Yesterday my family and inlaws devoured a 24 pound Thanksgiving dinner turkey. Every year we eat a big bird. Perhaps because of my major contributions to the devouring, I often dream of the turkey the night after Thanksgiving. In these dreams I imagine myself fleeing from a massive bird, the turkey literally shoving forest undergrowth aside with its huge chest as it chases after me. So far I have awakened before the bird catches me.
I know why I’m scared of that turkey. The reason is sitting on the floor of my bathroom. Its called a scale, and every year the morning after Thanksgiving it cries out to me that after my encounter with the turkey, I have gained pounds. Last year, three!
Not imaginary pounds, gained in some dream or nightmare, but real honest-to-Henry pounds of turkey that seem to have ended up as fat around my middle and that I am going to have to sweat a lot to get rid of.
So on the day after Thanksgiving I start once again to diet, to cut down on how much I eat and to increase how much I exercise. Like a smoker trying to kick the habit, this is for me a familiar pattern. Just as I easily gain a few pounds, so too can I easily shed a few — but it is much harder for me to loose the next five or ten. That’s because when I diet, my body senses the decreased food intake and compensates for it by slowing down my metabolism, burning calories more slowly.
Unfair as it seems, our bodies actively resist our loosing weight. Apparently our ancient ancestors did not have the diet of hamburgers and turkey dinners that we modern humans are accustomed to. They evolved a way to resist loosing body weight as an adaptation to prolonged starvation. When forced to go days with little or no food, their bodies adjusted for it by burning fuel at a slower rate.
Research in the last ten years has told us that humans keep the weight of their bodies near a certain “set point” value. Each person inherits a body weight that he or she can maintain within a range of about 10%. A 180-pound person, for example, might weigh from 162 to 198 pounds. Every time his or her weight falls below 162 or rises above 198, their body will take steps to bring the weight back to the set point.
How does your body do this? Appetite and rate of metabolism are largely controlled by a set of hormones exchanged between body and brain. Increases in body fat cause fat cells to secrete a hormone called leptin that travels in the blood to the brain. Certain neurons in the hypothalamus (site of the brain’s “eating control center”) respond to the leptin by making less of two appetite stimulants, NPy (neuropeptide Y) and Beacon. Other hypothalamus neurons respond to leptin levels by producing appetite suppressants. So when you gain weight, you tend to want to eat less.
Other mechanisms increase your metabolic rate to compensate for any weight gain. Similarly, if you loose more than a few pounds, your body tries to put them back on by lowering your metabolic rate and increasing your appetite.
That’s why dieting is such an unsuccessful experiment for so many of us. More than 90% of dieters gain back every pound they lose. Even when dieting is done carefully and relentlessly, it typically serves only to move your weight to the low end of your natural range, 10% below your set point. An expert panel of the National Institute of Health, reviewing all available data, said that dieters loose an average of 8% of their body weight after dieting for three months to a year, and that the goal of dieting after six months should be simply to keep off whatever weight has been lost.
Despite tempting promises, fad diets like the Atkins Diet Revolution, Fat Busters, and The Zone do not offer an easy way out. These diets, which purport to reduce body weight by adjusting what you eat rather than how much, have been under careful review by the U.S. Department of Agriculture. Preliminary results reported this fall indicate that none of the most popular fad diets work as advertized. To the extent the diets are able to lower body weight, they turn out to do so the old fashioned way, by reducing the amount of calories the dieter consumes. Nothing fancy. Just a way to help you eat less as you try to loose that 10% of body weight below your set point.
So the turkey’s annual Thanksgiving revenge is that to get back to my 10%-below-set-point goal, I am going to have to again loose the weight I ate at Thanksgiving dinner, one painful calorie at a time. As I sweat off each pound I am going to be thinking of that bird. I expect I’ll meet his cousin come Christmas dinner, just about when my Thanksgiving pounds are gone.