In my mind I will always weigh 165 pounds, as I did the day I married. The bathroom scale tells a different story, somehow finding another thirty pounds. I did not ask for that weight, do not want it, and am constantly looking for a way to get rid of it. I have not found this to be a lonely search — it seems like everyone I know past the flush of youth is trying to loose weight, too. And, like many, I have been seduced by fad diets, investing hope only to harvest frustration. Atkin’s Diet Revolution was the diet I tried. As a scientist I should have known better, but so many people seemed to use it — Atkin’s Diet Revolution is one of the ten best selling books in history, and was (and is) prominently displayed in every bookstore I enter. The reason this diet doesn’t deliver on its promise of pain-free weight loss is well understood by science, but not by the general public. Only hope and hype make it a perpetual best seller.
The secret of the Atkins diet, stated simply, is to avoid carbohydrates. Atkin’s basic proposition is that your body, if it does not detect blood glucose (from metabolizing carbohydrates), will think it is starving and start to burn body fat, even if there is lots of fat already circulating in your bloodstream. You may eat all the fat and protein you want, all the steak and eggs and butter and cheese, and you will still burn fat and loose weight — just don’t eat any carbohydrates, any bread or pasta or potatoes or fruit or candy. Despite the title of Atkin’s book, this diet is hardly revolutionary. A basic low-carbohydrate diet was first promoted over a century ago in the 1860s by William Banting, an English casket maker, in his bestselling book “Letter on Corpulence.” Books promoting low carbohydrate diets have continued to be best sellers ever since. I even find one on my mother’s bookshelf, in the guise of Dr. Herman Taller’s 1961 “Calories Don’t Count.”
When I tried the Atkins diet I lost ten pounds in three weeks. In three months it was all back, and then some. So what happened? Where did the pounds go, and why did they come back? The temporary weight loss turns out to have a simple explanation: because carbohydrates act as water sponges in your body, forcing your body to become depleted of carbohydrates causes your body to loose water. The ten pounds I lost on this diet was not fat weight but water, quickly regained with the first starchy foods I ate.
The Atkins diet is dangerous (all those saturated fats and cholesterol) and difficult to stay on. If you do hang in there, you will loose weight, simply because you eat less. The other popular diet these days, The Zone diet of Dr. Barry Sears, is also a low carbohydrate diet, although not as extreme as the Atkins diet. Like the Atkins diet, it works not for the bizarre reasons claimed by its promotor, but simply because it is a low calorie diet. In teaching my students at Washington University about fad diets, I tell them there are two basic laws which no diet can successfully violate:
1. All calories are equal.
2. (calories in) – (calories out) = fat
The fundamental fallacy of the Atkins diet, the Zone diet, and indeed of all fad diets, is the idea that somehow carbohydrate calories are different from fat and protein calories. This is scientific foolishness. Every calorie you eat contributes equally to your eventual weight, wether it comes from carbohydrate, fat, or protein.
To the extent these diets work at all, they do so because they obey the second law. By reducing calories in, they reduce fat. If that were all there was to it, I’d go out and buy Sear’s book. Unfortunately, loosing weight isn’t that simple, as anyone who has seriously tried already knows. The problem is that your body will not cooperate. If you try to loose weight by exercising and eating less, your body will attempt to compensate by metabolizing more efficiently. It has a fixed weight, what obesity researchers call a “set point,” a weight to which it will keep trying to return. Two years ago a group of researchers at Rockefeller University in New York, in a landmark study, found that if you loose weight, your metabolism slows down and becomes more efficient, burning fewer calories to do the same work — your body will do everything it can to gain the weight back! Similarly, if you gain weight, your metabolism speeds up. In this way your body uses its own natural weight control system to keep your weight at its set point. No wonder its so hard to loose weight!
Clearly our bodies don’t keep us at one weight all our adult lives. It turns out your body adjusts its fat thermostat — its set point — depending on your age, food intake and amount of physical activity. Adjustments are slow, however, and it seems to be a great deal easier to move the body’s set point up than to move it down. Apparently higher levels of fat reduce the body’s sensitivity to the leptin hormone that governs how efficiently we burn fat. That is why you can gain weight, despite your set point resisting the gain — your body still issues leptin alarm calls to speed metabolism, but your brain doesn’t respond with as much sensitivity as it used to. Thus the fatter you get, the less effective your weight control system becomes.
This doesn’t mean that we should give up and learn to love our fat. Rather, now that we are beginning to understand the biology of weight gain, we must accept the hard fact that we cannot beat the requirements of the two diet laws. The real trick is not to give up. Eat less and exercise more, and keep at it. In one year, or two, or three, your body will readjust its set point to reflect the new reality you have imposed by constant struggle. There simply isn’t any easy way to loose weight.