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evolution and the "obesity epidemic"
Dec. 9th, 2009 03:00 pmI hesitate to even post on this issue, because of how contentious it can be. But I've had a few thoughts about this lately and wanted to express them.
At the center of these thoughts was the insight that, from the standpoint of evolution there has never before been a survival advantage to losing weight. On the other hand, there have always been survival benefits from gaining and maintaining weight. Evolution would not have therefore have encouraged the development of a mechanism whereby weight can be lost; or, put another way, gaining or storing of weight is a switch that only switches one way, like a ratchet. If this is true, then the only way for a person to lose weight is by interrupting the fundamental metabolic processes by which weight is stored.
The traditional model of "a person's weight" is, like many models rooted in the late nineteenth century, based on a steam-engine-era kind of model. We can easily calculate how much wood it takes to keep the furnace burning at a given temperature; if you shovel in less than that, the fire burns lower; if you shovel in more, the fire burns higher.
As doctors have expressed it: a person of any given size requires a daily intake of X calories to maintain their present weight. Ipso facto, if one eats more than X, one gains weight, and if one eats less, one loses weight. The more active one is, the more calories one needs to take in, and the less active one is, the fewer calories one requires.
I hope it will not be a controversial thing to say that in actuality it is not nearly as simple as this. In fact, the doctors' formulation has not borne out as being even generally accurate.
And along comes the prominent journal Nature with an article about how some mice have cultures of gastrointestinal bacteria which are simply more efficient at harvesting nutrients out of food. If these mice eat the same amount of food as their peers, they get fat, while their peers stay slim, because they are getting more out of each morsel.
Do you see where this is going?
My thought is that what's happening is that we have simply gotten better at getting energy from the food we eat -- but some of us are much better at it than others. Humans evolved with bodies that became accustomed over thousands of years to eating a certain amount of food (X) in order to get a certain amount of energy (Y) needed for metabolism. With the advent of modern medicine, refrigeration, antibiotics, food inspection, better cooking, and so on, we now draw a certain higher amount of energy (Y' > Y) from that same amount of food X. But our bodies have not adjusted their hunger instincts to account for the fact that we could now eat some lesser amount of food (X' < X) in order to get Y. Our bodies do with the surplus what bodies learned over geological eons to do when there's a surplus -- they store it. And once one weighs too much, there's no natural mechanism for undoing it. The only way to shed weight is to essentially break the survival mechanism by unnatural means, such as pretending there's a famine ("eating less"), a tactic of less than optimum effectiveness as the metabolic cycle rapidly compensates for it.
What are we to do? The best answer is, I suppose, evolve more rapidly.
At the center of these thoughts was the insight that, from the standpoint of evolution there has never before been a survival advantage to losing weight. On the other hand, there have always been survival benefits from gaining and maintaining weight. Evolution would not have therefore have encouraged the development of a mechanism whereby weight can be lost; or, put another way, gaining or storing of weight is a switch that only switches one way, like a ratchet. If this is true, then the only way for a person to lose weight is by interrupting the fundamental metabolic processes by which weight is stored.
The traditional model of "a person's weight" is, like many models rooted in the late nineteenth century, based on a steam-engine-era kind of model. We can easily calculate how much wood it takes to keep the furnace burning at a given temperature; if you shovel in less than that, the fire burns lower; if you shovel in more, the fire burns higher.
As doctors have expressed it: a person of any given size requires a daily intake of X calories to maintain their present weight. Ipso facto, if one eats more than X, one gains weight, and if one eats less, one loses weight. The more active one is, the more calories one needs to take in, and the less active one is, the fewer calories one requires.
I hope it will not be a controversial thing to say that in actuality it is not nearly as simple as this. In fact, the doctors' formulation has not borne out as being even generally accurate.
One of Atkinson’s most memorable patients was Janet S., a bright, funny 25-year-old who weighed 348 pounds when she finally made her way to U.C.L.A. in 1975. In exchange for agreeing to be hospitalized for three months so scientists could study them, Janet and the other obese research subjects (30 in all) each received a free intestinal bypass. During the three months of presurgical study, the dietitian on the research team calculated how many calories it should take for a 5-foot-6-inch woman like Janet to maintain a weight of 348. They fed her exactly that many calories — no more, no less. She dutifully ate what she was told, and she gained 12 pounds in two weeks — almost a pound a day.
“I don’t think I’d ever gained that much weight that quickly,” recalled Janet, who asked me not to use her full name because she didn’t want people to know how fat she had once been. The doctors accused her of sneaking snacks into the hospital. “But I told them, ‘I’m gaining weight because you’re feeding me a tremendous amount of food!’”
from Fat Factors
And along comes the prominent journal Nature with an article about how some mice have cultures of gastrointestinal bacteria which are simply more efficient at harvesting nutrients out of food. If these mice eat the same amount of food as their peers, they get fat, while their peers stay slim, because they are getting more out of each morsel.
Do you see where this is going?
My thought is that what's happening is that we have simply gotten better at getting energy from the food we eat -- but some of us are much better at it than others. Humans evolved with bodies that became accustomed over thousands of years to eating a certain amount of food (X) in order to get a certain amount of energy (Y) needed for metabolism. With the advent of modern medicine, refrigeration, antibiotics, food inspection, better cooking, and so on, we now draw a certain higher amount of energy (Y' > Y) from that same amount of food X. But our bodies have not adjusted their hunger instincts to account for the fact that we could now eat some lesser amount of food (X' < X) in order to get Y. Our bodies do with the surplus what bodies learned over geological eons to do when there's a surplus -- they store it. And once one weighs too much, there's no natural mechanism for undoing it. The only way to shed weight is to essentially break the survival mechanism by unnatural means, such as pretending there's a famine ("eating less"), a tactic of less than optimum effectiveness as the metabolic cycle rapidly compensates for it.
What are we to do? The best answer is, I suppose, evolve more rapidly.
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