Studies have shown that more soy protein might be needed to maintain nitrogen balance when compared to egg-white protein, and that the difference may be eliminated by the addition of methionine to the soy diet. This indicates that sulfur amino acids can be limiting in soy. Similarly, the limiting amino acid in wheat protein is lysine. The Recommended Daily Allowance (RDA) for protein is estimated for people consuming complete proteins that prevent negative nitrogen balance due to the inadequate intake of limiting indispensable amino acids. The RDA recommendations also assume that the diet has enough nonprotein energy, such as carbohydrates and fats, to prevent the carbon skeletons of amino acids from being used to meet energy needs.