- Your basal metabolic rate is the amount of energy your body uses.
- Our basal metabolic rate is determined by a variety of factors, not just our age.
- There are only a few things that can directly increase our metabolic rate.
You’ve probably heard people talking about their metabolic rate and come across a variety of foods and supplements claiming to boost your metabolism and help you lose weight.
What exactly is your metabolism? Does it decrease with age, and can you do anything to increase it?
The basics
Your metabolism is the total amount of energy used by the chemical proesses in your body that allow you to move, think, and maintain and repair body components such as blood, body cells, organs and muscles.
Our total energy expenditure has three components: basal metabolism (BMR), physical activity and the thermic effect of food.
Your basal metabolic rate
Your basal metabolic rate (BMR) is the rate of energy your body uses to sustain life. This includes the energy needed to breathe and keep your heart beating.
It is easiest to think about the BMR as the energy you expend when sleeping without any disturbances. BMR is the largest component, representing 50 to 65% of your daily energy expenditure.
Every person’s BMR is different as it is influenced by your age, height, gender, body composition and genetic make-up. The more somebody weighs, the greater their total energy output.
However, the energy output per kilogram of body weight may vary depending on body composition. For example, a normal-weight adult may have a BMR that is 1.5 times greater than an obese adult when considering BMR per kilogram body weight. This is because lean muscle tissue is more metabolically active, and, therefore, uses more energy than body fat.
What about my age?
Age affects your BMR, but just not as profoundly as you may think. As you age, your BMR decreases in part due to hormonal changes that reduce your appetite and metabolism.
However, the main reason for this reduction in energy output is the loss of lean muscle tissue. This varies from person to person, depending on genetics, gender and their level of physical activity.
Other components that affect metabolism
The second component of total energy expenditure is physical activity, i.e. voluntary movements of the skeletal muscles. Depending on how often, how long and how intensely you move, this accounts for around 30% of your energy output.
Lastly, the thermic effect of food is an estimation of the energy required to digest, absorb, and process the food you eat. This is the smallest contributor at only 10% of your total energy expenditure.
What about my efforts to lose weight?
Why would someone want to increase their metabolic rate? Well, the higher your metabolic rate, the more energy you expend, and when it comes to weight loss, you want to be burning more energy than you consume.
The area where you can make the biggest change to your energy expenditure is your physical activity. By increasing the intensity, frequency, and duration of your exercise, you can burn more energy, and increase your overall metabolism.
Exercise also helps you lose fat mass and gain more lean muscle mass, which in turn helps to increase your BMR.
It is, therefore, important to continue performing regular strength and aerobic activities as we get older as this will help us to maintain our lean muscle mass and avoid accumulating fat.
We should, however, not have unrealistic expectations about the impact of physical activity on weight or fat loss because voluntary activity only accounts for 30% of our total energy expenditure.
Key points on metabolism
Your overall energy expenditure is determined by your BMR, physical activity and the thermic effect of food. Your BMR remains stable throughout adulthood but decreases slowly as you lose lean muscle mass.
Focusing on increasing lean muscle mass and losing fat mass will help increase your BMR. A normal, healthy person will not have a particularly slow or fast metabolism unless they have a disease that lowers or raises their BMR, as in the case of problems with the thyroid gland.
Physical activity is the only area where we can make somewhat of a difference to our overall metabolism and energy expenditure. No food or supplement such as caffeine, spicy food, chillies, alcohol, or green tea can directly increase our metabolic rate.
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