All calories are the same, right?
Perhaps not. Once you shed the pounds, the amount of carbohydrates, proteins and fats you chowed down on may effect whether or not you keep the weight off.
In a seven-month experiment during which 21 overweight people had their diets strictly controlled down to each bite, researchers showed that a low-fat diet seemed to make the participants metabolism slower than a high-protein diet, all when the participant was trying to keep the weight off near the end of the experiment.
The preliminary work, which was published Tuesday in the Journal of the American Medical Association, provides support for the notion that what people eat may be just as important as how much they eat.
“From a metabolic perspective, all calories are not alike,” said Dr. David Ludwig, director of the New Balance Foundation Obesity Prevention Center at Children’s Hospital Boston and lead researcher of the experiment. “The quality of the calories going in affects the quantity of the calories going out.”
Scientists knew that weight loss was accompanied by a slowdown in the body’s metabolism. To test whether different foods might change that, Ludwig recruited overweight adults from 18 to 40 years old. The 13 men and eight women attended a 12-week program that helped them lose 10% to 15% of their body weight, which was followed by a four-week weight-stabilization phase.
After that, each subject was fed three different diets for four weeks at a time, they include: a traditional low-fat diet (60% carbohydrates, 20% fat and 20% protein), a low glycemic index diet (with 40% carbs, 40% fat and 20% protein) and a very low-carbohydrate diet (with 10% carbohydrates, 60% fat and 30% protein).
At the beginning of the study and at the end of each four-week period, the subjects were hospitalized for three days to undergo tests.
Researchers looked at all the energy burned by the subject in a day using stable isotope analysis, which measures how quickly isotopes leave your body.
For all three diets, the rate of calories burned at rest was lower than before weight loss, but over the course of a day the subjects burned more than 300 additional calories on average when on the very low-carbohydrate diet compared with the low-fat diet.
“That’s roughly equal to an hour of moderate physical activity… without lifting a finger,” Ludwig said.
Subjects burned 200 additional calories on the “low glycemic index” diet than on the “low-fat” diet. The low glycemic index diet was rich in whole grains, fruits and vegetables and is designed to prevent sharp spikes in blood sugar.
Weight-loss experts who, while not involved in the research and also while acknowledging the research’s limitations, praised the study.
“It’s a small study, so I’d want to see it repeated. But I have no reason to doubt the result,” said Susan Roberts, a professor of nutrition and psychiatry at Tufts University in Boston.
If you’re looking for a natural way to boost your metabolism, check out these foods which are low in carbohydrates.