Lactose Malabsorption and Lactose Intolerance

Two ideas that need separating

Having bloating, wind or diarrhoea after drinking milk is quite common. But it should not be assumed that everyone with these complaints is “allergic to milk” or has to remove dairy products from their life entirely.

First, two ideas need to be separated from one another:

Lactose malabsorption: the failure of lactose to be sufficiently digested and absorbed in the small bowel.

Lactose intolerance: the appearance of complaints such as abdominal pain, bloating, wind or diarrhoea in a person with lactose malabsorption after they have taken lactose.

So not everyone with lactose malabsorption has lactose intolerance.

A person may absorb lactose insufficiently and still have no complaint at all.

What is lactose?

Lactose is a sugar found naturally in milk and dairy products.

For lactose to be absorbed from the bowel, it must first be split into two smaller sugars by an enzyme in the small bowel called lactase:

lactose → lactase enzyme → glucose + galactose → absorption from the bowel

If there is not enough lactase, part of the lactose reaches the large bowel undigested.

What happens in lactose malabsorption?

The lactose that reaches the large bowel undigested is fermented there by the bowel bacteria.

Gas and certain other substances are produced as a result. Water may also be drawn into the bowel.

In some people the result may be:

• Bloating,
• Wind,
• Rumbling in the abdomen,
• Abdominal pain or cramp,
• Diarrhoea,
• A sudden need to open the bowels.

But the severity of the symptoms varies considerably from person to person.

How common is it worldwide?

Lactose malabsorption is very common worldwide.

In most people the activity of the lactase enzyme in the bowel naturally begins to fall after childhood. It is estimated that lactase activity is reduced in adulthood in about two thirds of the world’s population.

But the frequency differs greatly between populations.

Lactase activity continuing into adulthood is commoner in populations of northern European origin; a fall in lactase activity is far commoner in Asian, African, South American and certain Middle Eastern populations.

The main reason for this difference is genetic, and is related to the milk-drinking habits of populations over thousands of years.

Important: that lactose malabsorption is common does not mean that the same proportion of people experience lactose intolerance.

A substantial proportion of people with malabsorption can take a certain amount of milk or dairy with no complaints at all.

What are the symptoms of lactose intolerance?

The complaints generally appear after foods or drinks containing lactose have been taken.

The commonest are:

• Bloating of the abdomen,
• Wind,
• Abdominal pain or cramp,
• Rumbling in the bowels,
• Diarrhoea,
• Nausea.

The severity of the symptoms does not depend on the amount of lactase enzyme alone.

The amount of lactose taken, whether it is taken together with other food, the bowel flora, the sensitivity of the bowel and how far the person perceives the symptoms all matter too.

Why does lactose malabsorption occur?

1. Primary fall in lactase

This is the commonest situation.

In infancy the lactase enzyme is high, because milk is the staple food. In many people the production of lactase falls progressively after childhood, in a genetically programmed way.

This is not a disease; it is a very common biological characteristic in human beings.

2. Secondary lactose malabsorption

Sometimes the reason for the fall in the lactase enzyme is another bowel disease.

For instance:

• Coeliac disease,
• Crohn’s disease,
• Certain bowel infections,
• Other diseases that damage the lining of the small bowel

can reduce lactase activity temporarily or permanently.

When the underlying disease is treated, tolerance of lactose may recover.

3. Congenital lactase deficiency

This is a very rare genetic disease.

The baby cannot digest lactose from birth, and severe diarrhoea can develop with foods containing lactose, including breast milk.

This is entirely different from the common lactose intolerance seen in adults.

Are lactose intolerance and milk allergy the same thing?

No. They are entirely different conditions.

Lactose intolerance: the problem is with the digestion of lactose, the sugar in milk. It is not a disease of the immune system.

Milk protein allergy: the immune system reacts against the proteins in milk. Hives, swelling, vomiting, breathing problems and, in some situations, serious allergic reactions can occur.

For this reason:

lactose intolerance ≠ milk allergy

How is the diagnosis made?

Which foods the patient’s complaints are related to is assessed first.

Different tests may be used where necessary.

The hydrogen breath test

This is today one of the methods used most often in assessing lactose malabsorption.

The patient is given a set amount of lactose, and the hydrogen in their breath is measured at set intervals.

If lactose is not sufficiently absorbed in the small bowel it is fermented by the bacteria in the large bowel, and the production of hydrogen increases.

But a positive breath test does not on its own mean “lactose intolerance”.

Alongside demonstrating malabsorption during the test, it is important that the patient’s symptoms are assessed too.

The lactose tolerance test

Another method is the lactose tolerance test.

After the patient is given lactose, the blood sugar is measured at set intervals.

When lactose is broken down and absorbed normally, a rise in the blood glucose is expected. The expected rise not happening may suggest that the lactose has not been sufficiently digested.

Today the hydrogen breath test is in many situations a more direct and practical method of assessment.

Does everyone with bloating have lactose intolerance?

No.

Bloating, wind, abdominal pain and diarrhoea can be seen in many different conditions.

For instance:

• Irritable bowel syndrome (IBS),
• Coeliac disease,
• Inflammatory bowel diseases,
• Certain bowel infections,
• Other carbohydrate intolerances

can cause similar complaints.

For this reason it is not always right to make a firm diagnosis from the observation “I drank milk and my abdomen swelled up”.

Are IBS and lactose intolerance the same thing?

No.

But the two can be present together.

In patients with IBS the bowel’s sensitivity to gas and to distension may be increased. The same amount of unabsorbed lactose may therefore cause no complaint at all in one person while producing marked bloating and pain in another who has IBS.

This shows that in lactose intolerance it is not only digestion that matters but the sensitivity of the bowel too.

Does someone with lactose intolerance have to give up dairy entirely?

Most of the time, no.

Lactose intolerance does not mean “you must consume zero lactose”.

Many people can tolerate about 12 grams of lactose at a time, particularly when taken together with other food. This amount corresponds to roughly a glass of milk.

But individual tolerance varies a great deal.

For this reason the aim should be:

not “to forbid all dairy products” but “to establish the amount the person can tolerate”.

Which dairy products are more easily tolerated?

Some dairy products contain less lactose or are more easily tolerated.

For instance:

• Yoghurt,
• Hard and matured cheeses,
• Lactose-free milk and dairy products

can be taken more comfortably by many people.

The amount of lactose in hard cheeses in particular is quite low.

Can the lactase enzyme be used?

In some people, tablets or drops containing the lactase enzyme can help.

These products make lactose easier to digest and can reduce complaints such as wind, bloating and diarrhoea.

But not everyone needs to use them continuously.

Is there a drawback to cutting out dairy entirely?

Removing all milk and dairy products from the diet unnecessarily can lead to an insufficient intake of:

• Calcium,
• Protein,
• Vitamin D,
• Certain other nutrients.

This matters more in children, in adolescents, in pregnancy and in people at risk of osteoporosis.

Unnecessary and excessively restrictive diets should therefore be avoided.

The important message

Lactose malabsorption and lactose intolerance are not the same thing.

Lactose malabsorption: the failure of lactose to be sufficiently digested in the small bowel.

Lactose intolerance: that malabsorption giving rise to symptoms such as bloating, wind, pain or diarrhoea.

Although lactase activity falls in adulthood in most of the world’s population, not everyone with malabsorption has complaints when they take milk.

Most patients do not need to give up all dairy products. The best approach is to establish the amount of lactose the person can tolerate, and to avoid unnecessary restrictions of food.

This content has been prepared for general information. Where digestive complaints are persistent or serious, assessment by a doctor is needed so that other conditions can be excluded and the right diagnosis made.