Hope's Edge_ The Next Diet for a Small Planet - Frances Moore Lappe [89]
Figure 14. The Food/Protein Continuum
This discovery does not call into question the perspective put forth here. It has been taken into account in setting protein allowances.
Is Meat Necessary?
Those who insist on the superiority, or indispensability, of meat as a protein source focus on both the large quantity and the high quality of protein in meat. Plant protein is seen as inferior on both counts. The result is that animal and vegetable protein are thought of as comprising two separate categories. In fact, this is a common mistake in our thinking about protein. It is much more useful and accurate to visualize animal and vegetable protein along a continuum.
Figure 14, “The Food/Protein Continuum,” will help you see the range of protein variability on two scales: protein quantity, based on the percent of protein in the food by weight; and usability, based on the NPU of the protein. (Weights for grains and legumes are calculated for cooked food.)
Quantity. When judging foods with the percentage of protein as the criterion, generalization is difficult. It is clear, however, that plants rank highest, particularly in their processed forms. Soybean flour is over 40 percent protein. Next come certain cheeses, such as Parmesan, which is 36 percent protein. Meat follows, ranging between 20 and 35 percent. Cooked beans, peas, and lentils have between 5 and 10 percent protein; though it might surprise you, eggs, milk, and yogurt are in the same range. There are, of course, other plants—some fruits, for example—that contain too little protein to even appear on the scale. (We are concerned here only with plants that are widely used as sources of protein.)
Warning: this quantity scale is misleading. It gives the percent by weight, yet the real issue in evaluating a protein source is not weight but calories. Can we get enough protein from a food without getting too many calories? Looked at from this angle, most plant foods qualify and some excel. Eating vegetables such as broccoli, cauliflower, mushrooms, and spinach, you get the same amount of protein for each calorie that you get with meat. But it would be difficult to get a full day’s protein allowance from cauliflower (unless you were prepared to eat 20 cups!). Nonetheless, such vegetables can contribute substantially to meeting our protein needs.
Usability. The protein usability scale generally ranges from NPU values of about 40 to 94. Clearly, animal protein occupies the highest rungs of this scale. Meat, however, is not at the top. It places slightly above the middle, with an average NPU of 67. At the top are eggs (NPU of 94) and milk (NPU of 82). The NPUs of plant proteins generally range lower on the continuum, between 40 and 70. But protein in some plants, such as soybeans and whole rice, approaches or overlaps the NPU values for meat.
Complementing Your Proteins
Because different food groups have different amino acid strengths and weaknesses, eating a mixture of protein sources can increase the protein value of a meal; here’s a case where the whole is greater than the sum of its parts. The EAA deficiency in one food can be countered by the EAA contained in other food. For example, the expected biological value of three parts bread and one part cheddar cheese would be 64 percent if eaten separately. Yet, if eaten together, their biological value is 76 percent because of the complementary relationship. The “whole” is greater largely because cheese makes up for bread’s lysine and isoleucine deficiencies. Such protein mixes do not result in a perfect protein that is fully utilizable by the body (only egg is near perfect). But combinations can increase the protein quality as much as 50 percent above the average of the items eaten separately.
Figure 15. Demonstrating Protein Complementarity
Eating wheat and beans together, for example, can increase by about 33 percent the protein actually usable by your body. Figure 15 will help you see why.