About: Undernutrition, malnutrition

"Animals can synthesize most, but not all, of the fatty acids they need. The essential fatty acids, the ones they cannot make, are certain fatty acids that are unsaturated(containing one or more double bonds). For example, humans require linoleic acid to make some membrane phospholipids. Because seeds, grains, and vegetables in the diets of humans generally furnish ample amounts of essential fatty acids, deficiencies in this class of nutrients are rare."

"When an animal is undernourished, a series of events unfold: The body uses up stored fat and carbohydrates; the body begins breaking down its own proteins for fuel; muscles begin to decrease in size; and the brain may become protein-deficient. If energy intake remains less than energy expenditure, the animal will eventually die. Even if a seriously undernourished animal survives, some of the damage may be irreversible."