ENERGY BALANCE
The energy balance equation has underpinned most efforts to explain the energy dynamics of obesity. Obesity is characterised by high energy stores and usually a high energy intake and expenditure (metabolic rate). To reach a state of obesity, there needs to be a chronic imbalance between energy intake and expenditure over a long period of time. However, an initial positive energy balance will cause energy stores to increase (both fat mass and fat-free mass) which in turn causes an increase in energy expenditure, due mainly to the increased resting metabolic rate from the greater fat-free mass. At some point, the weight gain and increased energy expenditure will offset the original imbalance and a new equilibrium will be achieved.
Therefore, the energy balance equation helps to explain how a positive energy balance leads to weight gain and how a new steady state is achieved. However, it fails to answer two critical questions: why did the positive energy balance occur in the first place and why does it remain chronic over long periods? The answers to these questions may come from an understanding of the regulation of individual macronutrients (carbohydrate, protein, fat, and alcohol). However, separating out each macronutrient balance equation can only be valid if the biochemical highways do not allow a free flow of nutrients. What are the restrictions for converting one nutrient to another for storage and, in particular, are glucose and alcohol converted into fat through the process called de novo lipogenesis?
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