Proteins are our chief dietary source of nitrogen. Someone in positive nitrogen balance is in a period of growth, like a child or pregnant woman. Negative nitrogen balance means that body proteins are being broken down and used as fuel. This condition may occur if carbohydrate and fat intake are insufficient to meet the need for energy. Nitrogen balance is affected by growth hormone and sex hormones that promote protein synthesis.
Glucocorticoids promote protein catabolism during times of stress.
Neither is used as fuel, but both are essential to our ability to use other nutrients. Minerals and vitamins cannot be synthesized by the body, and are required only in minute amounts. Indeed, excessive amounts are toxic and potentially lethal. In general, these vitamins are not stored by the body to any great extent, and excesses are excreted in the urine. They seldom accumulate to excess.