ABSTRACT
If the intake of metabolic fuels is lower than is required to meet energy expenditure, the body’s reserves of fat, carbohydrate (glycogen), and protein are used. Undernutrition may develop because of inadequate food intake (due to lack of food or pathological disorders of appetite), increased metabolic rate as a result of cancer and other chronic diseases, or malabsorption. Especially in lean people, who have small reserves of body fat, there can be a large loss of tissue protein (to provide substrates for gluconeogenesis) when food intake is inadequate. As the deciency continues, there is increasing loss of tissue, until eventually essential tissue proteins are catabolised as metabolic fuels-a process that obviously cannot continue for long.
