Editor's note: Amitai Etzioni is a sociologist and professor of international relations at George Washington University and the author of several books, including "Security First" and "New Common Ground." He was a senior adviser to the Carter administration and has taught at Columbia and Harvard universities and the University of California, Berkeley.

(CNN) -- Preparations are on the way for Thanksgiving and I, like millions of my fellow Americans, already worry about what the bathroom scale will show the day after. Like so many others, I have been dieting for years. I used to feel guilty when I gained a few pounds, during the holiday season or otherwise, and on top of the world when I lost some.

I felt guilty when I had a piece of chocolate cake, my favorite, and very virtuous when I munched on celery sticks, which I hate. But then I came across some data that changed my life -- and might change yours.

Before I can tell you why I am making such a grandiose claim, I need to ask you to participate in a small experiment. Make a list of 10 people you have known or known of for a long time. They can be family members, friends, or public figures -- say, Hillary Clinton and Oprah. Now note next to each if their weight has changed significantly during the time you have known them, as far as you can tell.

For instance, Hillary Clinton was always on the slender side, and although Oprah changed her weight quite drastically over the years, she is about the same shape now as she was a decade or two ago. Indeed, you will probably find that about eight out of 10 people on your list seem to weigh about the same as they did years ago. As one observer put it, some are greyhounds and some are bulldogs.

How can I tell? Because studies show that, despite all the public health campaigns, diet books, diet doctors and diet pills; despite millions of Americans spending inordinate amounts of psychological energy fussing about their body mass; whatever weight they take off, they put on again. Not all people, but about eight out of 10, according to a report in The American Journal of Clinical Nutrition.

That means that most Americans who diet spend good money, consume drinks and eat food that is artificially doctored, take medications that have side effects and engage in various fashionable diets that actually undermine their health. All in vain. In effect, eight of 10 dieters experience both the ill effects of excessive weight and the ill effects, and costs, of yo-yo dieting.

Why I am telling you all this? I am a student of public policy, not medicine. The reason is that all the hoopla about dieting, seen in the magazines at any check-out counter, deflects attention from the one group in which healthy eating, especially if combined with exercise, can make a significant difference -- children, the younger the better.

Think of body mass like cement. It is rather easy to shape when it is new, but once it settles, it is very resistant to change. Data show that weight ranges and body mass indexes are set early in life. According to a study by the Diabetes Center at Howard University, obesity in infants is only a 20 percent predictor of obesity in adulthood, but by the time children are 6 years old, it is 50 percent. By the time they are adolescents, it is 90 percent. Other data, though somewhat less dire, point in the same direction.

The lesson of all this is that the physicians, dietitians and other public health professionals who determine our health care policies should shift most of their efforts to working with parents. They should not focus on reducing the parents' body mass, but that of their kids.

Reforming the food that schools provide in their lunch programs, cafeteria and vending machines, and ensuring that gym classes are not canceled as schools face tight budgets, pays off more than focusing on obese and overweight adults.

I should pay credit where it is due. Michelle Obama's "Let's Move" campaign, which focuses on children, is right on target. It remains to be seen if the tens of thousands of school boards across the country, thousands of PTAs and tens of millions of parents will heed the message. If they do, we all, especially the next generation, will be better for it. As for me, I still have my celery and my chocolate days, only now I do celery when the kids are around -- and chocolate cake when they are not.

The opinions expressed in this commentary are solely those of Amitai Etzioni.