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Lactose intolerance

Lactose deficiency is the failure to express the enzyme that hydrolyses lactose into galactose and glucose in the small intestine ( Misselwitz B et al Nov 2019 )

What is it ? Lactose is the main carbohydrate in human and mammalian milk Lactose is the main source of calories in milk Normally when lactose is consumed it is hydrolyzed to glucose and galactose by lactase enzyme Lactase-phlorizin hydrolase → known as lactase is a beta-galactosidase -found in the small intestinal brush border These are absorbed by intestinal blood stream
○ glucose used as source of energy
○ galactose becomes component of glycolipids and glycoproteins
 Reduced intestinal lactase results in malabsorption of lactose →Unabsorbed lactose →Metabolised by colonic bacteria →Produces gas and short chain fatty acids → leading to the clinical manifestation 
Abdominal cramps , bloating , diarrhoea , flatulence It is not a cause of rectal bleeding

How common ?

Acquired primary lactase deficiency is considered to be highly prevalent – affects approximately 65 to 74 % of the world population Rare in children younger than 5 yrs of age Prevalence is variable among different ethinicities Nearly 100 % of patients with Asian , African or Native-American ancestry develop primary lactase deficiency by adulthood Secondary lactase deficiency is also seen frequently in clinical practice

Types -Primary Autosomal recessive Physiological decline in in lactase conc Lactase deficiency develops at various ages Some studies have shown that it is uncommon before 2-3 yrs of age

Secondary –Follows damage to the small bowel mucosal brush border 2ary to gastroenteritis Resolves when the dis process is over WHO- diarrhoea should have lasted 2 weeks before consideration of lactose intolerance. Causes include-gastroenteritis coeliac disease Crohn’s Ulcerative colitis chemotherapy antibiotics

Congenital-Extremely rare autosomal recessive disorder Manifests at birth soon after milk is introduced Lifelong disorder- failure to thrive and infantile diarrhoea Otherwise normal intestinal mucosa

Developmental-Occurs in premature babies
( < 34 weeks ) Improves once the intestine matures

Often confused with delayed non-IgE mediated cow’s milk protein allergy Lactose intolerance is not immune mediated Terms often used without a sense of different meanings
○ milk allergy
○ milk intolerance Often non IgE mediated disease symptoms are wrongly labeled as symptoms of intolerance People with irritable bowel syndrome have increased symptoms at lower levels of lactose consumption leading to increased self reported lactose intolerance and restriction ( they are also at ↑ed risk )

Presentation History-Abdominal pain ( often crampy ) Diarrhoea Bloating Flatus Loose watery stool- an hour or two after ingestion of milk Borborgymi Some occasions nause and vomiting Peri-anal excorciation due to acidic stool Bowel symptoms only Growth delay after first intake of any mammalian milk Past medical hx, family hx and dietary history

Lactose containing food-In diet as mammalian milk and dairy products Only trace amounts in butter , skimmed milk powder Widely used in food and pharmaceutical industry
○ bulking agent or filler
○ browning agent ( eg in bread )
○ add texture and bind water in processed meats as sausages and burgers , processed chicken
○ slimming products
○ soft drinks and lager beers

Differentials –Diverticular disease Ulcerative colitis Coeliac disease Cystic fibrosis Irritable bowel syndrome Cow’s milk allergy Other disaccharide deficiency Infantile colic Intestinal neoplasm or Polyp Viral gastroenteritis Giardiasis Bacterial infection

Diagnosis –No clear consensus or criterion standard for diagnosis Is testing is needed to confirm a diagnosis remains uncertain Several validated tests exist Food diary may help ( see external link ) Lactose tolerance test
 Lactose breath hydrogen test ( most commonly used )
○ simple and non-invasive
○ measures the hydrogen content of breath after ingestion of lactose
○ based on fermentation of undigested lactose by intestinal flora , 
producing hydrogens, Co2 and methane
○ 78 % sensitive and 98 % specific
 antibiotics taken within last 1 month colonic pH is acidic enough to inhibit bacterial activity adaptation in the bacterial flora as a result of continuous lactose exposureStool acidity test Small bowel biopsy ( gold standard ) Diet elimination confirmation Genetic testing.

It can be presumed to be a case of lactose intolerance if typical symptoms happen 1-2 hr after consumption of dairy containing products ( rather than other food )- review with food diary

Treatment-Recommend reduction in lactose component rather than strict avoidance Most people with primary deficiency can ingest up to 240 ml of fat containing milk ( 12g of lactose ) without any increase in symptoms Advice to divide daily milk intake into several small portions and to take with other foods Prehydrolyzed lactose products ( e.g cheese , milk , icecreams ) can be Yogurts ,curds and cheese may be better tolerated due to
○ thicker consistency → gastric emptying slower
○ lactose is partially hydrolysed by bacteria during preparation Encourage to gradually ↑ milk intake
○ causes changes in intestine that permit higher milk intake Milk-cereal mixtures
○ delay the entry of lactose into intestine → better absorption Ensure adequate calcium intake ( main source for vegetarians is usually milk ) Dietitian input Loperamide

Supplementation-Lactase enzyme supplements Calcium supplements Vitamin D Probiotics

Transient secondary Lactase deficiency-Can happen following a recent episode of gastroenteritis Suspect if symptoms continue beyond 2 weeks after illness It is temporary and can be treated by cutting down lactose containing milk for up to 8 weeks The child can go back to a normal diet as by 8 weeks the gut has healed Lactose free formula can be purchased OTC / Supermarket e.g Aptamil LF , SMA LF or Enfamil 0-Lac


Food journal ( diary ) for lactose intolerance from– consider reviewing with a completed food diary as restricting or excluding lactose from diet can lead to calcium deficiency

This page from answers most of the common questions that parents can pose about lactose intolerance including – post-infectious transient cases

Parents concerned and want to try lactose-free milk? print this and arrange a f/u appt –Lactose-free diet for babies produced by Prescribing Support Dieticians

Temporary Lactose Intolerance– another leaflet which can be printed from Nottinghamshire Area Prescribing Committee

British Nutrition Foundation– information about Lactose intolerance

For patients in Australia printable leaflet from Gastroenterological Society of
Australia ( GESA)

Guideline – National Institute of Health Statement on Lactose Intolerance and Health

Information about breath test from Genova Diagnostics



  1. Lactose intolerance BMJ 2007;334:1331
  2. Walsh J, Meyer R, Shah N, Quekett J, Fox AT. Differentiating milk allergy (IgE and non-IgE mediated) from lactose intolerance: understanding the underlying mechanisms and presentations. Br J Gen Pract. 2016;66(649):e609–e611. doi:10.3399/bjgp16X686521
  3. The Association of UK Dietitians Food Fact Sheet
  4. Lactose Intolerance Test and types  Patient UK
  5. Rapid Paediatrics and Child Health – Helen Brough et al Wiley-Blackwell Lactose Intolerance in Infants , Children and Adolescents Pediatrics September 2006 , VOLUME 118 / ISSUE 3
  6. Lactose intolerance Am Fam Physician .2002 May 1;65 (9) : 1845-1851
  7. Review article : lactose intolerance in clinical practice – myths and realities MCE Lomer , GC Parkes….. Alimentary pharmacology 2008 Wiley Online Library
  8. Lactose Intolerance Journal of the American College of Nutrition Volume 19 , 2000 – Issue sup2 CALCIUM JAMA Insights
  9. Clinical Update Clinical Approach to Lactose Intolerance Dejan Micic et al JAMA October 22/29, 2019 Volume 322 , Number 16
  10. Update on lactose malabsorption and intolerance : pathogenesis , diagnosis and clinical management Misselwitz B et al Gut 2019 Nov ; 68 (11): 2080-2091



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