Weight loss support involves reduction of body mass, fluids, fat or adipose tissue and/or muscles, tendons, or other connective tissue. It can be intentional as a result of dieting, or otherwise due to anorexia, weight loss exercise plan or lower food intake in relation to the amount of energy consumed. This can guarantee the expected weight reductions, whether they are desirable (as in obesity) or harmful (as in eating disorders).

Abnormal weight loss is a sign of an underlying disease and is therefore a symptom in itself that should be investigated. It can occur through muscle atrophy, reduction of fat, fluid loss or as a combination thereof. It is often considered as a medical problem for adults as it is occurs unintentionally, at least 10% of body weight is lost in six months.

Physical activity is specified as any bodily motion brought about by skeletal muscles which leads to a significant appreciation in energy expenditure over resting level.