When it comes to losing weight, success is only temporary for most people. A new study of strategies for weight loss and maintenance showed that a low-carb diet burned more calories than a low fat diet. The findings contradict the conventional wisdom that a calorie is a calorie, regardless of the source.
Carbs and the starvation response
Some nutrition experts say that any diet that reduces calories will work as long as you stick to it. But a new study published in the Journal of the American Medical Association suggests carbohydrate calories dramatically spike blood sugar and insulin. The subsequent crash triggers a starvation response, which slows metabolism, burns less calories and stores fat.
David Ludwig, a director of the New Balance Foundation Obesity Prevention Center at Children’s Hospital Boston and a professor at Harvard Medical School, designed a study to see how diet affects a person’s ability to maintain weight loss. His research found that a low-carb diet outperformed a low-fat diet for initial weight loss. A low-glycemic diet—food that doesn’t dramatically increasing blood sugar and insulin after meals—is the healthiest option for weight maintenance.
Which diet is best?
Scientists helped 21 obese participants lose 10-to 15 percent of their initial body weight (about 30 pounds). After their weight stabilized, each followed one of three different diets for four weeks:
- •A low-fat diet with 20 percent of calories from fat, high in whole-grain products and fruits and vegetables.
- •A low-carb diet with only 10 percent of calories from carbohydrates, high in fish, chicken, beef, eggs, cheese, some vegetables and fruits. Breads, pasta, potatoes and starchy vegetables were eliminated.
- •A low-glycemic diet, similar to a Mediterranean diet, with vegetables, fruit, beans, healthy fats (olive oil, nuts) and healthy grains, such as old-fashioned oats and brown rice.
Participants burned 325 more calories a day on the low-carb diet than they did on the low-fat diet—equivalent to an hour of moderate exercise, according to Ludwig. The low-glycemic diet burned about 150 calories more than the low-fat diet—about an hour of light exercise.
The happy medium
The low-fat diet had the worst effect on insulin, good HDL cholesterol and triglycerides associated with hardening of the arteries. The low-carb diet had the worst effect on chronic inflammation and hormonal stress, major heart disease risk factors. The low-glycemic index diet was the happy medium. It didn’t slow metabolism as much as the low-fat diet and it didn’t negatively affect heart disease risk.
The heart disease risk factors suggest a low-carb diet isn’t a healthy long-term option, even though it burned more calories. For weight maintenance and heart disease prevention, the low-glycemic diet is best according to Ludwig, mainly because it avoids processed carbohydrates. Calories from low-glycemic foods such as pears, apples, steel-cut oats and some pastas control hunger because they digest more slowly, helping to keep blood sugar and hormones stable after a meal.
Apparently a calorie isn’t a calorie after all.