Optimizing Protein Intake in Adults: Interpretation and Application of the Recommended Dietary Allowance Compared with the Acceptable Macronutrient Distribution Range

Abstract

The adult RDA is defined as the average daily level of intake sufficient to meet the nutrient requirements of nearly all healthy people. The RDA for protein for adults ≥18 y of age (0.8 g/kg) has been essentially unchanged for >70 y. In practice, the RDA for protein was derived to estimate the minimum amount of protein that must be eaten to avoid a loss of body nitrogen. The Acceptable Macronutrient Distribution Range (AMDR) (10-35% of calories as protein) was developed to express dietary recommendations in the context of a complete diet. It is noteworthy that the lowest level of protein intake reflected in the AMDR is higher than that of the RDA. Furthermore, recent studies, particularly in older individuals, suggest specific health benefits at levels of protein intake that significantly exceed the RDA. Translation of protein intake recommendations for the general adult population into dietary guidance for individuals requires an understanding of the derivation and intended use of both the protein RDA and AMDR. The following discussion will describe limitations to the derivation and practical application of the RDA compared with the use of the AMDR to help maximize health benefits associated with higher protein intake by using flexible calories inherent in different dietary patterns.

Keywords: AMDR; RDA; dietary pattern; nitrogen balance; protein.

FIGURE 1

Nitrogen balance as a tool to determine protein requirements. A simplified schematic of the model used to calculate the EAR and RDA for protein from nitrogen balance studies (A). Positive nitrogen balance values are considered to be artifacts. Results from the meta-analysis of nitrogen balance data that was used by the Food and Nutrition Board to calculate the EAR and the RDA (B). This represents the relation between individual nitrogen balances, corrected for dermal and miscellaneous losses, and nitrogen intake in healthy adults. In some cases the same individuals were tested at different levels of protein intake, whereas in other cases the subject was tested at only one level of protein intake. The values for EAR and RDA depend on the means by which they are calculated from this data set (11). EAR, Estimated Average Requirement. Panel B reproduced from reference with permission.

FIGURE 2

The relation of the caloric contributions of the RDA for protein and carbohydrate and the recommended minimal intake of fat to total caloric requirement as estimated for a 30-y-old man with low activity levels (36.5 kcal ⋅ kg⁻¹ ⋅ d⁻¹) (reference , Tables 5–22). Although energy requirements may vary according to sex, age, activity level, and other factors, at most, the RDA of the macronutrients can account for ∼40% of energy requirement. CHO, carbohydrate.