14 December 2010
Do We Really Get Fat by Overeating?
One of the commenters on my last MTM post linked to this article, and I think it’s brilliant. I mean, Gary Taubes is brilliant and writes things about dieting/nutrition that others wouldn’t dare. But this article really sums up why calories in/calories out isn’t always as straight-forward and “scientific” as we think it is. An excerpt:
…Obese people tend to be weight stable for long periods of their life, just like lean people. So when they’re weight stable, the obese and overweight are obviously in energy balance. They’re not overeating during these periods of stable weight. They’re eating to match their expenditure, doing exactly what the lean do (and get copious credit for). So one obvious question is why the overweight and obese are only in energy balance when they’re carrying 10, 20, 30 or maybe 100 pounds of excess fat, and lean people are in energy balance without the excess? What’s the culprit for that? Because the problem isn’t that the obese overeat when they’re obese, it’s that they overeat when they’re lean and they continue to overeat until they become obese.
…Let’s say you’re carrying around 40 pounds of excess fat and you put on that 40 pounds over the course of 20 years, as many of us do. When you’re in your late 20s, say, you’re still lean, and then, lo and behold, you celebrate your fiftieth birthday and you’re obese and your doctor is lecturing you on eating less and getting to the gym regularly (and probably writing you a prescription for Lipitor, as well). Now, if you gain 40 pounds of fat over 20 years, that’s an average of two pounds of excess fat accumulation every year. Since a pound of fat is roughly equal to 3500 calories, this means you accumulate roughly 7000 calories worth of fat every year. Divide that 7000 by 365 and you get the number of calories of fat you stored each day and never burned – roughly 19 calories. Let’s round up to 20 calories, so we have a nice round number. (In the new book I discuss this issue in a chapter called “The Significance of Twenty Calories a Day.”)
So now the question: if all you have to do to become obese is store 20 extra calories each day on average in your fat tissue — 20 calories that you don’t mobilize and burn — what does overeating have to do with it? And why aren’t we all fat? Twenty calories, after all, is a bite or two of food, a swallow or two of soda or fruit juice or milk or beer. It is an absolutely trivial amount of overeating that the body then chooses, for reasons we’ll have to discuss at some point, not to expend, but to store as fat instead… So really when we talk about being in energy balance – or practicing energy balance, as the experts now like to say – we actually have to be perfect in our matching of intake to expenditure or we’re going to get inexorably fatter (or leaner, if we err on the side of going hungry), or at least we have to average perfection over decades.
One way to get around this is to assume that we overeat by this trivial amount for a few years on end and then we realize we’ve put on five or ten pounds – maybe our clothes no longer fit well or we’ve had to let out the belt a notch or two – and then we decide to undereat every day for however long it takes to make up for it. So now we walk away from the table hungry until all is back to leanness. But then how do animals do it? They don’t have mirrors or clothes to tell them they’re getting fat, and the world is full of animals that have plenty of food available all year round, plenty of opportunity to overeat if they want to and do so long enough to get chubby…
And now go read the rest of it!
