Are All Calories Created Equal?

Are All Calories Equal?

Is a calorie just a calorie? In one sense, this is true -- carbohydrate, fat, and protein calories are in fact equal by the specific definition in terms of their energy content. However, the human body processes each of these in a different way, which can have effects on weight management.
A research study published in the Journal of the American Medical Association (JAMA) in June 2012 challenged the notion that "a calorie is a calorie." This study suggested that certain foods and diets may be more effective for burning calories and helping people maintain weight loss.
This study was designed to examine the effects of three different diets, which included a low-fat diet, a very-low-carbohydrate diet, and a low-glycemic-index diet. The participants included 21 men and women aged 18 to 40 years old who had a body mass index (BMI) of 27 or higher. These adults had previously lost 10 percent to 15 percent of their body weight on a certain predetermined diet. After their weight stabilized, they followed the three diets in the study in a random order, each for four weeks at a time.
Specifically, the diets were broken down as follows:
  • A low-fat diet: This plan reduced dietary fat and consisted of many whole-grain products, along with fruits and vegetables. It consisted of 60 percent of daily calories from carbohydrates, 20 percent from fat, and 20 percent from protein.
  • A low-glycemic-index diet: This plan included a minimal amount of processed grains, vegetables, healthy fats, legumes, and fruits. It consisted of 40 percent of daily calories from carbohydrates, 40 percent from fat, and 20 percent from protein. The low-glycemic-index carbohydrates digest slowly, which helps to keep blood sugar levels and hormones stable after a meal.
  • A very-low-carbohydrate diet: This plan was similar to the Atkins diet and included 10 percent of daily calories from carbohydrates, 60 percent from fat, and 30 percent from protein.
Although the participants ate the same number of calories on each of the three diet plans, the researchers found that the energy expenditure during weight loss maintenance was significantly different among the three diets.
Specifically, the participants burned approximately 300 calories less each day on the low-fat diet than they did on the very-low-carbohydrate diet. This study suggested that diets that reduce the surge in blood sugar after a meal (either the low-glycemic-index or very-low-carbohydrate diet) may be preferable to a low-fat diet for those who are trying to lose weight and keep it off.
In addition, the study showed that the low-glycemic-index diet had similar metabolic benefits to the very-low-carb diet without adverse effects of inflammation and stress as seen by those who were following the very-low-carb diet. The study also showed that diets that are high in fiber and low in processed foods (i.e., the very-low-carb and the low-glycemic-index diets) also improved cholesterol levels and insulin sensitivity, which is needed to effectively process blood sugar.
According to this study, diets that are very low in fat may actually slow down a person's metabolism to a point where it can't burn calories as effectively as it could. This research also showed that while people may lose weight on the very-low-fat and very-low-carb diets, a majority of them will end 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 of calories going out.
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