|Protein: Building Blocks of the Body|
|Written by Fred Kummerow, PhD|
|Tuesday, 04 October 2011 19:29|
All Proteins Are Not the Same
Protein is in the spotlight these days, with articles touting diets high in protein and advertisements for protein powders in the media. Protein is, of course, an important building block in the body, but it is not the only building block. And furthermore, protein is made up of a variety of substances, with the result that not all protein sources are equal in value.
Here are some of the facts about proteins: protein is essential to a healthy heart and a healthy body; animal sources of protein including eggs are â€śbetterâ€ť for you nutritionally since they contain all of the essential amino acids; as with most nutrients and vitamins, both too much and too little protein have detrimental effects on the body; and, protein cannot be â€śstockedâ€ť up like fat but must be eaten daily. Protein is the basic nutrient and plays an essential role in carrying cholesterol and preventing heart disease.
The human body in its complexity needs dozens of nutritive substances. The one that stands before all others is protein, or proteins, since there is not one but hundreds of kinds of protein.
Hereâ€™s what protein contributes:
â€˘ We are literally made of protein from our bones to our muscles, arteries and veins, skin, hair, and fingernails. Our heart, brain, liver, kidneys, and lungs are built of tissue made of proteins.
â€˘ Proteins help carry the oxygen that reddens our blood.
â€˘ In the form of enzymes, proteins digest our food, synthesize essential substances, and break down waste products for elimination.
â€˘ When fat and carbohydrates are insufficient, proteins produce the energy we need for life.
â€˘ Proteins in combination with a substance called sterols form hormones, which regulate the delicate chemical changes that constantly take place within the body.
â€˘ The chromosomes, which pass on our characteristics to our children, include protein in their structure.
â€˘ Protein is needed to â€ścarryâ€ť fat and cholesterol throughout the body.
To be short of protein is to be lacking in the very substance of life.
PROTEINS ARE BUILDING BLOCKS
Proteins, our most complex substances, are made up of varying combinations of nitrogen-containing amino acids.1 There are twenty different amino acids that are important to the body. These twenty combine together in hundreds of intricate chemical patterns to create a variety of complex protein structures. When we eat foods that are sources of protein, such as meat, milk, cheese, eggs, beans or peas, the digestive system first breaks down the food proteins into their amino acids, and after they are absorbed into the blood, enzymes in the body recombine them into certain sequences to produce the proteins suited to the bodyâ€™s special needs, such as making red blood cells or building muscles.
The body has the ability to make its own â€śbuilding blocksâ€ť out of whatever amino acids are on hand. However, there is one important limitationâ€”some of those amino acids are only available in food. These â€śraw materialsâ€ť so to speak must all be present to build the body properly; if they are not, the body, like a building made with shoddy materials, will not stand up over time.
Of the twenty amino acids needed for proper construction, eight are called essential amino acids for adults, nine for children, since the body cannot synthesize or make these for itself: histidine, isoleucine, leucine, lysine, methionine (which becomes cystine), phenylalanine (which becomes tyrosine), threonine, tryptophan, and valine. These essential amino acids must come from our diets.2 The other twelve can be manufactured within the body or, to continue our construction metaphor, they are made â€śon-site.â€ť At different ages, we need different amounts of amino acids for optimal functioning. Furthermore, not all protein sources have equal nutritional value.
Amount of Protein Needed Daily
The body requires not only food to supply the nine essential amino acids it cannot make on its own, but also food in the right amounts to help in the process of using and making those other twelve amino acids within the body.
Figure 1 presents the nine essential amino acids, as well as the amounts needed according to age, activity level, and health.3 Figure 3 illustrates this same data graphically (see page 36). (All of the figures contain the essential amino acids numbered as in Figure 1.)
Note how much more infants need of every essential amino acid compared to adults. Of all the sources of amino acids, the best source is natureâ€™s most perfect foodâ€”motherâ€™s milk.4 Figure 4 compares the amino acid needs of infants with those provided in motherâ€™s milk. Infants typically consume about one quart of milk per day (or the equivalent of 946 mL). Figure 5 shows that this amount meets the complete daily requirement of protein for an infant weighing about nine pounds (or four kilograms). Infants need higher levels of the essential amino acids than do adults, as shown in Figures 1 and 3.
The amino acids needed in greatest amounts are leucine (number 3), lysine (number 4), and phenylalanine (number 6). The bars of the graphs for these three should always be the longest to ensure adequate amounts of these amino acids. It is interesting to note that one quart of motherâ€™s milk contains the needed mixture in the right amounts of essential amino acids daily required by the infant, as shown in Figure 3. The amino acids that are required in greater amounts appear in greater volume in motherâ€™s milk.
The next question then concerns how much protein overall do we need each day? The National Research Council of the National Academy of Sciences has established a â€śRecommended Daily Allowanceâ€ť (RDA)3 for protein (see Figure 2), but it is important to recognize that no set allowance, based on averages, can speak for the widely differing requirements of individuals.
As with all other nutrients such as vitamins and minerals, the amount of protein required depends on the individualâ€™s age, weight, sex, level of activity, total intake of calories, and health. Other considerations may also be important; growing children and teenagers, pregnant women, and persons recovering from illness all need more protein than the â€śaverageâ€ť person. As shown in Figure 2, growing children and teenagers need more protein than adults. A sixty-five- pound child requires about fifty-nine grams of protein per day, more than his or her father weighing one hundred eighty pounds.
Pregnant women and breastfeeding mothers also need additional protein since they are not only maintaining their own bodies but also providing for the growth of their developing child. The pregnant teenager has an even greater need: she has to supply her own fast-growing body while nourishing the fetus developing within her womb. For a pregnant teenage girl of one hundred ten pounds, the protein requirement goes up to about 62.5 grams per day, much higher than for an adolescent of the same age. A pregnant teenager who does not eat enough protein will give birth to an underweight baby who may not survive. The data is based on both weight and other body requirements, such as pregnancy to predict the amount of protein needed. Since pregnant teenagers generally weigh less than adult women who are pregnant, the result is a lower amount of suggested protein for a pregnant teenager than for the pregnant adult.
PROTEIN TRANSIT TIME
It is worth pausing to consider the fact that the protein in our body is constantly being destroyed, that is, it is used up during normal metabolism. A study on the rate at which a protein is â€śused upâ€ť has been carried out in pigs.5 Pigs were used because the pig is the animal closest to us in the way food is metabolized. This study indicated that it took thirty-six hours before the protein was used up. â€śUsed upâ€ť in this case means the protein was freed of its nitrogen and no longer furnishing building blocks for body tissue. This study compared feeding pregnant pigs every day with feeding pregnant pigs with the same amount of food, but every three days. The pregnant pigs fed every day gave birth to heavier and healthier piglets than those fed every third day.
As far as Iâ€™m aware, studies on humans to date do not cover this â€śtransit timeâ€ť for proteins. However, I believe the protein metabolism works the same way in people. This means that eating a hamburger or a steak on Sunday will not still supply an adequate amount of essential amino acids on Tuesday, even though on Sunday all the essential amino acids were there. Even more problematical is eating soy-based cheese pizza five times a week. This food is likely missing an essential amino acid. Both soy products and wheat flour are considered â€śincompleteâ€ť proteins since they do not have all of the essential amino acids in adequate amounts. The body needs all the amino acids to make cells, such as those in muscles.
CHOLESTEROL AND PROTEIN
Cholesterol is carried in the blood by lipoproteins. Lipoproteins include (1) apoproteins, combinations of essential and nonessential amino acids in varying amounts; (2) phospholipid, a fat- and water-soluble complex; and (3) fat. These apoprotein carriers must be carefully constructed by the body out of the correct combination of essential and nonessential amino acids. These carriers cannot be made properly if one of the essential amino acids is missingâ€”another reason not to short yourself on the essential amino acids. The important role of apoproteins in transporting cholesterol in the blood has been documented6 and there has been an immense amount of research tying differences in apoproteins to a possible cause for heart disease.
Not only must all the essential amino acids be present, they must also be present in the right amounts to carry cholesterol. Chickens have a similar metabolism to human beings and are often used in scientific experiments. A study7 in which one-week-old chicks were fed various combinations of essential and non-essential amino acids showed that the lowest cholesterol level was always in the chicks fed the required essential amino acids in the correct amount. Whenever an essential amino acid was missing or even a non-essential amino acid was fed in excess, the cholesterol level increased. This may also happen in people eating unbalanced amino acid diets, although to verify such a study today is not possible in the human population. It has been assumed that Americans consume more than an adequate amounts of protein, although we do not know whether this happens every day and in the right amounts. An adequate amount of essential amino acids must be supplied every day of the week for optimum nutrition.
For the body to function properly we also need to take in considerably more protein than the amount we use. The rate of protein use or destruction in the body is about 0.33 grams of protein for each kilogram (2.2 pounds) of body weight per day.4 The RDA amounts in Table 1 refer to the protein itself, not the food it is found inâ€”the actual weight of the protein-containing food needs to be much higher since foods containing protein also contain other nutrients.
UNEQUAL PROTEIN SOURCES
The goal in any diet is to consume an adequate amount of each essential amino acid to satisfy the recommended daily requirement.3 However, just because various foods contain protein does not mean that those proteins are equal in nutritional value. Different proteins contain differing amounts of essential amino acids, and some, when eaten in a regular serving, do not contain enough to satisfy the bodyâ€™s requirements. Some sources, such as meat and eggs, are called â€ścompleteâ€ť proteins since they contain all nine essential amino acids. â€śIncompleteâ€ť proteins, such as in tofu made from soybeans, do not have large enough amounts of all the essential amino acids.
The amino acid profiles of a variety of complete and incomplete proteins are shown in Figures 3 to 16. The white bars on each of the figures indicate the food source that contains the greatest amount of the nine essential amino acids in grams out of one hundred grams. In looking at the figures, keep in mind that the longer the bar, the higher the amount of that amino acid. A protein source that contains two grams of an essential amino acid is more nutritious than one that contains one gram of an essential amino acid. These graphs were constructed from the percentage of essential amino acids in food items listed by the USDA Nutrient Data Laboratory.1 Each of the essential amino acids is numbered in the figures for easy reference.
Weâ€™ve discussed how motherâ€™s milk is natureâ€™s most perfect food, and Figure 5 shows the egg to be in second place because its amino acid content mimics the levels in motherâ€™s milk. Moreover, the egg is also inexpensive and readily available. If you doubled the portion to two whole eggs, these would contain even more essential amino acids than one quart of human milk, although our data here is based only on a one-egg comparison.
Figure 6 compares some common sources of animal proteins along with a common vegetarian source, tofu. As you can see, pork provides the highest levels of amino acids of all of these sources, and tofu, the least. It is a myth that eating tofu provides the same nutritional value as eating pork, beef, salmon or chicken. Tofu is especially deficient in methionine and tryptophan.
As shown in Figure 7, various parts of the egg contain different portions of the essential amino acids. Many people just eat one part of the egg, the white or the yolk, for ostensibly better health. If you just eat the white of the egg, youâ€™ll get less nutritional value than available from either the yolk or the whole egg. The white contains only protein, but no vitamins or minerals. If you eat just the yolk, youâ€™ll get less of one essential amino acid, tryptophan (number 8), than from either the white or the whole egg. The egg yolk also contains vitamins, minerals and important fatty acids. For maximum nutritional value, itâ€™s best to eat the whole egg.
PROTEIN FROM PLANTS
Plant foods do not provide the same quality protein as animal foods. First, we focus on wheat, an incomplete protein. The amino acid amount in the whole wheat kernel is greater than in wheat flour, whole wheat bread, and white bread. Wheat is lower in tryptophan (number 8) than is needed. The longest bars in Figure 8 indicate that the wheat kernel contains more of the nine amino acids than wheat flour, and that whole wheat bread contains more of the amino acids than white bread. Most of us eat wheat in bread, either of the whole wheat or the white bread variety, not a whole wheat kernel. Figure 8 illustrates the fact that the grains we currently eat do not furnish enough protein to be a major source of protein in our diet.
Figure 9 illustrates our concern with the lower amounts of essential amino acids in grains versus animal products. Here the comparison is between the protein in whole wheat kernels, a form most of us do not eat, and egg. Note how much more of the amino acids are in the complete protein, egg, versus the incomplete protein, wheat. The amounts of amino acids in 100 grams of navy beans and corn are compared in Figure 10. As shown, both are low in tryptophan (number 8) and methionine (number 5). Corn is also low in lysine (number 4). Corn contains more essential amino acids than beans for five of the nine amino acids, but beans can help balance the corn in the other four areas. That is why beans and corn are often served together in the Mexican diet, for example. Those who eat only vegetable proteins need to pay careful attention to the amount of amino acids in each source to make sure they have enough overall.
Figure 11 compares two incomplete proteinsâ€” navy beans and wheat breadâ€”with a complete protein, in this case chicken. You can clearly see the superiority of chicken in providing the essential amino acids. Yet the first two items, wheat bread and navy beans, are those the USDA recommends as sources of amino acids to substitute for meat, milk and eggs. This figure illustrates why such advice is faulty. It is a myth to say all protein sources are equal.
The incomplete proteins from grains and other plant sourcesâ€”corn, rice, peas, beans, nuts and sesame seedsâ€”contain all nine essential amino acids but not in the same amounts and not in adequate amounts as found in eggs, dairy products and meat. However, as we showed above, it is possible to obtain the nine essential amino acids, piecemeal fashion, by eating several kinds of vegetable protein, like grains and legumes, at the same time. It is true that if you eat an extra large amount of the incomplete proteins, you can get 100 percent of what you need. However, you may not have a large enough stomach to eat anything else and thus miss out on other important nutrients!
MILK VERSUS SOY
The amino acid content of various dairy products and soy milk, a substitute used for milk, are compared in Figure 12. Cheese products, both American (Cheddar) cheese and cottage cheese, contain all essential amino acids in large quantities. Every type of cowâ€™s milk from whole milk to skim milk has the same amount of amino acids; the only difference is in the fat and water content of the dairy product itself. Milk is used to make cheese; in fact it takes about five quarts of whole milk to make one pound of Cheddar cheese. Since cheese is so â€śconcentratedâ€ť and contains far less water than milk, it contains greater amounts of amino acids ounce for ounce (or gram for gram in this case) than milk. Cheese also contains ten times more fat than whole milk, as well as ten times more protein. The fat provides the flavor in cheese.
Comparing milk and soy milk, it is clear that soy milk has lower quantities of the essential amino acids overall, and is especially low in methionine (number 5) and tryptophan (number 8). It is not a good substitute for cowâ€™s milk, yet it costs more.
Milk and milk products provide both protein and calcium, which are needed by people at all ages. Many adults consider milk just for infants. However, the increasing amount of osteoporosis in the bones of both men and women indicates that many Americans donâ€™t drink enough milk or eat enough dairy products to retain normal bone function throughout the lifespan.
PROTEIN IN NUTS
Nuts (such as walnuts, pecans and almonds) are also incomplete sources of protein, although they can serve well as supplementary protein sources. Nuts also provide many vitamins, minerals and important fatty acids. Figure 13 shows the essential amino acids in pecans, sesame seeds and peanuts. Pecans contain lower amounts of eight amino acids than peanuts or sesame seeds. Peanuts have the highest amounts of six of the amino acids. Overall, nuts come up short when compared to animal sources of protein.
PROTEIN IN POPULAR FOODS
Continuing to look at grains as a source of protein leads to the next comparison, that of several kinds of starches. Figure 14 compares the amino acid contents of white rice, wild rice and pasta. None contain much protein. Pasta is made from wheat flour, which has less protein due to the milling process. White rice has some of its protein removed in the milling process as well. Wild rice is not polished so more of its protein remains, although in some instances, pasta is a better source of several amino acids than the other two. However, none of them is a good source of the essential amino acids.
Now letâ€™s compare two popular foods, hamburgers and pizzas. Figure 15 shows that a hamburger has more nutritional value than a cheese pizza. Hamburger has more than twice as much protein as pizza (25 percent and 11 percent respectively).
When the â€śrightâ€ť two incomplete proteins are combined, the value of their amino acids almost equals that of a complete protein. For example, a combination of 50 grams beans with 50 grams of corn is better than 100 grams of eggs but not quite as good as beef, as shown in Figure 16.
It is interesting to note that pet foods for dogs and cats are carefully formulated to include the right amounts of essential amino acids. My colleagues in the College of Veterinary Medicine tell me that the coronary arteries of pet dogs and cats contain very little atherosclerosis. Unfortunately, people do not have such a carefully formulated diet.
Although maligned in nutritional recommendations, eggs are the most nutritious and the least expensive protein source in the grocery store. At only 68 calories, one egg provides about 11 percent of your daily protein requirement. Eggs contain a variety of important nutrients including every vitamin, mineral and natural antioxidant that your body needs. (Those nutrients are enough to feed a growing chick so that it hatches healthy, but one egg is not enough for you to meet your daily requirement!) Studies at many major universities in the U.S. and abroad attest to the egg as an excellent source of protein. Many in the forefront of anti-aging research believe that moderate egg consumption of one per day should be an integral part of a complete anti-aging diet.8
Because eggs are high in natural cholesterol (210-220 mg of cholesterol per egg), there has been a concern that eating an egg would raise oneâ€™s cholesterol level to unhealthy levels.9 Restricting egg consumption became a key component in many health-related diets; this is actually a misguided recommendation since this has not been shown to be the case.10 Eating an egg raises the total cholesterol score only 2-3 mg/dl in well balanced diets. In healthy young men and women, even two eggs a day had little effect on total cholesterol levels.11
In a recent study, elderly subjects (more than sixty years old) were assigned to one of two dietary groups: one group ate three eggs per day and the other ate the same amount in egg substitutes for a one-month period.3 The result of this study was a significant increase in both LDL and HDL cholesterol for those who ate eggs, but the ratio between the two was not affected significantly. In other words, if the LDL went up, the HDL did too, thus counteracting the effect of the higher LDL. The study concluded that dietary cholesterol provided by eggs does not increase the risk for heart disease in an elderly population.
There have been a number of studies conducted looking at egg consumption and health risks. One at Harvard University included an eight- to fourteen-year follow-up study of approximately thirty-eight thousand men and eighty thousand women.12 There was no statistically significant difference in risk for heart attacks and strokes among people who ate eggs less than once a week compared with those who ate more than one egg a day. Other studies in a variety of settings found no evidence that eating up to an egg per day led to heart attacks or strokes.13,14 The Framingham study15 has investigated the effect of environmental factors and what people ate on the development of coronary heart disease since 1949. No relationship between egg intake and coronary heart disease incidence was found.
SUBSTITUTING PLANT FOR ANIMAL PROTEINS
Much of the world population tries to meet its need for protein with plant sources. Indeed even in the U.S., grains and cereals comprise a large part of the USDA-recommended diet for protein, vitamins and minerals. The possible effects of moving away from animal protein to those of plant sources should be considered.
In 1971, Frances Moore Lappe16 published her book, Diet for a Small Planet, a book that claims to have started a revolution in the way Americans eat. This book was revised as a second edition twenty years later. The book advocated the use of cereals and legumes rather than animal protein products for the American diet because it assumes that cereal grains fed to animals could be more effectively used to feed the human population. The book had an impact on diet recommendations of the American Heart Association and the USDA because grains and legumes do not contain cholesterol and therefore are assumed to be less likely to cause heart disease than the cholesterol in animal food products such as meat, cheese, and eggs. Lappe was aware that meat, cheese, and eggs had a greater biological value than either cereals or legumes because animal food products had an essential amino acid mix that was more complete than the amino acid content in the protein of either cereals or legumes. She reasoned that combinations of vegetable and grain sources such as wheat and beans or soybeans would provide a sufficient supply of essential amino acids.
There are three flaws in Lappeâ€™s thinking. One is the very nature of plant proteins and their manufacturing process. Processed cereals are deficient in minerals and vitamins. Furthermore plant proteins are incomplete proteins and need to be eaten in combination.
The second flaw is the lack of available land to grow plant proteins. Grassland that is used to graze animals cannot be converted easily into land to grow plant proteins nor should it be so converted. Third, animals actually function very effectively to convert plants, such as grass, that people could not live on, into animal protein that people can digest.
The truth is that in terms of protein quality and calories, vegetable proteins are not nearly the bargain they at first seem since they do not contain sufficient amounts of the essential amino acids. Plant sources of protein can be useful in a mixed diet that also includes protein from meat, milk and eggs, but alone, or as the major source, plant proteins fall short for most people.
This basic difference in quality also means that it can be risky to try to replace animal protein with vegetable protein substitutes, even when they are disguised through processing to resemble the real thing. For example, when â€śEgg Beatersâ€ť first came on the market, we tested them on rats.17 Rats were the best animals to use for the experiments we were conducting at the time. â€śEgg Beatersâ€ť were advertised as egg substitutes that were just as nutritious as farm fresh eggs and even better because they contained no cholesterol. We fed one group of rats on whole eggs and another on â€śEgg Beaters.â€ť The egg-fed rats grew strong and healthy, while the rats fed â€śEgg Beatersâ€ť became underweight and scrawny, lost their hair, and died after only a few weeks. The â€śEgg Beatersâ€ť formula was deficient in an essential vitamin, pantothenic acid. According to the listing of ingredients now on the box, that vitamin has been added and corn oil deleted from the original formula. The present formula, therefore, contains neither fat nor cholesterol, and now has less vitamin E than the original formula. This could lead to other problems. Today, a carton of â€śEgg Beatersâ€ť costs twice as much as a dozen eggs and still does not equal the nutritional value of the real thing.
A comparison of the biological value of substitutes for eggs, meat, and milk as protein sources brings up a concern for the consumer. Claims are made or implied that cholesterol-free substitutes will lower cholesterol levels in the blood with no clinical tests by the producers having been made as proof of its total nutritional value.
PLANT PROTEIN AND AGRICULTURE
If we increase our consumption of plant proteins, we would need to increase the acreage devoted to raising plants, but some problems of a practical nature in the way agriculture currently is practiced would occur. The limits of agriculture should be taken into consideration in diet recommendations. 18 Agriculture is defined as the cultivation of land as in raising crops, husbandry, and tillage farming. Unfortunately, only about 20 percent of the land in the U.S. can be cultivated for crops, but 26 percent can be used to pasture livestock.19 Half of the cropland is used to grow feed for livestock. In realistic terms, any major effort to supply additional plant protein for human consumption in the U.S. would require dismantling the nationâ€™s agricultural system, since most of American agriculture is directly or indirectly involved in producing livestock either through direct grazing on grasslands or by growing feed on cultivated land.
Critics of our countryâ€™s agricultural system persistently argue that instead of continuing to use our valuable farmland to grow feeds for animals, we should follow the example of the Chinese and concentrate on growing vegetable protein to be consumed directly by humans. The claim is often repeated that each pound of beef we eat costs four pounds of grain that should be going to feed people. By turning the land to the production of food crops for direct human consumption the argument goes, we would cut our intake of animal fat and cholesterol and at the same time increase the total food supply by eliminating the inefficiency inherent in animal production. This view, as agro-economists have often shown, overlooks a number of important considerations, quite apart from the questionable willingness on the part of the public to eat wheat, corn and soybeans in the place of meat, milk, and eggs. The simple truth is that the animal-oriented agricultural system as it has evolved over two centuries in America makes a more efficient use of available land to provide essential, high-quality protein, with fewer surplus calories, and at a lower cost, than any other system that has presently been devised.
In the U.S., a large area of the West is grassland that can only be used to feed animals. Not enough water is available to grow crops. Grazing animals can maximize efficiency in the production of nutrients. Feeder cattle are raised on land that is not fit for wheat, corn or soybeans. U.S. grasslands are either fertilized or sewn with alfalfa or clover to provide increased forage yields.
The fact is that animal agriculture is huge the world over. China, Thailand and Vietnam account for more than half the pigs and one-third the chickens produced worldwide. Brazil is expected to become the worldâ€™s largest meat exporter.20 In a world of rapidly increasing population and a potentially shrinking food supply, animal food products are presently an asset to adequate nutrition. Animals are converters of inedible proteins to edible ones. Animals can carry on this operation more economically than have food scientists to date. One should think of animals as â€śscreening and processing devices,â€ť which provide acceptable sources of nutrients.
The rapid expansion in urban development comes almost all at the expense of cultivated and grazing land. Better urban planning could save much of this land. Further expansion of land for cultivation in some countries is being carried out but this may be at the expense of the environment. Countries such as India, China or the U.S. are unlikely to convert land back to cultivation, so planning now may be the key to prevent this land from being turned into cities and removed from its potential in creating edible products.
USABILITY OF THE PROTEIN WE EAT
Nearly equal in importance to the completeness or quality of the protein we eat is how efficiently and completely the body can use it. Not only do we need all the eight (nine for children) essential amino acids in our diet, we also need them in our body in just the right proportions and at the same time. It does little good taking in a few essential amino acids one day and getting the others later in the week. The body simply cannot make effective use of them unless it has them all together at one time. Missing one of the essential amino acids is almost like trying to read a novel in which every ninth page is missing, except that our imaginations can fill in the plot line whereas our bodies cannot fill in the missing amino acid. Moreover, even if all the essential amino acids are present, too little of one can limit the bodyâ€™s effective use of the others.
The usability of various protein foods can be expressed in terms of digestibility and biological value.6 Digestibility simply refers to the percentage of protein in the given food that the body can absorb. Biological value represents the percentage of the absorbed protein that the body can actually put to work building cells for growth and maintenance. If we multiply digestibility and biological value, we get a measuring index known by nutritionists as Net Protein Utilization (NPU), which stands for the total percentage of the protein that the body can actually use.6 Without exception, animal proteins have a higher NPU than vegetable proteins. See Figure 17.
Net protein utilization tells us, among other things, that when we include animal protein in our diet, we can satisfy our daily protein requirements with smaller amounts of food than if we rely on vegetable products alone. Remember that even if you got your NPU from dried peas or navy beans, you would still be getting an incomplete, low-quality protein, deficient in the essential amino acids the body needs.6 In terms of quality and accessibility to the body, the animal protein in meat, milk and especially eggs goes further in meeting our needs than protein from plants.
BALANCE OF PROTEIN AND CALORIES
Proteins need to be consumed in the right proportion to fats. Studies with chickens tell us more about proteins, fat and cholesterol. In one study,21 we varied the fat-to-protein ratio in the diet. When the amount of protein in the diet was increased compared to the amount of fat in the diet, the cholesterol level in the chickenâ€™s blood dropped, and they had less fat on their bodies. The type of fat consumed made no difference. A â€śhardâ€ť fat such as beef tallow gave results similar to a â€śsoftâ€ť fat such as corn oil.22,23 Translating this to people means that if youâ€™re going to eat lots of fat of any kind, make sure you eat enough protein to lessen the increase in cholesterol and weight gain.
One way of monitoring the level of protein-to-fat is through the E/P ratio (energy/protein) of a food item or diet.21 Energy here is measured in calories, which are really units representing the energy-producing potential of a food. The E/P ratio is calculated by dividing the total calories in the food item or diet by its protein content. For example, white bread has an E/P ratio of 32 (275 calories divided by 8.5 percent of protein.) It is possible to label a food item for its energy content (E/P ratio) and thus add information to present food labeling. This ratio can be a measure of â€śempty calories,â€ť that is, foods likely to contribute to obesity, but without the nutrients required for good health. Low E/P ratios are good and high E/P ratios, bad, for our diets; thus an E/P ratio of 12 is good, and one of 65 is bad. As you can see from Figure 18, fish products, meats, milk, and eggs have a low E/P ratio; candy bars, doughnuts, cookies, and pies have a high energy-to-protein ratio. The E/P ratio of a meal can be drastically changed by an increase of a single food item such as a doughnut or by the deletion of a food item such as an egg.
Weâ€™ve explained how the balance between protein and calories is measured. Now we need to look at why this balance is important. The physiological reasons for needing a certain balance of protein and calories are complex; in general they have to do with the fact that it is the proteins that carry the fat, or lipids, in the blood. As previously stated, any excess calories we take in are converted into fat in our bodies, and we need additional protein to cope with it. It is a vast oversimplification, but we might think of protein as a kind of â€śfat-antidote.â€ť However, too many calories from any source overwhelm the system so protein no longer can work as an antidote and the antidote analogy breaks down. The total caloric intake is the problem, not just the fat-to-protein ratio. Eventually that extra fat is deposited in various places in our bodies.
DANGER OF PROTEIN EXCESS
Because protein is such an essential building block and has that fat-antidote link, some diet specialists have suggested making it the key food to consume. But this is not a good idea nutritionally. When no other nutrients are available, the body has only protein to use for energy. In order for protein to be converted to calories, the kidneys must remove nitrogen from the amino acids to convert them into a usable form of energy. This process is called deamonization. It overworks the kidneys, which can have some long-lasting, negative effects. An illustration of this comes from some early explorers in the U.S. who died after consuming a diet of rabbits. Rabbit meat is very lean and very high in protein. These early explorers had what was called â€śrabbit-starvation,â€ť since they relied on rabbits for their food.4 Without other nutrients, their bodies could not cope with the protein. Even Lewis and Clark noted the effects of too much protein in the diet. However, when explorers ate what was called â€śpemmican,â€ť they survived; pemmican contains both protein and fat. Today, a diet overloaded with protein also taxes the kidney. In other words, good diets must include a variety of nutrients.
As previously stated, protein deficiency is a serious matter. Growing children, especially, need large amounts of protein and are particularly sensitive to its quality. If they do not get enough of the right kind, their general growth and development suffersâ€”their minds as well as their bodies. In the unborn child and young infant, too little protein means that the cells do not form in sufficient numbers, and the cells that are formed are smaller in size. The childâ€™s growth is stunted, and no amount of protein consumed later in life can repair the damage. Protein deficient infants face a lifetime of being smaller, weaker, and less vitalâ€”physically, mentally and emotionallyâ€”than they need to be.
Protein deficiency can also be lethal. Children studied in hunger-torn Bangladesh in 1970-71 who were protein-deficient had a death rate four and one-half times higher than better nourished children in the same locality. Increases in protein can make a dramatic difference in the average physical development in whole populations. In Japan, over the period 1900-1955 when the national consumption of animal protein was increasing, sons grew two inches taller than their fathers, and daughters matured two years earlier than their mothers.6
PROTEIN AND HEART DISEASE
Protein is not only important for growth, but also for the prevention of heart disease. Protein carries fat throughout the body. If it is deficient, then fat gets deposited on the body, rather than whisked through it. However, if there is too much fat, even the protein cannot handle it and it still gets deposited. Itâ€™s been shown that people in lower income brackets even in industrialized nations have more heart disease than those in higher brackets; this may be due to the former eating less protein in relationship to the amount of fat consumed.
KEY POINTS ABOUT PROTEIN
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3. Recommended Dietary Allowance. Food and Nutrition Board. 18th rev. ed. ed. Washington D.C.: National Academy of Sciences; 1974.
4. Lupton JR. Dietary Reference Intakes: Energy, Carbohydrate, Fiber, Fatty Acids, Cholesterol, Protein, and Amino Acids - Part 1. Vol 25. Washington D.C.: Institute of Medicine of the National Academies; 2002.
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8. Greene CM, Zern TL, Wood RJ, et al. Maintenance of the LDL cholesterol:HDL cholesterol ratio in an elderly population given a dietary cholesterol challenge. J Nutr. 2005;135:2793- 2798.
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10. Knopp RH, Retzlaff BM, Walden CE, et al. A double-blind, randomized, controlled trial of the effects of two eggs per day in moderately hypercholesterolemic and combined hyperlipidemic subjects taught the NCEP step I diet. J Am Coll Nutr. 1997;16:551-561.
11. Vorster HH, Benade AJ, Barnard HC, et al. Egg intake does not change plasma lipoprotein and coagulation profiles. Am J Clin Nutr. 1992;55:400-410.
12. Hu FB, Stampfer MJ, Rimm EB, et al. A prospective study of egg consumption and risk of cardiovascular disease in men and women. JAMA. 1999;281:1387-1394.
13. Flynn MA, Nolph GB, Flynn TC, Kahrs R, Krause G. Effect of dietary egg on human serum cholesterol and triglycerides. Am J Clin Nutr. 1979;32:1051-1057.
14. Flynn MA, Nolph GB, Osio Y, et al. Serum lipids and eggs. J Am Diet Assoc. 1986;86:1541- 1548.
15. Dawber TR, Nickerson RJ, Brand FN, Pool J. Eggs, serum cholesterol, and coronary heart disease. Am J Clin Nutr. 1982;36:617-625.
16. Lappe FM. Diet for a Small Planet. New York, NY: Ballantine Books; 1971.
17. Navidi MK, Kummerow FA. Nutritional value of Egg Beaters compared with "farm fresh eggs". Pediatrics. 1974;53:565-566.
18. Kummerow FA. Optimum nutrition through better planning of world agriculture. World Rev Nutr Diet. 1985;45:1-41.
19. CIA. The CIA's World Factbook; April 25, 2007.
20. Valdes C. Brazil Emerges as Major Force in Global Meat Market. Amber Waves; 2006:2.
21. Kokatnur M, Rand NT, Kummerow FA. Effect of the energy to protein ratio on serum and carcass cholesterol levels in chicks. Circ Res. 1958;6:424-431.
22. Rand NT, Scott HM, Kummerow FA. Dietary Fat in the Nutrition of the Growing Chick. Poult Sci. 1958;37:1075-1085.
23. Kummerow FA, Ueno A, Nishida T, Kokatnur M. Unsaturated Fatty Acids and Plasma Lipids. Am J Clin Nutr. 1960;8:62-67.
This article appeared in Wise Traditions in Food, Farming and the Healing Arts, the quarterly magazine of the Weston A. Price Foundation, Fall 2011.
About the Authors
Board Certified Holistic Public Health Nurse in Private Practice
written by StaciJoy, Sep 22 2012
written by Gabriel, Jan 04 2012
|Last Updated on Friday, 30 March 2012 14:45|