Our culture seems entrenched in the notion that we are all at risk for protein deficiency and the best source of protein, and all the amino acids, are animal foods. It seems that the notion that one must eat animal foods for protein, will never go away.
At one point, we were all told that plant foods were incomplete proteins. And by this, they meant that plant foods do not contain all of the essential amino acids. Some were missing, and to get in enough protein and amino acids, you have to carefully combine certain plant foods. This was the incomplete protein theory
Then, years later, the story changed. What we were now told was the plants do have all the essential amino acids in them, but some of these amino acids are in very small amounts. These amounts may be too small to ensure adequate protein synthesis in the body. So, they were still considered "incomplete' but in a different way. This became known as the limiting amino acid theory.
These theories not only abound in the general public, but also amongst health professionals. Many doctors, dietitians, nurses and other healthcare professionals still beleive one of the two incorrect theories above.
One of the most common questions I get is how to you combat this misinformation. Often times, people get into long drawn out debates over the issues. I like to keep things simple and could sum it up as follow...
If "incomplete" means not containing all the essential amino acids then.... (the incomplete protein theory)
1) All plant foods are complete as they contain all the essential amino acids.
2) the only food that is not a complete protein is an animal food, gelatin.
If "incomplete" means lacking in sufficient quantity of one or more amino acids...(the limiting amino acid theory)
1) Getting all the amino acids in at once at the exact same time at the same meal, or even in the same day, as some may suggest, is not necessary due to the amino acid pool, which is a circulating level of amino acids in the blood, that the body can draw from if needed. As long as one follows the recommendations below, the amino acid pool will maintain a sufficient stock of any potentially needed (or limiting) amino acids.
2) However, as long as one consumes enough calories, eats a variety of food, and limits junk foods and refined foods, (and does not rely on all fruit diet), then they will get in enough protein and enough amino acids in sufficient quantity. There will be no limiting amino acids.
3) there is some evidence that the amino acids that are slightly lower (but adequate) in plant foods, may actually be beneficial to health and longevity and not a health concern.
Most every major health organization including the NAS, the WHO and the ADA all recognize these statements to be true.
One of the leading sources for this misinformation was the book, Diet For A Small Planet, which corrected this myth in the 10th anniversary edition back in 1982. Yet, the myth persists.
If anyone would just take the time to use the USDA SR 20 database and input foods based on the above recommendations, they would see their argument is incorrect.