When it comes to the concept of energy balance… i.e. calories in vs. calories out, there is a lot of confusion in the fitness world. I often hear things like the following:

“I ate in a calorie deficit and I didn’t lose weight.”

“I don’t believe in calories in vs. calories out because I lost weight and never counted calories.”

“Calories in vs. calories out violates the second law of thermodynamics”

“Not all calories are created equal”

Your TDEE (total daily energy expenditure) is composed of a few different components:

-Basal Metabolic Rate (BMR) which accounts for 50-60% of your TDEE (for most people) and is the amount of energy required by the body to ‘keep the lights on.’ That is, the amount of energy it would require for your organs and entire system to function while doing absolutely nothing.

-Non-Exercise Activity Thermogenesis (NEAT) which is highly modifiable & can account for around 10-30% of TDEE. NEAT refers to unintentional movements throughout the day such as fidgeting or spontaneous activity. 

-Thermic Effect of Food (TEF) accounts for about 10-15% of your TDEE. TEF refers to the amount of energy that is required to extract the energy (calories) from the foods you eat. 

-Exercise Activity (EA) accounts for 0-30% of TDEE for most people. Those who do no exercise will have a greater of their TDEE come from BMR while those who exercise a lot will have a greater contributing fraction of their TDEE come from EA vs. BMR.

Taken together, TDEE = BMR + NEAT + TEF + EA

Now Balance that with Energy (calorie) Intake (EI) and calories in calories out (CICO) looks like the following:

If EI > TDEE = Weight Gain
If EI < TDEE = Weight Loss
If EI = TDEE = Weight Maintenance

Is it really that simple? Well, yes and no. While energy balance itself is simple, the components are complicated moving parts. For example, many people do not realize that calories in and calories out are not independent variables. Changing one will change the other. If you decrease your energy intake, your TDEE will also go down, mostly from reductions in BMR and NEAT. Typically, the TDEE drop is never as much as the calorie drop, so you do lose weight, for a while anyway. Eventually however, what was once a deficit will become your new maintenance calories. This has led some people to make the confused statement “I ate in a calorie deficit and didn’t lose weight.” No, you ate in what SHOULD HAVE been or what USED TO be a calorie deficit, but if you did not lose weight, then it was not a calorie deficit.

Another issue is that MOST people underestimate their food intake. They believe they are eating in what should be a calorie deficit but, they are eating far more. In fact, most people consume about 30-50% more calories than they report. Not because they are lying but because most people have no idea of what a REAL serving size of food is. If you look at a serving of ice cream which claims 150 calories and think there is 150 calories in a BOWL of ice cream, you are kidding yourself. Weigh it out and you will be quickly shocked to find it is likely closer to 500-600 calories! In fact, if you want to be depressed try weighing out peanut butter, nuts, cereal, and a variety of other snacks.

People who believe that CICO (calories in calories out) violates the laws of thermodynamics (the law that says systems of more order must move towards more disorder) do not understand the law. They claim that the first law of thermodynamics (energy cannot be created or destroyed, only transferred) only applies to a closed system. Since the human body is not a bomb calorimeter (devices that measure calorie content of foodstuffs) the first law does not apply to us. While the human body is not a closed system itself, it is a closed system in the context of the universe. Yes, we waste energy and we do not capture all the energy we eat (2nd law) but that energy is given off (thermogenesis) into the universe and is accounted for by our TDEE anyway. BMR, NEAT, & TEF all account for the fact that energy conversion is not perfect.

Those who claim that all calories are not created equal do not understand calories. Calories are not molecules. A calorie simply refers to a unit measurement of how much energy something contains. It is literally a measurement of heat and how much energy is contained within the chemical bonds of the molecules in food. So, all calories are equal because it’s simply a measurement. This would be like saying all degrees of temperature are not created equal. That said, all SOURCES of calories are not equal in terms of their effects on our energy expenditure for TEF. While the TEF of fat and carbohydrate are around 0-3% and 5-10% respectively, protein is 20-30%! That means if you eat 100 calories of protein, you only get around 70-80 calories out of it. 100 calories from carbohydrate yields around 90-95 calories of metabolizable energy and fat gives us the most at only 0-3 calories wasted per 100, making the yield 97-100 calories of metabolizable energy per 100 calories consumed. This may explain in part why high protein diets tend to produce more fat loss than calorie equated low protein diets.

What about those that say they do not believe in CICO because they lost weight without tracking calories? Well, that is like saying you don’t believe that you need to save more money than you spend in order to accrue wealth because you were able to save money without a budget. Sure, you can lose weight without counting calories but let’s be clear, you lost weight because your energy expenditure exceeded your energy intake, not magic. You may not count calories, but calories always count.