What happens to the RER at a rested-fed state?

The respiratory exchange ratio (RER) is a measure used to indicate the fuel being utilized by the body during metabolic processes, particularly during rest or exercise. In a rested-fed state, particularly after carbohydrate intake, the body experiences an increase in the availability of glucose. This leads to increased carbohydrate metabolism and, as a result, a higher RER.

When carbohydrates are consumed, they are often converted into fat through the process of de novo lipogenesis, particularly when there is an excess of energy. This process also contributes to a rise in RER values because carbohydrate oxidation generally yields a higher RER than fat oxidation.

In a rested state, if an individual is in a fed state with significant carbohydrate intake, the body favors glucose-based fuel rather than fatty acids. This shift leads to a higher RER, reflecting increased reliance on carbohydrates for energy. The metabolic responses during this state indicate that the body is synthesizing fat from the excess carbohydrates, which promotes a rise in the RER.

Understanding this relationship highlights the metabolic adaptations and shifts in fuel utilization that the body undergoes following ingesting carbohydrate-rich meals, particularly in a state where energy balance is positive.