This guide explains what basal metabolism is, how it is calculated according to scientific evidence, and how to apply it to estimate daily energy needs. It can be useful for both people who want to lose fat and those who seek to increase muscle mass healthily.
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What is basal metabolism?
Basal metabolism (BM), also known as resting energy expenditure (REE), is the minimum amount of energy the body needs to maintain vital functions while at physical and mental rest. It includes essential processes such as:
- Heartbeat and blood circulation
- Brain activity and nervous system function
- Respiration
- Maintenance, repair, and regeneration of tissues
- Hormone production and regulation
For most people, basal metabolism accounts for approximately 60% to 75% of the total calories expended throughout the day.
What factors influence basal metabolism?
Metabolic expenditure can vary significantly between individuals. Some of the influencing factors are:
The more muscle mass one has, the more energy the body consumes at rest, as muscle tissue is metabolically active.
Metabolism tends to decrease with age and, on average, is higher in men due to a higher percentage of lean mass.
Biological and lifestyle factors can accelerate or reduce basal metabolism.
Components of total daily energy expenditure (TDEE)
Total daily energy expenditure, known as TDEE, is the sum of all calories the body expends in a day. It includes four main components:
| Component | Approximate Percentage | Description |
|---|---|---|
| Basal Metabolism (BM/REE) | 60–75% | Energy needed to maintain the body's vital functions |
| Physical Activity (NEAT + exercise) | 15–30% | Daily movement, spontaneous activity, and planned exercise |
| Thermic Effect of Food (TEF) | 8–10% | Energy used to digest and metabolize food |
| Additional factors | Variable | Such as stress, fever, pregnancy, or lactation |
How to calculate basal metabolism
Several scientific formulas allow estimating basal metabolism. One of the most commonly used in nutrition for adults is the Mifflin–St Jeor formula, especially for healthy people who want to control their body weight. However, it is important to understand its actual scope.
The Mifflin–St Jeor formula is useful for estimating basal metabolism in adult individuals with stable weight, and it is often used in general nutrition, weight loss, and fitness contexts. However, according to a study published by Weijs et al. in 2008 in the scientific journal Clinical Nutrition, this was not the most accurate formula when compared to actual measurements of resting energy expenditure in adult patients.
Calculation with the Mifflin–St Jeor formula
Men: BM = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
Women: BM = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
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What is the most accurate formula according to scientific evidence?
It is important to differentiate between the most commonly used formulas and the most accurate ones according to scientific research. The study by Weijs et al. (2008), which analyzed 18 formulas in 48 outpatients and 45 hospitalized patients, concluded that the FAO/WHO/UNU (1985) formula including weight and height showed the lowest prediction error compared to indirect calorimetry, in both:
- Outpatients
- Hospitalized patients
- Underweight individuals
The study also highlights that the revised Harris–Benedict formula (1984) was a good alternative, with similar precision results. In contrast, the Mifflin–St Jeor formula showed good results especially in hospitalized and underweight patients, but was not the most accurate overall.
How to apply basal metabolism to adjust energy intake
Once basal metabolism and total daily energy expenditure (TDEE) are known, it is possible to adapt energy intake to the goal:
- Weight loss: approximately a 10–20% reduction in daily calories to promote gradual fat loss.
- Muscle mass gain: approximately a 5–15% increase in daily calories to promote muscle development.
- Weight maintenance: consuming a calorie level similar to TDEE keeps weight stable.
Common mistakes that can affect metabolism and progress
Some practices can hinder the achievement of desired results:
- Reducing calories too much, which can slow down metabolism
- Consuming too little protein, essential for preserving muscle mass
- Not adjusting intake when weight or activity level changes
- Focusing only on calories and not on nutritional quality
- Leading a sedentary lifestyle with little daily activity
Based on scientific evidence
The information on this page has been written taking into account the data from the study by Weijs et al. (2008) published in the journal Clinical Nutrition, which comparatively analyzed the accuracy of 18 formulas for estimating resting energy expenditure in adults. This study concluded that the FAO/WHO/UNU (1985) formula with weight and height was the most accurate in outpatients, hospitalized patients, and underweight individuals. This provides a useful framework for understanding the real role of each formula, even for people who want to manage their weight outside of a clinical setting.
Scientific source: Validation of predictive equations for resting energy expenditure in adult outpatients and inpatients (Weijs et al., 2008).