Do Women Need To Be Fat?

An evolutionary biologist suggests that our healthiest size may be a few pounds heavier than the diet industry would like

Here's another great reason not to make a diet-based New Year's Resolution this week: Evolution wants you to be fat. 

Or at least, a little bit fatter than the thintastic bodies currently bouncing across every Lucille Roberts commercial. Think Jennifer Hudson's Oscar-winning before body, not the svelte version that sings back at her in that weird new Weight Watchers ad. 

This is the argument laid out by evolutionary biologist Steven J. C. Gaulin and retired doctor of public health William D. Lassek in their new book, Why Women Need Fat. As Gaulin explains in a Salon.com interview, the female tendency to gain weight with age and particularly after the birth of your first child is the result of natural selection because smaller women tend to have smaller first babies (key for their survival during the thousands of years of reproduction before the C-section) and bigger women tend to have bigger second babies -- who tend to be healthier and more robust. 

But those extra pounds aren't just helpful for reproduction. Lots of data shows that being somewhat overweight correlates with better health and longevity. Gaulin explains: 

"Many MDs have bought this fallacious line that the optimal weight for women in terms of their health is what MDs call normal weight, a BMI between 18.5 and 25. And they have thought this to be true because women with higher BMIs exhibit a series of physiological measures that are indeed risk factors for disease in men. But they are not systematically risk factors for disease in women. If you actually look at the data from the National Health and Nutrition Examination Survey and data from studies done in other countries, the optimal weight for women who have had a kid is what doctors currently call 'overweight.' I'm not saying that obesity is optimal, but all the findings show that overweight women survive better than normal weight women." 

At the same time, Gaulin says there's no question that Americans have lost touch with what he calls our "natural weight," because our diet has shifted to include so many highly processed foods, particularly those heavy in omega-6 fatty acids. "Being overweight is not nearly as bad as your doctor has been telling you," he says in the Salon interview. "But if we ate a more natural diet [...] we would all weigh less." 

Gaulin admits he "walks a fine line," and it reminds me of the "weight loss is impossible/I still want to lose weight!" dance that Tara Parker-Pope did in her recent New York Times Magazine article on "The Fat Trap." For some reason, whenever the public health community (researchers, journalists, policy makers) begin to embrace the science behind Health At Every Size, they feel an immediate compulsion to follow it up with a reminder that fat is still, nevertheless, the root of all evil. For Gaulin and Lassek, it's right there in the subtitle of their book: "How 'Healthy' Food Makes Us Gain Weight and the Surprising Solution for Losing It Forever." Ah, a promise of a "surprising" weight loss strategy that will let you keep the weight off forever (even though all the research shows 95 percent of us can't)? That's the ole "it's not a diet, honest!" sales tactic of, um, every diet ever.

I'm also nervous that they zero in on one Bad Guy Food (making omega-6 the new saturated fat/trans fat/carbohydrate/sugar/high fructose corn syrup/etc), not because I doubt that we're eating way too much of it as an overly industrialized society, but because I've never found the good food/bad food mentality to be particularly helpful when it comes to individual well-being.  

But even with those red flags, their core argument is sound. And they certainly aren't prescribing the kind of unrealistic weight loss goals that are so rampant this time of year. We'd all be better off if we had a basic understanding of how our bodies have evolved to function, instead of fighting their natural instincts (and size) with obsessive diets that are doomed to fail. 

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