Complete protein
Protein source containing all nine essential amino acids
From Wikipedia, the free encyclopedia
Concept
Protein nutrition is complex because any proteinogenic amino acid may be the limiting factor in metabolism. Mixing livestock feeds can optimize for growth, or minimize cost while maintaining adequate growth. Similarly, human nutrition is subject to Liebig's law of the minimum: The lowest level of one of the essential amino acids will be the limiting factor in metabolism.
- If the content of a single indispensable amino acid in the diet is less than the individual's requirement, then it will limit the utilization of other amino acids and thus prevent the normal rates of synthesis even when the total nitrogen intake level is adequate. Thus the "limiting amino acid" will determine the nutritional value of the total nitrogen or protein in the diet.[6]
Protein sources are thus rated by their limiting amino acids.[7]
Most people eat a varied diet with multiple sources of protein. Incomplete sources can complement each other and become complete when combined.[8] Combining does not need to happen for every single meal: so long as the diet is varied and meets caloric needs, even vegans and vegetarians – people who tend to have more "incomplete protein" in their diet – can easily meet their amino acid needs. In other words, most people do not need to consider the completeness of proteins of single foods.[9]
Amino acid profile
The following table lists the optimal profile of the nine essential amino acids in the human diet, which comprises complete protein, as recommended by the US Institute of Medicine's Food and Nutrition Board. The foodstuffs listed for comparison show the essential amino acid content per unit of the total protein of the food; 100g of spinach, for example, only contains 2.9g of protein (6% Daily Value), and of that protein 1.36% is tryptophan.[2][10](note that the examples have not been corrected for digestibility)
| Essential amino acid | mg/g of protein | percentage of total protein | raw, whole chicken egg[11] | quinoa[12] | raw spinach[13] |
|---|---|---|---|---|---|
| Tryptophan | 7 | 0.7% | 1.33% | 1% | 1.36% |
| Threonine | 27 | 2.7% | 4.42% | 3.2% | 4.27% |
| Isoleucine | 25 | 2.5% | 5.34% | 4.2% | 5.14% |
| Leucine | 55 | 5.5% | 8.65% | 7.3% | 7.8% |
| Lysine | 51 | 5.1% | 7.27% | 6.1% | 6.08% |
| Methionine+Cystine | 25 | 2.5% | 5.18% | 2.7%+1.3% | 1.85%+1.22% |
| Phenylalanine+Tyrosine | 47 | 4.7% | 9.39% | 4.3%+3.6% | 4.51%+3.78% |
| Valine | 32 | 3.2% | 6.83% | 5% | 5.63% |
| Histidine | 18 | 1.8% | 2.45% | 3.1% | 2.24% |
| Total | 287 | 28.7% | 50.86% | 41.8% | 43.88% |
Total adult daily intake
The second column in the following table shows the amino acid requirements of adults as recommended by the World Health Organization[14] calculated for a 62 kg (137 lb) adult. Recommended Daily Intake is based on 2,000 kilocalories (8,400 kJ) per day,[15] which could be appropriate for a 70 kg (150 lb) adult.
| Essential amino acid | Required mg/day for a 62 kg (137 lb) adult |
|---|---|
| Tryptophan | 248 |
| Threonine | 930 |
| Isoleucine | 1240 |
| Leucine | 2418 |
| Lysine | 1860 |
| Methionine+Cystine | 930 |
| Phenylalanine+Tyrosine | 1550 |
| Valine | 1612 |
| Histidine | 620 |
| Total | 11,408 milligrams (11.408 g) |
| Total Protein | 46 to 56 grams (46,000 to 56,000 mg) |