Edible protein per unit area of land
Edible protein per unit area of land is a measure of agricultural productivity. This measure for various major foodstuffs is shown in the chart below. Values are expressed for one calendar year. Biological Values and usable protein values have been added to the chart to show the true relative value of each foodstock for human consumption. Usable protein values are determined by the Biological Value of each foodstuff and represent the amount of protein that is fully digested by humans, it is calculated as follows (Edible protein * Biological Value = Usable protein).
|Edible protein||Biological Value||Usable protein|
|Selected averages as computed in the 1970's|
The figures may be deceptive, because some of the edible protein produced by certain foodstuffs is actually not as "usable" as that produced by others. Protein is made up of a number of different amino acids, of which eight are essential. An imbalance between these amino acids can prevent the body's absorption and use of the protein. Because of this, not all protein is of the same quality--a fact which is not taken into account by the measure of edible protein per unit area of land. Different proteins have different Biological Values (BV), which signify the extent to which the body is able to digest and make use of the protein. Although egg is ranked relatively low on the list to the right, it is "a nearly perfect amino acid food" because whole egg traditionally has a BV of 100, although adjusted scales sometimes rank it lower. For that reason, it is often used to set the scale for judging the quality of protein. Likewise, the protein used in soy and legumes--two foodstuffs considered highly productive by this measure, actually have measurably lower BVs (74 and 49, respectively).
Protein is also just one of many nutrients, so it is impossible to use this one measure alone to say that one crop is more efficient use of land than another. For example, soybean would seem efficient using this measure--but they do not supply "all-important fat soluble vitamins D and preformed A (retinol) which act as catalysts for the proper absoprtion and utilization of all minerals and water soluble vitamins in the diet" and may in fact actually block the absorption of key nutrients with "anti-nutrients" like phytic acid.
It is also important to note that these numbers are averages computed in the 1970's. Different agricultural methods and improvements will yield a number which is different for each farm and each year. Additionally, different methods of food processing and cooking can alter the usability of a foodstuff's protein. For example, cooked eggs have slightly less digestible protein than raw eggs  and some common processing methods can make soy protein unusable.
- John Lobell (1981); The Little Green Book: A Guide to Self-Reliant Living in the 80's. Boston: Shambhala. ISBN 0-394-74924-3
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