Saturday, April 29, 2006

JAMA's Bad Science: Live Longer With Calorie Restriction?


A lot of people these days are pushing severe "calorie restriction" diets as a way to boost longevity, based on studies in mice showing that they live a good deal longer if you reduce their caloric intake by as much as 40%.

Do those diets work on humans? Only time will tell. A friend of mine, pursuing a version of these diets (the alternate fast diet) recently sent me a study from the Journal of the American Medical Association (JAMA) that supposedly supports this theory.

If you ask me, the study is just another example of the remarkably bad science that gets published even in purportedly reputable journals such as JAMA.

In the study ("Effect of 6-Month Calorie Restriction on Biomarkers of Longevity, Metabolic Adaptation, and Oxidative Stress in Overweight Individuals, JAMA Vol. 295, No. 13, Apr. 5, 2006, in case you care), the researchers looked at the effects of three restricted calorie diets over a six month period on a group of overweight subjects. (They were only moderately overweight, with body mass indices between between 25-30--anything under 25 is considered fine.)

The study showed, not surprisingly, that in overweight individuals, each of the three calorie restricted diets (one was half calorie restriction and half exercise) resulted in improved "metabolic" indicators after six months compared to a control group that simply maintained its overweight status.

The authors concluded: "Our findings suggest that 2 biomarkers of longevity (fasting insulin level and body temperature) are decreased by prolonged calorie restriction in humans ."

WRONG!!!!

What the study really showed is that if you put a group of overweight individuals on a severe diet for six months, their health will improve. Is that a big surprise? No. Does that merit publication in JAMA? Not really--it's nothing new. All it shows is that if you're a bit overweight and you manage to take the pounds off (and thus get to "normal" weight), then you might live longer--because you are now healthier!

To test the theory that calorie restriction promotes longevity, you need to take completely healthy individuals (of normal weight), restrict their caloric intake, and then see if that improves their "biomarkers of longevity." (If this works, it will probably mean longer, more miserable, lives.)

So here's to JAMA and bad science.

1 comment:

Anonymous said...

I read a review book on stress in lab animals that said that studies show that giving them food that is available all the time was more stressful then giving them small amounts of food on occassion. Maybe the longevity seen in lab animals is only due to the excitement the poor, bored, caged animals get by being fed or not fed...so exciting for them!