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What is metabolism

Your metabolism is the whole range of chemical reactions in your body’s cells that turn the food you eat into living tissue, energy, and waste products. Your metabolism is a combination of two processes:

  • Catabolism, when food is broken down into simpler components. This is accompanied by the release of energy that heats the body, enables the body to move and provides fuel for anabolism;
  • Anabolism, when the body uses the energy released as a result of catabolism to make new cells, maintain body tissues and store energy for future use.


These two complementary metabolic processes are controlled by systems of hormones which switch your body from anabolic to catabolic mode and vice versa. One result of this metabolic switching system is that your body gains or loses weight.

Your daily calorie burn is affected by how much you exercise the amount of fat and muscle in your body and your basal metabolic rate (BMR). Your BMR is the speed at which your body burns up energy (calories) while at rest. This can determine your tendency to gain or lose weight.

What factors influence my BMR?

  • Genetics: Some of us are born with a faster metabolism and some with a slower metabolism.
  • Gender: Men have a greater muscle mass and a lower body fat percentage so they generally have faster metabolism.
  • Age: Younger people have more actively dividing body cells. Cell division consumes a lot of energy and that is why theirmetabolism is very fast. Your metabolism slows down by approximately 2% every 10 years after you turn 20.
  • Height: The taller a person is, the faster their metabolism because their body surface area is larger and so heat loss is greater.
  • Body composition: It requires more energy to sustain muscle mass than fat. The more muscle mass you have, the faster your metabolism.
  • Glands: Thyroxin (produced by the thyroid gland) is a key BMR-regulator, which regulates the metabolic activity of the body. The more thyroxin produced, the higher your BMR. Adrenaline also increases your BMR but to a lesser extent.
  • Hormones: Some surveys have found that a woman’s metabolism dips just before ovulation and again at menstruation. BMR then starts to rise when the body temperature climbs. Menopause causes the metabolism to slow down.
  • Stress: Stress hormones can raise your BMR.
  • Exercise: This not only burns calories, it also helps raise your BMR by building extra muscle.
  • Diet: Excessive calorie restriction, or starvation, can dramatically slow down your metabolism.
  • Stimulants: Your metabolic rate rises temporarily after ingesting caffeine and nicotine. This also raises your heart rate.
  • Temperature: A low external temperature results in a faster metabolism. This creates the extra heat needed to maintain the body’s internal temperature.
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