Dear Jack,

I recently got into a debate with a friend who insisted that quinoa, hemp, amaranth, buckwheat, and spirulina are all complete proteins. When I told him soy is the only complete vegetarian protein, he told me he avoids all soy due to its negative effect on men’s health. I wondered where this guy learned this and a quick google search on vegetarian complete proteins got me here. I checked out your page on protein. That chart listing the essential amino acids in so many plant foods made me realize that in fact many plant foods do contain all the essential amino acids but at such low levels it’s hard to list them as ‘complete proteins’ in the true meaning intended. So my take is that the only vegetarian protein that comes close to really being a complete protein (meaning it has essential amino acid levels similar to those of animal proteins) is soy. Would you agree?

Answer:

[As an aside, the research to date indicates that moderate amounts of soy do not harm men’s health.]

Because this question about complete proteins comes up on a regular basis, I decided to do some number crunching to get to the bottom of it. Mind you, there are many more numbers to crunch if someone wanted to take the time, but I think I’ve covered enough to draw some conclusions.

I see two ways of looking at the question of whether a food has complete protein:

– How much of the food is needed to meet the RDA for all the essential amino acids (EAA)?

– How much variation is there in a food’s ability to meet the RDA for each individual EAA?

If you look at Table 3 of Where Do You Get Your Protein?, you will see what it takes to meet the RDA for each EAA for a variety of foods.

I have taken some of the data from Table 3 and constructed the table below to look more closely at what foods might contain a “complete protein”. In the table below, the numbers in the right-hand column represent the following equation:

A – B = R

Where:

A = servings required to meet the RDA for least plentiful EAA

B = servings required to meet the RDA for the most plentiful EAA

R = range

Food Range of Servings to

meet RDA for all EAA Tuna 1.7 – 1.3 = .4 Chicken leg 2.9 – 1.9 = 1.0 Ground beef 3.2 – 1.4 = 1.8 Edamame 3.3 – 1.8 = 1.5 Lentils 3.4 – 1.7 = 1.7 Pinto beans – refried 3.7 – 2.0 = 1.7 Tofu 3.8 – 1.1 = 2.7 Milk 5.6 – 2.9 = 2.7 Quinoa 6.1 – 3.6 = 2.5 Soy milk 6.2 – 3.3 = 2.9 Egg 6.6 – 3.9 = 2.7 Almonds 9.6 – 4.7 = 5.2 Corn 11.5 – 5.0 = 6.5 Spirulina 12.9 – 5.4 = 7.5

From the chart above, it appears that tuna is the most complete protein with a range of only .4 servings and only 1.7 servings required to meet the RDA for all the EAA. Chicken, beef, edamame (whole, cooked soybeans), lentils, and pinto beans all do quite well. I think it’s fair to consider all of them a “complete protein”. Tofu, milk, quinoa, soy milk, and eggs do significantly better than most grains and nuts which have a much wider range.

As for spirulina…not so much.

One thing to note about this is that all the numbers depend on the serving size. I tried to pick what I thought were reasonable (or common) serving sizes for each food (you can see what they are in Table 3).

The USDA database has a lot of specific entries for some of the food categories above (like ground beef). I chose what looked like a common version of the food, but I did not average the data across more than one version.

As for the remaining, supposed complete proteins mentioned in the original question above, here is what I found:

Amaranth

The USDA lists 9 g of protein per cup of cooked amaranth. That’s a good amount when compared to other grains, but I’m not sure if it’s as easy to eat a cup of amaranth as a cup of, say, rice or corn. The USDA had no amino acid info.

Hemp

There was no info in the USDA database. I found many sources saying that it is a complete protein but none that I know to be reliable.

Nutritional yeast

No info in the USDA database. According to this site, it has 9 g of protein per 3 tbsp serving. That’s a decent amount, but I’m not sure if we can trust that info.

In conclusion, edamame, lentils, and pinto beans fared pretty well with chicken and beef for being a complete protein. Tofu, soymilk, and quinoa were on par with eggs and milk.