Introduction

This is a collection of energy expenditure and energy balance studies. Use the table of contents above this headline to navigate and find the studies you want to read. The studies are all categorized by topic and sub-topic. Contact me at adam@sci-fit.net if you want to contribute studies or reviews to this collection.

Plain language explanations of central terms

All the relevant terms and definitions are organized below. These terms are central to understanding energy expenditure. Give it a quick read before diving into the research. Click the blue buttons and red footnotes to read relevant quotes from studies.

Thermogenesis

Thermogenesis is when the body produces heat (energy). As explained below, there are several ways this can happen.

Energy Expenditure (EE) and Energy Balance (EB)

The human body is always expending energy. Whether you are sitting, moving, eating, shivering, etc. The more active you are, the more energy you expend (energy out). The more energy you expend, the more food you need to eat to maintain body weight (energy in). You are in energy balance when you are eating the same amount of energy that you are expending. ~10% of the energy we eat is lost in feces, urine, or via the skin.

Quotes

“In humans, about 90% of energy ingested is metabolizable energy, with the rest being lost in the feces, urine, or leaving the body via the skin” - Lam and Ravussin, 2016 The figure below shows how different amounts of lean body mass correlate with energy expenditure (more mass = more energy expended per 24h). Figure by Casperson et al., 2017 (edited for clarity)

Total Daily Energy Expenditure (TDEE)

Your total daily energy expenditure is how much energy you expend every day. It is typically measured in kcal (kilocalories aka calories). According to the dietary guidelines of Health.gov, the average sedentary american requires 2,400 kcal (men) or 2,000 kcal (women) to maintain body weight. TDEE consists of resting metabolic rate, the thermic effect of food, and activity expenditure. These terms are explained further down.

TDEE calculators (these may not necessarily be accurate):

Quotes

“Total daily energy expenditure is comprised of three components: resting (or basal) metabolic rate (RMR), the thermic effect of food (TEF; also known as diet-induced thermogenesis), and activity energy expenditure.“ - Lam and Ravussin, 2016 “The major energy components of TDEE are resting metabolic rate (RMR), diet-induced thermogenesis (DIT), and activity thermogenesis.” - Donahoo et al., 2004 Total energy expenditure (TEE) is composed of the energy costs of the processes essential for life (basal metabolic rate (BMR), 60–80% of TEE), of the energy expended in order to digest, absorb, and convert food (diet-induced thermogenesis, ~10%), and the energy expended during physical activities (activity energy expenditure, ~15–30%) - Heydenreich et al., 2017

Resting Metabolic Rate (RMR) aka Resting Energy Expenditure (REE)

Resting metabolic rate refers to how much energy your body expends to maintain basic physiological functions. As the name implies, it is measured at rest.

Quotes

“RMR refers to the energy required to sustain the biochemical systems of the body at complete rest and accounts for ∼70% of TDEE in sedentary individuals [41].” - Lam and Ravussin, 2016 “RMR is the largest component of TDEE (60–75%), and represents the energy required to maintain essential vital functioning. Three-quarters of the variability in RMR is predicted by lean body mass [5].” - Donahoo et al., 2004 “Major factors contributing to individual variation in REE include age, gender, body size, body composition, ethnicity, physical fitness level, hormonal status, and a range of genetic and environmental influences (21–25).” - Hills et al., 2014

Activity Expenditure (AE) aka Activity Thermogenesis (AT)

Activity expenditure is the energy expended during movement during normal day-to-day activities and exercise. We divide activity expenditure into exercise energy expenditure (EAT), and non-exercise energy expenditure (NEAT).

Quotes

“Energy cost of physical activity is the most variable component of TDEE, which accounts for energy consumed in muscular work during spontaneous and voluntary exercise. It has been estimated that activity energy expenditure ranges from ∼15% in very sedentary individuals to up to 50% in highly active individuals [47].” - Lam and Ravussin, 2016 Physical activity is the third main determinant of TEE. It is defined as the additional energy expenditure above REE and TEF, which is required for performing bodily activity. It can be categorized into exercise related activity thermogenesis (EAT) and nonexercise activity thermogenesis (NEAT). Both vary widely within and between individuals. For the majority of subjects in industrialized countries exercise is believed to be negligible (13,15). - Loeffelholz, 2014

Exercise Activity Thermogenesis (EAT) aka Exercise Energy Expenditure (ExEE)

This is the energy you expend during exercise.

Quotes

“in untrained subjects, an exercise-induced increase in activity energy expenditure is compensated by a training-induced increase in exercise efficiency.” - Westerterp, 2017

Non-Exercise Activity Thermogenesis (NEAT)

This is the energy you use during activity and movement outside of exercise.

Diet-Induced Thermogenesis (DIT) aka Thermic Effect of Food (TEF)

You expend energy digesting, absorbing, and storing foods. TEF/DIT accounts for about 10% of TDEE. Protein leads to the greatest diet-induced energy expenditure. Combined with its positive effects on satiety and lean body mass, protein is an important macronutrient during weight loss.

Quotes

“DIT is the increase in energy expenditure associated with the digestion, absorption, and storage of food and accounts for approximately 10– 15% of TDEE [6].” - Donahoo et al., 2004 “TEF refers to the energy expenditure that relates to food consumption, i.e., energy required to digest, absorb, assimilate, and store nutrients, and thus is dependent on the amount and the type of nutrients consumed. TEF has been reported as 5–10%, 0–3% and 20–30% of the energy content of carbohydrates, lipids, and proteins respectively [50] and in the case of energy balance on a Western diet accounts for ∼10% of TDEE [51].” - Lam and Ravussin, 2016 “In conclusion, the main determinants of diet-induced thermogenesis are the energy content and the protein- and alcohol fraction of the diet. Protein plays a key role in body weight regulation through satiety related to diet-induced thermogenesis.” - Westerterp, 2004

Excess Post-Exercise Oxygen Consumption (EPOC)

After exercise, your body continues to expend energy beyond what it normally would if you were sedentary. This has also been called the Afterburn Effect. Sprints and strength training seem to increase EPOC more than low intensity steady state training (i.e. jogging).

Quotes

“In the recovery period after exercise there is an increase in oxygen uptake termed the 'excess post-exercise oxygen consumption' (EPOC), consisting of a rapid and a prolonged component.” - Børsheim and Bahr, 2003 “the amount of exercising skeletal mass is an additional variable to consider when relating exercise to EPOC.” - Elliot et al, 1992

Adaptive Thermogenesis (AT)

When we lose weight, the body might reduce its energy expenditure to prevent further weight loss. It will also try to regain lost weight.

Quotes

“The adaptive component of thermogenesis that has been documented under conditions of negative energy balance is under the influence of hormones and sympathetic nervous system activity that have been shown to explain variations in EE beyond what could be explained by changes in body weight and composition.9, 37, 38, 39, 40, 41, 42, 43, 44 Indeed, leptin,11, 39, 45 insulin,46, 47, 48 thyroid hormones 9, 38, 41, 43, 45 as well as sympathetic activity37, 41, 42, 45 have been shown in several studies to be associated with a greater than predicted variation in EE. Moreover, fat depletion per se has also been considered as a determinant factor for adaptive thermogenesis.7, 49” - Major et al., 2007 “The over 80% recidivism rate to pre-weight loss levels of body fatness after otherwise successful weight loss is due to the coordinate actions of metabolic, behavioral, neuroendocrine, and autonomic responses designed to maintain body energy stores (fat) at a CNS- defined “ideal”. This “adaptive thermogenesis” creates the ideal situation for weight regain and is operant in both lean and obese individuals attempting to sustain reduced body weights. Much of this opposition to sustained weight loss is mediated by the adipocyte-derived hormone “leptin””. - Rosenbaum and Leibel, 2010