The common belief that eating 3,500 fewer calories - or burning them off exercising - will always result in a pound of weight loss has been challenged in a new study.
Researchers at the National Institutes of Health have created a mathematical model - and an accompanying online weight simulation tool - of what happens when people of varying weights, diets and exercise habits try to change their weight.
Instead, the researchers' computer simulations have indicated that this assumption overestimates weight loss because it fails to account for how metabolism changes. The computer simulations show how these metabolic changes can significantly differ among people.
"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," said Kevin Hall, Ph.D., an obesity researcher and physicist at the NIH's National Institute of Diabetes and Digestive and Kidney Diseases and the paper's first author.
"Our computer simulations can then be used to help design personalized weight management programs to address individual needs and goals," added Hall.
The online simulation tool based on the model enables 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 simulates how factors such as diet and exercise, can alter metabolism over time and thereby lead to changes of weight and body fat.
To test the model, the researchers compared predicted weight changes to actual changes in people.
"Mathematical modeling lets us make and test predictions about changes in weight and metabolism over time," said Hall.
"We're developing research tools to accurately simulate physiological differences between people based on gender, age, height, and weight, as well as body fat and resting metabolic rate," added Hall.
For example, the team found that people's bodies adapt slowly to changes in dietary intake. They also found heavier people can expect greater weight change with the same change in diet, though reaching a stable body weight will take them longer than people with less fat.
The study has been detailed in Lancet.