Last updated 2024-09-06 to add more content.

You may know that complete proteins are good because they contain every essential amino acid. But you might not know that that’s not the full story.

Take wheat. Wheat is a complete protein—it contains all nine essential amino acids. But it has a problem. Wheat only contains 27mg of lysine (an essential amino acid) per gram of protein, whereas the Food and Agriculture Organization recommends 48mg of lysine per gram. To make full use of a gram of protein, your body needs to get those 48mg. It doesn’t matter that wheat has lots of other essential amino acids. Once your body uses up all the lysine, it can’t make good use of the other amino acids in wheat protein.

You can evaluate the protein quality of a food using the Digestible Indispensable Amino Acid Score (DIAAS). This score determines the quality of a source of protein based on which essential amino acid will run out first, adjusted for digestibility. A score of 100 means the protein has plenty of every essential amino acid.

Sometimes you can improve the protein quality of your food by mixing different ingredients. Wheat has a DIAAS of 57 because it only has 57% as much lysine per gram as your body needs. Peas have a score of 82 because they don’t have enough methionine + cysteine. But peas have 131% of the lysine requirement, and wheat has 149% of methionine + cysteine, so mix them together and they cover for each other’s weaknesses. A 50/50 mixture of wheat and pea protein has a DIAAS of 94.

With this calculator, you can determine the DIAAS for mixtures of different protein sources.

Ingredient Content (%)
Soy
Wheat
Pea
Fava bean
Hemp
Rice
Potato
Oat
Corn
Rapeseed
Lupin
Canola
Whey

DIAAS
Limiting amino acid
Full amino acid profile: (100 = recommended dose)
HistidineIsoleucineLeucineLysineMet + CysPhe + TyrThreonineTryptophanValine

Good combinations of plant proteins

  1. Soy protein alone has a DIAAS of 102.
  2. 22% pea + 36% fava bean + 42% hemp has a DIAAS of 96.
  3. 50% wheat + 50% pea has a DIAAS of 94.
  4. 28g of wheat protein plus a 500mg lysine pill has a DIAAS of 94.

Table of amino acid profiles

Amino acid values are scaled to the reference values for adult amino acid requirements such that a score of 100 matches the reference value.

Calculated using the amino acid values from Herreman et al. (2020)1 and the reference values from FAO Expert Consultation (2011)2.

Protein source DIAAS Histidine Isoleucine Leucine Lysine Met + Cys Phe + Tyr Threonine Tryptophan Valine
Soy 102 149 132 110 114 107 186 130 170 102
Wheat 57 148 97 94 57 149 138 97 164 99
Pea 82 124 108 94 131 82 147 117 99 89
Fava bean 65 135 113 103 113 65 151 113 88 89
Hemp 64 155 113 92 64 142 166 108 129 106
Corn 43 138 96 175 43 148 178 107 67 97
Rice 56 116 95 87 56 122 151 93 147 102
Potato 125 125 166 155 145 135 266 205 165 148
Oat 68 114 107 102 68 177 171 105 142 110
Rapeseed 80 134 96 84 80 147 117 120 137 99
Lupin 80 151 111 96 89 80 153 120 93 84
Canola 85 131 99 85 86 142 123 120 144 94
Whey 106 106 177 149 156 155 128 216 232 125

References

  1. FAO Expert Consultation (2011). Dietary protein quality evaluation in human nutrition. ↩

  2. Herreman, L., Nommensen, P., Pennings, B., & Laus, M. C. (2020). Comprehensive overview of the quality of plant- and animal-sourced proteins based on the digestible indispensable amino acid score. ↩