7.5: Protein and the Questions of Health
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Many of us have come to associate a high protein diet with good health. The concept holds some truth and quite a lot of fantasy.
It’s true that those nations with diets rich in animal proteins tend to have populations with long lives. Conversely, those nations with low protein diets of mainly plant protein tend to have shorter lives.
Averages in our nation of about 331 million can hide millions whose food isn’t fully sufficient in protein. The reason can be lack of money, lack of information, or indifference. Also, fad “disease curing” or reducing diets (e.g., severely limited to only a few foods) can be seriously deficient.
But the meaning of this can be deceptive. While lack of protein is a major food problem of developing countries, there are many other factors involved. Animal foods are expensive, and in nations where there’s money for animal foods, there’s generally money for education, medical care, immunizations, proper sanitation, better housing, and all of the other things which help give people long, healthy lives.
The simple fact is that while protein and amino acids are a basic necessity of life and health, they aren’t miracle nutrients, as some promoters would have us believe. When we have adequate protein with adequate amounts of essential amino acids, additional amounts have no further biologic value. As long as the cells have all the amino acids they need, more won’t be put to work. To pour excess amino acids into the body is no different than delivering to a mason more bricks than the mason needs to build a house.
Do We Get Enough Protein?
How much protein is needed in the diet to meet the body’s protein needs? For most of us, the amount needed is that required to replace normal losses (i.e., maintain body proteins). This replacement need is calculated on the basis of normal body weight. Children and pregnant or nursing women need more protein in proportion to their body weight because children and pregnant women are adding body tissue, and nursing women are “exporting” protein in their milk.
The Recommended Dietary Allowance (RDA) for protein is given in Table 7-1. It’s based on needs for growth, maintenance of body proteins. The composite quality of protein in the U.S. diet, e.g., the RDA for a 150-pound adult who’s not over-fat and eats a “typical American diet,” is 54 grams (150 x 0.36 = 54) per day. (For a rough estimate of adult RDA, divide normal body weight by 3.)
The average protein intake in the U.S. is well above the recommended levels. Most of us not only get what we need, but much more. Moderately excessive protein intakes are thought to be safe, but it’s best to keep it within 10-35% of total calories for those over age 18, 10-30% for ages 4-18, and 5-20% for ages 1-3.1
A protein intake of 10-35% of calories is 50-175 gm/ day for someone who takes in 2000 calories/day. [10-35% of 2000 calories = 200-700 calories. Protein = 4 cal/gm. 200-700 cal/(4 cal/gm) = 50-175 gm.]
Most rich protein sources, such as meats, are among our most expensive foods, and when we try to add to a protein consumption which is already ample, we waste money. This may not be a burden for our wealthier citizens, but it can be a critical nutrition factor for some people in our society.
| Age (years) | RDA (gm/lb)* |
| 0.6-1 | 0.68 |
| 1-3 | 0.50 |
| 4-13 | 0.43 |
| 14-18 | 0.39 |
| 19 and older | 0.36 |
| Second half of pregnancy | 0.50 |
| Nursing | 0.59 |
*Grams protein recommended per pound normal body weight per day. RDA for pregnant women is based on pre-pregnancy weight, and increases only during the 2nd half of pregnancy
Table 7-1: Recommended Dietary Allowance (RDA) for Protein1
What Happens to Excess Amino Acids?
When dietary protein provides more amino acids than we need, the surplus isn’t stored. Rather, the nitrogen portion of the amino acid is removed, and what remains is a fat or carbohydrate-like structure (depending on the structure of the particular amino acid) that can be converted to body fat or broken down to provide calories.
Excess protein and amino acids aren’t stored.
As for the nitrogen portion, it’s a liability for the body, since it can convert to ammonia, which is toxic even in fairly low concentrations. To prevent this toxicity, the discarded nitrogen is made into urea, which is disposed of in the urine. When large excesses of protein are consumed, a correspondingly large amount of urea is formed. The kidneys, in turn, must make more urine. Thus, those taking in large excesses of amino acids need more water—and are thirstier—because they urinate more.
The first step in getting rid of excess amino acids is to remove the nitrogen part, and discard it in the urine as urea.
This need to get rid of urea through urination is one reason why high-protein weight-loss diets can be effective in the short run: the body is forced to dump water in a hurry, often resulting in a sudden loss of weight. Of course the loss is in water, not fat. When the water stores are replenished, the weight goes up.
Do We Need to Eat Sunflower Seeds?
Our food choices are so very broad because the building blocks of protein—the 20 amino acids— are the same for all of life. Bean protein is just as useful to us as beef protein. We break both down to the same amino acids that our cells require.
This calls into question the claims that certain foods have extraordinary properties as protein sources. Many seeds and sprouts, for example, are sold with this sales pitch.
For protein synthesis, the food source of the amino acids doesn’t matter. If the amino acid lysine is what the protein blueprint calls for, the transfer RNA will bring lysine and nothing else—without concern for whether that lysine came from hot dogs, canned tuna, sunflower seeds, soy sprouts, or a bottle of “free amino acids,” Nor could the lysine from one source be different from any other. If it were, it wouldn’t fit the uniform blueprint and couldn’t be used to make protein.
Do Athletes Need More Protein?
The Roman gladiators thought so. During their training, and especially on the night before their trial on the Coliseum floor, they were given meat to make them strong.2
Today’s athletes still tend to follow a similar regimen, except now they’re much more “scientific” and talk of protein and amino acids instead of meat. Like the gladiators before them, they commonly seek extra protein for their athletic endeavors. But many of today’s athletes take their “meat” as spoonfuls of “free amino acids.”
How realistic is this idea that athletes need more protein? Contrary to popular belief, heavy exercise requires only a little extra protein. Cross country skiers need only a little more protein when they race 40 to 50 miles a day as they do while relaxing—and they typically already eat much more protein than they need.
The Food and Nutrition Board of the Institute of Medicine, the official body that sets the Recommended Dietary Allowances, states, “It is commonly believed that athletes should consume a higher-than-normal protein intake to maintain optimum physical performance. However, since compelling evidence of additional need is lacking, no additional dietary protein is suggested for healthy adults who undertake resistance or endurance exercise.”1
Protein is digested into amino acids before being absorbed into the bloodstream, so the body can’t differentiate between “free amino acids” coming from ordinary food and that coming from an expensive powder in a jar.
Simply eating more protein doesn’t make the body build more muscle. Muscle size is determined by ordinary growth, heredity, and hormones, and by exercise. What we eat merely supplies the materials for making muscle.
When we build more muscle, say, through exercise, don’t we need extra protein to make it? Yes, we do need a little more, but the RDA is generous, and also the typical American diet already provides an extra amount—the typical diet of an athlete provides even more.
Vegetarian Diets
As said earlier, most of the vegetarians in the world aren’t vegetarians by choice. They would eat animal protein if available and affordable. These people are often suffering from the many ills of poverty, and their strictly vegetarian diet is a poor one.
In contrast, most of the vegetarians in this country are vegetarians by choice and/or religion, and their situation is far different from those in developing countries. Moreover, many of the vegetarians in this country are lacto-ovo vegetarians.
A lacto-ovo vegetarian diet can easily be nutritionally adequate, since dairy products (lacto) and eggs (ovo) are not only rich sources of high quality protein, but provide other important nutrients as well. Milk, for example, is a good source of calcium and the B vitamins riboflavin and vitamin B12—nutrients which are often low in strictly vegetarian diets. But milk and eggs are low in iron, so they are vulnerable to iron-deficiency anemia, as are strict vegetarians. As will be discussed in Chapter 17, the iron in plant foods isn’t as easily absorbed as iron in meat.
Those who choose to become strict vegetarians (vegans) as adults can have nutritionally adequate diets, when they are knowledgeable about nutrition and foods and apply their knowledge to their eating. Including sources of vitamin B12 (multivitamin tablets, B12-fortified breakfast cereal, etc.) is particularly important because B12 isn’t found naturally in plant foods.
Infants and young children are at higher risk of developing nutrient deficiencies on strictly vegetarian diets. They need more nutrients, including protein and calories, in proportion to their body weight, and need higher quality protein than adults. They should eat complementing plant proteins in the same meal to improve protein quality (see Chap. 6). In this country, growth retardation is often the first sign seen in children on strictly vegetarian diets.