By BARRON H. LERNER, M.D.

When I was growing up, the word “willpower” was used a lot. If only one was strong enough to resist sweets, according to logic of the time, one could stay thin.

Yet today, based on a series of scientific discoveries, the importance of willpower in promoting weight loss is becoming an obsolete notion. Is it worth saving?

The concept of willpower came less from scientific data than from Christian teachings about the dangers of temptation. Gluttony, after all, was one of the seven deadly sins, up there with pride, greed, extravagance, envy, wrath and sloth.

The late 19th century was perhaps the heyday of the revolt against what John C. Burnham, a historian at Ohio State University, calls “bad habits.” Groups like the Salvation Army and the Women’s Christian Temperance Union urged sinners to stop drinking, gambling and smoking.

Comparable sentiments characterized writings about obesity. In 1946, Wilson G. Smillie, a public health professor at Cornell, wrote that the physician should appeal to the obese patient’s “ability to manifest self-control.” Weight-loss programs like Overeaters Anonymous and Weight Watchers have reflected this philosophy.

Similarly, many physicians have also discouraged surgical procedures like stomach stapling or shortening of the intestines, not only because of their risks but also because they were somehow seen as quick fixes for lazy patients who do not stick to their diets.

But as critics have pointed out, while willpower can work, it usually does not. A study published in The Journal of the American Medical Association in 2005 found that regardless of the diet attempted, patients lost an average of only 5 percent of their baseline weight after one year. And dropout rates exceeded 40 percent. [A newer study is reported on this page today, in Vital Signs.]

As a result, strategies for promoting weight loss have recently begun to shift from a focus on individual behaviors to a public health approach.

As the late Dr. Donald H. Gemson of the Mailman School of Public Health at Columbia once put it, “the causes of the obesity epidemic are environmental, and the answers will be as well.” Rather than simply urging people to eat better and exercise more, experts like Dr. Gemson have increasingly argued that society has to facilitate such changes by reducing the availability of high-calorie foods, advertisements of junk food to children and reliance on automobiles, while increasing access to healthy foods and exercising.

The environmental theory of obesity is prompting governmental interventions, like New York City’s ban on most trans fats in restaurant food. And environmental strategies have successfully been used in other areas that formerly relied on moral suasion. For example, taxes on cigarettes have contributed greatly to lowered smoking rates. Legislatures have enacted laws making restaurants liable if they permit drunk patrons to drive home.

So will people necessarily lose weight if society actively discourages fattening foods? Maybe not. Consider the genetic hypothesis, the latest reassessment of the obesity problem.

Research suggesting a strong hereditary predisposition to obesity goes back several decades, but several recent findings have put this theory into the forefront. In 1994, for example, Jeffrey M. Friedman, a molecular geneticist at Rockefeller University, discovered the appetite-regulating hormone leptin. Dr. Friedman believes that people’s appetites are largely controlled by genetics, which causes them to have different “set points” at different times in their lives.

A study in The Journal of the American Medical Association in May suggested another way in which genetics might affect changes in weight. Researchers from Children’s Hospital in Boston reported that differences in how young adults secrete the hormone insulin determine how well they respond to various dietary interventions.

So maybe it is time for health professionals to stop reflexively assuming that personal sacrifice will lead to weight loss. But this will not be easy.

For one thing, there certainly are success stories of people who have dropped dozens of pounds by drastically altering their lifestyles. Moreover, watching one’s diet can have beneficial health effects beyond losing weight.

And I just cannot conceive of a session with an overweight patient that does not involve a discussion of being careful at holiday meals, controlling portion size, avoiding bedtime snacks and trying to exercise three times a week. Somehow it still seems to me that part of a doctor’s job is to push patients to try harder. Just call me old-fashioned.

Barron H. Lerner teaches medicine and public health at Columbia University Medical Center.