Catabolism is a destructive process which occurs in the body as various complex compounds are broken down into simple ones. This process occurs all the time all over the body, and it is used to provide energy as well as to create basic building blocks which can be used to build up complex compounds. In a classic example of catabolism, proteins are broken down into amino acids, which can in turn be recombined to make new proteins.
Together with anabolism, which involves building things up, catabolism contributes to metabolism, the system used to maintain the balance of energy in the body. The body's ability to break down the various compounds it encounters and makes is critical to its function, with catabolism providing energy for individual cells by breaking down compounds which are too complex for the cells to access. This process can also be used to take advantage of stored energy, which allows the body to create energy reserves which can be accessed when needed.
In addition to proteins, catabolism can also be used to process lipids, nucleic acids, and polysaccharides. Usually multiple steps are involved in the process, as the body creates progressively smaller and simpler compounds, usually releasing energy along the way. Enzymes are a major catalyst for catabolism, and the process is usually carefully regulated with hormones. When balances of enzymes and hormones go awry, they can cause problems with the metabolic system as a whole, which can lead to conditions such as cachexia, in which the body breaks down its own tissues for energy.
When compounds are broken down, the body usually develops waste products in addition to usable compounds. These waste products are carried out of the cells to the kidneys, so that they can be expressed in the urine. Doctors can analyze urine to look at the levels of various catabolic byproducts to learn more about a patient's general health, and to look for clues to a patient's medical problems. Unusually high or low levels can be indicators that something is going on inside the patient's body.
Many health conditions can influence someone's catabolism. In diabetes, for example, the process of glucose catabolism is disrupted, which leads to health problems because the body cannot access the stored energy in glucose. A classic symptom of some forms of diabetes is a high concentration of glucose in the urine, indicating that the body is expressing the glucose as a waste product because it cannot break the molecules up into usable compounds.