How Important Are Calories?

by | Aug 3, 2021 | Nutrition, Real Food

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Different people derive different amounts of calories from the same food, determined by individual factors. One such factor is the gut microbiome, which varies widely.

What is the biggest word on the nutrition facts label? Calories. In fact, the FDA insists on it. Does this mean it should be the most important factor in food selection? 

To answer that question, it’s important to understand that calories are NOT a measurement of nutritional value. Rather, they are a way to measure energy. There are many reasons why comparing consumed calories to a theoretical goal of reduced calorie intake is not likely to lead to a desired health goal.  

For one thing, different people derive different amounts of calories from the same food, determined by individual factors. One such factor is the gut microbiome, which varies widely. Current estimates indicate there are roughly as many microorganisms in the body as there are cells. These bacteria are all over the body, but a lot of them live in the gut, and they eat what you eat, as part of the digestive process.   

Some of the bacteria found in the gut microbiome are better at extracting energy from food than others. If an individual has more of those specific bacteria, they could potentially absorb more calories. So even if you were to follow the same diet as your friend, eating the same calories, you may experience very different results due to your differing gut bacteria.  

The composition of food also impacts how many calories the body absorbs. Compare, for instance, half a plain bagel to a bunch of broccoli, both 100 calories. The bagel is mostly refined flour, which the body quickly breaks down, leading to a relatively sudden increase in blood sugar. 

Broccoli, on the other hand, is a whole food that is much harder to break down. It takes longer to chew, the stomach must work harder to break it down, and the fibrous quality requires the intestines to work harder to extract nutrients. The fiber in broccoli slows down the release of glucose into the bloodstream. Additionally, broccoli contains an abundance of micronutrients, vitamins, minerals, and other nutrients that improve the function of the body. 

More generally, the macronutrient makeup of food (fats, proteins, and carbohydrates) also affects how many calories the body derives from food. How the body metabolizes proteins is a prime example. It takes a fair amount of energy to digest protein, so the number of calories you end up getting out of a high protein dish is quite different from the theoretical number of calories that the food label says are in the food. 

The bottom line is that multiple factors influence the number of calories that you get from food and what happens to that energy in your body. The number of calories the food label states are in the food is far from the most important thing to know about that food. If the desire is to lose weight, or to better manage the body’s energy, it is important to understand that the nature of the food that provides the calories is much more critical than the number of calories you consume.1

Fundamentals of Health Alliance

Fundamentals of Health Alliance


The Fundamentals of Health Alliance works to publish useful and reliable information about nutrition and health. Their mission is to empower readers to be informed with honest, non-biased information about food, nutrition and the vital components of health.


  1. It’s often the case that people don’t get the results they are seeking when they try to lose weight by reducing calories, and that whatever weight loss they do see is temporary. That’s because when you reduce the number of calories you consume, your body automatically reduces the amount of energy it is using, seeking to conserve the energy stores it already has, and increases your appetite for food. This phenomenon is explained more fully in Chapter 3 of The Obesity Code, by Dr. Jason Fung.

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