We’re all familiar with the old “calories-in vs. calories-out” diet strategy for weight loss. You consume less food and burn more calories, and viola – the weight just falls off, right?

If you’re shaking your head no right now, you’re not alone. In fact, most people who try to lose weight by restricting calories and moving more find their results are short-lived at best. 

It seems that although this theory makes sense on the surface, our bodies just aren’t as simple as we would like to believe. 

But does calories-in calories-out have any validity? In this article, we’ll look at the research on why it may be time to put this old paradigm to rest. 

What Is Energy Balance Theory (EBT)?

Energy balance theory (EBT), also known as “calories-in calories-out,” asserts that body mass will remain steady over time as long as your average daily intake of calories is equal to your daily energy expenditure of calories. 

In other words, the number of calories you consume from food (fat, protein, and carbohydrates) is equal to the number of calories you burn daily via your basal metabolic rate (BMR) plus any added energy expenditure from daily activities and exercise. 

  • BMR: The amount of energy you burn while at rest to keep vital functions going, such as heartbeats and breathing.
  • Added energy: Anything outside of BMR that also expends energy, such as low-intensity movements (making the bed, walking to the car, etc.), or higher-intensity movements (running, weight training, etc.).

EBT also asserts that if your energy intake (calories) exceeds your average daily energy expenditure, your weight will go up, and if your energy intake is lower than your average daily energy expenditure, you will lose weight.[1]

According to EBT, our current global obesity crisis is the result of too many energy-dense foods in the diet, paired with low physical activity. In light of this view, health authorities have prescribed the “eat less, move more” approach to weight loss, which in theory should push the needle of energy balance into a calorie deficit, and body mass should go down.[2]

Sounds pretty straightforward, right?

Well, there’s one glaring problem; despite the fact that EBT has been the prevailing theory in weight loss research for years, people are still not losing weight. 

Holes In The Calories-In Vs. Calories-Out Theory

Calories-in vs. calories-out should make perfect sense on the surface. We know that when we consume an excess of energy, our body stores energy as fat, and we know that weight loss results from the body burning up more energy than it’s receiving. So what gives?

If there is anything we can say for sure about the human body, it’s that it is a complex and very non-straightforward machine. More often than not, what seems to make sense on the surface doesn’t fully check out because we are still learning how all of the intricate and dynamic parts of our bodies work together. 

With that being said, there are some obvious holes in the calories-in calories-out theory, so let’s go deeper. 

#1 Energy Balance Theory Assumes All Macros Are Burned For Energy 

According to EBT, to lose weight, you have to oxidize (burn) all of the calories you consume from food. The problem is that normal physiology would never allow for that. 

Think for a moment about your physical body – cells, tissues, bones, hair, eyes, etc. Do you know what all of that is made of? In one form or another, your body is made up of the molecules that come from the fat, carbohydrates, and protein you consume (along with several vitamins and minerals). 

And while day to day you won’t notice significant changes in how your body looks, if you could zoom in on a cellular level, you would see that your body is constantly deteriorating and renewing itself. This is why people starve to death; you need food not only to maintain energy but also to maintain your physical form. 

To illustrate this point, here are just a few ways in which protein, fat, and carbohydrates from your diet can contribute to your physical form:[3][4][5]

  • The amino acids in protein are required for the synthesis of muscle fibers 
  • Glucose from carbohydrates is used to synthesize ribose, an important part of nucleic acids that make up DNA.
  • Fatty acids from fat are used to make up the membranes that surround every cell in your body. 

Therefore, the assumption that all macronutrients are destined for metabolic energy production is inherently flawed. In truth, there are a substantial fraction of nutrients that go directly towards rebuilding and sustaining the structure and function of your physical form. 

#2 If All Protein Is Burned, You Will Experience Muscle Wasting 

Sticking with the same theme as number one, if your body burns all the protein you eat for energy, one of the biggest contributors to body mass would rapidly become depleted – your muscle. As mentioned, the amino acids that make up protein are vital for muscle synthesis. If all of your protein was burned for energy, you would have nothing less to maintain muscle mass. In other words, if all energy input (calories in) was burned (calories out), you would actually lose weight instead of maintaining it.[6]

#3 Thermic Effect of Foods

The calories-in calories-out hypothesis asserts that you’ll lose weight as long as you burn more calories than you consume – regardless of where those calories come from. 

Physiologically, this means that all calories are created equal; therefore, no matter what type of diet you eat, the conversion process from food to energy will be the same. Put another way, whether you consume 2000 calories of protein or 2000 calories of carbohydrates, you should end up with the same amount of net energy supply. But that just isn’t so. 

Why? Because of something called the thermic effect of food (TEF). 

TEF is a measurement that describes the amount of energy it takes to metabolize a specific type of food. Biologically, protein has a higher thermic effect than fat or carbohydrates because It’s a more challenging macronutrient for your body to break down and absorb. Therefore, it requires more calories to break down and absorb protein than it does fat and carbs.[7]

An obvious issue occurs when we measure this understanding against the energy balance theory: two meals with the same calorie content but different macronutrients will result in two different net energy balances. 

For example, let’s say you have 100 calories worth of chicken on your plate and 100 calories worth of rice; the net energy cost of each food item will be vastly different because protein is more “energy expensive” than carbs. 

Energy balance theory doesn’t account for the thermic effect of food, which means that we’re once again missing the mark. 


Beyond the physics and biological aspects of energy balance theory, this method has another obvious downfall: people don’t like counting calories. Even if low-calorie dieting did work, having to track total calories every day and structure your food choices around what will provide the lowest calorie intake is exhausting and unsustainable.

It’s also important to note that energy balance theory doesn’t actually account for fat loss vs. muscle loss, so you may lose body weight from muscle but still not be at a healthy weight metabolically.

So if consuming fewer calories than you burn doesn’t work for long-term weight management, then what does?

From the evidence reviewed here, it seems as though weight loss is more about calories in vs. calories USED, as opposed to calories out. 

What does this mean? The idea that we must “burn” all of the calories we use is outdated; a good portion of the food you eat is actually neither being burned nor being stored as fat – it’s being used to build and maintain your body.  

Therefore, the corrected calculation for calories in vs. calories out would look more like this;

Calories in must equal calories burned, or used for physical maintenance, in order to achieve a stable weight. 

While there’s still a lot to learn about human physiology and how weight loss works, many people find success using lower-carb diets. For people with diabetes and metabolic syndrome, low-carb dieting has also been shown to improve metabolic markers and even reverse the progression of these conditions. 

This may be due partly to the high-protein nature of low-carb diets and the fact that many people report greater satiety when limiting carbs — regardless of caloric intake. For people with type 2 diabetes, low-carb dieting also has the added benefit of helping to control blood sugar.

To learn more about what type of diet may be best for you, visit BioCoach, where you’ll have the opportunity to explore a range of dietary approaches for optimal weight loss and metabolic health.


  1. Hill, James O., Holly R. Wyatt, and John C. Peters. "Energy balance and obesity." Circulation 126.1 (2012): 126-132.
  2. Wilborn, Colin, et al. "Obesity: prevalence, theories, medical consequences, management, and research directions." Journal of the International Society of Sports Nutrition 2.2 (2005): 4.
  3. Bismut, H., et al. "Glucose contribution to nucleic acid base synthesis in proliferating hepatoma cells: a glycine-biosynthesis-mediated pathway." Biochemical Journal 308.3 (1995): 761-767.
  4. Jackman, Sarah R., et al. "Branched-chain amino acid ingestion stimulates muscle myofibrillar protein synthesis following resistance exercise in humans." Frontiers in physiology 8 (2017): 390.
  5. De Carvalho, Carla CCR, and Maria José Caramujo. "The various roles of fatty acids." Molecules 23.10 (2018): 2583.
  6. Arencibia-Albite, Francisco. "The energy balance theory is an inconsistent paradigm." Journal of Theoretical Biology (2022): 111240.
  7. Westerterp, Klaas R. "Diet induced thermogenesis." Nutrition & metabolism 1.1 (2004): 1-5.

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