Lactose intolerance. Everything you need to know

Lactose is a sugar found in milk and dairy products. The small intestine - the organ in which nutrients are absorbed - produces an enzyme called lactase. Lactase breaks down lactose into two simpler forms of sugars: glucose and galactose. The body then absorbs these simpler sugars (monosaccharides) into the bloodstream.

Figure 1. The molecule of Lactose (disaccharide) consists of one molecule of glucose and one molecule of galactose (monosaccharide)

What is lactose intolerance?

Lactose intolerance is a condition in which people have symptoms of indigestion, such as bloating, diarrhea, and gas, after consuming milk or dairy products.

Lactase deficiency and lactose malabsorption can lead to lactose intolerance:

1. Lactase Deficiency: Τhe small intestine of people with lactase deficiency produces low levels of lactase and cannot digest large amounts of lactose.

2. Lactose malabsorption: Lactase deficiency can cause lactose malabsorption. During the malabsorption of lactose, indigestible lactose passes into the large intestine where it is broken down by bacteria to form the gases Hydrogen, Carbon Dioxide, and Methane. These gases cause various abdominal symptoms while both unabsorbed sugars and fermentation products increase the osmotic pressure in the large intestine, causing increased water flow to the intestine resulting in diarrhea. Of course, not all people with lactase deficiency and lactose malabsorption have digestive symptoms.

People develop lactose intolerance when lactase deficiency and lactose malabsorption cause digestive symptoms. Most people with lactose intolerance can consume a certain amount of lactose without the symptoms of indigestion. Patients differ in the amount of lactose they can tolerate.

Some people sometimes confuse lactose intolerance with milk allergy (IgE) and milk intolerance (IgG). While lactose intolerance is a digestive disorder, milk allergy and milk intolerance are reactions by the body's immune system to one or more milk proteins resulting in the production of antibodies (IgE & IgG, respectively). An allergic reaction to milk can be life-threatening, even if the patient consumes only a small amount of milk or dairy product. Milk allergy is more common in the first year of life, while lactose intolerance is more common during adolescence or adulthood.

Types of lactase deficiency

There are four types of lactase deficiency that can lead to lactose intolerance:

Primary lactase deficiency is the most common type of lactase deficiency. In this case, lactase production decreases over time. The decline usually begins at the age of 2 but may begin later in life. Children with this type of lactase deficiency may not show symptoms of lactose intolerance until adolescence or adulthood. Primary lactase deficiency is genetically determined.

Secondary lactase deficiency results from diseases of the small intestine, such as infections or other conditions that damage the small intestine, e.g., surgery. Causes of secondary lactase deficiency include acute gastroenteritis, giardiasis, ascariasis, Crohn's disease, celiac disease, gastrinoma, radiation enteritis, diabetic gastropathy, carcinoid syndrome, Whipple syndrome, HIV enteropathy, kwashiorkor, chemotherapy. Treating the underlying condition usually improves lactose tolerance.

Developmental lactase deficiency can occur in premature infants. This condition usually only lasts for a short time period after birth.

Congenital lactase deficiency is an extremely rare disorder in which the gut produces little or no lactase from birth. It is a genetic disease and is inherited with an autosomal recessive character.

Who is more prone to develop lactose intolerance?

In some individuals, lactose intolerance is more common than in others. In Greece, it is estimated that 30 to over 60% of the population suffers from lactose intolerance. Studies have shown that reduced lactase activity is very common among those of Africa, Asia, Native Americans, Arabs, Jews, Hispanics, Italians, and Greeks.

Figure 2. Global distribution of Lactose Intolerance.

What are the symptoms of lactose intolerance?

The most common symptoms of lactose intolerance include:

• Flatulence, the feeling of fullness, swelling in the abdomen
• Abdominal pain
• Diarrhea
• Gases
• Nausea

Symptoms appear 30 minutes to 2 hours after consuming milk or dairy products. Symptoms range from mild to severe, depending on the amount of lactose consumed and the amount the patient can tolerate.

How does lactose intolerance affect our health?

In addition to causing unpleasant symptoms, lactose intolerance can affect the health of patients because it can prevent them from taking essential nutrients, such as calcium and vitamin D. People with lactose intolerance may not get enough calcium if they do not eat calcium-rich foods or if they do not take supplements. Milk and dairy products are important sources of calcium and other nutrients in the diet. Calcium is essential at all ages for bone growth and maintenance, among others.

Reducing dairy products does not mean that one can not get enough calcium. Calcium is found in many other foods, such as:

• Salmon, sardines, and other fish
• Milk substitutes such as soy milk and rice milk
• Broccoli
• Oranges
• Beans
• Spinach and other green leafy vegetables
• Vegetable and fruit juices
• Almonds
• Bread

It is also important for the patient to get enough vitamin D. Eggs, liver, and yogurt contain vitamin D and the body produces vitamin D when exposed to the sun.

How is lactose intolerance diagnosed?

The diagnosis of lactose intolerance is based on:

• Individual’s medical and family history
• The physical examination
• Medical examinations

Medical examinations. The suspicion of lactose intolerance is based on the symptoms and the (positive) response of the patient to the reduction of dairy foods in his diet. The following tests must be done to confirm the diagnosis:

Lactose tolerance test: The lactose tolerance test measures the body's response to a fluid containing high levels of lactose. After consuming the fluid, blood samples are taken to measure the amount of glucose in the blood (at intervals of 0, 60, and 120 minutes). If the blood glucose level does not rise, it means that the gut (i.e. lactase) did not properly break down and absorb lactose. This test has some drawbacks, such as the possible appearance of annoying symptoms of intolerance, the long waiting time, and the fact that it cannot be applied to patients with diabetes.

Hydrogen breath test: This test also requires taking a fluid that contains high levels of lactose. The amount of hydrogen in the breath is then measured at regular intervals. Under normal conditions very little hydrogen is detectable. However, if the body does not break down lactose, indigestible lactose will be fermented in the large intestine releasing hydrogen and other gases, which are absorbed by the intestine and eventually exhaled. If the amounts of exhaled hydrogen are greater than normal, then it is concluded that there is no complete breakdown and absorption of lactose. This test has also some negatives, such as the possible appearance of the annoying symptoms of intolerance, the long waiting time of the patient in the doctor's office, its high cost but also the fact that its results can be affected by the point that its intestinal microbiome may not be able to produce hydrogen (e.g. due to previous antibiotics), thus giving a false negative result. Also, smoking and certain foods and medications can affect the accuracy of the results.

Stool test for carbohydrates: This test may be used for infants and children who may not have another type of test. Fermentation of indigestible lactose creates lactic acid and other acids that can be detected in a stool sample. The test result is indicative only, as it is highly influenced by the type of diet and the gut microbiome, while intolerance to other carbohydrates (e.g. fructose) can give the same result.

Molecular testing of LCT gene. Lactose intolerance in adulthood is caused by a gradual decrease in the activity (expression) of the LCT gene after infancy. The LCT gene is responsible for the synthesis of the enzyme lactase. LCT gene expression is controlled by a DNA sequence called a regulatory element, which is located in a nearby gene called MCM6. Both of these genes are located on chromosome 21 (position 2q21.3). Some people have inherited changes in this element that lead to prolonged production of lactase in the small intestine and the ability to digest lactose throughout their lives. People without these changes have a reduced ability to break down lactose as they get older, resulting in signs and symptoms of lactose intolerance. With the molecular test that we do in the Diagnostiki Athinon, we check the presence of a specific polymorphism at position 13910 of the LCT gene. Results are given as Normal Homozygote (LCT -13910 T/T), Normal Heterozygote (LCT -13910 T/C) or Pathological Homozygote (LCT -13910 C/C). This test is genetic, completely reliable, is not affected by diet, and is done with a simple blood sample or by taking genetic material from cheek cells. Unlike other methods, it does not cause symptoms of intolerance and it is fast and efficient at a low cost.

Figure 3. The LCT gene is located on chromosome 21 (2q21.3) while the gene that regulates its expression, the MCM6 gene, is in the same loci.

How much lactose can a person with lactose intolerance consume?

Most people with lactose intolerance can tolerate small amounts of lactose in their diet and do not need to avoid completely milk and dairy products. Avoiding milk and dairy products completely reduces the intake of calcium and vitamin D.

Individuals differ in the amount of lactose they can tolerate. Various factors, including the amount of lactase produced by the small intestine, can affect the amount of lactose that a patient can tolerate. For example, one patient may have severe symptoms after consuming a small amount of milk, while another patient may consume a large amount without symptoms. Others can easily eat yogurt and hard cheeses, while not being able to consume other dairy products without digestive symptoms.

Studies show that adults and adolescents with lactose intolerance may consume at least 12 grams of lactose in one take, with few or without symptoms. This amount corresponds to the lactose contained in 1 cup of milk. People with lactose intolerance may be able to consume more lactose if consumed with meals or in small amounts throughout the day.

How can lactose intolerance be treated?

Many patients can manage the symptoms of lactose intolerance by changing their diet. Some of them may just need to limit the amount of lactose they eat or drink. Others may need to completely avoid lactose intake. Using lactase-containing products can help some people manage their symptoms.

For people with secondary lactase deficiency, treating the underlying cause improves lactose tolerance. In infants with developmental lactase deficiency, the ability to digest lactose improves as they develop. Patients with primary and congenital lactase deficiency cannot change their body's ability to produce lactase.

Diet and Nutrition

Milk and dairy products. Gradually introducing small amounts of milk or dairy products can help some people adjust to a situation with fewer symptoms. Some people may tolerate milk and dairy products better when taken with meals, such as milk with cereal or cheese with some bread. People with lactose intolerance are generally more likely to tolerate yellow hard cheeses, such as gruyere or kasseri cheese, than a glass of milk. A serving of 50 g of cheese has less than 1 gram of lactose, while a 1 cup of milk has about 11 to 13 grams of lactose.

Lactose-free milk and milk with reduced lactose. There are lactose-free and low in lactose dairy products and they are nutritionally similar to regular milk and dairy products. In these cases, the milk and dairy products are processed with the enzyme lactase resulting in the breakdown of lactose. Lactose-free milk remains fresh for about the same time and may have a slightly sweeter taste than regular milk.

What products contain lactose?

Lactose is found in many food products and in some medicines.

Foods

Lactose is present in all kinds of milk and dairy products. The food industry often adds milk and dairy products to canned, frozen, packaged, and prepared meals. Patients who have indigestion after consuming even small amounts of lactose should be aware that many food products may contain even small amounts of lactose, such as:

• Bread and other bakery products
• Waffles, pancakes, cookies
• Processed foods such as donuts, sweets, etc.
• Processed breakfast cereals
• Ready mixes for instant puree and soups
• Potato chips, corn chips, and other processed snacks
• Processed meats such as bacon, sausages, ham, etc.
• Margarine
• Sauces
• Powdered meal substitutes
• Powders and protein bars
• Candies
• Cream powder for coffee etc.

Patients with lactose intolerance should check the ingredients on food labels to find possible sources of lactose in food products. If a food label contains any of the following words, the product contains lactose:

• Milk
• Lactose
• Whey
• Cheese curd
• Dairy by-products
• Milk solids
• Skimmed milk powder

Medicines

Some medicines contain lactose, including some prescription medicines such as contraceptives and medicines for stomach hyperchlorhydria. These drugs can cause symptoms in people with severe lactose intolerance.

Conclusions
 

• Lactose is a sugar found in milk and dairy products.
• Lactose intolerance is a condition in which patients experience symptoms of indigestion, such as bloating, diarrhea, and gas, after ingesting milk or dairy products.
• The diagnosis of lactose intolerance is made on the basis of individual and family medical history, clinical examination, and certain laboratory tests.
• A diagnosis based only on the patient's symptoms without laboratory testing can be misleading, because gastrointestinal symptoms are very common and can be the result of many different conditions, in addition to lactose intolerance.
• Most people with lactose intolerance can tolerate some of the lactose in their diet and do not need to completely avoid milk or dairy products. However, the amount of lactose they can tolerate varies.
• Studies show that adults and adolescents with lactose intolerance may eat or drink at least 12 grams of lactose in a single dose, with only a few or without any symptoms. This amount of lactose corresponds to 1 cup of milk.
• Many people can manage the symptoms of lactose intolerance by changing their diet. Some patients may just need to limit the amount of lactose they take while others may need to exclude lactose-containing products from their diet.
• Lactose is found in all kinds of milk and dairy products. The food industry often adds milk and dairy products to canned, frozen, packaged, and ready-to-eat foods. Patients with lactose intolerance should always check the ingredients on food labels.

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