1.7.3 Too little protein
If insufficient protein is present in the diet for the body's needs, then it starts to break down its own proteins. Since muscles contain large amounts of protein, the result of a low-protein diet is muscle-wasting. Individuals who have a poor appetite, perhaps due to some underlying medical condition, may also be short of protein and muscle weakness is common. Muscle wasting is particularly hard to detect in obese patients where the reduction in size of the muscles is not easily detectable beneath the layer of fat.
In some parts of the world, many millions of people are short of protein in their diet, though they are probably short of other essential dietary components too, and it is not easy to identify the particular part that protein deficiency plays in their overall malnutrition. Protein-energy malnutrition (PEM) is a condition where the diet of adults and children is lacking in a range of nutrients and overall food intake is too low for their bodily requirements. Marasmus is a severe form of PEM, resulting from a long-term insufficiency in energy intake. It is a condition that is often seen in famines, although low-level marasmus can occur throughout a vulnerable population, with only the most severe cases being noticed. If no other source of energy is available, the protein in the body's muscles and organs is broken down to provide energy. The cells lining the digestive system are affected, leading to poor absorption of nutrients from the inadequate diet. This cycle of inadequate diet and poor absorption of nutrients leads to the severe body wasting seen in famine victims. Kwashiorkor is protein deficiency in children. It can occur when children are weaned from breast milk onto protein-poor foods such as cassava (a root vegetable) or plantain (green bananas). Repeated childhood infections and a lack of vitamins and minerals make the condition worse. The characteristic features are oedema, which is swelling of parts of the body due to fluid retention, and a general lack of energy for any activity. Growth stops and there is severe liver damage, loss of weight and loss of pigmentation from the skin.