Abnormalities of Fuel Utilization as Predisposing to the Development of Obesity in Humans

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Abstract
A number of recent investigations in man have demonstrated that a low ratio of fat to carbohydrate oxidation (i.e., a high respiratory quotient or RQ) was associated with actual and/or subsequent body weight gain in obese non‐diabetic Pima Indians, in American men of various ages and in post‐obese European women investigated shortly after the cessation of a hypocaloric diet. It is well known that numerous exogenous and endogenous factors influence the RQ at rest such as: the level of feeding (positive vs. negative energy balance), the composition of food eaten (high vs. low carbohydrate), the size of the glycogen stores, the amount of adipose tissue as well as genetic factors. It should be stressed that some nutritional situations can coexist during which a low ratio of fat to carbohydrate is observed (i.e., a high RQ) despite weight loss. Furthermore, in most studies mentioned above, the low fat to carbohydrate oxidation ratio explains less then 10% of the variance in weight gain, suggesting that numerous additional factors also play a substantial role in the onset of weight gain. It is concluded that: 1) A low fat to carbohydrate oxidation ratio or an abnormal fat oxidation is difficult to define quantitatively since it is largely influenced by the energy level and the composition of the diet. 2) Following a dynamic adaptation phase to positive energy balance, a low fat oxidation is progressively compensated: increased body fat is the price to pay for normalizing fat oxidation since, at least in resting conditions, there is an increase in fat oxidation of approximately 20 g/day for each 10 kg additional fat gain. The subject with a low fat to carbohydrate oxidation ratio will equilibrate at a body fat level allowing to reach a new fat balance.

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