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  • Writer's picturefranceswalker@thefoodinto

Lactose Intolerance: a quick guide

Updated: Apr 8

Main Points

  • Lactose Intolerance occurs in over 60% of people worldwide

  • Treatment: reduce lactose in the diet to manageable levels

  • The amount of lactose tolerated is very individual

  • The use of lactase enzymes is often found to be useful, although not strongly supported by evidence

  • Probiotics may have a promising role in the future for managing lactose intolerance.

Over 60% of humans have lactose intolerance (1), and up to 90% in Asian communities!

Although Australia has lower rates (10%) and Northern Europe ( ranges from 2- 20%), these levels are still high (2, 3, 4).

Given these high rates , it is quite surprising that lactose intolerance is often overlooked.

Even more surprising when you think that we have known about how some people have gut symptoms with drinking milk since the days of Hippocrates over 2000 years ago (5).


Essentially lactose intolerance is the body's inability to break down the sugar in milk (= lactose).

A person who is lactose intolerant has reduced amounts of the enzyme LACTASE which is responsible for breaking down lactose.

Lactose is made up of 2 simple sugar units joined together. Hence lactose is called a di-saccharide (2 sugars).

Under normal conditions, lactose is broken down by the lactase enzyme in the gut (small intestine) into its simple sugar units (glucose and galactose).

This allows these two simple sugar units to be rapidly absorbed across the gut wall and be used by the body.

LACTASE (scissors) cuts the link in the lactose to produce the 2 simple sugars: glucose and galactose which can be absorbed in the gut.

If lactose is not broken down into its 2 sugar units (glucose and galactose) then it cannot be absorbed across the gut wall and stays in the gut.

The lactose in the gut irritates the gut wall, attracts extra water into the gut and reaches the large intestine where it is rapidly is fermented by the gut bacteria.

The result is diarrhoea, stomach pain and excess gas, although a small percentage actually report constipation rather than diarrhoea (6).

Lactose is also called a FODMAP and is one of the 4 small carbohydrates that come under the FODMAP name due to the fact that it is a small carbohydrate that is malabsorbed and consequently can cause undesirable gut symptoms.

The other FODMAPs are called fructose, polyols and oligosaccharides, which can also be malabsorbed for different reasons.


LACTOSE is only found in one food: the milk that comes from MAMMALS.

Not only is cow's milk high in lactose but other mammals as well such as goats, sheep, camel, buffalo, reindeer and of course human breast milk. Human milk contains MUCH higher levels of lactose than cow's milk.

Production of the enzyme LACTASE is often pre-programmed to change over time.

Lactase levels are highest for babies at birth who rely on lactose in breast milk for important energy to grow.

The very high level of lactose in breast milk may be linked to the rapid growth of the brain in infancy, and possibly the galactose component of lactose being an important component in brain tissue.

It is extremely rare for a baby have a genetic lactose intolerance. Such a baby will not survive without a special diet from birth.

Lactase levels start to reduce between the ages of 2-5 years of age in some populations, and fall again sharply in later childhood (4).

While lactose intolerance is more common for adults, there are still a significant number of adults who can tolerate lactose.

This is more commonly seen in adults who come from Northern Europe, and it is thought this is an adaptive trait developed in early populations who were able to domesticate cows and use milk for nutrition (6).

Other adult mammals do not retain the ability to tolerate lactose (7).


Short term lactose intolerance can occur when something injures the gut lining and causes the cells on the tips of the microvilli of the small intestine producing the lactase enzyme to be sloughed off.

LACTASE enzyme sits perched on the tip of the microvilli lining the inside of the gut.

Gut wall damage may be caused by:

  • Gastroenteritis

  • Parasitic infection

  • Coeliac Disease

  • Inflammatory bowel disease for example Chron's disease

  • Some drug treatments

  • Bowel surgery (6)

All these processes can cause short term irritation/damage to the lining of the gut wall and effectively wipe out the lactase producing cells.

It takes time for the young or immature specialised lactase producing gut cells that are at the base of the microvilli to develop and migrate to the tip of the microvilli and start producing lactase.

Over time, once the trigger has stopped, gut healing will occur and production of lactase resume, BUT continued injury to the gut wall will continue to remove the mature lactase producing cells sitting perched on top of the microvilli in the gut and cause ongoing secondary lactose intolerance.

Only when the trigger is stopped can gut healing and replenishment of the lactase producing cells occur (4).


There are a few different things that can affect how much lactose you tolerate:

  • Amount of lactose consumed

  • Individual level of lactase enzyme produced

  • What else has been eaten with the lactose food

  • How quickly food moves through your gut (= gut transit time)

  • Your gut microbiome (6)

As you can see, these factors can vary and be very individual. Most people with lactose intolerance can tolerate 5g of lactose in a sitting and more if lactose is eaten with other nutrients (8).

Continuing to eat very small amounts of lactose over time may actually improve your lactose intolerance which most likely occurs via promotion of beneficial gut bacteria that can break down the lactose, however the evidence supporting this is weak (4, 9, 10).


lactose intolerance is commonly diagnosed via a lactose breath test or by an elimination diet and challenge that can confirm that lactose is causing the gut issues.


Taking lactose out of the diet is made a lot easier these days with the plethora of lactose-free food products now available.

It is easy to find lactose-free milk or lactose-free yoghurt, and even foods like lactose-free ice cream and lactose-free cream cheese. Hard cheeses contain minimal lactose so are tolerated well as is butter.

Lactose is often used as a food additive and as a result can be found throughout many foods. It can be added as ingredients such as milk powder or condensed milk which are both very concentrated sources of dairy and can also be added in the form of evaporated milk, milk solids, buttermilk and whey.

The trick here is to read the food label to see if dairy has been added. By law, the addition of dairy must be stated, whether it be bolded next to an ingredient or in an allergen type statement.

Lactose is often added to medications- when added to tablets it is such a small a mount it can be consumed without issues, except in a few very sensitive individuals or if a very large number of lactose containing pills is taken at the same time.

Watch out for liquid or syrup types of medications where lactose may be present.


Although the evidence for lactase enzymes is weak (11, 12) many people do report it can help.

The impact of taking lactase enzymes is very short lived, so should be taken when eating a food or meal containing lactose if any benefit is to be felt.

Useful when eating or drinking foods containing large amounts of lactose.

There are many products available, for example Lactaid and Lacteeze. Practical advice is to have 2 standard tablets with a glass of milk and 1-2 with a dairy dessert.

A standard individual tub of yoghurt may require none or a maximum of 1 given that some of the lactose is already broken down due to the yoghurt fermentation process.


Lactase-containing microorganisms in yogurt and fermented milk break down lactose and can often be tolerated in greater amounts despite having lactose intolerance.

Furthermore, there is increasing evidence that probiotics may help reduce the symptoms of lactose intolerance depending on the species or strain of the probiotic (6).

A recent review of how well different strains of probiotics can help manage lactose intolerance has highlighted how gut improvements can be made and in some cases almost resolution of the lactose intolerance.

However, there are only a small number of studies and the impact can be affected by the dose or concentration of the probiotic, how the probiotic is prepared and the activity of the enzyme (13).

Overall results are still inconclusive at this stage but looking promising!

In Conclusion

Lactose Intolerance is widespread, and can be managed by limiting the amount of lactose consumed in a sitting to be less than 4-5g, choosing lactose-free alternatives such as lactose-free milk and use of lactase enzymes taken with the food containing lactose.

The use of probiotics remains controversial although there are some promising studies that may enhance management of lactose intolerance in the future!


1. Oak SJ, JHA, R. The effects of probiotics in lactose intolerance: A systematic review. Crit Rev Food Sci Nutr. 2018 Feb 9:1-9. doi: 10.1080/10408398.2018.1425977.

2. Swallow D.M. Genetics of lactase persistence and lactose intolerance. Annu. Rev. Genet. 2003;37:197–219. doi: 10.1146/annurev.genet.37.110801.143820.

3. European Food Safety Authority (EFSA) Scientific opinion on lactose thresholds in lactose intolerance and galactosaemia. EFSA J. 2010;8:1777. doi: 10.2903/j.efsa.2010.1777.

4. Joy Anderson. Food-sensitive babies. Dietary Investigation for breastfed babies. Specialist Dietetics and lactation Services, 2016.

5. Matthews S.B., Waud J.P., Roberts A.G., Campbell A.K. Systemic lactose intolerance: A new perspective on an old problem. Postgrad. Med. J. 2005;81:167–173. doi: 10.1136/pgmj.2004.025551.

6. Fassio F, Facioni MS, Guagnini F. Lactose Maldigestion, Malabsorption, and Intolerance: A Comprehensive Review with a Focus on Current Management and Future Perspectives. Nutrients. 2018;10(11):1599. Published 2018 Nov 1. doi:10.3390/nu10111599

7. Deng Y., Misselwitz B., Dai N., Fox M. Lactose intolerance in adults: Biological mechanism and dietary management. Nutrients. 2015;7:8020–8035. doi: 10.3390/nu7095380.

8. Shaukat A., Levitt M.D., Taylor B.C., MacDonald R., Shamliyan T.A., Kane R.L., Wilt T.J. Systematic review: Effective management strategies for lactose intolerance. Ann. Intern. Med. 2010;152:797–803. doi: 10.7326/0003-4819-152-12-201006150-00241.

9. Hertzler S.R., Savaiano D.A. Colonic adaptation to daily lactose feeding in lactose maldigesters reduces lactose intolerance. Am. J. Clin. Nutr. 1996;64:232–236. doi: 10.1093/ajcn/64.2.232.

10. Briet F., Pochart P., Marteau P., Flourie B., Arrigoni E., Rambaud J.C. Improved clinical tolerance to chronic lactose ingestion in subjects with lactose intolerance: A placebo effect? Gut. 1997;41:632–635. doi: 10.1136/gut.41.5.632.

11. Ojetti V., Gigante G., Gabrielli M., Ainora M.E., Mannocci A., Lauritano E.C., Gasbarrini

12. Montalto M., Nucera G., Santoro L., Curigliano V., Vastola M., Covino M., Cuoco L., Manna R., Gasbarrini A., Gasbarrini G. Effect of exogenous β-galactosidase in patients with lactose malabsorption and intolerance: A crossover double-blind placebo-controlled study. Eur. J. Clin. Nutr. 2005;59:489–493. doi: 10.1038/sj.ejcn.1602098.

13. Savaiano D.A. Lactose digestion from yogurt: Mechanism and relevance. Am. J. Clin. Nutr. 2014;99(Suppl. 5):1251S–1255S. doi: 10.3945/ajcn.113.073023.


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