Nutrition Myths
Lactose intolerance symptoms


Lactose intolerance symptoms, causes and treatment

What is lactose intolerance (dairy intolerance)?

Milk and other dairy products contain a sugar called lactose. Lactose is a disaccharide that is composed of two simple sugars (monosaccharides): glucose and galactose.

Our bodies normally produce an enzyme called lactase in the small intestine.

This enzyme breaks down lactose into these simple sugars, in order to transport them across the cell membranes of the small intestine into the bloodstream.

If the lactase enzymes are missing or insufficient, then lactose remains in the intestine.

Breakdown of lactose

Lactose in the intestine starts to attract fluids into the bowel through a process called osmosis. (1) The sudden increase of fluids inside the intestine results in diarrhea.

Unabsorbed lactose present in the colon is fermented by bacteria to produce gas (especially hydrogen), fatty acids and monosaccharides, which cannot be absorbed by the colon.

Since lactose molecules are not broken down or absorbed, they attract even more fluids to the small intestine, again through the process of osmosis.

The inability to break down lactose and to absorb its components results in havoc inside the intestine and produces lactose intolerance symptoms.

Lactose intolerance is sometimes called dairy intolerance. Lactose intolerance is the correct term, however, since it refers specifically to lactose.

Can you develop lactose intolerance?

Lactose intolerance can develop at any age. Although babies and children can be affected, the most common age range is between 20 and 40 years.

Lactose intolerance is caused by one of the four types of lactase deficiency: (2)

  1. Primary lactase deficiency: caused by inheriting genes, with the African, Asian and Hispanic populations mostly affected. This is the most common type of intolerance.

    Infants produce a large amount of lactase, since their diet consists primarily of milk. Since with age, milk gets replaced by various foods, high amounts of lactase are no longer needed and its production drops.

    It doesn’t completely stop however; lactase continues to be produced to be able to break down the lactose in an adult’s diet.

    In the case of primary lactose deficiency, this decrease of lactase production is  significant, which is why adults with this condition cannot digest milk products;

  2. Secondary lactase deficiency: may be caused by an infection or disease related injury to the small intestine. If the underlying causes are treated in time, lactose tolerance can improve.
  3. Developmental lactase deficiency: is a temporary, short term intolerance which may occur in prematurely born babies.
  4. Congenital lactase deficiency: is a very rare genetic disorder, where the small intestine doesn’t produce lactase at all or produces very little from the time of birth.

Symptoms of lactose intolerance

The most common symptoms of lactose intolerance usually occur within 30 minutes to a few hours after consuming lactose-containing products.

These symptoms can vary in intensity, from mild to severe, depending on the amount of lactose consumed in one sitting and the extent to which an individual can tolerate lactose. (3, 4)

Lactose intolerance symptoms

The symptoms of lactose intolerance include:

  • Abdominal cramps or lower abdominal pain;
  • Flatulence;
  • Gas and bloating;
  • Gurgling in the abdomen area;
  • Loose stools, diarrhea or foamy stools;
  • Nausea and sometimes vomiting;
  • Swelling or feeling of fullness in the abdomen.

Lactose intolerance symptoms, of different levels of severity, occur in about 70% of the world population, with the highest prevalence in the African, African-American, and Asian populations.

On the other hand, lactase persistence which occurs in approximately 30% of the world population, is the ability to break down lactose.

It is mostly common in people with European ancestry but also in some areas in Western Africa, the Middle East and South East Asia. (read more..)

Lactose intolerance and impact on nutrients

Individuals with lactose intolerance usually limit or avoid dairy products due to the unpleasant symptoms.

NOTE: even if you are lactose intolerant, depending on the level of intolerance, you can still have some dairy products and not experience any side effects. (read more..)

If milk and dairy products are limited or absent in the diet, deficiencies of some essential nutrients might occur if the right dietary substitution is not made.

Dairy products are the main source of calcium and vitamin D in the western diet and an important source of protein and fat for children.

Calcium is essential for building up and maintaining bones regardless of age. The lack of calcium in the diet may cause a reduction of the bone density, leading to osteoporosis.

Therefore, after reducing or eliminating milk and dairy, it is essential to replace them with other calcium food sources. (read more..)

Milk is also a good source of vitamin D. Vitamin D is usually obtained from the exposure to the sun.

However, this is not always possible and vitamin D deficiencies have been known to occur in areas of high latitude or with prolonged winter seasons.

It can also be related to other factors, such as restricted ultraviolet B exposure. Common deficiencies of vitamin D lead to muscle myopathy, nutritional rickets and osteomalacia.

If exposure to the sun is limited for any reason in the individuals that cannot drink milk, other vitamin D sources should be included in the diet (read more..). (5)

Milk and dairy products are also rich in energy, vitamins B2, B5 and B12, phosphorus, potassium, selenium and zinc. (read more..)

If you are lactose intolerant, you must insure the adequate nutrient substitution from other food sources.

List of foods with lactose

The largest amount of lactose is found in milk and milk products.  However, many other processed and non-dairy products, such as canned, packaged or frozen foods, also contain some added amounts of lactose.

For information purposes, lactose containing products must show on their label one of the following ingredients: caseinates, cheese, butter, yogurt, curds, dry milk solids, lactose, milk, milk by-products or non-fat dry milk powder.

In addition to dairy products (such as milk, yogurts, cheese, cream, ice-cream, dairy dessert and dairy blend spreads), the following products may also contain lactose:

  • Additives and food ingredients: herbs, seasonings and spices
  • Alcoholic beverages, such as cream-based liqueurs
  • Biscuits/cookies
  • Breads and bread products
  • Breakfast cereals
  • Cakes, slices and other battered products
  • Candies
  • Condiments, such as dressings, pastes and sauces
  • Egg products, such as scrambled eggs or omelettes
  • Hamburgers, pizzas and other take-out products
  • Margarines
  • Noodles and pasta products
  • Non-dairy liquid and powdered coffee creamers
  • Non-dairy whipped toppings
  • Pastries, pies and tarts
  • Pancakes
  • Processed meats
  • Protein powders and energy bars
  • Snack foods such as muesli bars or potato or corn chips
  • Soups
  • Sugar, confectionery and sweet spreads

For comprehensive lists of foods that contain lactose in Australia and the U.S. go to the corresponding links in the references section. (6, 7)

Medications containing lactose

Lactose has excellent compressibility properties and for that reason is used by the pharmaceutical industry as a component for tablets.

Other uses of lactose in pharmaceutical products are in dry-powder inhalators as diluent powder.

The amounts of lactose in the medications are very small and do not cause any symptoms in most cases, except with severe lactose intolerance.

For more information on which drugs contain lactose please visit (8)

Lactose intolerance diet

If you need to avoid or limit dairy products, it is advisable to see a registered dietitian or nutritionist to design a nutrition plan for you.

This is important not only to manage the lactose intolerance but also to insure that you get an adequate range of nutrients to avoid deficiencies and resulting health problems.

Some of the main points to be aware of are:

  • Find out what your lactose limit is. How much dairy and what type of products you can consume without experiencing intolerance symptoms. The assistance of the dietician/nutritionist is advisable;
  • If you need to limit or avoid dairy, it is crucial to increase the intake of foods rich in calcium. Please see the table of the richest calcium sources here;
  • Choose lactose-free dairy products, such as lactose-free milk;
  • You may consider taking lactase supplements, which will help you break down lactose from the dairy products;
  • Make sure that you have enough exposure to sunlight to obtain your daily dose of vitamin D or from the diet; (read more..)
  • Insure that you have enough of the other micronutrients that milk and milk products are rich in including: vitamins B2, B5 and B12, phosphorus, potassium, selenium and zinc.

The most important thing to remember is: rather than excluding dairy from your diet, find out what your lactose threshold is (how much is too much milk, cheese or yogurt for you) and add to your diet those milk products in the amounts that don’t cause any symptoms. (read more..)

Will drinking too much milk cause lactose intolerance symptoms?

Yes, everybody has a limit of how much milk (containing lactose) they can have in one dose or throughout the day.

This limit is determined by the amount of lactase one is able to produce. Even if you can tolerate lactose well, if you consume extremely high quantities of milk you may experience lactose intolerance symptoms, since your small intestine has a limited ability to produce lactase.

While lactose tolerant individuals can handle larger (but still, not extreme) amounts of lactose, in the case of lactose intolerant people, the lactose limit is much lower and varies.

One intolerant person can have a glass of milk without displaying any symptoms while another can be severely affected just after a few sips. Often people who cannot drink milk at all, can handle hard cheese or yogurt without being affected.

Most lactose intolerant adolescents and adults can tolerate 12g of lactose (1 glass of milk) in a single dose (especially when accompanied by food), either without experiencing any symptoms or with only minor symptoms.

A total of 24g in one sitting produces considerable symptoms, however when distributed throughout the day with other foods and nutrients, it may be well tolerated. (9, 10)

Lactose intolerance test

Lactose intolerance can be diagnosed by various methods:

  • Physical exam, by checking the usual signs and symptoms such as abdominal bloating, tenderness or pain and listening for the sounds in the abdomen using a stethoscope.
  • Checking family medical history and diet history and eliminating other possible causes of the symptoms.
  • Elimination diet

    An efficient method to test for lactose intolerance is the elimination method where lactose is eliminated from the diet and if symptoms disappear, it may indicate lactose intolerance.

    This test needs to be thoroughly planned, however, since other ingredients eliminated together with dairy products may be responsible for the symptoms.

  • Lactose Intolerance tests performed in the laboratory.

    There are two tests available:

    – hydrogen breath tests – since undigested lactose produces higher levels of hydrogen, measuring the amount of hydrogen in the breath after a drink with a known amount of lactose gives an indication of a higher than usual amount of hydrogen.

    – stool acidity test – undigested lactose produces lactic acid which gets excreted in the stool. Higher acidity of the stool or undigested glucose in the stool indicates undigested lactose.

Treatment of lactose intolerance

There is no cure for lactose intolerance. The most effective method of eliminating symptoms of lactose intolerance is to limit or avoid (depending on the severity of symptoms) foods containing lactose from your diet.

However, lactase enzymes are available in health food stores in the form of liquid, tablets or capsules.

By adding them to milk or taking them just before a lactose containing meal, it helps breaking down the lactose and reduces the symptoms of lactose intolerance. (11)

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