Are All Calories Created Equal?

Health Professional, Medical Reviewer

We've all heard the phrase "calories in, calories out" when it comes to managing our weight.   Is weight loss just as simple as "eat less, move more?"   Are all calories created equal, or is it more complicated than that?

What is a Calorie?

A calorie is a unit of energy.  One calorie is the amount of energy needed to heat one gram of water one degree Celsius.    So when you see the total number of calories on a food label, that number is the amount of potential energy in that food that the human body can use.   Our bodies use this energy not only for physical activity, but also for metabolism, digestion, breathing, and all other functions essential to life. When we consume excess calories above and beyond what the body needs for these functions, they are stored as body fat.   This is why excess calorie consumption over time leads to weight gain.

Are All Calories the Same?

As far as our bodies are concerned, all calories are equal in the amount of energy they provide. Macronutrients (protein, carbohydrates, and fat) differ, however, in the amount of calories they provide.   Carbohydrates and protein provide four calories per gram, while fat provides nine calories per gram (which is about the weight of a small paper clip).   Alcohol provides seven calories per gram, but it is not classified as a macronutrient since we don't need it to survive.

How Macronutrients Differ

Once these nutrients are consumed, they differ in how they function in the body. Protein takes more energy to digest and store--more than fat and carbohydrates.   Fat and protein both take longer to break down in our digestive tract, which is why eating them helps to make you feel fuller for longer.   Fiber found in carbohydrates also takes longer to digest, which is why complex carbohydrates (such as fresh fruit, vegetables, and whole grains) make you feel fuller for longer than simple carbohydrates (such as those found in a sugary cereal).

The Right Balance for Weight Loss

Many studies have been performed to look at the right balance of protein, carbohydrates, and fat for weight loss, all with varying results.  Most research shows that people who follow a low-carbohydrate diet seem to be more successful at short-term weight loss than those who follow a very low-fat diet.

This seems to be because people burn more calories in the weight loss stage by following a low carbohydrate/low glycemic index diet. The combination of low carbohydrates and low glycemic index foods appears to improve insulin sensitivity and curb hunger.   However, long-term studies show that when you restrict too much of one macronutrient, weight loss is not sustained. People who follow a very low-carbohydrate diet (or even a very low-fat diet) seem to gain weight back in the long term.   This supports evidence that having a balance of fat, protein, and carbohydrates in your diet is the right formula for long-term weight maintenance. Most experts suggest close to equal percentages of each macronutrient.

The Bottom Line

In the scientific sense, all calories are created equal in the amount of energy that they supply to your body. But they all differ in the way they perform in your body: how they are digested, metabolized, and used for fuel.   Having the right amount of each in your diet seems to be the key to weight loss and long-term success.   If you are having trouble losing weight, talk to your doctor or a registered dietetian, who can help in designing the right diet for your weight loss.

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