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Are All Calories Created Equal?

by Nilima Desai, MPH, RD

Most people who are on a quest for weight loss have all heard, “a calorie is a calorie” and that it doesn’t matter if the calorie is a carbohydrate calorie, a protein calorie, or a fat calorie. In fact, all calories do have the same amount of energy: one kilocalorie contains about 4184 Joules of energy, which is the amount of energy needed to increase the temperature of one gram of water by one degree Celsius. While technically the statement about all calories being the same is true, metabolically speaking it is not. Each macronutrient we consume goes through different biochemical pathways in our bodies and utilizes energy differently.

Carbohydrates and proteins contain only 4 calories per gram while fats have 9 calories per gram. Therefore, it was thought that the only way to lose weight to was to reduce caloric intake from fat. If the “calorie is a calorie” approach were true, everyone would be very successful at achieving weight loss by following a low-fat diet.

However, there are several studies that dispute the myth of the effectiveness of eliminating all fats from the diet. One such study published in the Journal of the American Medical Association found that lower carbohydrate diets resulted in greater energy expenditure than low fat diets during weight-loss maintenance.1 In this study, researchers enrolled 21 participants who lost weight prior to the study and separated them into three diet groups, all consuming 1600 calories per day. The diets were low-fat, low glycemic index, and very low carbohydrate. The participants followed the assigned diet for one month.

The objective of the study was to evaluate how energy expenditure differed with varied macronutrient distribution following weight loss. Those consuming a low-fat diet ate food consisting of 60% carbohydrates from whole grains, fruits, and vegetables, 20% fats, and 20% proteins. The low-glycemic index diet consisted of 40% carbohydrates from minimally processed grains, legumes, vegetables, 40% fats, and 20% protein. And the very-low carb diet consisted of 10% carbohydrates, 60% fats, and 30% protein.

The researchers found that those participants who consumed the very low-carb diet that was higher in fat expended approximately 300 calories more per day, and those who ate the low-glycemic index diet expended about 150 calories more per day compared to those following the low-fat diet.

While this study has some limitations, including the small number of participants, controlled meals, and a short-term study period, it gives us insights into how macronutrients are metabolized and utilized by the body. Evidence from this study, current research on healthy fat consumption and the new dietary guidelines indicate that in order to improve our health, we need to stop being afraid to eat fats. All calories do not have the same effect on our bodies. Consumption of healthy fats such as avocados, nuts/seeds, olive oil, and salmon should be encouraged and consuming poor quality calories from refined and processed carbohydrates such as white bread, white pasta, refined cereals, fruit juices, and desserts should be discouraged and avoided.


  1. Ebbeling C et al. Effects of dietary composition on energy expenditure during weight-loss maintenance. JAMA. 2012; 307(24):2627-2634.

Nilima Desai, MPH, RD

Nilima Desai is Sr. Manager of Medical Marketing and Metagenics Institute. Nilima is a Registered Dietitian (RD) who received her undergraduate degree from California State University Long Beach in Nutrition and Dietetics and her Master’s in Public Health Nutrition from Loma Linda University. She has over 14 years of experience delivering medical nutrition therapy in the areas of diabetes, renal disease, weight management, and vegetarian nutrition. She also served on the board of the Renal Practice Group of the Academy of Nutrition and Dietetics from 2012-2016 as the Membership Chair. In her free time she runs half marathons and shuttles her two kids to their activities.

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