Metabolism is the series of chemical reactions that cells use to maintain the structure and balance of the body. It is actually two processes.
Catabolism primarily breaks down the molecules from our food into smaller parts or energy that cells can use (ex. a sandwich broken down into carbohydrates, proteins and fats).
Anabolism involves the construction of structures from smaller units (ex. proteins from the sandwich being rearranged to make muscle).
The speed at which our cells metabolize is called our metabolic rate. This rate varies quite a bit from person to person. People often say they wish they had a higher metabolic rate but our bodies are complex machines and how we metabolize our food involves a lot of different factors. These factors include:
how many calories we eat
how much we exercise
body temperature
our overall body shape
genetic makeup
the levels of our metabolic hormones.
Metabolic Wastes
Metabolic waste is the left over products of both catabolism and anabolism. This waste includes salts, phosphates, sulfates, excess substances, and nitrogenous wastes like urea which are eliminated through urine. Waste products have to be processed and removed from the cells, as they can build up, poison, and eventually kill the cells.
The kidneys work hard to get rid of our metabolic waste and it's a nonstop process. We also lose metabolic waste through sweating and exhaling (carbon dioxide is another waste product). Toxins from infections can also build up in cells and these are often eliminated through urine along with the nitrogenous waste left over from our food. The intestines also absorb excess water or mineral salts, and compact undigested foods into feces for excretion.