Weight Loss and Your Metabolism

Is a Calorie Just a Calorie?

So when we talk about metabolism being the number of calories your body needs to function, what do we mean when we say a calorie? Does the body process calories from different sources differently? Would diets that have the same number of calories but have variations in the levels of carbohydrates, fat, and protein make any difference?
Some research has been done to determine if it matters where your calories come from. One study in particular looked at whether certain foods and diets may be more effective for burning calories and helping people maintain their weight loss. This study included participants following three different diets that contained the same number of calories: a low-fat diet, a low-carbohydrate diet, and a low-glycemic-index diet designed to prevent a surge in blood sugar levels. Each participant followed the three diets in the study in random order, each for four weeks at a time.
The study found that although the participants ate the same number of calories in each of the three diet plans, the energy expenditure and other aspects of metabolism were significantly different among the three. The results showed that the number of calories burned daily differed among the three plans. Here was the breakdown, on average, of daily calories burned:
  • Low-carb diet = 3,137 calories burned daily
  • Low-glycemic diet = 2,937 calories burned daily
  • Low-fat diet = 2,812 calories burned daily.
The study also showed that hormone levels and other metabolic measures varied with each diet. Although the low-carb diet had the most improvement in metabolism, the participants had higher levels of the stress hormone cortisol, which increases the risk for diabetes and heart disease. The low-glycemic-index diet had fewer negative effects with metabolic measures.
So what does this data tell us? Eating low-glycemic foods such as vegetables, legumes, and grains that reduce the surge in blood sugar after a meal may be the best choice for lasting weight loss and preventing heart disease.
The study also found that people were more likely to stick with a low-glycemic-index diet, as it does not restrict entire classes of food and makes it easier for people to follow. This research also showed that diets that are very low in fat might actually slow down a person's metabolism to a point where it can't burn calories as effectively as it could. The study found that while people may lose weight on the very-low-fat and very-low-carb diets, a majority of them wind up gaining the weight back rather rapidly.
The main conclusion from this study is that calories are not all the same from a metabolic standpoint. The quality of the calories consumed may affect the number going out.
(See Are All Calories Created Equal? for more information.)
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