Weight loss is a physical condition that results from a negative caloric balance, such as when metabolic utilization and excretion of essential nutrients exceed the caloric supply. Weight loss is considered clinically important when it exceeds 10 percent of the normal body weight and is not associated with fluid loss. Weight loss can result from many different mechanisms that share the common feature of insufficient caloric intake or availability to meet metabolic needs. Causes vary markedly from intentional restriction of calories in order to reduce weight in an obese patient, to weight loss associated with life threatening illness.

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