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The main purpose of metabolism is to maintain homeostasis, which is the maintenance and regulation of the body’s processes.
The main purpose of metabolism is to maintain homeostasis, which is the maintenance and regulation of the body’s processes.
Many people think of metabolism as merely the rate at which the body burns calories. It gets a little more complicated; metabolism accounts for ALL of the body’s life-sustaining chemical processes! It is influenced by many factors, such as age, gender, muscle-to-fat ratio, amount of physical activity and hormone function [1].
Generally speaking, the two main metabolic processes are 1) the breakdown of nutrients from food, and 2) building and repairing the body. These are catabolism and anabolism, respectively.
Catabolism
Catabolism
refers to the breakdown of carbohydrates, fats, and proteins into their simpler forms, which can then be used in anabolism to create energy and provide the basic building blocks needed for growth and repair.
NOTE: These mechanisms describe the big picture; metabolism is not limited to the overall synthesis and breakdown of nutrients, but also includes thousands of enzymatic reactions within these processes!
Anabolism
Anabolism
refers to the building or repairing of the body. It requires energy that comes from our food.
NOTE: It is often said that having a “fast metabolism” means that if you consume the same number of calories as an individual with a “slow metabolism,” you will gain less body fat than them. This is an oversimplification of the concept. In more accurate terms, the connection between metabolism and fat gain is that when more energy than required for daily anabolism is consumed, it is typically stored as fat.
Total daily energy expenditure (TDEE)
Total daily energy expenditure (TDEE)
- Basal metabolic rate (BMR)
Even at rest, the body uses energy to keep itself functioning (heartbeat, adjusting hormone levels, cell repair, etc.)
- Physical Activity
- Thermogenesis
This is the thermic effect of food, or the energy your body uses in digestion
Your total energy expenditure (TDEE) can be divided into three components:
The thyroid gland, hypothalamus, and pituitary gland control many metabolic processes, including protein synthesis and digestive functions [2]. Thyroid hormone triiodothyronine (T3) is the active form of thyroxine (T4), and is the hormone responsible for these biochemical processes. These hormones are stimulated by the release of thyrotropin, or thyroid-stimulating hormone (TSH), by the pituitary gland. This relationship occurs in a negative feedback loop: TSH levels decrease in the presence of T3 and T4 [3].
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