Energy Partitioning, Substrate Oxidation Rates, and Obesity

Energy partitioning reflects the distribution of substrate energy in body tissues to maintain homeostasis. It considers the specific features of each component of macronutrient balance and gives priority to precise regulation of protein, carbohydrate, and alcohol balance. The corollary is that any significant deviation in energy balance represents a deviation in fat balance that appears as the vulnerable component of the global macronutrient balance. This is partly explained by the reduced ability of lipid to promote its own oxidation and satiety. In individuals prone to obesity, this vulnerability is more obvious in the weight-reduced obese state that is characterized by a low relative fat oxidation. The concept of energy partitioning also integrates the notion of metabolic flexibility, which is particularly relevant in patients with type 2 diabetes who are known to display a reduced ability to switch from lipid oxidation in the fasting state to glucose utilization under insulin-stimulated conditions. As discussed in this chapter, energy partitioning varies according to substrate distribution in oxidative tissues such as skeletal muscle and brown fat versus subcutaneous and visceral fat. It is also affected by genetics, although environmental factors play a significant role in their variations.