When it comes to nutrition for improving your body composition, energy balance is the most important factor. Energy balance describes the relationship between calories in (a.k.a. energy intake) and calories out (a.k.a. energy expenditure).

If you consume fewer calories than you expend in a day, you are in a calorie deficit and your body will use mostly stored body fat for energy. If you consume more calories than you expend in a day, you are in a calorie surplus and your body will store fat.

Now, to figure out how many calories you need to eat in a day to lose fat, you first need to know how many calories you expend on an average day. Or in other words, we need a good estimate of your total daily energy expenditure.

Generally, online calorie calculators can provide a decent estimate of your total daily energy expenditure. But, as you can imagine, a generic formula can’t be 100% accurate. The human metabolism is too complex for this to be true.

In this article, we are going to look into how the human body expends energy so you can gain a deeper understanding of how your “metabolism” works and why just using a simple formula is not enough to accurately determine your maintenance calories. In part 2 of this series, we will delve deeper into how you can accurately figure out your average daily energy expenditure.

The Components of Energy Expenditure

Energy Expenditure: How Your Body Burns Calories

Your energy expenditure essentially is the total number of calories you burn in a day. Some think that if they consume 2000 calories per day, they have to “burn off” 2000 calories through exercise in order to maintain their weight. Luckily, this is not true. The human body also expends energy while at rest and even after you eat.

In nutritional and exercise sciences, total daily energy expenditure is divided into 4 primary components:

  1. Basal metabolic rate
  2. Thermic effect of food
  3. Non-exercise activity thermogenesis (NEAT)
  4. Exercise activity thermogenesis (EAT)

In the next few paragraphs, we’ll look into each individual component and its role in human energy expenditure.

Basal Metabolic Rate

Basal metabolic rate essentially refers to the number of calories you burn while at rest. Even when you’re just sitting around or sleeping, vital bodily processes occur that require energy. Think about processes like blood circulation, cellular activity, the process of breathing, muscle recovery etc.

For moderately-active individuals, the basal metabolic rate is by far the most impactful component of energy expenditure. For the average person, around 60-70% of total daily energy expenditure tends to come from the basal metabolic rate.

Fun fact: about 20% of your basal metabolic rate comes from vital processes dedicated to muscle maintenance. So the amount of muscle you carry has an effect on how many calories you burn at rest. For every pound of muscle you gain, research shows you burn an additional 6-10 calories per day. Basically, getting jacked can help you burn a small number of extra calories per day.

Thermic Effect of Food

The food we eat contains energy. But converting food into chemical energy that’s readily usable by the body also requires, you guessed it, energy. The thermic effect of food refers to the number of calories you expend to digest and process the foods you’ve eaten.

For most people, the thermic effect of food makes up about 10% of daily energy expenditure. The thermic effect of food is a perfect example that shows that the number of calories you consume (calories in) directly affects your energy expenditure (calories out).

Now, the thermic effect of food is not the same with every single type of food you consume. In fact, each macronutrient has a different thermic effect.

energy expenditure: thermic effect of food

As you can see in the picture above, protein has the highest thermic effect. This is part of the reason why high-protein diets tend to be effective for fat loss (read more about protein & fat loss here).

In contrast, there’s also research showing that highly processed foods tend to have a smaller thermic effect than whole-foods. The difference is only about 10 calories per 100 kcals consumed, but this can have a small effect on fat loss if someone consistently eats mostly processed foods.

Non-Exercise Activity Thermogenesis (NEAT)

NEAT is the most variable component of daily energy expenditure. Your NEAT refers to the calories burned during spontaneous activity. Think about walking to the store, walking up the stairs or fidgeting at your desk.

Research shows NEAT varies substantially across individuals. The same study found that variances in NEAT can be as large as 2000 calories per day between individuals of similar body size.

NEAT is reflective of someone’s lifestyle. A person who has an active day job and constantly moves throughout the day will have high NEAT. A person with a desk job that moves very little throughout the day will have a low NEAT. Because of the wide variance, NEAT can account for 15% to up to 50% of someone’s daily energy expenditure.

Energy Expenditure: NEAT metabolism

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The large variances between individuals in NEAT help explain why some people seem to have a “faster” metabolism than others. Those who can eat a lot and not gain weight generally just have a higher energy expenditure through NEAT.

One study shows this quite well. The researchers overfed non-obese individuals with 1000 extra calories per day. Some compensated for the increased calorie intake by substantially increasing their spontaneous activity (NEAT), whereas others experienced only a slight increase in their NEAT and gained a ton of fat.

Exercise Activity Thermogenesis (EAT)

This one is simple. EAT refers to the number of calories you burn during training. Like NEAT, EAT can vary widely across individuals. Those who train more often expend more energy from EAT than those who train infrequently.

Unless someone practices an extreme sport or performs no form of exercise at all, EAT is generally around 15-30% of someone’s daily energy expenditure.

Calculating Energy Expenditure

Now that you know how your body burns calories, it’s easy to see why calorie calculators are not 100% accurate. A formula that takes a few general factors into account (like weight, age, height etc.) cannot predict something that’s so variable like your daily energy expenditure with 100% accuracy.

Now, even though calorie calculators are not 100% accurate, they do provide a good starting point. Instead of just maintaining a random number of calories, you at least get close to your “maintenance level” (number of calories you burn per day) when using calorie calculators.

I would see using a calorie calculator as step 1 when it comes to figuring out your maintenance calories. Based on how you progress with your calculated maintenance level, you have to adjust your calorie intake.

In part 2 of this blog series (which is live now!), we will delve deeper into all the steps you need to take in order to accurately determine your average daily energy expenditure. If in the meantime you want to play around with a calorie calculator to see where it puts you, check this website. Again, this is a starting point. For now, don’t worry if it seems a bit off.

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