Better Way to Predict Weight Loss?

Aug. 25, 2011 -- If you’ve ever been on a diet, chances are you know the 3,500-calorie rule: Since there are 3,500 calories in a pound of fat, you have to eat 500 fewer calories a day to lose a pound a week.

But researchers now say the formula is wrong because it fails to account for a slowing metabolism, the fact that dieters lose muscle as well as fat, and other factors that influence weight loss.

Researcher Kevin Hall, PhD, of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) says the 3,500-calorie rule leads to unrealistic expectations and may undermine people’s efforts to lose extra pounds.

Web Model Predicts Weight Loss

Hall and colleagues with the World Health Organization, Columbia University, and the Harvard School of Public Health have developed a web-based model that they say more accurately predicts a dieter’s expected weight loss over time.

The body weight simulator, which can be found on the NIDDK web site, was announced today in London at a news conference held to highlight a special obesity-focused edition of The Lancet.

Hall tells WebMD that weight loss actually occurs more gradually than is thought. He says a better guide for the typical overweight adult is that cutting 10 calories a day from their diet will lead to the loss of a pound over three years.

So reducing calorie intake by 250 calories a day will eventually lead to a 25-pound weight loss, but it will take three years for most overweight or obese adults to get 95% of the way there, Hall says.

He adds that about half the weight will be lost in the first year of dieting, with weight loss slowing after this.

“This new way of analyzing body weight trajectories over time should give dieters a more realistic sense of what to expect from a diet and exercise program,” Hall says. “To put a positive spin on it, the new model shows that even though weight loss slows over time, people who stick to their diets will continue to lose weight for long periods.”

Based on their model, the researchers conclude that to achieve average weight levels similar to those seen in the 1970s, moderately obese people would have to cut 500 calories out of their diet a day for several years.

“500 calories a day is a lot, especially in the world we all live in today," says researcher Steven L. Gortmaker, PhD, of the Harvard School of Public Health. “This is why we really should be focusing more on preventing weight gain in the first place, especially among children.”