Because the system for disposal of excess nitrogen is efficient, protein intakes moderately above requirement are believed to be safe.
Brenner et al. (1982) postulated that excess protein intake accelerates the processes that lead to renal glomerular sclerosis, a common phenomenon of aging. There is supportive evidence from studies in animals, but not in humans on this point. Urinary calcium excretion increases with increased protein intake if phosphorus intake is constant. If phosphorus intake increases with protein intake, as it does in U.S. diets, the effect of protein is minimized.
Habitual intakes of protein in the United States are substantially above the requirement, and although there is no firm evidence that these intake levels are harmful, it has been deemed prudent to maintain an upper bound of no more than twice the RDA for protein.
Recommended Dietary Allowance (RDA) - the average daily dietary nutrient intake level sufficient to meet the nutrient requirement of nearly all - ~97% - healthy individuals in a particular life stage and gender group.
The process for setting the RDA depends on being able to set an Estimated Average Requirement (EAR). If an EAR cannot be set, no RDA will be set. The EAR is the daily intake value of a nutrient that is estimated to meet the nutrient requirement of half the healthy individuals in a life stage and gender group.
The RDA is set at the EAR plus twice the standard deviation (SD) if known (RDA = EAR + 2 SD). If data about variability in requirements are insufficient to calculate a standard deviation, a coefficient of variation for the EAR of 10% is ordinarily assumed (RDA = 1.2 x EAR).
The RDA for a nutrient is a value to be used as a goal for dietary intake by healthy individuals. The RDA is not intended to be used to assess the diets of either individuals or groups or to plan diets for groups.