Energy Balance & Metabolism

Updated: Aug 19

Energy balance is defined as the balance between the calories you consume each day through food and drink, and the number of calories you expend through physical activity and your body’s normal physiological processes. This principle can be stated even simpler by the phrase Calories In vs Calories Out (CICO). However, problems arise with understanding how surprisingly complex this balance is and how it is not a fixed value. The human body is constantly trying to keep a careful equilibrium between the building and breakdown of every cell in your body. To do this, you must eat enough calories per day including several essential nutrients from your diet to account for the energy lost from just keeping your body functioning normally. When you start expending more energy by exercising or start ingesting too much energy through excess food and drink, the balance between your calories in and your calories out are no longer in equilibrium and changes in your body composition occur (i.e. you will lose or gain weight). To understand why this equilibrium is so complex you need to first understand the four components that comprise the calories out side of the calories in vs calories out equation. These four components are known as your Total Daily Energy Expenditure (TDEE).

Total Daily Energy Expenditure (TDEE)

The four components of your total daily energy expenditure are your Basal Metabolic Rate (BMR), Non-Exercise Activity Thermogenesis (NEAT), The Thermic Effect of Food (TEF), and Exercise Activity (EA). Each component has a varying contribution to your TDEE dependent upon whether you are in a caloric deficit or surplus, the amount of activity you are engaged in, and the types of food you eat.

Basal Metabolic Rate (BMR)

BMR is the largest component of your TDEE, making up approximately 60 - 70% (however, this percentage may be lower in very active individuals). BMR is the minimum amount of energy needed to sustain life and accounts for all the energy that is required to run all your basic bodily functions including, pumping blood around your body, creating hormones, thinking, breathing, etc. BMR can be measured using a Metabolic Cart after a 12-hour fast while resting and in a neutral temperature environment. However, for most people predicted BMR calculations (covered later in this chapter) are used as a cheaper and more convenient alternative for determining BMR. Your BMR is largely determined by how much lean mass you have (i.e. muscle) and how efficient your body has become at obtaining needed energy from your food. Overweight people are more efficient at obtaining energy from food and as a result store greater amounts of excess energy as body fat. Lean people are much more wasteful and therefore do not store as much body fat due to a less efficient ability to obtain needed energy from their food. However, during periods of caloric restriction your body will become more efficient at obtaining energy from your diet and your BMR will reduce as a result.

Non-Exercise Activity Thermogenesis (NEAT)

NEAT is the second-largest component of your TDEE, making up approximately 15% in sedentary individuals and as much as 50% or more in highly active individuals. NEAT accounts for all the involuntary movements you make each day like using your devices, fidgeting, talking, moving around, etc. NEAT can decrease significantly when you become more active as you unconsciously move less in your day-to-day activities to compensate for the energy you are expending by engaging in more structured exercise. It is therefore recommended to include goals for staying active during your day, as well as exercise goals when trying to lose weight to help attenuate this effect.

Thermic Effect of Food (TEF) 

This component accounts for the energy used to ingest, metabolise, absorb, and store energy from your food and makes up approximately 8 - 15% of your TDEE. The process for storing fat is very efficient and as a result, has the lowest TEF (0 - 3%). Carbohydrates and protein require more energy to convert surplus energy into body fat and as a result have a higher TEF (Carbs: 5 - 10%, Protein 20 - 30%). In theory, 3 months of 400 excess calories of fat or carbs vs 400 excess calories of protein could result in a greater effect on weight gain. However, this component of your TDEE remains relatively stable, unless in a caloric deficit where it may reduce slightly. Eating a high protein diet may help to attenuate this effect and also aid in satiety (i.e. feeling fuller), which could result in better diet adherence.

Exercise Activity

This component is what is referred to when generic government advice says “move more” and only accounts for 15% of the average adult’s TDEE and as much as 30% in active individuals. You can see why the phrase “eat less, move more” doesn’t cover the complexity of the calories in vs calories out equation and causes confusion. Despite this relatively small contribution to your TDEE, exercise activity is still the component you have the greatest influence upon and increasing your exercise levels will have a significant effect on the number of calories you expend. The amount of energy expended during exercise (i.e. calories burned), is determined by the duration and intensity of the activity performed. The effect exercise has on your TDEE is known as metabolic cost and is measured in Metabolic Equivalents (METs), which represents multiples of your BMR. Resting is equal to 1 MET and all exercise costs more METs. For example, strength training equals 6.0 METs, meaning you will burn 6 fold the number of calories while engaged in strength training exercise compared to resting. To help you understand how to calculate your TDEE we will use two hypothetical example individuals with varying body composition and activity levels. These will be Mr Couch-Potato and Miss Gym-Bunny.

BMR Calculations

TDEE calculators work by first trying to estimate your BMR using key variables such as weight, age, sex etc., then using an activity factor to account for your exercise levels and demands of your daily life. There are a vast number of BMR calculators available, however, the best 2 are the Müller et al. equation and the Harris-Benedict equation. The Müller et al. equation is slightly more accurate as it accounts for lean mass and body fat and is my recommended choice. However, if you do not know your body fat percentage, the Harris-Benedict equation is a good alternative but may slightly over-predict your BMR.

Activity Factor

Now that you have your BMR it’s time to account for the calories you burn off through physical activity. To achieve this, we must multiply your BMR by an activity factor based upon how much you are exercising and how physical your daily life is. For example, a sedentary person engaged in no regular exercise needs far fewer calories than someone working a hard manual labour job and training regularly.

Now let’s apply these activity factors to Mr Couch-Potato and Miss Gym-Bunny.

Mr Couch-Potato: 1,906 kcal/day x 1.2 (Sedentary) = TDEE of 2,248 kcal/day

Miss Gym-Bunny: 1,295 kcal/day x 1.725 (Highly Active) = TDEE of 2,234 kcal/day

Remember, your TDEE is the number of calories you need to consume to maintain your weight and you will need to eat above or below this maintenance amount to make changes to your weight. While it is possible to gain muscle mass and lose body fat within a calorie deficit, it is impossible to gain weight while in a calorie deficit.

Calories In

As stated at the beginning of this chapter the ‘calories in’ side of our equation consists of the total amount of food and drink you consume each day including alcohol. This is not to say that there aren’t other factors that can affect this side of the equation i.e. hormones like Leptin and Ghrelin, genetics like the FTO gene, an obesigenic food environment, socioeconomics, sleep, stress, etc., but rather all of these factors potentially effect metabolic adaptations or influence how much food you consume by either affecting hunger levels, increasing the palatability of foods, or affecting your food choices, which leads to the overconsumption of calories. Put simply, carbs don’t make you fat, fats don’t make you fat, your hormones don’t make you fat, eating too many calories (i.e. more than your TDEE) and not increasing your energy expenditure does make you fat.

This is a short excerpt from my my latest book. If you would like to learn more about your energy balance and metabolism and how to practically apply this info to help you reach your goals, please check out Eat Move Perform: Volume 1 - Nutrition & Supplements which is available for pre-order from Waterstones now (see link below).

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