Metabolic Rate

What Is Metabolism?

Metabolism refers to all the chemical processes in the body. A person with a faster metabolism needs more calories. Metabolism is the reason why some people can eat as they like without gaining weight, while others need to be careful in order not to store fat in the body. Metabolism speed is generally called metabolic rate. Metabolic rate, also known as calorie expenditure, is the number of calories we burn in a given period of time.

Metabolic rate is divided into categories:

Basal Metabolic Rate (BMR): The metabolism during sleep and deep rest. It is the minimum metabolic rate needed to keep the lungs, heart and brain working and to keep body temperature in balance.

Resting Metabolic Rate (RMR): The minimum metabolic rate needed to keep a person going at rest. It makes up 50-75% of average calorie expenditure.

Thermic Effect of Food (TEF): The number of calories the body burns while digesting food. It represents about 10% of total energy expenditure.

Thermic Effect of Exercise (TEE): The energy burned during exercise.

Non-Exercise Activity Thermogenesis: The amount of energy needed for activities other than exercise. This includes changing posture, standing and moving around.

Factors That Affect Metabolic Rate

1) Age: Metabolic rate slows with age.

2) Muscle mass: The more muscle mass there is in the body, the higher the metabolic rate.

3) Body size: The bigger a person is in body size, the more calories they burn.

4) Ambient temperature: A study carried out in 2014 showed that even a small effect of ambient temperature gave results pointing towards fat storage in cold weather.

5) Physical activity: All physical movement requires energy. The more active a person is, the more calories they burn. Metabolism will speed up accordingly.

6) Hormonal disorders: Conditions such as Cushing's syndrome and hypothyroidism slow the metabolic rate.

Why Does Metabolic Rate Differ?

Metabolic rate starts to develop from birth and differs between people accordingly. Although genetic factors play an important role, scientists do not agree on how much genetic factors affect metabolic rate, weight gain and obesity. Interestingly, most studies show that people with obesity have a higher total and resting metabolic rate than people of normal weight.

Researchers say that this is partly because people with obesity have a larger amount of muscle to help support their extra weight. Even so, research shows that people with obesity have higher metabolic rates independent of their muscle mass.

One thing is very clear on this subject: when it comes to metabolic rate, everyone is not created equal. This difference comes from people's age as well as environmental factors and individual behaviours.

However, metabolic rate differs by sex, age and in athletes, and muscle mass is directly related to metabolic rate.

That said, the role of genetics in these individual differences needs to be studied further.

Basal Metabolic Rate and Daily Energy Expenditure

Basal metabolic rate (BMR) is the energy the body uses at rest for basic functions such as breathing, circulation and body temperature, and it usually makes up the largest part of daily energy expenditure. Energy spent on physical activity and on digesting food (the thermic effect of food) is added to the daily total.

Muscle mass, age, sex, height and weight, and thyroid hormones affect BMR. Regular resistance exercise, enough protein and sleep can support metabolic health; there is no single food or tea that "speeds up metabolism". If you suspect a thyroid problem, see your doctor for a diagnosis.

This article is for general information only; please consult your doctor and dietitian about your own situation.