Allergy to dairy strikes after adulthood sets in

Zhang Long never thought last weekend could have been ruined by a bowl of baby formula.

On Friday, he tried a new kind of formula milk, which later caused him excessive diarrhea that lasted for more than two days. Zhang, 36, was at a loss since his little girl has been drinking the same formula but nothing happens to her.

Actually, in the past few years, Zhang had experienced occasional abdominal distension or even minor diarrhea after drinking milk, which he didn't pay much attention to. This time it was serious, so Zhang searched online and found out the explanation for all these episodes - he is lactose intolerant.

Lactose intolerance is the inability to digest lactose, a natural sugar found in dairy products including milk. It causes various symptoms, including flatulence, cramps, diarrhea and even vomiting.

"It's a result of insufficient amounts of lactase, an enzyme that catalyzes the breakdown of lactose in the body," explained Zhang, also a high school biology teacher.

It's a common condition among adults. Mammals lose lactase as they grow up and stop drinking breast milk. About three quarters of adults worldwide experience a decrease in lactase activity during adulthood.

Studies show that the situation varies among different countries and ethnic groups. For example, intolerance is more common in Asian and African regions, with upwards of 80 percent of those populations affected. Compare that to just 11 percent of English people or 12 percent of American Caucasians, according to a 2006 research report published in Modern Food Science and Technology.

The difference stems from a genetic change in most people derived from Western Europe, due to the prevalence of milk in the Western diet, and they developed lactose persistence beyond infancy, which means they are able to digest lactose for their entire lives.

"One interesting fact is that many kittens worldwide become intolerant when they mature, but a lot of European breeds don't have such a problem, because of a similar genetic difference caused by persistent milk consumption," said Zhang.

It seems that among Chinese, lactose intolerance is common, but not everyone affected is aware of it. Like Zhang himself, many learn the hard way.

In TV land, Leonard Hofstadter, one of the lead characters of The Big Bang Theory, is lactose intolerant. His lactose-induced farting is a comedy fixture on the popular American sitcom.

In the real world, lactose intolerance is less of a laughing matter. When enjoying a latte with friends, Mai Zi, a 28-year-old Beijinger who works in Internet advertising, said it was really hard.

In 2009, Mai could still enjoy some milk products. But milk started to cause him diarrhea and it kept getting worse. Today, consuming milk products means having loose bowels for several days.

Mai has never tried cheese, and doesn't dare to, considering the fact that many people have severe reactions against other dairy products, such as cheese, cream and butter.

Yogurt is tolerable by most lactose intolerant people because it contains lactase produced by the bacterial cultures. Clarified butter and frozen yogurt without added milk solids are among the few dairy products that have low levels of lactose.

But yogurt is not a cure for all. Mai cannot have yogurt, either. For people like him, soy milk, rice milk, almond milk, coconut milk and other plant-based milks are the best alternatives.

Consuming milk in small portions or together with grains is also helpful for those with mild intolerances, said Gu Zhongyi, a clinical nutritionist at Beijing Friendship Hospital.

"It's not a disease and there's no cure. That doing exercises can help is a rumor, and not true," remarked Gu.

"Not drinking milk is not a big deal. People have already lost faith in milk products in China," said Mai, referring to the milk safety scandals of the last few years. "Look on the bright side - you won't get poisoned by the unscrupulous dairy producers."

Perhaps it's time for the domestic dairy industry to create low-lactose or lactose-free products specially for the Chinese who suffer from intolerance.

A report in June by Xinhua News Agency said scientists at a North China university have bred the world's first genetically-modified calf that will produce low-lactose milk. Whether or not the experiment was a success will be determined when the calf matures in two years.

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