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Column originally published Jul 20, 2004

Mild Lactose-Intolerance Can Follow Gastroenteritis

Question: Our daughter is five months old. Three weeks ago, she developed flu-like illness with vomiting and diarrhoea. I have been breast-feeding her since she was born. Our doctor told us the best treatment for her was to continue breast-feeding. She did recover and her vomiting stopped after a couple of days. However, she still has more frequent and loose stool than before her illness. Otherwise she is completely healthy and gaining weight. I searched the internet and found that this may be the result of lactose-intolerance. However, I don’t understand it completely from what I read. I have lactose-intolerance myself. Does it mean that our daughter will develop the same problem?


What you found on the internet is correct. The most likely cause of your daughter’s on-going problem is lactose-intolerance. Let me try to explain to you more clearly here.

Every child is born with both small and large intestines. Most of the digestion and absorption of food occur in the small intestine. On the inside surface of the small intestine is a layer of cells called intestinal mucosa. These cells are rich in enzymes that help to digest all kinds of food.

The primary food in newborn babies is milk, which contains sugar, fat, and proteins. The kind of sugar present in breast milk, as well as most cows’ milk formula, is lactose. By itself, lactose cannot be absorbed directly into the body: it needs digestion at the intestinal mucosa by an enzyme called lactase. Lactase breaks apart lactose into glucose and galactose. These two simple sugars can be absorbed easily into the body.

Almost all newborn babies are equipped with lactase when they are born. Babies that are born prematurely might not have enough lactase and sometimes cannot tolerate breast milk or regular formula. As a result, lactose intolerance rarely occur in normal newborns.

However, when your daughter contracted the virus that caused vomiting and diarrhoea, the infection temporarily damaged her intestinal mucosa, resulting in shortage of the enzyme lactase. When you continues to nurse her during and after her illness, which is the right thing to do, the amount of lactose present in your breast milk cannot be digested by the reduced amount of enzyme lactase that is still present. As a result, some undigested lactose passes into the large intestine. It is then fermented by normal bacteria that are present in the large intestine, producing acid and gas, and resulting in more frequent and loose bowel movements as well as passing of gas.

Fortunately, this is a temporary problem. Over time, the intestinal mucosa gradually regenerates and produces new cells that contain the enzyme lactase. You will see that her stool gradually returns to the pre-diarrhoea state in frequency and consistency. This, however, may take a little longer time. As long as she is still healthy and growing, you should not be too concerned with her bowel movements. Her body can compensate for the small amount of lactose that she cannot digest or absorb in the meantime.

For those infants who take formula and develop gastroenteritis and persistent diarrhoea because of temporary shortage of enzyme lactase, the formula can be changed to one that doesn’t contain lactose. These lactose-free formula are available as cows’ milk or soy formulas.

Your daughter’s temporary lactose intolerance is quite different from your own problem. Lactose-intolerance in adults is a genetic condition that is much more prevalent in some parts of the world. In North America, about 15% of adult Caucasians are affected. In contrast, 80% of blacks and slightly fewer Asians have severe deficiency in the enzyme lactase when they reach adulthood.

When your daughter gets older, she is going to consume less milk. As a result, the amount of lactase enzyme present in her small intestine will naturally decrease over time. Whether she will develop the adult form of lactose-intolerance or not depends on the genes that she inherited from both of you. She needs both genes (one from you, and one from her father) that call for lactose-intolerance in order to develop the condition. You would have carried both of these genes and passed one of them to her. If she has inherited the same gene from her father, then she will develop this condition.

Adults with lactose-intolerance cannot ingest any significant amount of milk and dairy products, otherwise they will develop symptoms like abdominal pain, distention, loud noises in the abdomen, and diarrhoea. These are very uncomfortable symptoms. Most adults with lactose-intolerance know instinctively to avoid dairy products.

Fortunately, better understanding of medical science has contributed to a simple solution for you and many adults with this condition. The enzyme lactase has been manufactured commercially, and available in drops and pills. They can be taken at the same time when dairy product is ingested. Many adults with lactose-intolerance can now enjoy ice cream, cheese, etc., that were completely off limits before. Lactase is now added to cows’ milk to pre-digest lactose so that lactose-free milk can be purchased directly from supermarkets.

I hope this information will give you peace of mind about your daughter. Enjoy your motherhood and nurse her as long as you can.