Food is necessary to provide the body with energy. The oxidation of carbohydrate, fat and protein eventually leads to the generation of high energy bonds in AIP, which is then used for all energy requirements. In addition to providing energy, some of these oxidative products are utilized to generate the carbohydrates, fats and proteins of which the body is composed.
Energy balance is the difference between energy intake and energy expenditure.
ENERGY INTAKE can be estimated from dietary information and in the past has been used to decide daily energy requirements.
Glucagon acts mainly on the liver and has no action on muscle. It increases glycogenolysis and gluconeogenesis, as well as increasing ketone body production from fatty acids. It also stimulates lipolysis in adipose tissue. Catecholamines have a similar action to glucagon but also affect muscle metabolism. These agents both act via cyclic AMP to stimulate lipolysis, producing free fatty acids that can then act as a major source of energy. Cytokines, such as interleukin 1, interleukin 6 and tumour necrosis factor (TNF) have also been shown to playa role in regulating metabolism. TNF, which inhibits lipoprotein lipase, has been identified as the cachexia factor in cancer patients.
Patients are sometimes seen with loss of weight or malnutrition (failure to thrive in children) as the primary symptom. Mostly, however, malnourishment is only seen as an accompaniment of some other disease process, e.g. malignancy.
The major cause of the weight loss is failure to eat due to anorexia. A careful history may indicate the cause of the weight loss but, if nothing obvious is found, hyperthyroidism must be considered. Anorexia nervosa commonly occurs in young adolescent
females. Patients who have lost more than 10% of their body weight (unless dieting) suffer from malnutrition. Indicators of malnutrition are given. The clinician can usually decide whether the patient is malnourished by the patient’s general appearance. Retrospective dietary evaluation is not helpful, unfortunately, because of the degree of error in patients’ recollection of their intake.
Severe malnutrition is mainly seen with advanced organic disease or after surgical procedures followed by complications. PEM leads to a depression of the immunological defence mechanism, leading to decreased resistance to infection
When malnutrition is obvious and the underlying disease cannot be corrected at once, some form of nutritional support is necessary. Nutrition should always be given enterally if the gastrointestinal tract is functioning adequately. This can most easily be done by encouraging the patient to eat more often and by giving a high-calorie supplement. If this is not possible, a liquefied diet may be given intragastrically via a fine-bore tube. If both of these measures fail, parenteral nutrition is given.