To accommodate a doubled protein intake, which nutrient must also increase?

To accommodate a doubled protein intake, the nutrient that must also increase is pyridoxine, commonly known as vitamin B6. Pyridoxine plays a crucial role in protein metabolism, as it is required for the synthesis of amino acids and the conversion of amino acids into neurotransmitters. It also assists in transamination reactions, which are vital for the utilization of amino acids from dietary proteins.

When protein intake increases significantly, the body's demand for pyridoxine also rises to support the enhanced metabolic processes associated with processing these proteins efficiently. This makes it necessary to ensure adequate levels of pyridoxine to optimize protein utilization and prevent deficiencies that could impair metabolism and overall health.

Other nutrients mentioned, such as folic acid, niacin, and vitamin C, while important in their respective roles in the body, do not have the same direct correlation with protein metabolism as pyridoxine does. Thus, they do not need to increase proportionately with an increase in protein intake.