Proteins from plants provide enough of all of the amino acids that are essential in human nutrition.
Human beings grow so slowly that the quality of plant proteins is not a problem in human nutrition.
You don’t need to eat beans along with your rice to get a complete protein. People do not get deficiencies of any of the essential amino acids from eating a plant-based diet.
Scientists have known for more than 150 years that some protein sources are less nutritious than others.
For example, gelatin is not useful as a protein source in human nutrition.
Gelatin is protein that has been extracted from the bones and hides of animals.
However, the extraction process destroys some essential amino acids. Gelatin is therefore an incomplete protein: it does not supply all of the amino acids that you need to get from your food.
In contrast, the proteins that come from plants are complete, as far as human protein requirements are concerned. Plant foods supply enough of all of the amino acids that human beings need.
As I explained in Chapter 3 proteins are made up of smaller building blocks called amino acids. To make all of its proteins, your body needs all 20 of the amino acids.
However, it does not need to get a ready-made supply of all 20 from the food. For a healthy person, only 8 (some say 9) of those amino acids have to come ready-made from your food.
They are phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, and lysine (and possibly histidine).
Your body can make the other amino acids, sometimes out of one of the essential amino acids.
For example, your body can make cysteine out of methionine, as long as you are getting enough methionine from your food.
Thus, methionine is an essential amino acid, but cysteine is not Six more of the amino acids, including cysteine, are classified as conditionally indispensable, which means that under some conditions, the body cannot make enough of them to meet its needs.
For example, premature babies cannot make enough cysteine, even if they are getting more than enough methionine.
For that reason, premature babies must get some cysteine from their food.
Fortunately, even premature babies can get plenty of cysteine from breast milk or even from ordinary formula. Their need for cysteine becomes a concern only if they are being fed intravenously.
Ordinary diets would provide enough of even the conditionally indispensable amino acids, as long as the person is eating enough food to get enough calories.
The foods in the table above were sorted according to their protein content, as a percentage of total calories.
Since broccoli and asparagus are low-calorie foods, it would be hard to overdose on protein from eating too much of them.
However, it would be possible to get too much protein from eating a lot of steak and eggs or even too many beans.
In contrast, nobody gets sick from protein deficiency from basing their diet on the lower-protein foods at the bottom of the table.
Fortunately, the only incomplete protein that people are likely to find on their plate is gelatin, which is manufactured from animal bones.
In contrast, the proteins in plants are complete, as far as human nutritional needs are concerned.
The data in the table came from the work of a group of researchers led by William Cumming Rose.
Not only did he discover threonine (the last of the essential amino acids to be discovered), but in the 1940s he led the research to figure out which amino acids are essential in human nutrition and how much of each one people need.
The row labeled Rose’s minimum shows the smallest amount that was sufficient for all of the volunteers in his study.
Just to be on the safe side, Rose recommended that people should eat at least twice that amount, which is a generous margin of safety.
A shortage of protein, or of any of the essential amino acids listed, would be a problem.
In the late 1970s, dozens of people died suddenly of heart rhythm problems after eating nothing but a liquid protein supplement made from gelatin.
Gelatin contains practically no uyptophan. In contrast, the proteins in ordinary plant foods are complete.
As a result, you can easily get enough protein, and enough of all of the essential amino acids, as long as you are getting enough calories from any sort of reasonable plant-based diet.
Therefore, you can stop worrying about the annum or quality of protein in plant-based diets.
In other words, on any reasonable plant-based diet, if you take care of the calories, the protein takes care of itself. You don’t even need to eat beans with your rice to complement the proteins.
As you can see now, rice provides a complete protein. So do beans. You don’t have to combine the two to get a complete protein.