Are you really lactose intolerant?

If you've cut down on milk because you think your gut can't tolerate the sugar in it - called lactose - you might be doing your health a disservice, a new study suggests.

Researchers found that in fact, more than half the patients who thought they couldn't digest lactose were mistaken. When they drank a lactose solution corresponding to an entire litre of milk in the lab, their gut absorbed the sugar normally and they experienced less cramping, gas and other bowel trouble than at home.

"There is extended belief among patients with abdominal symptoms that these are caused by lactose in dairy products," the Spanish researchers write in the journal Clinical Gastroenterology and Hepatology.

"Although one should think that symptom intensity has to be greater after a large lactose load than in daily life at home, our study shows just the opposite," they add.

Normal absorption of lactose

The ability to digest lactose depends on an enzyme in the gut called lactase. When there isn't enough of this enzyme, bacteria feast on the leftover sugar, producing lots of gasses in the process.

In contrast to this so-called lactose malabsorption or maldigestion, lactose intolerance refers to the symptoms - for instance, flatulence and stomach pain - that occur after ingesting lactose.

The new study adds to a body of evidence showing that perceived lactose intolerance may actually not be rooted in a biological inability to absorb the sugar. Of 353 individuals referred to specialists for suspected lactose maldigestion, as many as 189 turned out to absorb the sugar normally, with fewer symptoms than at home.

It's not entirely clear why people who have no trouble digesting lactose would get symptoms. The Spanish researchers, from the Hospital Universitari Vall d'Hebron in Barcelona, speculate that some patients could be suffering from irritable bowel syndrome, which has similar symptoms.

Memory of over-consumption

Another possibility is that the symptoms are linked to a memory of earlier over-consumption.

"If you did have an instance when you consumed too much, then you'd have symptoms, and you'd remember that," said Carol J. Boushey, a nutritional scientist at Purdue University in West Lafayette, Indiana, who was not involved in the study. "It's something that's in your head after a while."

Boushey, who is also a registered dietitian, said that cutting back on dairy products as a result of perceived lactose intolerance could have a negative health impact, including lower bone mass, higher blood pressure and colon cancer.

She recommends that people who think they are lactose intolerant try to drink small amounts of milk.

"You could drink a quarter cup of milk and see if you can handle it," she told Reuters Health. "But don't ever go over a cup. Every single person that I asked to do that came back and said you're right." - (Frederik Joelving/Reuters Health, May 2010)

(Source: Clinical Gastroenterology and Hepatology, online April 10, 2010)