succumbing to peer pressure

Friday, May 11, 2007

New obesity study

Or rather, new article about old-ish obesity studies. Dr.s Hirsh and Leibel conducted some very interesting (and probably unethical) studies, starting in the 1950s. Many of these results were confirmed in the 1980s using adoption and twin studies. The bottom line? There is a significantly stronger genetic link to weight (and weight gain) than environmental (or psychological) influences. Most interestingly, the 1950 experiments, during which obese patients lived in a hospital for 8 months, agreed to a rigorous diet, and lost on average 100 pounds, revealed that these now 'normal' weighing individuals showed physical and mental signs of starvation! Regardless of the fact that they were consuming what should have been a reasonable nutritional diet.

The findings also provided evidence for a phenomenon that scientists like Dr. Hirsch and Dr. Leibel were certain was true — each person has a comfortable weight range to which the body gravitates. The range might span 10 or 20 pounds: someone might be able to weigh 120 to 140 pounds without too much effort. Going much above or much below the natural weight range is difficult, however; the body resists by increasing or decreasing the appetite and changing the metabolism to push the weight back to the range it seeks.

The message is so at odds with the popular conception of weight loss — the mantra that all a person has to do is eat less and exercise more — that Dr. Jeffrey Friedman, an obesity researcher at the Rockefeller University, tried to come up with an analogy that would convey what science has found about the powerful biological controls over body weight.

He published it in the journal Science in 2000 and still cites it:

“Those who doubt the power of basic drives, however, might note that although one can hold one’s breath, this conscious act is soon overcome by the compulsion to breathe,” Dr. Friedman wrote. “The feeling of hunger is intense and, if not as potent as the drive to breathe, is probably no less powerful than the drive to drink when one is thirsty. This is the feeling the obese must resist after they have lost a significant amount of weight.”

The entire article is worth clicking through and reading, and provides specific examples of how and why it's so hard for some people to put on weight and for others to lose weight. But it all still leaves me wondering - empirical evidence (which, sorry, I am too busy to look up at the moment) indicates that we (at least, Americans) weigh more on average today as compared to just a few decades ago and prevalence rates of diabetes keep increasing. I agree that the 'obesity epidemic' has been poorly handled on nearly all fronts, and that there are more important measurements than simply the numbers on a scale. But I am convinced that there is something significantly different about our current population in terms of weight and weight-related health than even one generation ago. So if weight really is so strongly linked to genetics, and if our bodies really do regulate us to a comfortable weight range, have we been self-selecting our population to increase in size? Can evolution even happen that fast? And if either answer is no, what underlying thing is happening?


Anonymous Smike said...

I'm guessing that part of it is that people are now better able to take care of ourselves than we have been in the past. Which means that people are now able to reach their genetically regulated weight, whereas they might not have had the resources to previously. Another factor that likely plays a role is that, provided nothing significant happens, humans continue to naturally gain weight as they age. So an older population will be heavier than a younger one.

These two factors also run against the currently accepted measurement for obesity, the body mass index. I wish I could find the basis for the definitions of regions on that chart, but it seems that the numbers they choose to reflect what is healty or not seem rather arbitrary. It's worth keeping that in mind when comparing studies of obesity to make sure they are using the same BMI values to describe conditions.

12:45 PM  
Anonymous RuddCenter said...

It defies the current understanding of genetic science to suggest that genes are to blame for the rapid increase in childhood obesity in this country. At the same time, the memetic dichotomy of gene vs. environment needs to be updated with a focus on the gene-environment interaction. Perhaps the strong genetic disposition towards obesity is reacting with the significant changes that we have seen in our food and exercise environment in the last thirty years. Researchers at Yale's Rudd Center for Food Policy and Obesity on these issues frequently. We'd like to hear your thoughts as well.

1:43 PM  
Blogger Sudiptya said...

Completely tangential: what was the name of that resort in Costa Rica that you posted about months ago?


3:20 PM  

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