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Protein Fundamentals

by Donald G. Snyder, PhD

This article is sponsored by Proper Nutrition, Inc., a proprietary company


Editor’s Note:
Many of us lack a true understanding of the fundamental concepts involved with protein nutrition, even though this major component of our diets is so essential in nearly all aspects of cellular metabolism. A good background in protein matters, we believe, is especially important if we are to explore and understand newer concepts in health and disease. Accordingly, it is fortuitous that Dr. Donald Snyder has prepared a series of educational articles on protein for our readers. The article that follows on the concepts of the essential and limiting amino acids in protein is the first in the series.

Dr. Snyder is well-equipped to report on protein and the factors related to the utilization of protein. After a classical education in biochemistry and nutrition at Georgetown University, he became Director of a large multi-disciplinary food-related research laboratory for the US Department of the Interior. In addition, he was Interior's representative on the US Government's Interdepartmental Committee on Nutrition and a member of the Expert Protein Advisory Committee for the UN. He also served as a foods and protein supplements consultant to the Office of Agriculture Bureau of Technical Assistance in the Agency for International Development.

As a member of a special committee of the National Academy of Sciences, Washington, DC, he provided counsel on international efforts to translate underutilized ocean fish into a protein powder (Fish Protein Concentrate) suitable for use as a dietary supplement in deficient diets worldwide. At the time, a large US effort on fish protein concentrate was underway at the research laboratory under Snyder's direction. FDA approval of the use of whole fish as a raw material for fish protein concentrate (FPC), a six-year effort involving considerable research dollars and many government agencies, was one of the accomplishments of the laboratory. Snyder then became Director of Sciences for a large Food Trade Organization in Washington and continued to consult for the World Bank, Food and Agricultural Organization (FAG), United Nations Industrial Development Organization (UNIDO), World Health Organization (WHO), the US State Department, private organizations worldwide, and foreign government agencies on world feeding matters with emphasis on protein availability and utilization.

Dr. Snyder is currently associated with Proper Nutrition Inc, a company that manufactures and sells a dietary pre-digested protein supplement, SEACURE, from deep-ocean white fish. SEACURE is one of the dietary supplements developed under the aegis of the National Academy of Sciences' program on world feeding.

We hope you'll enjoy this series of articles on protein. Let us hear from you.

Essential and Limiting Amino Acids
It wasn't too long ago that the value of a food was judged solely on the basis of the energy it provided. In time, however, scientists observed that certain nitrogen compounds in our diets were also vital for the normal functioning of our cells, Two pioneering scientists, Osborne and Mendel, found out that not all of these nitrogen compounds, subsequently called proteins, were equal in value. For instance, observations revealed that growth and performance of many animals improved when their diets contained mostly animal proteins such as milk, beef, and fish; and growth and performance declined when their diets included mostly vegetable proteins such as corn, wheat, and soy.

Research later showed that all proteins were formed from the union of small nitrogen-containing, weak-acid compounds called amino acids, about 20 of them, strung together in long chains. All protein, it seemed, contained some of each of these amino acids.1 But if each of these amino acids is present in all proteins, why then, as Osborne and Mendel determined, did the value of various proteins differ?

Through the continuing imaginative research of many dedicated scientists, the answer eventually became clear: the nutritional value of protein depends on the relative abundance of certain amino acids in the protein. Their discoveries led to the concept we know today as essential amino acids and then later to the concept of limiting amino acids.

Essential Amino Acids
Most of our knowledge about the indispensability of certain amino acids in the diet came from the outstanding work of Rose at the University of Illinois. He concluded that without the presence of certain amino acids from protein in the diet, life processes would cease. In other words, there are essential amino acids that we must consume in our diets because they cannot be manufactured by our bodies. About eight of these are essential (critical) for adults and for optimal growth in infants and children. About eight more amino acids are commonly found in protein but are considered non-essential because the body can synthesize or manufacture them from other dietary sources.2 I should emphasize here that an amino acid's being considered non-essential does not mean that the animal does not need it, but rather that the animal is able to manufacture it in the body from other sources at a rate adequate to meet the demands of growth and health. Interestingly enough, in critically ill patients, in the management of certain pathological conditions, and in serious injury, demands may vary. We'll discuss these and similar issues in a future article in this series.

This concept of the indispensable nature of certain amino acids eventually gave rise to a corollary concept: that of limiting amino acids.

Limiting Amino Acids
The nutritional value of various proteins is often measured by a unit of worth called biological value. Biological value is a measure of the food nitrogen in protein that the body retains. The more nitrogen from ingested protein that is actually retained in the body, the better the quality of the protein is assumed to be. It turns out that the biological value of beef protein is 0.67, whereas the biological value of wheat protein is 0.42. This is consistent with the original observations that animal protein diets yielded better growth and performance than vegetable protein diets. Remember, too, that scientists were curious to know why the value of the proteins differed. Once they understood that certain amino acids were essential, they began investigating just how much of each was essential.

Investigation showed that if vegetable proteins were supplemented with specific essential amino acids, the overall biological value of that protein improved. It also showed that small amounts of a particular amino acid added to the overall diet of an animal on vegetable protein resulted in small improvements, whereas larger amounts showed greater improvement - but only up to a point. After that, no matter how much more of that particular amino acid was added to the diet, the biological value did not improve any further. However, if another essential amino acid were added, biological value might be improved still further. In other words, in every native protein there is a particular essential amino acid that limits that protein's value to the overall diet. Once that limitation (minimum requirement) is met or exceeded, another amino acid becomes limiting and so on until there is derived a theoretically perfect balance of amino acids for optimal growth and performance. Further supplementation will not improve the diet.

The concept of limiting essential amino acids has been heavily applied in agriculture. Ideal diets have been investigated for many animals. Indeed it's been said that more is known about the nutritional requirements of a chicken than any other animal, and application of the limiting amino acid concept to the broiler chicken industry has yielded amazing economic benefits. Let's examine how this knowledge is applied. This information will give us insight into the value of the concept of limiting amino acids.

We find that the poor biological value of vegetable proteins is usually due to their low levels of essential amino acids tryptophan, methionine, and lysine. These are said to be their limiting amino acids. Corn, for instance, is limiting in lysine, and soybean is limiting in methionine. Because corn and soy make up the major source of protein in formulated broiler chicken diets, additions of lysine and methionine are required to optimize the growth of the chicken on a corn/soya diet. Diet formulators, now armed with this information, search for the least-expensive source of providing the additional nutrients. For many years this source has been fish meal, which is high in both lysine and methionine. It has also led to the development of strains of high-lysine corn and methods of producing synthetic methionine. Today, growers can consistently provide 4.2-pound market-ready broilers in only six weeks after hatching. And, incidentally, a pound of chicken can be produced with under two pounds of feed.

The importance of understanding protein values, essential amino acids, and limiting amino acids is not limited to agriculture, of course. These fundamentals take on great importance in problems associated with world hunger, principally protein malnutrition.

World Hunger
Utilizing the concepts of essential and limiting amino acids, the World Health Organization (WHO) of the United Nations has modeled an idealized level of amino acids (see below) for humans. Unfortunately, in much of the world this diet is only a distant hope.

Protein malnutrition called Kwashiorkor comes from eating too little protein or protein of poor quality. Most places in the world survive on the poorer quality starchy diets. This could easily be corrected as with chickens, by adding supplemental levels of good-quality, high-value animal protein like fish. And if we concentrate the raw protein into an easily managed powder, we can change the level of protein from 18% in the unprocessed fish to 80% in the powdered form. Thus only a very little of the concentrate is needed as a supplement to significantly increase the total protein in the diet and to support those essential amino acids found to be limiting in the traditional globally-deficient diets. This goal is the objective of many world-feeding programs sponsored by various organizations such as the United Nations. It was in pursuit of this goal that SEACURE was developed.

Proper Nutrition Inc.'s SEACURE is a concentrate of pre-digested protein from deep-ocean white fish. The concentrate was developed years ago by a multi-disciplinary team of top-notch scientists out of the University of Uruguay under the direction and counsel of the US National Academy of Sciences. The purpose was to find a satisfactory means of translating the vast stores of underutilized ocean fish into concentrates that would serve as a protein supplement to the diets of starving people, especially children, in third-world nations. Although other efforts were underway, the Uruguayan effort was the only one with a process derived from nature that led to the pre-digestion of fish protein which not only maintained the value of the native protein but actually enhanced it.

The value of the protein provided by SEACURE is outstanding. Compare SEACURE to the model or ideal balance suggested by the World Health Organization (WHO) of the United Nations. Values are expressed in terms of milligrams of amino acids per gram of protein. Values for soybean meal and corn are provided for comparison reasons.

Isoleucine 40 43 28 4
Leucine 70 85 33 10
Lysine 55 95 27 3
Methionine & Cystine 35 44 15 4
Phenylalanine & Tyrosine 60 82 21 5
Threonine 40 46 17 4
Tryptophane 10 12 6 1
Valine 40 50 22 4

As can be seen, the amino acid balance of SEACURE exceeds that of the WHO model for every essential amino acid.

Although the SEACURE concentrate of fish protein was never used worldwide because of escalating fish prices and loss of political interest in world-feeding, the product was subsequently tested by medical personnel in Uruguay for its wide range of therapeutic values on thousands of sick babies and adults in clinics and hospitals. Outstanding results were observed.

After a hiatus of a few years, recognizing the potential benefits of SEACURE, Proper Nutrition, Inc. secured SEACURE with the purpose of bringing benefits to those seeking to attain and maintain good health. We are pleased to relate that through reports from doctors and patients, Proper Nutrition confirms daily the results earlier obtained. Feel free to write to us for further information.

In our next article, we'll talk about protein digestibility and factors that affect protein digestibility and how it is measured.

Dr. Donald G. Snyder
Proper Nutrition, Inc.
P.O. Box 13905
Reading, Pennsylvania 19612 USA


  1. Gelatin is an exception.

  2. Adults require the amino acids called lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Infants need these six plus arginine and histidine. Cystine and tyrosine are substitutes in part for methionine and phenylalanine, so they are considered quasi-essential.

  3. Values from Feedstuffs, Annual References Issue 1996.

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