The mechanisms of weight loss are: the reduced food intake, malabsorption, and loss of calories increased energy requirements (fig 1.). The changes in body weight may be due to those experienced by the tissue mass or fluid volume containing the body changes. In general, a deficit of 3500 kcal corresponds to a loss of 0.45 kg of body fat, but water (1 kg / L) to be won or lost must also be considered. Weight loss lasting weeks to months almost always involves a loss of tissue mass.
Energy balance and pathophysiological aspects of weight reduction In food intake is influenced by a variety of visual stimuli, olfactory and gustatory, plus genetic, psychological and social factors. The absorption may decrease if pancreatic insufficiency, cholestasis, celiac spree, intestinal tumors, radiation injury, inflammatory bowel disease, infections or drug effects. The manifestations of these abnormal pictures can be suspected if there are alterations in the frequency of defecation and stool consistency http://andygwilliam.staff.shef.ac.uk/story.php?title=hypothyroidism-revolution-review
They can lose calories through vomiting or diarrhea, with glycosuria of diabetes mellitus or the existence of fistulas. The resting energy expenditure decreases with age and may change with the state of thyroid function. Body weight begins to decrease after 60 years at a rate of 0.5% annually. Body composition also changes with aging; adipose tissue and increases lean muscle mass decreases with age. Meaning of weight loss
The unwanted weight loss, particularly in the elderly, is not a rare event, and carries increased morbidity and mortality, even after taking into account the coexisting pathologic conditions. Prospective studies indicate that unintentional weight loss of significant magnitude associated mortality rate of 25% in 18 months. In retrospective studies of significant weight loss of the elderly has been shown that mortality rates are 9-38% in the next two to three years.