Thursday, November 08, 2007

Skinnies burn fast, plumpies less demented

I caught this Kolata article in the NYT a few days ago, but I hard a hard time finding it just now. I suppose the results seemed so odd that most bloggers have rejected it as yet more evidence that medical science has a consistency problem . (A position towards which I have some sympathy.)

It turns out that skinnies die younger than the pleasingly plump (but not obese). Odd indeed, since near-starvation diets promote longevity in worms and mice alike. Not only that, the skinnies get demented faster.

I think there's a quite plausible explanation. First the article (emphases mine)...

Causes of Death Are Linked to a Person’s Weight - Gina Kolata - New York Times

About two years ago, a group of federal researchers reported that overweight people have a lower death rate than people who are normal weight, underweight or obese. Now, investigating further, they found out which diseases are more likely to lead to death in each weight group.

Linking, for the first time, causes of death to specific weights, they report that overweight people have a lower death rate because they are much less likely to die from a grab bag of diseases that includes Alzheimer’s and Parkinson’s, infections and lung disease. And that lower risk is not counteracted by increased risks of dying from any other disease, including cancer, diabetes or heart disease.

As a consequence, the group from the Centers for Disease Control and Prevention and the National Cancer Institute reports, there were more than 100,000 fewer deaths among the overweight in 2004, the most recent year for which data were available, than would have expected if those people had been of normal weight.

Their paper is published today in the Journal of the American Medical Association.

The researchers also confirmed that obese people and people whose weights are below normal have higher death rates than people of normal weight. But, when they asked why, they found that the reasons were different for the different weight categories.

Some who studied the relation between weight and health said the nation might want to reconsider what are ideal weights.

“If we use the criteria of mortality, then the term ‘overweight’ is a misnomer,” said Daniel McGee, professor of statistics at Florida State University.

“I believe the data,” said Dr. Elizabeth Barrett-Connor, a professor of family and preventive medicine at the University of California, San Diego. A body mass index of 25 to 30, the so-called overweight range, “may be optimal,” she said.

... A woman who is 5 foot 4, for instance, would be considered at normal weight at 130, underweight at 107 pounds, overweight at 150 pounds and obese at 180.

... The higher death rate in obese people, as might be expected, was almost entirely driven by a higher death rate from heart disease.

But, contrary to expectations, the obese did not have an increased risk of dying from cancer. They were slightly more likely than people of normal weights to die of a handful of cancers that are thought to be related to excess weight — cancers of the colon, breast, esophagus, uterus, ovary, kidney and pancreas. Yet they had a lower risk of dying from other cancers, including lung cancer. In the end, the increases and decreases in cancer risks balanced out.

As for diabetes, it showed up in the death rates only when the researchers grouped diabetes and kidney disease as one category. Diabetes can cause kidney disease, they note. But, the researchers point out, the number of diabetes deaths may be too low because many people with diabetes die from heart disease, and often the cause of death is listed as a heart attack...

Now, how do I make sense of this and say it strikes me as quite plausible (I'm technically on the low end of overweight based on my BMI, thank you)?

I'll wager it's the aging clock and an associated "burn rate". The old "metabolism" metaphor doesn't do too badly, though I think it's fundamentally an aging rate issue.

If you have a slower-aging clock you tend to burn slower and gain weight. If you have a fast aging clock you tend to burn faster and stay skinnier.

In today's calorie and taste rich and exercise-light environment most people with normal or subnormal BMI have pretty fast clock and fast burn rates. They age more quickly, and so develop dementia and age-associated cancers more often.

People with very slow burn rates and slow clocks become obese, and die of obesity complications. (Though if they make it to old age I think they can last quite a long time.) In a world of fewer calories and more exercise they might do the best of all, however.

People with average to slow burn rates and average to slow clocks get plump and, if they dodge diabetic complications, they live longer and better. They do need to work to stay shy of obese however.

Which would put us back to the weight/health definitions we used in the 1980s, before new BMI standards made everyone overweight.

Oh, and the near-starvation diet and the ultra-skinny mice? That's a different effect, a physiologic response to prolonged famine. The clock slows down.

So the diet pill of tomorrow will both slow the clock (like the near-starvation diet) and cause the body to dump its calories into the GI tract.

Great news for all those plump folks out there ...

PS. Note this means that stuffing a skinny with calories won't actually help them. You'd need to slow the clock.

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