ABSTRACT
In common with all living organisms, man requires energy. Human biology drives us to assimilate nutrients containing energy stored in the form of protein, fat, carbohydrates and alcohol (feeding). Ingested nutrients are processed to provide compounds that provide energy for immediate needs, and for energy stores that can provide a continuing supply of energy during periods of high energy requirements (e.g. exercise) or food shortage. Energy stores are essential to any living organism if it is to survive periods of food (energy) scarcity, or episodes of increased and frequently unpredictable energy demands (movement, pregnancy, illness). Human evolution has required that man has behavioural drives, and physiological and metabolic mechanisms that favour energy storage. Adipose tissue is the organ that serves this function. An ability to store energy efficiently and adequately, is advantageous to the survival of the individual and necessary for successful reproduction. It seems likely that the mechanisms favouring fat storage will have been genetically amplified by evolution. In very recent years, societal conditions in the developed world have altered so that energy expenditure has decreased and food availability increased. These factors have resulted in individuals, genetically adapted to a harsher environment, being prone to excessive fat storage and weight gain. Obesity is the term that describes this state in which energy stores (as fat) have become excessive to the point of disadvantage to health. Obesity is both a risk factor for many diseases, including coronary heart disease and diabetes, as well as a disease in its own right. It now affects 15% of the adult population in the UK and its prevalence is increasing year by year. An understanding of the mechanisms involved in human energy metabolism and fat deposition is perhaps one of the most pressing public health issues for the end of the millennium.
