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Mastering Metabolism: The Guide to Understanding Your Inner Energy


You’ll often hear the term “metabolism” being thrown around a lot in the fitness world, but have you ever considered what it means for your health?

In short, metabolism refers to all the chemical processes and reactions going on inside your body that yield energy and allow normal function. The maintenance of these processes and their normal functioning is called homeostasis.1 Many different factors can interact with your metabolism.

In this article, we’ll explore metabolism, what affects it, and how it relates to our overall health.

Metabolic Processes

Metabolism is a complex group of processes that can be split into two key concepts: catabolism (breakdown) and anabolism (build-up).


Catabolism is the breakdown of foods we eat, like carbohydrates, fats, and proteins into their less complex forms. This allows them to be used for energy and provides the building blocks needed for growth and repair.

AnabolismAnabolism is the process by which the energy produced during catabolism is used to build and repair the body. For anabolism to occur, energy is essential. If we eat more than the body needs to repair itself, the excess can be stored as fat.

Energy Metabolism

The most abundant energy-carrying molecule is adenosine triphosphate (ATP). It’s the biochemical way the body stores energy, often referred to as the ‘energy currency.’2

When you eat food, each macronutrient is digested and broken down into smaller constituents. For example, carbohydrates are broken down into sugar or glucose, which, through a complex process of chemical reactions, are then converted to ATP.

The cells then take up ATP, enabling them to function properly.

Hormones and Enzymes Involved in Metabolism

Several hormones play a key role in metabolism, such as:

  • Thyroid hormones
    • Triiodothyronine (T3)
    • Thyroxine (T4)
  • Cortisol
  • Estrogen

Enzymes are fundamental, too. They are responsible for breaking down the foods we eat into components that can be digested and transformed into energy.

Quite simply, without enzymes, cell metabolism couldn’t happen.

How is Metabolism Measured?

When measuring metabolism, there are three main components to consider. They are:

  1. Basal metabolic rate (BMR) - the number of calories your body needs to perform its basic, life-sustaining functions, such as breathing or pumping blood from the heart. Your body is burning calories even when it is at rest, just to keep you alive.
  2. Thermogenesis - also known as the thermic effect of food. Thermogenesis is the energy required to digest, absorb, and get rid of the nutrients you eat. The thermic effect of food raises your BMR not long after you eat, peaking two to three hours later.
  3. Physical activity - is the energy you use during exercise or movement and will vary depending on how much you do each day. Physical activity can include things like playing a team sport or going for a run, but also includes activities like housework, gardening, and even walking the dog. The energy we burn during exercise is the only energy expenditure we can control.

Calculating BMR

The easiest way to calculate your BMR is to use an online calculator. But if you want to do it the good old-fashioned way, there are two available formulas; one for men and one for women.3

  • BMR calculation for men: 66.47 + (13.75 x weight [kg]) + (5.003 x height [cm]) - (6.755 x age [years])
  • BMR calculation for women: 65.51 + (9.563 x weight [kg]) + (1.85 x height [cm]) - (4.676 x age [years])

Calculating Thermogenesis

Calculating the thermic effect of feeding (TEF) can be difficult, but the gold standard is determining the difference in energy expenditure between fed and fasting states.4 To calculate TEF, you’ll need to multiply the BMR by 0.1.

BMR = 1650
1650 X 0.1 = 165 calories burned as a result of the thermic effect of feeding.

Can I Change My Metabolism?

Several mechanisms can affect our metabolism or BMR. Some factors we have control over, while others we do not.

Things We Can’t Control

  • Age - As we get older, our metabolism naturally slows down because of a variety of reasons, such as a loss of muscle tissue and hormonal and neurological changes.
  • Sex - Generally, men have faster metabolisms than women.
  • Genes - Your genetic makeup may play a role in your metabolic rate.

Factors We Can Control

  • Body composition - The larger our body size, the higher our basal metabolic rate because larger bodies have more metabolizing tissue. Staying fit will help to keep our BMR at an optimal level.
  • Temperature - If the environmental temperature is either high or low, the body must work hard to maintain its usual core temperature, which can increase your BMR.
  • Drugs - Even substances like nicotine and caffeine can increase your BMR.
  • Physical activity levels - When the muscles are working hard, they require more energy. Over time, exercise can increase your BMR because it teaches your body to burn calories at a faster rate.
  • Nutrition - Fads like fasting or crash dieting can result in a slow metabolism because you won’t be eating enough food to convert to energy. This can result in a decrease in BMR and a reduction in lean muscle tissue.

Metabolism and Health

Your overall health and metabolism are closely linked. For example, metabolic conditions, hormone imbalances, and even diet and exercise can affect your metabolism.

The Relationship Between Metabolism and Weight

Maintaining a healthy weight for your size and physical activity level is important because your weight can affect your metabolism. Some people might blame weight loss or gain on a fast or slow metabolism, but your metabolism will rarely cause weight fluctuations. However, losing weight can increase your BMR.5

You are, indeed, unable to change your genetic makeup. Still, in many cases, weight gain is due to behavioral changes, like an increase in calorie intake and a decrease in exercise, rather than a slow metabolism.6

Thyroid Disorders and Metabolism

Thyroid disorders can play havoc with energy. The thyroid is a small butterfly-shaped gland in your neck that’s responsible for secreting hormones needed by your cells to work properly.7

Hypothyroidism or underactive thyroid is a condition that causes your thyroid to produce a low level of these hormones, causing your metabolism to slow down.8 Common symptoms include:

  • Weight gain
  • Feeling tired
  • Depression
  • Dry skin and hair
  • Aching muscles
  • Sensitivity to the cold

How to Boost Your Metabolism

If you’re looking to increase your metabolism, here are some of the things you can do:

  • Stay active - Aim to complete at least 150 minutes of moderate-intensity exercise combined with two days of strength training each week.
  • Nutrition - Only eat the amount of food your body needs to help you maintain your weight. Try to pack your diet with metabolism-boosting foods like fresh fruit and vegetables, whole grains, and good sources of protein.
  • Rule out any underlying conditions - Your metabolism can be affected by hormonal imbalances or chronic conditions, such as thyroid disorders. If you suspect these may be affecting your metabolism, speak to your doctor about a medical check.
  • Quit smoking - Although smoking can increase metabolism slightly, it comes with an increased risk of heart disease and cancer, which can seriously affect your health.
  • Avoid diet fads - Things like fasting and skipping meals can have a detrimental effect on your metabolism. That’s because it can adapt quickly. So, if you restrict your calorie intake, your body will break down muscle for energy, slowing your metabolism.

Let’s Recap:

Metabolism is the engine that keeps our bodies running smoothly, involving various chemical processes. Basal metabolic rate (BMR) serves as a benchmark for our daily caloric needs to fuel our essential functions. Remember, our metabolism is not controlled by a single factor but is influenced by a unique combination of variables. By understanding and optimizing these factors, we can unlock the potential for a thriving, energetic, and balanced life.

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