This paper describes the interplay among energy intake, energy expenditure and body energy stores and illustrates how an understanding of energy balance can help develop strategies to reduce obesity. First, reducing obesity will require modifying both energy intake and energy expenditure and not simply focusing on either alone. Food restriction alone will not be effective in reducing obesity if human physiology is biased toward achieving energy balance at a high energy flux (i.e. at a high level of energy intake and expenditure). In previous environments a high energy flux was achieved with a high level of physical activity but in today's sedentary environment it is increasingly achieved through weight gain. Matching energy intake to a high level of energy expenditure will likely be more a more feasible strategy for most people to maintain a healthy weight than restricting food intake to meet a low level of energy expenditure. Second, from an energy balance point of view we are likely to be more successful in preventing excessive weight gain than in treating obesity. This is because the energy balance system shows much stronger opposition to weight loss than to weight gain. While large behavior changes are needed to produce and maintain reductions in body weight, small behavior changes may be sufficient to prevent excessive weight gain. In conclusion, the concept of energy balance combined with an understanding of how the body achieves balance may be a useful framework in helping develop strategies to reduce obesity rates.

Globally, bodyweight and obesity are rising in both the developing and developed world. To maintain a stable bodyweight, energy intake must, over time, exactly equal energy expenditure, a state known as energy balance. An understanding of the physiologic control of energy balance may be useful for designing interventions to tackle the obesity epidemic worldwide. Obesity occurs when the body’s energy balance is positive (i.e. when energy intake exceeds energy expenditure). Human physiology is biased towards maintaining energy balance at high levels of energy intake and expenditure. As a result, strategies to combat obesity should include a focus on increasing physical activity along with strategies for modifying food intake. An understanding of energy balance leads to the conclusion that prevention of weight gain should be easier than treatment of obesity. Components of energy balance are interdependent, and weight loss requires major behaviour changes, which trigger compensatory decreases in energy expenditure that facilitate weight regain. Prevention of weight gain can be accomplished by smaller behaviour changes. In addition to being easier to sustain than larger behaviour changes, smaller ones produce less compensation by the energy balance regulatory system. It has been estimated that relatively small changes in energy intake and expenditure totaling 100 kcal per day could arrest weight gain in most people. Interventions that advocate small changes have shown promising levels of success.

With the rising prevalence of obesity, hedonic eating has become an important theme in obesity research. Hedonic eating is thought to be that driven b