Predicting How Diet and Exercise Affect Weight

Researchers have created a mathematical model — along with an accompanying online weight simulation tool — of what happens when people of varying weights, diets and exercise habits try to change their weight. The model challenges long-held assumptions about weight loss.

Organizations promoting weight loss often state that eating 3,500 fewer calories or burning them off exercising will result in a pound of weight loss. But the reality is more complicated. A growing body of evidence shows that the body’s metabolism can change as you lose weight and alter your exercise habits. These changes can significantly differ among people as well, depending on age and other factors.

A research team led by Dr. Kevin Hall of NIH’s National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) set out to develop a computer simulation taking metabolic changes into account. They designed their model to accurately simulate physiological differences between people based on gender, age, height and weight, as well as body fat and resting metabolic rate. To test the model, the researchers compared predicted weight changes to actual changes in people. Their results appeared on August 26, 2011, in the Lancet.

The team found that people’s bodies adapt slowly to changes in dietary intake. The simulation highlights how long it takes for the body to reach a new steady weight after a dietary change. Heavier people can expect greater weight change with the same change in diet, but reaching a stable body weight will take them longer.

The model also revealed a potential simplified method to approximate weight loss in an average overweight adult. For every pound you wish to lose, permanently cut 10 calories from your current intake per day. At that rate, it will take about a year to achieve half of the weight loss, with 95% of the total weight change within about 3 years.

An online simulation tool based on the model will enable researchers to accurately predict how body weight will change and how long it will likely take to reach weight goals based on a starting weight and estimated physical activity. The tool, at http://bwsimulator.niddk.nih.gov/, also allows researchers to plan for a weight loss phase followed by a weight maintenance phase.

“This research helps us understand why one person may lose weight faster or slower than another, even when they eat the same diet and do the same exercise,” Hall says. “Our computer simulations can then be used to help design personalized weight management programs to address individual needs and goals.”

The researchers hope to continue refining the tool and using it to gain insights into what changes are required to achieve and maintain goal weight. For example, a comprehensive mathematical model of human metabolism was used recently to design an NIH clinical trial comparing the effects of reducing fats versus carbohydrates in obese adults.

The online tool isn’t meant as a weight-loss guide for the public. The program can run simulations for changes in calories or exercise that would never be recommended for healthy weight loss. People should consult with their physician prior to embarking on a diet plan.