Pleasures and perils of being overweight

During the first year of medical school, we students were taught that the number of chromosomes in a human cell was 48. It turned out that someone had counted them (accurately) and so by year's end the number changed. It's 46.

Chimpanzees, our closest living relative among Mammalia continue to have 48. The lesson we learned was that science can change its mind when presented with new facts. But the new facts have to stand up to critical examination. The chromosome number had been in controversy since 1912 and only new techniques in 1954 enabled counting with accuracy.

If your house is like ours you probably over-indulged a little over the holidays. If so you may also have received comforting sounding news. The TV and newspapers announced results of a US study which seemed to offer immediate absolution for our slight (or not so slight) gluttony. The new study of mortality risk involving three million people worldwide showed that being overweight (but not obese) actually lowered the risk of dying. The study, led by Dr Katherine Flegal, is a meta-analysis, (a statistical technique for combining findings from independent studies) of 97 studies worldwide that indicated a 6 per cent lower risk of mortality for those moderately overweight. Obesity was associated with 15-20 per cent greater risk.

Buoyed by these findings one could readily forgive oneself those second helpings of dessert.

I was tempted to give in to the further sin of sloth and forego at least one of my daily gym routines. And of course, if I had done so, acting on the basis of that study I'd have been on my way to the sin of ignorance in that whatever that study shows, it offers no real guidance on diet or exercise or even on the relationship between weight and health.

Far from giving permission for that extra slice of pie, the authors make clear that the study is about risk of mortality from all causes. While that's 6 per cent lower in the moderately overweight group, it's still 15-20 per cent higher in obese people.

Two caveats.

Recall that correlation is not the same as causation. People who are overweight may not be exposed to the same risks as normal weight people who are likely to be more active than sedentary. With some activity - sports, for example - may come exposure to risk.

Criticism of the study from researchers at Harvard's Public Health School point to the increase in metabolic diseases, diabetes, hypertension, heart disease, more common among the overweight. Dr Flegal did take pains to acknowledge that her statistics say nothing about morbidity, that is, the illnesses that may result from unhealthy lifestyles, leading to overweight in the first place.

In the process of review I came across two other sets of data. One was research from the Centers of Disease Control about diets and weight gain. They concluded that while any number of diets, low carbohydrate, high protein, low fat, watermelon, etc may lead to short-term weight loss, the fundamental long-term issue is the body economy. It's caloric intake versus output. If you take more in, you need to work more off.

The other is an hypothesis from evolutionary biologists Daniel E Lieberman of Harvard and Dennis M Bramble of the University of Utah. They published a seminal article in the journal Nature titled Endurance Running and the Evolution of Man that posits that man evolved with brains proportionately larger than his body out of running and endurance that helped him catch prey. The authors suggest that we need to continue activity into old age if we want to maintain that brain function. "Jogging your memory" has more than one meaning.

What can we really take from all of this? It's still a good idea to eat your veggies and get plenty of exercise, not only to live longer but to live better. Doing anything that decreases fitness, and motility may be dreamily pleasant for a while but in the long run it'll make a monkey out of you.