Protein from Rice?
A friend recently commented to her husband, who was just learning about quinoa, that it could be considered a protein, as compared to rice which was a starch. Quinoa (pronounced keen-wah) is an old grain, but is not all that well known by many of us. Let’s use the comparison of rice and quinoa to discuss our protein requirements and what foods supply these requirements.
Most plant foods provide much more than the minimum protein requirement.
You may have heard protein recommendations in the form of grams per day. However, different people have different needs and so most grams-per-day recommendations are geared toward a particular sized adult. But larger adults require more protein than smaller adults. So more accurate protein recommendations are based on grams of protein per day per pound (or kilogram) of human body weight. But this type of metric is challenging to put into practice. To start with, you would need to multiply your body weight by the per-pound protein recommendation. This would give you your recommended grams of protein per day. Then you would need to know the grams of protein in what you eat which you could calculate from the grams of protein per serving times your number of servings. Whew – that’s a lot of work.
But there is a better way. We start by noticing that people that are larger also eat more calories per day. Protein requirements also increase with heavy physical activities. So athletes and people with jobs that require heavy exertion will need more protein. But these people also need more calories. It turns out that the protein an adult person requires tracks remarkably to the number of calories they consume. So we can express the protein requirements in terms of protein calories needed as a percent of total calories consumed. Then we can examine the foods we eat and see which ones provide that percentage of proteins. If on average we eat foods that have the recommended protein percentage, we don’t have to track how much of each food we eat and do complex calculations. We just need to know the set of foods that are high enough in protein and eat them.
So what percentage of calories do we need to be protein? Experiments on adults1,2 range from 2.7% to 4%. Human breast milk3 contains about 5% of its calories as protein, so we can assume that for rapidly growing infants, 5% is about right. Note that these numbers are far smaller than the unhealthy American diet that averages about 20% protein.
So what levels of protein do foods provide? First, vegetable oil and sugar have none4,5. Vegetable oil is all fat and sugar is all carbohydrates. Scientists have been known to construct a diet of only oil and sugar in order to provide plenty of calories while intentionally producing a protein deficiency in order to study it. But hopefully, this is not a diet that any of you will eat.
Let’s move on to our first real food, the apple. At first glance, the nutrition label6 for an apple lists its protein content as 0g. But when we look closer, we find that it is 0g only due to rounding down anything less than 0.5g. Apples really have protein of 1.1 calories out of 65 total calories per serving amounting to 2% of the total. The web site in the link below conveniently lists this percentage near the top of the page just under the triangle. So while an apple a day may keep the doctor away, at 2% protein, a diet of only apples would not give us enough protein and we would soon need a doctor. This conclusion is probably not a surprise to anyone, as fruits are generally not considered to be protein sources, although it may be surprising to you to learn that apples have about half of the protein that you need. Moving to other fruits we find bananas7 have 4% protein, oranges8 and strawberries9 have 7% protein. So if fruit was the only thing that we could find to eat, as long as it was oranges and strawberries, we would have plenty of protein.
Now it’s time to get back to our original comparison of rice to quinoa and we will also compare them to other foods that are generally considered starches. Baked potatoes10 and corn11 each contain 7% protein, which is well above the minimum. Brown rice12 has even more at 8%, oatmeal13 has 12%, and wheat14 and quinoa15 each have 15%. So if we eat these foods, we do not need to concern ourselves with getting enough protein. And so my friend was right that quinoa is a good source of protein, but so is rice! And potatoes and corn are too.
Let’s look at some colored vegetables, which have a wide range of protein levels. Carrots16 have 6% protein (plenty), broccoli17 20% protein (lots), and spinach18 has a whopping 30%! It’s no wonder Popeye’s muscles were bulging out after he ate spinach.
Traditionally, we point to beans and legumes as the plant world’s protein sources, and they don’t disappoint us. Peas19 are 22% protein, pinto beans20 are 22%, black beans21 are 23%, and lentils22 provide 27% protein. Nuts and seeds also can be high in protein, but because they also tend to be way high in fat, its best to avoid or minimize eating nuts and seeds.
The figure above shows the protein content of all of the foods mentioned above on a single chart so that you can compare them to each other and to the minimum adult range (gray bar) and to the percentage of protein in human breast milk.
When you first look at the chart, you may notice that plant foods have a broad range of protein content. However, I want you to look at the chart to see which foods have protein levels that extend to the right past the adult minimums. Nearly all of them! So if we asked what plant diet would get us in trouble, the answer would be only an all-apple diet. And if we were thinking about the protein needs of infants, we would say a diet of only apples and bananas. Other than that, we’re getting enough protein. This observation is good news indeed, because it means that by eating a whole plant diet containing a mix of starches, vegetables, and legumes, we just don’t have to worry about getting enough protein.
Because of the meat and dairy producers, our society has become dangerously fixated on protein, especially animal protein. It is common to go into a restaurant and as the waiter discusses options with you, they may ask you your choice of protein. What they mean by that of course is do you want beef, pork, or chicken. Or perhaps if they are really advanced, they might offer a tofu option. But you can now confidently tell them that the potato, corn, rice, or wheat food which they think of as a side dish supplies you with more than enough protein, thank you very much.
Based on the data, you can now quit specifically seeking out protein. You will get plenty of protein just by eating foods made from whole plants including beans, vegetables, and starches such as potatoes, corn, wheat and rice. And why not give quinoa a try too?
1 Hegsted, DM 1968 http://ajcn.nutrition.org/content/21/5/352.long Computed from Table 1.
2 Rose, W 1957 The amino acid requirement of adult man. Nutr Abst Rev. 27:63-67 as quoted by McDougall, J The Starch Solution, 2012, page 94. 20g*4cal/g / 3000 cal = 2.7%
3 Jenness R 1979 http://www.ncbi.nlm.nih.gov/pubmed/392766 Calorie percentage computed from center ranges of mass percentages.
4 Vegetable Oil: http://nutritiondata.self.com/facts/fats-and-oils/580/2