New Studies Eat Into Diet Math

How many calories must a dieter cut to lose a pound?

The answer most dietitians have long provided is 3,500. But recent studies indicate that calories can't be converted into weight through a simple formula.

The result is that the 3,500-calorie rule of thumb gets things very wrong over the long term, and has led health analysts astray. Much bigger dietary changes are needed to gain or shed pounds than the formula suggests.

Consider the chocolate-chip-cookie fan who adds one 60-calorie cookie to his daily diet. By the old math, that cookie would add up to six pounds in a year, 60 pounds in a decade and hundreds of pounds in a lifetime.

But new research—based on studies of volunteers whose calorie consumption is observed in laboratory settings, rather than often-unreliable food diaries—suggests that the body's self-regulatory mechanisms tamp down the effects of changes in diet or behavior. If the new nutritional science is applied, the cookie fiend probably will see his weight gain approach six pounds, and then level off, pediatrician David Ludwig and nutrition scientist Martijn Katan wrote in the Journal of the American Medical Association earlier this year. The same numbers, in reverse, apply to weight loss.