Metabolism is a biochemical process that allows an organism to live, grow, reproduce, heal, and adapt to its environment. Anabolism and catabolism are two metabolic processes, or phases. Anabolism refers to the process which builds molecules the body needs; it usually requires energy for completion. Catabolism refers to the process that breaks down complex molecules into smaller molecules; it usually releases energy for the organism to use.
|Introduction||Metabolic process that builds molecules the body needs.||Metabolic process that breaks down large molecules into smaller molecules.|
|Energy||Requires energy||Releases energy|
|Hormones||Estrogen, testosterone, insulin, growth hormone.||Adrenaline, cortisol, glucagon, cytokines.|
|Effects on Exercise||Anabolic exercises, which are often anaerobic in nature, generally build muscle mass.||Catabolic exercises are usually aerobic and good at burning fat and calories.|
|Example||: amino acids becoming polypeptides (proteins), glucose becoming glycogen, fatty acids becoming triglycerides.||proteins becoming amino acids, proteins becoming glucose, glycogen becoming glucose, or triglycerides becoming fatty acids.|
Anabolic and Catabolic Processes
Anabolic processes use simple molecules within the organism to create more complex and specialized compounds. This synthesis, the creation of a product from a series of components, is why anabolism is also called "biosynthesis." The process uses energy to create its end products, which the organism can use to sustain itself, grow, heal, reproduce or adjust to changes in its environment. Growing in height and muscle mass are two basic anabolic processes. At the cellular level, anabolic processes can use small molecules called monomers to build polymers, resulting in often highly complex molecules. For example, amino acids (monomers) can be synthesized into proteins (polymers), much like a builder can use bricks to create a large variety of buildings.
Catabolic processes break down complex compounds and molecules to release energy. This creates the metabolic cycle, where anabolism then creates other molecules that catabolism breaks down, many of which remain in the organism to be used again.
The principal catabolic process is digestion, where nutrient substances are ingested and broken down into simpler components for the body to use. In cells, catabolic processes break down polysaccharides such as starch, glycogen, and cellulose into monosaccharides (glucose, ribose and fructose, for example) for energy. Proteins are broken down into amino acids, for use in anabolic synthesis of new compounds or for recycling. And nucleic acids, found in RNA and DNA, are catabolized into nucleotides as part of the body's energy needs or for the purpose of healing.
Many of the metabolic processes in an organism are regulated by chemical compounds called hormones. In general, hormones can be classified as anabolic or catabolic based on their effect within the organism.
Anabolic hormones include:
- Estrogen: Present in males as well as in females, estrogen is produced mainly in the ovaries. It regulates some female sexual characteristics (growth of breasts and hips), regulates the menstrual cycle, and plays a role in strengthening bone mass.
- Testosterone: Present in females as well as males, testosterone is produced mainly in the testes. It regulates some male sexual characteristics (facial hair, voice), strengthens bones, and helps build and maintain muscle mass.
- Insulin: Produced in the pancreas by beta cells, it regulates the blood level and use of glucose. The body cannot use glucose, a main source of energy, without insulin. When the pancreas cannot create insulin, or when the body struggles to process the insulin it makes, this leads to diabetes.
- Growth hormone: Produced in the pituitary, growth hormone stimulates and regulates growth during the early stages of life. After maturity, it helps regulate bone repair.
Catabolic hormones include:
- Adrenaline: Also called "epinephrine," adrenaline is produced by the adrenal glands. It is the key component of the "fight or flight" response that accelerates heart rate, opens up bronchioles in the lungs for better oxygen absorption and floods the body with glucose for fast energy.
- Cortisol: Also produced in the adrenal glands, cortisol is known as the "stress hormone." It is released during times of anxiety, nervousness or when the organism feels prolonged discomfort. It increases blood pressure, blood sugar levels and suppresses the body's immune processes.
- Glucagon: Produced by the alpha cells in the pancreas, glucagon stimulates the breakdown of glycogen into glucose. Glycogen is stored in the liver and when the body needs more energy (exercise, fighting, high level of stress), glucagon stimulates the liver to catabolize glycogen, which enters the blood as glucose.
- Cytokines: This hormone is a small protein that regulates communication and interactions between cells. Cytokines are constantly being produced and broken down in the body, where their amino acids are either reused or recycled for other processes. Two examples of cytokines are interleukin and lymphokines, most often released during the body's immune response to invasion (bacteria, virus, fungus, tumor) or injury.
How Metabolism Affects Body Weight
A person's body weight will be the end result of catabolism minus anabolism: in essence, how much energy is released into the body, minus how much energy is used by the body. Excess energy added to the body is stored as fat or as glycogen stored in the liver and in muscles. If a person's goal is to lose weight, the basic method is to increase energy use while reducing energy intake, preferably under medical supervision.
Most people point to metabolism as the reason for being overweight or underweight, but metabolic processes vary little from person to person. The belief that some people enjoy a "high" or "fast" metabolism while others suffer from a "slow" or "low" metabolism is not supported by science.  What does differ to a significant degree is the amount of physical activity and the quality/quantity of food ingested by people with so-called "fast" and "slow" metabolisms. The people who are overweight simply have a metabolic (energy) imbalance wherein their body takes in more energy than they use on a regular basis, with the excess stored as fat.
There are metabolic disorders than can affect body weight, such as hypothyroidism or hyperthyroidism. Hypothyroidism is the condition where the thyroid reduces its hormonal output, lowering the body's level of energy use. People with hypothyroidism tend to gain weight unless they follow a very strict regimen of diet and exercise. The opposite occurs with hyperthyroidism, a disorder in which the thyroid's hormonal output increases drastically and the body's energy use becomes excessive.
As changing the base metabolic rate is nearly impossible for those with metabolic disorders, the best option to reach ideal body weight is long-term changes in diet and exercise levels. The anabolic process of building muscle mass through exercise, dancing, yoga, gardening or other physical activity eventually leads to leaner body mass (less fat) and a higher need for energy (catabolism) to feed the muscle cells. The nutritional quality of food is also a key factor, avoiding "empty" calories, mainly excess fat and sugars, that the body cannot use and ends up storing. Catabolism breaks everything down, regardless of its nutritional value. For anabolic processes to work at optimum levels, the body must have the proper nutrients. Eating healthier foods helps the body build itself in healthier ways.
Anabolic and Catabolic Exercises
Anabolic exercises are generally those that build muscle mass, such as weight lifting and isometrics (resistance). However, any anaerobic (non-oxygen using) exercise is basically anabolic. Anaerobic exercises include sprinting, jumping rope, interval training or any activity done at high intensity for brief periods of time. With these activities, the body is forced to use its immediate reserves of energy and then remove the lactic acid build-up in muscles. To prepare for another effort, the body increases muscle mass, strengthens bones and uses amino acids to increase protein reserves. Some of the amino acids will come from fat stored in the body.
Catabolic exercises are largely aerobic, meaning they consume oxygen, and help burn calories and fat. The use of oxygen is a key factor in catabolism, as oxygen is a reducing agent in many chemical processes. Typical catabolic/aerobic exercises are jogging, cycling, swimming, dancing or any physical activity done for at least 20 minutes at moderate intensity. Time is a major factor in getting results because after about 15-20 minutes, the body switches from using glucose and glycogen to using fat to sustain the energy requirements of the body. For that catabolic process, oxygen is required. By combining aerobic and anaerobic exercises on a consistent basis, a person can use anabolic and catabolic processes to reach or maintain an ideal body weight as well as improve and sustain overall health.
The idea that some foods can foster catabolism and thus induce weight loss is not supported by science. In biological terms, digestion is meant to extract nutrition and energy from food; if the process induced catabolism, the living organism would suffer damage from acquiring less resources than it invested to gain them. In terms of physics, a catabolic food would cost more energy to process than what it would provide the organism, leading to energy loss that ends in death. No digestive process could have a net energy loss and keep an organism alive.
There are, however, some foods where the caloric expenditure to process them is a little higher than the calories they provide the system. The clear example is water, especially ice-cold water. The body needs to warm it up before absorbing it, leading to a small caloric debt. Foods with very high water content, such as celery, also have this tiny catabolic effect. But the nutritional value of water and celery are not high enough to properly sustain an organism, so relying solely on these foods to lose weight can lead to serious health complications.