Set Point ~ Settling Point Part II: Substrate Balance & Body Composition

Continuing the discussion of Point 9 from this paper, and Part I,

Although less obvious than the fact that energy intake must be equal to energy expenditure, weight stability also requires that the substrate mixture oxidized be equivalent, on average, to the composition of the nutrient mix consumed. When “substrate balance” is not achieved, changes in body composition occur, which in time are bound to elicit adjustments in food intake.

The contributions made by carbohydrate and by fat to the fuel mix oxidized is reflected in the ratio of CO2 produced to O2 consumed. This ratio is known as the “respiratory quotient” or “RQ.” It varies between the values of 1.0, when CHO is the predominant fuel, and 0.7, when oxidation of fat provides most of the body's energy. The ratio of CO2 produced to O2 consumed during the biological oxidation of a representative sample of the diet consumed is defined as the “food quotient” or “FQ”. Stable body compositions will only be sustained if the average RQ matches the average FQ of the diet.

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