Hope's Edge_ The Next Diet for a Small Planet - Frances Moore Lappe [86]
The body depends on protein for the myriad of reactions that we call “metabolism.” Proteins such as insulin, which regulate metabolic processors, we call “hormones;” other proteins, catalysts of important metabolic reactions, we call “enzymes.” In addition, hemoglobin, the critical oxygen-carrying molecule of the blood, is built from protein.
Not only is protein necessary to the basic chemical reactions of life, it is also necessary to maintain the body environment so that these reactions can take place. Protein in the blood helps to prevent excess alkalinity or acidity, maintaining the “body neutrality” essential to normal cellular metabolism. Protein in blood serum participates in regulating the body’s water balance, the distribution of fluid on either side of the cell membrane.
Last, and of great importance, new protein synthesis is needed to form antibodies to fight bacterial and viral infections.
How Much Is Enough?
The protein allowances I use in this book are those recommended by the Committee on Dietary Allowances of the National Academy of Sciences, Food and Nutrition Board. It’s interesting to learn how the committee arrives at these recommended allowances. Keep in mind that the procedure is full of assumptions (some of which are disputed within the scientific community), estimates, and averages. Realizing this, R. J. Williams’s advice takes on even greater importance: observe your own body carefully to find out what is best for you.
To come up with the recommended allowance for an entire population, the committee followed four steps:
Step 1. Estimating average need. Since nitrogen is a characteristic and relatively constant component of protein, scientists can measure protein by measuring nitrogen. To determine how much protein humans need, experimenters put subjects on a protein-free diet. They then measure how much nitrogen is lost in urine and feces. They add to this an amount to cover the small losses through the skin, sweat, and internal body structure. For children, additional nitrogen for growth is added. The total of these nitrogen losses is the amount you have to replace by eating protein, and is therefore the basis of the average protein requirement for body maintenance—24 grams of protein for a 154-pound man (also expressed as .34 gram of protein per kilogram of body weight).
Step 2. Adjusting for individual differences. To allow for individual differences and to cover 97.5 percent of the population, the committee sets this protein requirement 30 percent above the average, arriving at 30 grams per day of protein for a 154-pound man, or .45 gram per kilogram of body weight per day. This assumption that 30 percent above the average requirement will cover 97.5 percent of the population is one of the issues in dispute by nutritionists.
Step 3. Adjusting for normal eating compared to experimental conditions. Scientists have discovered that protein is used less efficiently when people are eating a normal diet containing some extra protein than when they are eating at or near their protein requirement, as they do under experimental conditions. Apparently, when people are deprived of protein their bodies compensate by more fully using what’s there and excreting less. So to account for the less efficient use of protein in ordinary eating patterns, the committee adds another 30 percent. This brings the allowance up to 42 grams for a 154-pound “average” American man, .57 gram per kilogram of body weight per day.
Step 4. Adjusting for protein usability. The protein in our food is not fully used by the body. The above estimates are all based on an ideal “reference protein” (I’ll