intolerance do not currently have a cure.

• #21 Can changing the microbiome reverse lactose intolerance?: 2019 News: News: News & Events: Department of Biology: Indiana University Bloomington

  https://biology.indiana.edu/news-events/news/2019/foster-lactose-intolerance.html

  It seems possible, even probable, that such trauma to the digestive tract can trigger the same epigenetic change that normally turns off the lactase gene in childhood. Scientists have found other cases of such environmentally induced epigenetic changes, although more research is needed to establish the persistence and consequences of these alterations. […] Recently researchers have shown that one of the SNPs changes the level of epigenetic modification of the DNA in the lactase gene control regions. Specifically, the SNP prevents small chemical units, called methyl groups (which consist of one carbon and three hydrogen atoms) from being attached to the DNA. Methyl groups are especially important in regulating gene activity because when they are added to the DNA, they turn off the gene. […] These studies imply that after early childhood, the lactase gene is usually shut off by DNA methylation. The SNPs that alter the DNA sequence in the control region, however, prevent this methylation from happening. This, in turn, results in the production of lactase because the gene is kept on.

• #22 LCT gene: MedlinePlus GeneticsLock

  https://medlineplus.gov/genetics/gene/lct/

  The LCT gene provides instructions for making an enzyme called lactase. This enzyme helps to digest lactose, a sugar found in milk and several other dairy products. […] Rarely, LCT gene variants (also called mutations) cause congenital lactase deficiency. In this disorder (also known as congenital alactasia), infants are unable to break down lactose in breast milk or formula. Infants who are unable to process lactose are considered lactose intolerant. […] Variants in the LCT gene can change single protein building blocks (amino acids) in the lactase enzyme. In some cases, variants cause cells to create lactase enzymes that are abnormally short. The variants are believed to interfere with the processing and function of the lactase enzyme, leading to undigested lactose in the small intestine and causing severe diarrhea. […] Lactose intolerance in adulthood can also be caused by the gradually decreasing activity (expression) of the LCT gene after infancy. This condition is known as lactase nonpersistence, and it occurs in most humans. It can also have non-genetic causes.

• #23 Lactase – Wikipedia

  https://en.wikipedia.org/wiki/Lactase

  Lactase is an enzyme produced by many organisms and is essential to the complete digestion of whole milk. It breaks down the sugar lactose into its component parts, galactose and glucose. People deficient in lactase or lacking functional lactase may experience the symptoms of lactose intolerance after consuming milk products. […] Without lactase, lactose-intolerant people pass the lactose undigested to the colon where bacteria break it down, creating carbon dioxide which leads to bloating and flatulence. […] Lactase supplements can be used to treat lactose intolerance. […] The overall reaction that lactase catalyzes is as follows: lactose + H2O → D-galactose + D-glucose + heat. […] The catalytic mechanism of D-lactose hydrolysis retains the substrate anomeric configuration in the products.

• #24 Lactase – Wikipedia

  https://en.wikipedia.org/wiki/Lactase

  Studies of E. coli lactase have proposed that hydrolysis is initiated when a glutamate nucleophile on the enzyme attacks from the axial side of the galactosyl carbon in the β-glycosidic bond. […] The enzyme is liberated from the β-galactosyl moiety upon equatorial nucleophilic attack by water, which produces D-galactose. […] Proposed mechanism of lactose hydrolysis by Lactase enzyme. […] Commercial lactase is used as a medication for lactose intolerance. Since it is an enzyme, its function can be inhibited by the acidity of the stomach. […] Humans are born with high levels of lactase expression. In most of the world’s population, lactase transcription is down-regulated after weaning, resulting in diminished lactase expression in the small intestine, which causes the common symptoms of adult-type hypolactasia, or lactose intolerance. […] Mutations are believed to interfere with the function of lactase, causing affected infants to have a severely impaired ability to digest lactose in breast milk or formula.

• #25 Managing Lactose Intolerance Naturally – Institute for Natural Medicine

  https://naturemed.org/managing-lactose-intolerance-naturally/

  Lactase enzyme deficiency is the cause of primary lactose intolerance and can occur at any age, as the activity of this critical digestive enzyme starts to decline soon after birth. […] Secondary lactose intolerance occurs when injury or diseases (such as celiac disease) damage the intestines. […] Many individuals struggle with lactose intolerance as they get older. This is called Acquired Lactase Deficiency. […] Research indicates that most people with intolerance can digest about 12 grams of lactosethe amount in a cup of milkexperiencing only mild or no symptoms. […] In addition to natural remedies such as lactase digestive enzymes, prebiotics, and probiotics, research shows some people with lactose intolerance can enjoy dairy again symptom-free. […] Through a process called adaptation, a person regularly consumes small amounts of dairy, helping the body gradually adapt and eventually tolerate lactose. […] Preliminary studies suggest that combining prebiotics and probiotics with the adaptation strategy could positively influence the gut microbiome, potentially reversing lactose intolerance entirely.

• #26 Can changing the microbiome reverse lactose intolerance?: 2019 News: News: News & Events: Department of Biology: Indiana University Bloomington

  https://biology.indiana.edu/news-events/news/2019/foster-lactose-intolerance.html

  The symptoms of lactose intolerance include diarrhea, stomach pain, cramps, bloating and flatulence, all of which result from failure to break down lactose in the small intestine. As undigested lactose moves into the large intestine, water enters to reduce the lactose concentration, producing diarrhea. The lactose is eventually eaten by microorganisms in the large intestine, producing, as byproducts, various gases that cause bloating, cramping and flatulence. […] Recent studies have shown that the symptoms of lactose intolerance can be relieved in some people by changing the population of their intestinal microbes, called the microbiome, to encourage lactose-digesting bacteria. Specifically, bacteria, called lactic acid bacteria, eat the lactose but produce the byproduct lactic acid instead of gas. While lactic acid has no nutritional value, it does not produce the unpleasant symptoms of lactose intolerance. This adaptation of the intestinal microbiome may be how some ancient pastoral populations with no genetic evidence of lactase persistence tolerated a dairy-rich diet.

• #27 Frontiers | Association of gut microbiota with lactose intolerance and coeliac disease: a two-sample Mendelian randomization study

  https://www.frontiersin.org/journals/nutrition/articles/10.3389/fnut.2024.1395801/full

  Background and objectives: Lactose intolerance and coeliac disease are common clinical nutrient malabsorption disorders, with an unclear pathogenesis and limited therapeutic options. […] This study provides novel insights into exploring the role of gut microbiota in lactose intolerance and coeliac disease; however, further experiments investigations are required to elucidate the specific underlying mechanisms. […] Evidence has demonstrated a close association between gut microbiota and lactose intolerance as well as coeliac disease. […] The clinical manifestations of lactose intolerance are influenced by small intestinal bacterial overgrowth and the composition of the gut microbiome. […] Furthermore, studies have shown that gut microbiota is involved in lactose metabolism. […] The mechanisms through which gut microbiota influences the onset or progression of coeliac disease may involve activation of the innate immune system responses, modulation of epithelial barrier, or exacerbation of an alcohol-soluble protein-specific immune response.

• #28 Update on lactose malabsorption and intolerance: pathogenesis, diagnosis and clinical management | Gut

  https://gut.bmj.com/content/68/11/2080

  The association between self-reported LI, objective findings and clinical outcome of dietary intervention is variable. […] Lactose malabsorption (LM) is a necessary precondition for lactose intolerance (LI). However, the two must not be confused and the causes of symptoms must be considered separately. […] The onset of these symptoms is strongly correlated to the appearance of hydrogen gas during breath tests. […] Further, undigested lactose in the small intestine lead to osmotic trapping of water and the osmotic load in the colon is increased about eightfold by fermentation of lactose to SCFA. […] The likelihood of developing symptoms after lactose ingestion is multifactorial. […] Other patient factors not directly related to lactose digestion are also associated with LI. These include the presence of anxiety disorders, high levels of psychosocial stress and the presence of functional GI disorders such as IBS.

• #29 Lactose Sensitivity and Lactose Malabsorption: The 2 Faces of Lactose Intolerance

  https://www.jnmjournal.org/journal/view.html?doi=10.5056/jnm20094

  In contrast, the physiopathology of LS remains unknown. This disorder, also named functional LI was previously reported in patients referred for investigation of digestive symptoms. […] The pathophysiological basis of LI in IBS-D patients was provided by a study showing increased counts of mast cells, increased intraepithelial lymphocytes, and increased enterochromaffin cells in the terminal ileum and the ascending part of the colon. Moreover, the release of pro-inflammatory cytokines after lactose ingestion was associated with hypervisceral sensitivity. […] The present study shows that 30% of patients that report LI have normal lactose absorption and normal LS. In the other 70% of patients, LI could be associated with LM (9%), LS (42%), or both LM and LS (19%).

• #30 Lactose Intolerance in Adults: Biological Mechanism and Dietary Management

  https://www.mdpi.com/2072-6643/7/9/5380

  Bacterial fermentation of lactose with production of short-chain fatty acids and gas in the small bowel may be particularly likely to trigger abdominal symptoms. […] Lactose malabsorption causes symptoms by several mechanisms: unabsorbed lactose leads to osmotic diarrhea; products of its bacterial digestion lead to secretory diarrhea and gas can distend the colon. […] Diagnosis of lactose malabsorption is based on detection either of the genetic mutation, loss of lactase activity in the enteric mucosa or evidence of malabsorption in the blood or breath. […] However, the presence of lactose malabsorption does not necessarily imply that abdominal symptoms are related to this process.

• #31 Top four lactose intolerance symptoms

  https://www.henleynutrition.co.uk/single-post/top-four-lactose-intolerance-symptoms

  Many cases of gastrointestinal infections from bacteria and viruses have been shown to cause lactose intolerance, often termed Post-infectious lactose intolerance. […] SIBO Small Intestinal Bacterial Overgrowth is a condition in which the small intestine is excessively populated by certain bacteria. Disturbances to the gut lining and motility changes can cause bacteria to multiply, causing SIBO symptoms of diarrhoea, bloating, flatulence, and abdominal discomfort. […] It is important to have your doctor check your symptoms to rule out other conditions with similar symptoms to lactose intolerance, such as coeliac or Crohn’s disease or milk allergy, particularly for children.

• #32 Pediatric Lactose Intolerance: Background, Pathophysiology, Etiology

  https://emedicine.medscape.com/article/930971-overview

  Childhood-onset and adult-onset lactase deficiency are extremely common and are inherited in an autosomal recessive manner. […] Acquired lactase deficiency, which is a transient phenomenon by definition, is due to damage of the intestinal mucosa by an infectious, allergic, or inflammatory process and resolves once the disease process is corrected and healing of the intestinal mucosa restores the brush border enzymes. […] This deficiency results from an unusual mechanism that involves a developmentally regulated change of the lactase gene product, resulting in a reduced synthesis of the precursor protein. […] Low lactase activity in the small intestine allows undigested lactose to pass into the colon.

• #33 Lactose Intolerance: Symptoms, Diagnostic Tests & Treatment

  https://my.clevelandclinic.org/health/diseases/7317-lactose-intolerance

  Secondary lactose intolerance may not be permanent. If your small intestine recovers its usual function, you may regain the ability to digest lactose. […] If you want to be able to digest lactose, you need lactase in your gut. Most people with lactose intolerance cant produce lactase naturally. Lactase supplements can give your body the lactase it needs to break down lactose. […] Secondary lactose intolerance caused by damage to your small intestine might be reversible after your small intestine recovers. […] If you have primary or congenital lactose intolerance, you wont ever start naturally producing more lactase.

• #34 Lactose Intolerance (Causes, Symptoms, and Treatment)

  https://patient.info/doctor/lactose-intolerance-pro

  This article deals with lactose intolerance, which is defined as symptoms that occur upon exposure to lactose in individuals with lactose malabsorption. It is the result of an enzyme deficiency, rather than lactose allergy, which is an IgE-mediated reaction. […] Lactase is the enzyme that hydrolyses lactose to the monosaccharides, glucose and galactose and is present in the tips of the villi of the small intestine. […] Primary lactase deficiency is rarely a cause of symptoms in children under the age of 3 years. […] Secondary lactase deficiency follows damage to the intestinal mucosa – eg, acute viral or bacterial gastroenteritis, parasitic infection, uncontrolled coeliac disease, inflammatory bowel disease, chemotherapy, long courses of antibiotics or severe malnutrition. […] Symptoms result from reduced absorption of lactose which is then broken down by intestinal bacteria, forming gas and short-chain fatty acids.

• #35 Pathophysiology and management of second | Biomedical Research

  https://www.currentpediatrics.com/articles/pathophysiology-and-management-of-secondary-lactose-intolerance-in-infants-role-of-caseinbased-nutritional-supplement-25121.html

  Lactose intolerance is a clinical syndrome characterized by gastrointestinal symptoms such as abdominal pain, abdominal discomfort, diarrhea, nausea, flatulence, and bloating followed by the consumption of lactose or lactose-containing foods. […] Secondary Lactose Malabsorption (SLM) is characterized by the onset of Lactose Malabsorption (LM) in those capable of digesting lactose. […] Lactase is located at the tip of intestinal villi, making it vulnerable to intestinal damage, particularly since fresh immature enterocytes lack lactase. […] Acute viral infection caused by rotavirus can damage the small intestine, resulting in the loss of lactase-containing epithelial cells from the villi’s tips. […] Lactase deficit is expected in the young epithelial cells that replace them, resulting in secondary lactose shortage.

• #36 Pathophysiology and management of second | Biomedical Research

  https://www.currentpediatrics.com/articles/pathophysiology-and-management-of-secondary-lactose-intolerance-in-infants-role-of-caseinbased-nutritional-supplement-25121.html

  SLM induced by infectious gastroenteritis is more common and can be clinically significant, especially in infants for whom milk is the principal food. […] Lactose malabsorption can result from acute infectious diarrhea, which damages lactase-containing epithelial cells on the ends of the intestinal villi. […] The replacement of older epithelial cells with new ones often results in the cells being immature and lacking enough lactase, which worsens lactose malabsorption and extends the duration of diarrhea. […] Slight intestinal atrophy occurs in infants with severe malnutrition, resulting in secondary lactase insufficiency. […] Malnutrition is associated with lactose malabsorption and carbohydrate intolerance in lactose malabsorption has also been associated with poor growth. […] Lactose restriction reduces the duration of gastrointestinal symptoms in children with prolonged diarrhea following acute gastroenteritis.

• #37

  https://link.springer.com/article/10.1007/s42399-021-00792-9

  Enzyme supplementation therapy with lactase from nonhuman sources to hydrolyze lactose is another important approach. The intake of exogenous lactase is expected whenever foods containing lactose are ingested. […] Although the results of these studies are in contrast with each other, it can be said that the administration of exogenous lactase represents, in most cases, a valid therapeutic option.

• #38 Lactase Enzyme Supplementation In Lactose Intolerance – Walter Bushnell Healthcare Foundation

  https://wbhf.walterbushnell.com/publications/gastro-flash/item/385-lactase-enzyme-supplementation-in-lactose-intolerance

  Various tests are available for the diagnosis of lactose intolerance including lactose tolerance test, hydrogen breath test and DNA based diagnostic test. […] Treatment of lactose intolerance should not only aim at reducing malabsorption but also at improving gastrointestinal symptoms. […] The selection of therapy should be based on the underlying type of deficiency. Therefore, it is important to differentiate between primary and secondary lactase deficiency. […] Non-pharmacological treatment options consist of lactose restricted diet or the use of milk in which the lactose has been pre-hydrolyzed via treatment with lactase supplements. […] Pharmacological treatment strategies include enzyme replacement therapy with lactase from nonhuman sources to hydrolyze lactose, probiotics, gut decontaminating agents and antimicrobials.

• #39 Lactase Enzyme Supplementation In Lactose Intolerance – Walter Bushnell Healthcare Foundation

  https://wbhf.walterbushnell.com/publications/gastro-flash/item/385-lactase-enzyme-supplementation-in-lactose-intolerance

  Enzyme supplementation therapy with lactase from non-human sources is an important adjunct to diet therapy in patients with lactose intolerance. […] Lactase deficiency and lactose malabsorption are the primary cause for the development of lactose intolerance. The therapeutic strategies for the management of the condition include restriction of lactose containing diet and administration of lactase enzyme supplementation.

• #40 Lactose intolerance – Walter Bushnell Healthcare Foundation

  https://wbhf.walterbushnell.com/publications/bush-beats/item/56-lactose-intolerance

  While diagnosis of lactose intolerance can be made by clinical history and supported by findings of breath hydrogen or lactose tolerance test the management typically initiates with dietary modulation. […] Oral supplementation of exogenous lactase enzyme is an important adjunct to dietary restriction approach that seems to ensure efficacy at any level of lactose intolerance. […] Lactase preparations from Aspergillus oryzae are stable in an acidic environment and are practically pH independent. […] While lactase enzyme supplementation decreases the symptoms of bloating abdominal pain and disturbed bowel movement in majority of patients with lactose intolerance this may also possibly alleviate certain long-term consequences of diary restriction that people begin to follow while suffering from self-perceived or real lactose intolerance.

• #41 Fermented foods and probiotics: An approach to lactose intolerance | Journal of Dairy Research | Cambridge Core

  https://www.cambridge.org/core/journals/journal-of-dairy-research/article/fermented-foods-and-probiotics-an-approach-to-lactose-intolerance/77AD1896FA744AA7453AE047FD85BD17

  Previous studies have shown that lactose digestion and the symptoms of lactose intolerance can be improved using probiotics that modify gut pH, express -gal, and exert positive effects on intestinal activity and overall colonic microbiota. […] It has been demonstrated that lactic acid bacteria ferment lactose to produce lactate, hydrogen, methane, carbon dioxide and short-chain fatty acids. […] During fermentation, lactase present in lactic acid bacteria cleaves unabsorbed lactose to glucose and galactose and is then absorbed into the body. […] The increase in the number of lactic acid bacteria is due to microbial digestion during fermentation. […] The degrees of lactose intolerance in different individuals are due to the variability of colonic microflora in fermenting lactose. […] As a result, dairy foods that contain active cultures can be used to reduce the symptoms of lactose intolerance.

• #42 Prebiotic Strategies to Manage Lactose Intolerance Symptoms | Oregon State University

  https://health.oregonstate.edu/research/publications/103390nu16071002

  Prebiotics like galactooligosaccharides (GOS) can enhance the growth of beneficial lactose-fermenting gut bacteria such as Bifidobacterium and Lactobacillus in individuals with lactose intolerance. Increasing these bacteria may help reduce symptoms of lactose intolerance. This finding suggests prebiotics could be a useful dietary approach to manage symptoms for the 65-75% of the global population with lactose intolerance. […] The proposed mechanism is that GOS and lactose enhance Bifidobacterium and Lactobacillus which ferment lactose efficiently without producing gas. This may reduce symptoms caused by bacterial gas production and osmotic pressure from undigested lactose. […] Lactose intolerance, which affects about 65-75% of the worlds population, is caused by a genetic post-weaning deficiency of lactase, the enzyme required to digest the milk sugar lactose, called lactase non-persistence.

• #43 Fermented foods and probiotics: An approach to lactose intolerance | Journal of Dairy Research | Cambridge Core

  https://www.cambridge.org/core/journals/journal-of-dairy-research/article/fermented-foods-and-probiotics-an-approach-to-lactose-intolerance/77AD1896FA744AA7453AE047FD85BD17

  The consumption of active and live cultures in addition to the use of enzyme -galactosidase (lactase) that break down lactose and the consumption of probiotics might be beneficial to individuals with lactose-intolerance. […] Probiotics exhibit direct effects in the gut in the treatment of lactose digestion. […] The effectiveness of probiotics also depends on the tolerance of a strain to bile and acid in addition to the strain’s lactase level or lactose transport. […] Lactose maldigestion symptoms significantly improved with the consumption of fermented dairy products containing specific probiotic strains in appropriate amounts. […] Future studies should focus on the selection of probiotic strains that can enhance the production of -gal as the addition of such probiotics in various food products seems to be the most effective means of alleviating lactose intolerance.

• #44

  https://www.healio.com/news/gastroenterology/20180405/novel-prebiotic-could-help-treat-millions-with-severe-lactose-intolerance

  RP-G28, a novel prebiotic in development for the treatment of lactose intolerance has the potential to become the first FDA-approved treatment for lactose intolerance, a condition that affects millions of Americans, according to the developer Ritter Pharmaceuticals. […] The understood mechanism of action of RP-G28 for mitigating lactose intolerance symptoms is by promoting colonic adaptation. Specifically, RP-G28 preferentially stimulates the growth of lactose-metabolizing bacteria in the GI tract, which compensates for the lack of endogenous lactase activity. The result is the breakdown of lactose, reducing gas production and water retention, thus reducing gastric symptoms for patients. […] RP-G28 has the potential to become the first U.S. FDA-approved treatment for lactose intolerance, a condition that affects approximately 40 million people in the U.S. with a target market of 9 million moderate to severe individuals, representing a significant medical need.

• #45

  https://www.healio.com/news/gastroenterology/20180405/novel-prebiotic-could-help-treat-millions-with-severe-lactose-intolerance

  After the 30-day course of treatment, it is expected that patients will be able to freely consume dairy foods symptom-free. […] Durability of treatment is still being assessed clinically, but we predict patients may be tolerant for a long time. A particular subset of patients may need to take another treatment periodically.

• #46 The importance of lactose intolerance in individuals with gastrointestinal symptoms | Revista de Gastroenterología de México

  https://www.revistagastroenterologiamexico.org/en-the-importance-lactose-intolerance-in-articulo-S2255534X20300426

  Lactose intolerance is a condition with an elevated prevalence worldwide, especially in Latin American, Asian, and African countries. […] The pathophysiologic mechanism of deficient lactose absorption in the intestine can be primary, secondary to other enteropathies, or coexistent with other intestinal diseases with similar symptoms, such as irritable bowel syndrome, bacterial overgrowth syndrome, or celiac disease, causing confusion in relation to diagnosis and treatment. […] Lactose is digested by lactase, an enzyme found in the brush border of enterocytes. Its maximum expression is in the middle jejunum, where it is subject to little fermentation because the bacterial burden at that level is low. Lactose hydrolysis produces glucose and galactose, conferring beneficial effects. […] Lactase is encoded and synthetized in the enterocyte by the MCM6 gene, located on the chromosome 2q21 region. At least 3 polymorphic variants of the single nucleotide polymorphism (SNP) are known to regulate its gene expression.

• #47 The importance of lactose intolerance in individuals with gastrointestinal symptoms | Revista de Gastroenterología de México

  https://www.revistagastroenterologiamexico.org/en-the-importance-lactose-intolerance-in-articulo-S2255534X20300426

  LNP does not appear to be associated with other digestive diseases, even though individuals with irritable bowel syndrome have been shown to have a greater probability of presenting with LI than the general population. […] The most accurate diagnostic method for corroborating LI is the challenge, i.e., the secondary presence of symptoms immediately after dairy product consumption. […] Poor concordance between symptoms suggestive of LI and deficient digestion, as well as the fact that many uncomfortable symptoms are shared with other gastrointestinal diseases (bacterial overgrowth, celiac disease, gluten-sensitive enteropathy, irritable bowel syndrome), the prebiotic effect of lactose, possible implications for the microbiota, the role of dairy products on bone health, gastrointestinal health and health in general are a good reason for promoting and confirming the diagnosis of deficient lactose digestion.

• #48 Lactose Sensitivity and Lactose Malabsorption: The 2 Faces of Lactose Intolerance

  https://www.jnmjournal.org/journal/view.html?doi=10.5056/jnm20094

  The degradation of lactose in the colon creates a call for water in the small intestine, occasioning an acceleration of intestinal transit with diarrhea, gas, gut pain, bloating, and borborygmi. These symptoms may be present sometime after the ingestion of lactose when the undigested lactose reaches the colon and is degraded by colonic bacteria. They are similar to those of irritable bowel syndrome (IBS), and nearly two-thirds of IBS patients associate symptoms with eating a meal. […] Many factors could influence the variability of clinical manifestations related to lactose ingestion: physiological like gastric emptying, small bowel transit time, water absorption capacity, patients subjective sensitivity to pain, or nutritional like the fat content of foods with lactose. Also, SIBO could trigger a secondary LM, which in consequence can produce LI symptomatology.

• #49 Association between Inflammatory Bowel Disease and Lactose Intolerance: Fact or Fiction

  https://www.kjg.or.kr/journal/view.html?uid=5626&vmd=Full

  LI is a condition with an inability to digest or absorb lactose disaccharide and may occur in IBD patients because of the resulting changes in the structure and function of the GI tract related to the chronic inflammatory state of IBD. It is largely due to loss of the enzyme lactase phlorizin hydrolase (LPH) in the gut. The mechanism causing the loss of lactase enzyme is unknown, even though recent studies have shown that random mutations upstream of the LCT gene could be a contributing factor. Owing to the inability to digest lactose, it accumulates in the gut, which is then digested by the colonic bacteria, yielding methane and other metabolites, causing symptoms related to luminal distention and stimulation of mechanoreceptors. […] Based on this analysis, both UC and CD patients had a significantly higher risk of having LI after adjusting for the possible confounding factors, including age, race, gender, obesity, and tobacco use. This study confirmed the findings of the largest meta-analysis by Szilagyi et al., which included 17 studies and 1,935 IBD patients. The risk of lactose maldigestion was reported to be higher among IBD patients than the controls.

• #50 Association between Inflammatory Bowel Disease and Lactose Intolerance: Fact or Fiction

  https://www.kjg.or.kr/journal/view.html?doi=10.4166/kjg.2020.76.4.185

  It is largely due to loss of the enzyme lactase phlorizin hydrolase (LPH) in the gut. […] The mechanism causing the loss of lactase enzyme is unknown, even though recent studies have shown that random mutations upstream of the LCT gene could be a contributing factor. […] Owing to the inability to digest lactose, it accumulates in the gut, which is then digested by the colonic bacteria, yielding methane and other metabolites, causing symptoms related to luminal distention and stimulation of mechanoreceptors. […] Based on this analysis, both UC and CD patients had a significantly higher risk of having LI after adjusting for the possible confounding factors, including age, race, gender, obesity, and tobacco use. […] The risk of lactose maldigestion was reported to be higher among IBD patients than the controls.

• #51 Association between Inflammatory Bowel Disease and Lactose Intolerance: Fact or Fiction

  https://www.kjg.or.kr/journal/view.html?doi=10.4166/kjg.2020.76.4.185

  In the active phases of the disease, both UC and CD patients showed improved symptoms after being given lactose-free diets. […] Therefore, it is important to evaluate IBD patients for LI before subjecting them to a lactose-restricted diet, given its potential adverse effects. […] This study revealed a strong association between IBD and LI and highlighted the importance of LI screening in IBD patients.

• #52 Is intestinal discomfort due to lactose intolerance? – Yogurt in Nutrition

  https://www.yogurtinnutrition.com/is-intestinal-discomfort-due-to-lactose-intolerance/

  However, the symptoms associated with lactose intolerance are not specific to this condition and can be observed in other frequent gastrointestinal dysfunctions such as irritable bowel syndrome, inflammatory bowel diseases (Crohns disease and ulcerative colitis) and intolerance to FODMAP. […] Moreover, a temporary lactose malabsorption, appearing in cases of infectious diarrhea, radiotherapy, mucosal damage due to coeliac disease or some medicine use, can also give rise to similar symptoms. […] Thus, self-diagnosis of lactose intolerance based solely on intestinal discomfort and made without proper medical diagnosis, is not possible. Self-diagnosed lactose intolerance can lead to unnecessary avoidance of dairy food.

• #53 Frontiers | Association of gut microbiota with lactose intolerance and coeliac disease: a two-sample Mendelian randomization study

  https://www.frontiersin.org/journals/nutrition/articles/10.3389/fnut.2024.1395801/full

  Our study elucidates the independent effects of different bacteria on lactose intolerance and coeliac disease. […] This study highlights the potential role of gut microbiota in the pathogenesis and treatment of lactose intolerance and coeliac disease, suggesting new avenues for research in this area.

• #54 Lactose intolerance and malabsorption: Clinical manifestations, diagnosis, and management – UpToDate

  https://www.uptodate.com/contents/lactose-intolerance-and-malabsorption-clinical-manifestations-diagnosis-and-management

  The terms „lactase deficiency,” „lactose malabsorption,” and „lactose intolerance” describe different aspects of a pathogenetic process. Not all patients with lactose intolerance will have lactase deficiency or lactose malabsorption. Each of these conditions has different clinical relevance and therapeutic consequences. […] „Lactose malabsorption” refers to incomplete absorption of lactose in the small intestine with the consequence that ingested lactose reaches the colon. The ingestion of lactose-containing food by people who have primary lactase deficiency is the most common cause of lactose malabsorption worldwide. Lactose malabsorption may result in symptoms (intolerance) that can be treated by diet and other means. […] „Lactase deficiency” refers to a lack of the activity of the enzyme lactase, which is the disaccharidase responsible for digestion of the disaccharide lactose. Lactase-deficient persons who are exposed to lactose may develop lactose malabsorption, depending on the amount of ingested lactose.

• #55 Lactose intolerance and malabsorption: Clinical manifestations, diagnosis, and management – UpToDate

  https://www.uptodate.com/contents/lactose-intolerance-clinical-manifestations-diagnosis-and-management

  The terms „lactase deficiency,” „lactose malabsorption,” and „lactose intolerance” describe different aspects of a pathogenetic process. Not all patients with lactose intolerance will have lactase deficiency or lactose malabsorption. Each of these conditions has different clinical relevance and therapeutic consequences. […] „Lactose intolerance” refers to reports of gastrointestinal symptoms after ingesting lactose or lactose-containing food. […] „Lactose malabsorption” refers to incomplete absorption of lactose in the small intestine with the consequence that ingested lactose reaches the colon. The ingestion of lactose-containing food by people who have primary lactase deficiency is the most common cause of lactose malabsorption worldwide. Lactose malabsorption may result in symptoms (intolerance) that can be treated by diet and other means. […] „Lactase deficiency” refers to a lack of the activity of the enzyme lactase, which is the disaccharidase responsible for digestion of the disaccharide lactose. Lactase-deficient persons who are exposed to lactose may develop lactose malabsorption, depending on the amount of ingested lactose.

• #56 Lactose Intolerance: What It Is, Types, Symptoms, How to Diagnose, and Much More!

  https://www.synlab-sd.com/en/blog/health-and-wellness-en/lactose-intolerance-how-can-diagnosis-help-with-treatment/

  Lactose malabsorption refers to any cause of failure to digest and/or absorb lactose in the small intestine and is a necessary precondition for lactose intolerance. […] However, the two should not be confused, as many individuals with malabsorption do not show symptoms after consuming dairy products. […] The main limitation of genetic, enzymatic and gaxilose tests is that malabsorption is common in healthy individuals, and a positive result does not confirm that symptoms are caused by this condition. Generally, the hydrogen breath test is the method of choice as it provides reasonably reliable information about digestive function and patient symptoms. […] Once lactose intolerance is diagnosed, the doctor may recommend a low-lactose diet to improve symptoms and avoid the long-term risk of malnutrition.

• #57 Lactose Intolerance in Adults: Biological Mechanism and Dietary Management

  https://pmc.ncbi.nlm.nih.gov/articles/PMC4586575/

  Bacterial fermentation of lactose with production of short-chain fatty acids and gas in the small bowel may be particularly likely to trigger abdominal symptoms. […] Recent studies have provided important new insight into the complex relationship between lactase deficiency, lactose malabsorption and symptom generation. […] Understanding the biological mechanism for food intolerance to lactose and FODMAPs will help clinicians make a definitive diagnosis and guide rational dietary and medical management.

• #58 Lactose Intolerance, Dairy Avoidance, and Treatment Options

  https://www.mdpi.com/2072-6643/10/12/1994

  Lactose intolerance refers to symptoms related to the consumption of lactose-containing dairy foods, which are the most common source for this disaccharide. While four causes are described, the most common is the genetically-determined adult onset lactose maldigestion due to loss of intestinal lactase governed by control of the gene by a 14,000 kb promoter region on chromosome 2. […] Gastrointestinal symptoms from lactose have expanded to include systemic effects and have also been confounded by other food intolerances or functional gastrointestinal disorders. […] This narrative article reviews the complexities of the perception of lactose intolerance, its epidemiology, and pathogenesis. […] The most common form of lactose maldigestion is adult onset hypolactasia, which is genetically controlled as described.

• #59 Lactose Intolerance, Dairy Avoidance, and Treatment Options

  https://www.mdpi.com/2072-6643/10/12/1994

  The classical term lactose intolerance (LI) has been applied to the development of gastrointestinal symptoms (of gas, bloat, abdominal cramps, and pain sometimes associated with mushy to watery diarrhea and, on occasion, with nausea and vomiting) after ingesting large amounts of lactose-containing food. […] Symptoms of LI are considered to be caused by intraluminal osmotic forces which depend on the rapidity and the quantity of undigested disaccharide entering the small and large bowel. […] Rapid bacterial fermentation of lactose to gases and SCFA contribute to symptoms. […] Therefore, one can perceive LI as an interaction between level of lactase and the dose of single ingestion of lactose.

• #60 Lactose Intolerance in Adults: Biological – ProQuest

  https://www.proquest.com/scholarly-journals/lactose-intolerance-adults-biological-mechanism/docview/1721919597/se-2

  Lactose intolerance related to primary or secondary lactase deficiency is characterized by abdominal pain and distension, borborygmi, flatus, and diarrhea induced by lactose in dairy products. […] The biological mechanism and lactose malabsorption is established and several investigations are available, including genetic, endoscopic and physiological tests. […] Lactose intolerance depends not only on the expression of lactase but also on the dose of lactose, intestinal flora, gastrointestinal motility, small intestinal bacterial overgrowth and sensitivity of the gastrointestinal tract to the generation of gas and other fermentation products of lactose digestion. […] This review summarizes recent advances in our understanding of the genetic basis, biological mechanism, diagnosis and dietary management of lactose intolerance.

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