Because of spam, I personally moderate all comments left on my blog. However, because of health issues, I will not be able to do so in the future.

If you have a personal question about LI or any related topic you can send me an email at I will try to respond.

Otherwise, this blog is now a legacy site, meaning that I am not updating it any longer. The basic information about LI is still sound. However, product information and weblinks may be out of date.

In addition, my old website, Planet Lactose, has been taken down because of the age of the information. Unfortunately, that means links to the site on this blog will no longer work.

For quick offline reference, you can purchase Planet Lactose: The Best of the Blog as an ebook on or Almost 100,000 words on LI, allergies, milk products, milk-free products, and the genetics of intolerance, along with large helpings of the weirdness that is the Net.

Thursday, April 30, 2009

Exercise and Lactose Intolerance

A question arrived in email from Ken, because he couldn't find the information on my website.

Is there any evidence that strenuous exercise can trigger LI symptoms?

I had to laugh. Not at Ken, but at the medical profession. Here's my reply.
I'm not surprised you couldn't find an answer to this question, though. It appears only on my "Questions Even I Couldn't Answer" page. Seriously.

No real medical study has ever been done trying to correlate LI symptoms with other everyday activities. Anecdotal response works both ways. People have told me that their symptoms sometimes increase or go away with exercise. It's hard to come up with a mechanism that would account for either if LI is the cause. Somewhat more plausible are conditions like Irritable Bowel Syndrome, which can be triggered by milk products, offers similar symptoms, and is correlated with body activities.

All I can say is to try taking lactase pills with any milk products you have before or after exercise, or see if avoiding milk entirely for a few days makes a difference. If the symptoms appear anyway then at least you've eliminated one cause.

Questions Even I Couldn't Answer is one of the oldest pages on my website. The last revision was in, gulp, 2000. And you know what? None of those questions have ever been answered.

Some are just odd. But most of the rest fall into the same category, the one I mention in my response to Ken. Almost all research ever done on lactose intolerance (LI) involves simple yes/no thinking. Doctors, ethnologists, medical researchers, and geneticists have all looked at individuals or populations with one thought in mind: determining whether or not the people examined have the gene for or test in the laboratory for LI.

A bit of testing has followed the progression of meals through the gastrointestinal system, so that we know that symptoms are reduced when lactose is taken as part of a meal or, to a lesser degree, when any solids are involved, even a comparison between chocolate or regular milk. The reason for this seems to be that solids lengthen the time that the lactose-containing food takes during its trip through the small intestine and that given the remaining lactase in a system more time to work.

That's it. Whether symptoms differ with sex or age, with amount or type of exercise, with time of day, week, month, or year, with the consumption of alcohol or use of cigarettes, with vitamin, mineral or nutritional supplements, or with any other factor you might think of has not been tested at all.

The reason is unfortunately simple as well. LI is not dangerous, not life-threatening, not hospitalizing. It can be mitigated with pills or food avoidance. Medical tests are costly. People have complicated lives. Trying to conduct reasonably sized and lengthed tests for foods or factors that are medically serious is a near-impossible task. Nobody will fund the dozens or hundreds of tests involving thousands of people that would be minimally required to answer these LI questions.

We'll probably never know the answers to seemingly basic questions that I keep being asked by sensible people attempting to better understand their lives. It's a pity.

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is said...

I recently became slightly LI and i've been ramping up my exercise habits quite a bit. It seems like a possible correlation. I've never had milk problems before

Anonymous said...

I've been LI since I was 28. I'm almost 50 now. It was very well under control before I started exercising vigorously 3 times a week. I've read "lactate is constantly produced during normal metabolism and exercise", and "does not increase in concentration until the rate of lactate production exceeds the rate of lactate removal."

It would be wonderful if 'someone' could prove or disprove vigorous exercise as being a lactic acid source inducing LI symptoms.

Everyone else in the world seems to focus on ingestion as the only means of LI.

Tony F.

Steve Carper said...

Lactate and lactose are totally different things. Lactate and the lactic acid produced during exercise have nothing to do with lactose. No lactose is produced by the body during exercise or any other time. Ingestion is indeed the only means of LI.