These hormones are produced in large amounts when much tissue has been damaged and pain inflicted and their action rapidly breaks down body protein; they are known as catabolic hormones. Those that build up body tissue are the anabolic hormones and are secreted subsequently during the recovery phase. High energy intake during illness is of paramount importance. Protein intake should be kept high.
Break-down and production of tissue can occur simultaneously. When loss of body protein is large it may be accompanied by weakness, poor healing, lowered resistance to infections and may lead to unexpected death, especially if there has been malnourishment just prior to the illness. During the recovery period there is a marked need for protein of high biological value . In an adult in good health relatively little protein is needed each day for general tissue maintenance, but during recovery from illness the amount of protein needed becomes similar to that of a rapidly growing young child. There must also be extra water intake for the renal excretion of the waste substances produced by the increased protein metabolism. A urine output of at least 750 ml/day is desirable if the kidneys are healthy. There are two groups of diseases during which a high-protein diet is undesirable: these are diseases in which liver function is badly disturbed and diseases in which there is severe kidney damage. Under these conditions it is necessary not to feed more protein than the liver can metabolise and to make sure that the end products of that metabolism can be excreted by the kidneys or removed by dialysis. In subjects who have lost considerable body protein it may be necessary to attempt to replete them before undertaking surgery or debillitating therapy (cancer chemotherapy; radiotherapy). Most patients are emotionally stressed, which may cause loss of appetite (though rarely some may eat too much). Thus it is essential that extra food given to them should be acceptable as well as being nutritionally sound.
During an acute illness there is need for increased vitamin intake, especially for the vitamin B group and vitamin C. The exact amounts required are not known but it is believed that as much as five times the normal intake is desirable for at least vitamins B and C. A large intake for a limited time, even if not needed, would be harmless.
Medicinal drugs can cause a nutrient deficiency by reducing appetite, inducing nausea or vomiting, by interfering with the intestinal uptake of specific nutrients or by preventing the proper action of essential nutrients at the tissues. Such actions can lead to serious deficiencies of vitamins and minerals. Patients on drugs known to have such effects must be closely monitored so that deficiencies can be corrected, especially if the drugs are taken for long periods.
Exclusion of nutrients
In some conditions it may be necessary to exclude certain nutrients from the diet or to provide them in only limited amounts. For example, in the condition known as phenylketonuria (PKU) it is essential to carefully limit the dietary intake of the essential amino acid phenylalanine as soon after birth as possible; in lactose intolerance the sugar lactose (present in milk) needs to be kept at a low level; in diabetes mellitus glucose and sucrose intake must be carefully controlled; in conditions in which dietary fat is poorly absorbed by the intestine the fat in the diet must be kept low; in patients with excessive body iron the dietary intake of the metal has to be restricted; when the blood calcium levels are abnormally raised calcium in the diet needs to be lowered; in obesity the energy content of the diet should be diminished; when there is excessive water in the body and the kidneys are unable to excrete it, water intake has to be limited; in liver and kidney failure dietary protein and perhaps sodium have to be very low; in high blood pressure reducing the salt eaten may be of value.