What is metabolic rate?
Metabolic rate refers to the amount of energy expended by an organism’s body per unit time. It represents the minimum energy required to keep the body functioning at rest. There are a few key types of metabolic rates:
- Basal metabolic rate (BMR) – The energy expended by the body at rest to maintain essential body functions like breathing, blood circulation, hormone levels, body temperature regulation, etc.
- Resting metabolic rate (RMR) – Similar to BMR but measured under less restrictive conditions than basal conditions. RMR is usually measured after fasting and while relaxing.
- Total daily energy expenditure (TDEE) – The total number of calories burned in a day including the energy spent on physical activity.
So in summary, basal metabolic rate and resting metabolic rate refer specifically to the energy expended by the body at rest or minimal activity. They indicate the minimum calories required to sustain vital body functions.
What determines metabolic rate?
There are several factors that account for differences in metabolic rate between individuals:
- Body size: Larger bodies have higher metabolic rates. This is because larger bodies have greater energy needs for maintaining more tissue.
- Organ mass: Organs like the brain, liver, heart and kidneys are metabolically active and account for a major chunk of resting energy expenditure. Higher organ mass increases metabolic rate.
- Muscle mass: Muscles account for about 20% of resting metabolic rate. More muscle mass equals higher metabolic rate.
- Age and sex: Metabolic rate slows down with age. Men tend to have higher metabolic rates than women.
- Genetics: Some people inherit a naturally faster metabolism.
- Hormones: Thyroid hormones T3 and T4 directly regulate metabolic rate.
- External temperature: Colder environments can increase metabolic rate slightly.
So in summary, the metabolic rate is influenced by multiple physiological factors like body composition, organ mass, age, sex and genetics. Environmental temperature also plays a small role.
Typical metabolic rate values
Here are some typical values for resting or basal metabolic rates in adults:
| Category | Metabolic rate range (kcal/day) |
|---|---|
| Men (18-30 years) | 1600-1800 |
| Women (18-30 years) | 1400-1600 |
| Athletes and highly active people | 2000-2500 |
As a general rule, men tend to burn more calories at rest than women. Highly active people or athletes also tend to have higher resting metabolic rates.
Metabolic rate declines gradually as we age due to loss of muscle mass and slowing of other physiological processes. A small percentage of the population can have metabolic rates significantly higher or lower than the normal population averages due to genetic factors.
Can metabolic rate be increased?
There are a few strategies that may help slightly elevate resting metabolic rate:
- Increasing physical activity and muscle mass
- Eating more protein in the diet
- Staying well hydrated
- Getting adequate sleep
- Consuming metabolism boosting foods like chili peppers, green tea etc
- Taking supplements that may raise metabolism like caffeine, green tea extracts etc
However, the effects of these strategies tend to be modest at best for the majority of people. Structured exercise and a protein-rich diet are likely to have the most measurable impact on metabolic rate.
Genetic influences tend to be the most significant determinant of metabolic rate that cannot be easily altered. But optimizing modifiable factors like diet and activity levels can still make a difference. Talk to a doctor before attempting to increase metabolism through supplements, as their effects are highly variable.
Conclusion
Metabolic rate refers to the minimum energy required to sustain the body’s vital functions at rest. It is determined by a variety of factors like body size and composition, organ mass, age, genetics and hormones. Typical values are 1600-1800 kcal/day for men and 1400-1600 kcal/day for women on average. Metabolic rate can be increased slightly through diet, exercise and certain supplements. But genetic factors tend to have the largest influence over resting metabolic rate. Monitoring metabolic rate is important for understanding total daily energy needs and creating an appropriate nutrition plan.