Obesity energy expenditure

Obesity is probably the oldest metabolic disturbance. People in a society become obese as soon as enough food and leisure are available to cause an imbalance between energy intake and energy expenditure. Obesity is becoming a more important risk factor for the development of diabetes, hypertension and cardiovascular disease. It has multiple causes the development of obesity is a complex interaction between genetic, psychological, socioeconomic and cultural factors. Individuals have unique genetic and environmental factors that affect how food is processed there are, therefore, individual differences in susceptibility to obesity. 

Papamandjaris, A.A., MacDougall, D.E., and Jones, P.J.H. Medium chain fatty acid metabolism and energy expenditure obesity treatment implications. Life Sci. 62, 1203-1215, 1998. 

Obesity results from an energy imbalance, when energy intake exceeds energy expenditure over a prolonged period of time. The excess energy is stored in the form of triglycerides in the adipose tissue. 

Leptin is a homeostatic hormone. It inhibits food intake and promotes energy expenditnre. Therefore, in the face of a loss in body fat, the levels of leptin decrease and food intake is stimnlated. In contrast, if body fat stores increase, the levels of leptin increase as well and food intake is decreased and energy expenditure increased. Therefore, leptin tends to maintain body weight within fairly close limits. Since ob/ob mice are genetically deficient in leptin, it follows that administration of leptin shonld tend to restore normal body weight. That is exactly what happens. Injection of leptin into ob/ob mice reduces their food intake dramatically and they tend toward the body weights of their normal littermates. In these mice at least, leptin is a powerful force for treatment of obesity. 

Weight Reduction Treatments. Obesity is simple to understand in theory, but often difficult to reverse in practice. Obesity occurs when energy intake exceeds energy expenditure for a sustaiued period of time. The surplus calories from this energy imbalance are stored for later use iu the form of fat. Despite this simple equation, the potential causes for this imbalauce are myriad and often difficult to determine in a given individual. 

The great advantage of the technique is that the measurements do not affect normal daily activities in any way, so it can be used to measure energy expenditure in a number of different activities or conditions (e.g. by cyclists in the Tour de France race, climbers on Mount Everest, members of a trans-Antarctic expedition, women during pregnancy or lactation, obese animals including humans carrying out their normal daily activities) (Prentice 1988). 

It can underestimate the energy expenditure in children and in very obese individuals. 

After 60 hours of starvation in lean subjects, fat utilisation (i.e. ketone bodies plus fatty acids) accounts for three-quarters of the energy expenditure (Table 16.1) a value which will rise even higher as starvation continues. Much of this increase is accounted for by hydroxybutyrate oxidation (the major ketone body) since, by 60 hours of starvation, the plasma concentration of hydroxybutyrate has increased 26-fold compared with a threefold increase in the concentration of fatty acid (the glucose concentration falls by less than 30%). By eight days of starvation there has been a sixfold increase in fatty acid concentration, whereas the concentration of hydroxybutyrate has increased about 50-fold (Table 16.2). The changes in these three major fuels in obese subjects during starvation for 38 days are shown in Figure 16.10. 

Recent studies of H3-receptor knockout mice demonstrate that absence of this receptor results in animals with increased food intake, decreased energy expenditure, and obesity. They also show insulin resistance and increased blood levels of leptin and insulin. It is not yet known whether the H3 receptor has a similar role in humans, but intensive research is underway to determine whether H3 agonists can be used in the treatment of obesity. 

Carbohydrates provide energy and fiber to the diet. When they are consumed as part of a diet in which caloric intake is equal to energy expenditure, they do not promote obesity. 

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