Proteins & Amino Acids
Compiled by Walter Sorochan Emeritus Professor San Diego State University

Posted: March 12, 2010; Updated November 3, 2021.Disclaimer

Protein is one of the basic and essential foods [ There are seven major classes of nutrients: carbohydrates, fats, fibre, minerals, protein, vitamin, and water] in everyone’s diet. Most of us know proteins as the meat in our diet but few realize that protein is made up of many molecules of different amino acids or that amino acids are found in foods other than meats.

This article briefly reviews the role of amino acids in the diet and addresses some of the controversies about proteins and whether vegetarians can get adequate protein from sources other than meat.  

% Protein in Diet:

Protein is so abundant in the foods Americans eat that most of us, children and adults alike, consume more than we need. This has contributed to a growing controversy about the amount and the kind of protein we should be eating. Indeed, many persons are concerned that vegetarians may not be getting enough protein in their diets while scientists argue that meat eaters may be eating too much protein! Adding fuel to the controversy is research that points to over-indulgence of protein may be contributing to many of our chronic health problems. [ Cordain ]


Amino acids are the building blocks of proteins. Another way of thinking of this is to compare amino acids to the beads of a necklace. Without the string to hold them together, amino acids are just beads. The amino acids in formula are different from amino acids in food because they are already broken down. Because they are already separated from each other, they are absorbed quickly and all at once, giving the body a small amount of time to use them.


 A protein is a chain of amino acids connected together. You can think of this like a beaded necklace. The beads (amino acids) are connected together by a string (bond), which forms a long chain (protein). Therefore, a protein is "intact" or "whole."

 Proteins are connected together; free amino acids are not.

So how much protein do we need?

The Dietary Reference Intakes, previously recommended dietary allowance (RDA), for protein is based on how much you weigh. Although the National Academy of Sciences initially set the amount of RDA at about 0.4 grams protein for every pound of body weight, they then added an additional 0.4 grams as an added margin of safety; thereby advocating 0.8 grams of protein for every pound of body weight. It is the doubling of the protein RDA that has been hidden and misinterpreted when discussing the amount of protein really needed in our diets!

On the other hand, the World Health Organization has established a minimum daily requirement for protein to be approximately 5 percent of daily calorie intake. Trumble ] Since these allowances, as measured in grams, are difficult to comprehend, it may be easier to just express the amount ingested as percent [ % ] calories of the daily diet. Thus, the percent amount of protein recommended varies from about 2.5 % to 35 % [ Nutrient levels in diet ].

Adding fuel to the controversy are studies showing that people can lead healthy, active lives while consuming only 2.5 percent of calories a day as protein equivalent to 20 grams a day for an adult male, and even less for an adult female. Trumble Article by Tremble: Protein cvoncerns is no longer active.

Except for malnourished people in third-world nations [ whose diets are low in all nutrients ] protein deficiency is virtually unheard of. Nevertheless, in the United States, where we are practically drowning in a sea of protein, people still feel the need to load up on protein-rich foods, consuming all the fat and cholesterol that usually come with them. [ You can easily meet your protein needs by choosing a balanced diet with approximately 10-35% of your total daily calories coming from protein.  Protein Needs - US Guidelines on Protein and Diet  UCLA Protein Info ]

The body does not have a storehouse for protein as it does for carbohydrates [ glycogen in the liver and muscles ] and fat. Protein must be continuously ingested in order for the body to maintain optimal health. Now, while the body does not have a storehouse per se, it does have a sort of “pool” of amino acids in the form of those that are in the bloodstream at any given time. Amino acids in the blood have a half-life of roughly 4-6 hours.

So what is protein and what does it do?  

Proteins are large, complex molecules that play many critical roles in the body. They do most of the work in cells and are required for the structure, function, and regulation of the body’s tissues and organs.

Proteins are made up of hundreds or thousands of smaller units called amino acids, which are attached to one another in long chains. There are 22 different types of amino acids that can be combined to make a protein.

Of the twenty-two standard amino acids, eight are called essential amino acids because the human body cannot synthesize them from other compounds at the level needed for normal growth, so they must be obtained from food. However, the situation is quite complicated since cysteine, taurine, tyrosine, histidine and arginine are semi-essential amino acids in children, because the metabolic pathways that synthesize these amino acids are not fully developed in children. The amounts required also depend on the age and health of the individual, so it is hard to make general statements about the dietary requirement for some amino acids.

When protein is consumed, the body breaks it down into amino acids, the building blocks of all proteins. Some of the amino acids are designated nonessential. This does not mean that they are unnecessary, but rather that they do not have to come from the diet because they can be synthesized by the body from other amino acids. Other amino acids are considered essential, meaning that the body cannot synthesize them, and therefore must obtain them from the diet.For example:








Aspartic Acid




Glutamic Acid














*) Essential only in certain cases



Need more than Amino Acids in the diet  

Just as vitamin D and calcium intake by themselves do not help unless other nutrients or co-factors are present in the diet, so amino acids need co-factors to make them available to the body cells and organs.  The body constantly conducts many complicated series of chemical reactions in precisely controlled ways to keep us healthy. Over 5,000 reactions occur every second in a cell. By utilizing the natural substances in optimal quantities to re-establish a normal balance, you can help correct the cause of some disease processes in a non-toxic way.

Amino acid metabolism disorders are becoming recognized as a major factor in many disease processes. Helping medical doctors to better understand this relationship between amino acids and diseases are metabolic tests.One such test is amino acid analysis of urine or plasma to assess vitamin and mineral status. Many of the enzymes which catalyze the inter-conversion of amino acids require vitamin and mineral co-factors to function optimally. In many cases where incomplete conversion of one product to another is due to sluggish enzymes, this may indicate a functional need for increasing levels of a co-factor. Article by Sahley: Nutrients is no longer active.

Another misunderstood aspect of food ingestion is the assumption by many that our digestive system absorbs all or most of the quantities of vitamins, minerals and amino acids that are stated in the supplemental labels.It is what ends up in the blood stream that really counts and not what is advertized in the label.

 Do you need to eat meat to get adequate protein in the diet?

The answer is “No!” Although it is important to consume the full range of amino acids, both essential and nonessential, it is not necessary to get them from meat, fish, poultry, and other complete-protein foods. In fact, because of their high fat content-as well as the use of antibiotics and other chemicals in the raising of poultry and cattle [ and toxic chemical build up in fish ] --- most of those foods should be eaten in moderation.

The American Dietetic Association (ADA) in its 1988 position paper on vegetarianism, stated that intentional combining of amino acid foods, is not necessary. A varied diet of grains, beans, plant seeds and vegetables provides all the essential amino acids, even without intentional combining. As physician John A. McDougall, M.D. has written, "...the combination of amino acids in proper proportions takes place long before our foods reach the dinner table. Nature has designed vegetable foods to be complete. If people living before the age of modern dietetics had to worry about achieving the correct protein combinations in their diets, our species would not have survived for these millions of years." [ Trumble ]

Plants and amino acids:

Fortunately, there is a good alternative way to get amino acids than from meat and dairy products. You can get more than enough amino acids from high-fiber, low-fat, plant-based foods.

It should be obvious by now that the seeds of plants are store-houses of amino acids. Plants need amino acids for growth and maintenance! Amino acids are required by plants throughout all their growing stages and especially in germination or when seeds begin to grow as embryos into plants. Amino acids are the starting points for the synthesis of cellular molecules including vitamins, nucleotides, chlorophyll, enzymes, proteins and so on. Because of their importance in plant germination, seeds are rich sources of amino acids.

Seeds  provide the same nutrition for humans and animals as plants. In fact, the majority of food consumed by human beings are seed-based foods. Edible seeds include: cereals (such as maize, wheat, and rice), legumes (such as beans, peas, and lentils), flaxseeds and nuts. Oilseeds are often pressed to produce rich oils, such as sunflower, rapeseed (including canola oil), and sesame.  One of the earliest food recipes made from ground chickpeas is called hummus, which can be traced back to Ancient Egypt times.

Plants, of course, are able to make all the amino acids. Humans, on the other hand, do not have all the enzymes required for the biosynthesis of all of the amino acids.

 Conclusion about Proteins:  

Conclusion: Plants can supply adequate amounts of all amino acids to maintain your health. Protein sources Animal protein and vegetable protein probably have the same effects on health.  So which should you eat and how much? 

Here is some good advice from the Harvard School of Public Health:  "It’s the protein package that’s likely to make a difference. A 6-ounce broiled porterhouse steak is a great source of protein—38 grams worth. But it also delivers 44 grams of fat, 16 of them saturated. That’s almost three-fourths of the recommended daily intake for saturated fat. The same amount of salmon gives you 34 grams of protein and 18 grams of fat, 4 of them saturated. A cup of cooked lentils has 18 grams of protein, but under 1 gram of fat.

So when choosing protein-rich foods, pay attention to what comes along with the protein. Vegetable sources of protein, such as beans, nuts, and whole grains, are excellent choices, and they also offer healthy fiber, vitamins and minerals. The best animal protein choices are fish and poultry. [ For more protein sources check references for: Protein_Foods ] If you are partial to red meat, stick with the leanest cuts, choose moderate portion sizes, and make it only an occasional part of your diet. " Article ny Harvard School of Public health “The Nutrition Source Protein,” is no longer active.

Essential amino acids make up over 50% of every protein in your body, so a deficiency in any one of them can have detrimental effects on muscle preservation, athletic training, recovery, and more—which is why Essential Amino Acids are the ideal supplement to fuel your performance.

Option:   A protein supplement consideration for vegetarians is brewer’s yeast. Brewer's Yeast, labeled nutritional yeast, is a good source of protein for vegetarians because over 50% of its weight is protein. A nutritional analysis of Brewer’s Yeast, made by Lewis Labs, states the following on the label:

Supplemental Facts Brewer’s Yeast

Serving size: 2 tbsps 30g;Gluten free;not blended or fortified



 % Daily value

Total fat

0 g


Trans fat












Total Carbs



      Dietary fiber





Daily value not established




Vitamin A



Vitamin C



Vitamin D



Vitamin E



Vitamin Thiamin



Vitamin  Riboflavin



Vitamin Niacin



Vitamin B6



Vitamin Folic acid



Vitamin B12



Vitamin Biotin



Vitamin Pantothenic acid





Daily value not established



Daily value not established



Daily value not established



Daily value not established































% Daily Values based on a 2000 calorie diet.

These statements have not been evaluated by FDA.  The product is not intended to diagnose, treat, cure or prevent any disease.

Distributed by Lewis Labs Article by Lewis Lab Nutiritional facts is no longer active.


Amino Acids

Content in each serving mg

% Composition of yeast protein







Aspartic acid






Glutamic acid










































This information appears on label of Lewis lab product. These statements have not been evaluated by FDA. The product is not intended to diagnose, treat, cure or prevent any disease.

Lewis Labs Brewer's Yeast is grown on sugar beets.

As a rich source of B vitamins, Brewer's Yeast aids in metabolizing carbohydrates, proteins, and fats. Brewer's yeast contains all the essential amino acids, 14 minerals, and 17 vitamins. It is one of the best natural sources of the B-complex vitamins thiamin, riboflavin, niacin, B6, pantothenic acid, biotin, and folic acid. It is also high in minerals, including chromium, zinc, iron, phosphorus, and selenium.  Brewer's yeast is a very good source of protein. Brewer's yeast is also a good source of RNA, an immune-enhancing nucleic acid that may help in the prevention of degenerative diseases and slowing the aging process. Article by Brewer's Yeast is no longer active.

In order to avoid biochemical imbalances, amino acid supplementation should be taken under the supervision of a nutritionist or health professional. [ Article by Sahley: Nutrients is no longer active. ]


Alpha Nutrition Center,”Proteins and Amino Acids.” Article by Alpha Nutrition Ctr is no longer active.

Bewer’s yeast, University of Maryland Medical Center, Article by Brewer's Yeast is no longer active.

Block Gladys, “Researcher finds one third of U.S. country-region diet comprised of junk food,” California, Berkley, January 06, 2004. Article by Block UC Cal., is no longer active.

Brewer’s yeast, HealthLine: Article by Brewer's Yeast: Healthline is no longer active.

“Vegetarians have used brewer's yeast as a source of protein, vitamins, and minerals for many years. In addition to being an excellent nutritional supplement, brewer's yeast is often recommended to regulate blood sugar levels, improve the health of the skin, control diarrhea, lower cholesterol, and repel insects. 

Brewer's yeast is one of the best sources of the mineral chromium. Two tablespoons of brewer's yeast yields about 120 micrograms (μg) of chromium, an amount equal to the recommended daily allowance. Chromium is an important factor in regulating blood sugar levels. High levels of chromium increase glucose tolerance. Diabetes and hypoglycemia are two conditions in which blood sugar levels are unstable. Brewer's yeast has been reported to help improve symptoms of diabetes and hypoglycemia, and may act to prevent diabetes from developing in persons with a family history of diabetes and in those who have problems with blood sugar metabolism. One Danish study reported that people with hypoglycemia showed an improvement in their symptoms after taking 2 tbsp of brewer's yeast every day for one month.

B-complex vitamins are important for healthy skin and nails. Persons deficient in these vitamins may benefit from taking brewer's yeast as it is rich in B-complex vitamins. A compound derived from brewer's yeast, skin respiratory factor (SRF) reportedly has wound healing properties. SRF has been a component in over-the-counter hemorrhoid remedies for more than four decades. SRF also has been used to treat skin problems. Brewer's yeast has been used in the treatment of contact dermatitis, a condition of the skin characterized by red, itchy, and inflamed skin.

Another component of brewer's yeast also has wound healing properties. Glucan, a substance derived from the yeast, has been shown to improve wound healing in mice by activating macrophages and promoting the growth of skin cells and capillaries.

Brewer's yeast may help to prevent constipation. Thirty grams of brewer's yeast contains approximately 6 grams of dietary fiber (24% of the recommended daily amount). Fiber is an important part of the diet as it helps increase the bulk of fecal matter, thereby promoting healthy bowels and intestines. Brewer's yeast has also been found to be helpful in cases of diarrhea. The yeast acts to encourage the growth of good bacteria in the intestines.

Studies show that brewer's yeast may be helpful in decreasing cholesterol and raising HDL levels (the good cholesterol). A study performed at Syracuse University in New York reported that persons who consumed 2 tbsp of brewer's yeast daily for two months reduced their cholesterol levels by 10%.“
[ Brewer’s yeast,  HealthLine:

Cordain Loren, S Boyd Eaton, Anthony Sebastian, Neil Mann, Staffan Lindeberg, Bruce A Watkins, James H O’Keefe and Janette Brand-Miller, " Origins and evolution of the Western diet: health implications for the 21st century," American Journal of Clinical Nutrition, Vol. 81, No. 2, 341-354, February 2005. Diet composition uS 2005

Diet and Fitness

The Nutrition Source,” Protein Harvard School of Public health 

High Protein Foods List: source: 

High Protein Foods List:

Animal Protein Foods


1 gram edible protein
per 100g (3.5 oz) in weight


Plant and Dairy Protein Foods

1 gram edible protein
per 100g (3.5 oz) in weight





Beef Topround, Lean


protein foods per 100 grams36.12g




Pork Bacon


protein foods per 100 grams 35.73g


Pumpkin Seeds

protein foods per 100 grams32.97g

Beef Brisket, Lean


protein foods per 100 grams33.26g


Peanut Butter

protein foods per 100 grams25.09g

Beef Steak, Lean


protein foods per 100 grams31.06g


Cheddar Cheese

protein foods per 100 grams24.90g

Beef Top Sirloin, Lean


protein foods per 100 grams30.55g


Monterey Cheese

protein foods per 100 grams24.48g

Pork Top Loin


protein foods per 100 grams30.48g


Colby Cheese

protein foods per 100 grams23.76g

Bluefin Tuna


protein foods per 100 grams29.91g



protein foods per 100 grams23.68

Turkey Bacon


protein foods per 100 grams29.60g


Mozzarella Cheese

protein foods per 100 grams22.17g

Chicken, Dark Meat


protein foods per 100 grams28.99g



protein foods per 100 grams 22.09g



protein foods per 100 grams28.81g


Pistachio Nuts

protein foods per 100 grams21.35

Beef Tenderloin, Lean


protein foods per 100 grams28.51g



protein foods per 100 grams 19.50g

Turkey, White Meat


protein foods per 100 grams28.48g



protein foods per 100 grams17.19g

Beef Kidney


protein foods per 100 grams27.27g



protein foods per 100 grams16.89g



protein foods per 100 grams26.69g


Egg Yolk

protein foods per 100 grams15.86g

Cooked Trout


protein foods per 100 grams26.63g


Cashew Nuts

protein foods per 100 grams15.31g

Veal Cooked


protein foods per 100 grams25.93g



protein foods per 100 grams 15.03g

Beef Liver


protein foods per 100 grams25.51g



protein foods per 100 grams15.03g

Cooked Salmon


protein foods per 100 grams25.56g


Fried Egg

protein foods per 100 grams 13.63g



protein foods per 100 grams25.16g



protein foods per 100 grams13.10g



protein foods per 100 grams24.60g



protein foods per 100 grams12.93g

Lamb Cooked


protein foods per 100 grams24.52g


Cottage Cheese

protein foods per 100 grams12.49g

Freshwater Bass


protein foods per 100 grams24.18g


Ricotta Cheese

protein foods per 100 grams11.26g



protein foods per 100 grams24.16g



protein foods per 100 grams 9.50g

Beef T-bone


protein foods per 100 grams24.05g



protein foods per 100 grams 9.02g

Hamburger 80% lean


protein foods per 100 grams24.04g


Wheat Bread

protein foods per 100 grams8.80g



protein foods per 100 grams23.48g


Acorn Nuts

protein foods per 100 grams 8.10g



protein foods per 100 grams23g


Lima Beans

protein foods per 100 grams 7.80g

Pork Chop


protein foods per 100 grams21.91g


Macadamia Nuts

protein foods per 100 grams 7.79g

Turkey Gizzard


protein foods per 100 grams21.72g


Mungo Beans

protein foods per 100 grams 7.54g

Turkey Heart


protein foods per 100 grams21.47g



protein foods per 100 grams5.54g



protein foods per 100 grams20.35g


Green Peas

protein foods per 100 grams5.36



protein foods per 100 grams20.50g


Pinto Beans

protein foods per 100 grams4.86g

Shrimp moist heat


protein foods per 100 grams20.91g


Kidney Beans

protein foods per 100 grams4.83g

Turkey Liver


protein foods per 100 grams20.02g



protein foods per 100 grams3.47g

Alaska King Crab


protein foods per 100 grams19.35g


Non-fat Milk

protein foods per 100 grams 3.37g

Chicken, White Meat


protein foods per 100 grams16.79g


Whole Milk

protein foods per 100 grams 3.22g





White Rice

protein foods per 100 grams2.69g





Brown Rice

protein foods per 100 grams2.58g






protein foods per 100 grams~1g or less

Kwashiorkor and marasmus: When protein intake is inadequate, but total caloric intake is sufficient, a condition known as kwashiorkor may occur. Symptoms of kwashiorkor include an enlarged stomach, loss of hair and hair color, and an enlarged liver. Conversely, if protein and caloric intake are both inadequate, a condition known as marasmus occurs. Marasmus symptoms include a stoppage of growth, extreme muscle loss, and weakness.  Read more: Nutrients - calcium, food, nutrition, deficiency, needs, body, diet, absorption, carbohydrate, health, protein, fat, carbohydrates, vitamin, amino, acids, water, vitamins, soluble

Lewis Labs Nutritional facts: Article by Lewis Lab Nutritional facts is no longer active.

Norris Jack, “Where do you get your) Protein (?),”, December, 2009. Article by Norris: Where get protein? is no longer active.

Nutrient levels in diet: The amount ingested varies each year and for different ethic regions. Here is a sample of such a prediction by the US Department of Agriculture and Cordain, Mayo Clinic, “Nutrition and Healthy Eating.” Article about Nutrient levels in diet is no longer active.


Nutrient % Cals Grams/day
Protein 10 - 35 50 - 175
CHO 10 - 35 50 - 175
Fat 10 - 35 50 - 175
Based on a 2,000-calorie-a-day diet, this amounts to about 50 to 175 grams a day.

There is no agreement about the estimates of the amount of protein, fat and CHO ingested.  For example, a study by Cordain  [  Diet composition uS 2005   ] estimates the following: CHO=51.8%   Fat = 32.8%   Protein = 15.4%.  

Protein Needs - US Guidelines on Protein and Diet  

RDA  for Protein:  As a general guide, the recommended dietary allowance in the USA, for protein is 0.8 grams per kilogram of body weight of adults.   This protein RDA is said to meet 97.5% of the population's needs.

Table: Dietary Reference Intakes (DRIs) [ previously RDA ]: daily recommended intakes of protein for individuals. [ Source: Food and Nutrition Board, Institute of Medicine ]

Age, gender, life stage group 

Protein (grams/day)


0–6 mo 


7–12 mo 



1–3 years 


4–8 years



9–13 years


14–18 years 


19–30 years 


31–50 years




> 70 years



9–13 years


14–18 years 


19–30 years


31–50 years




> 70 years 



14–18 years 


19–30 years 


31–50 years 



14–18 years


19–30 years 


31–50 years 


 Note: Daily Reference Intakes (DRIs) have been developed, since 1996 by the Food and Nutrition Board, Commission on Life Sciences, National Research Council, to replace the Recommended Dietary Allowances (RDAs).

Sahley Billie J., Understanding Amino Acids,” Optimum Nutrition Magazine Autumn 2000 issue and The Institute for Optimum Nutrition. Article by Sahley: Nutrients is no longer active.

Trumble Walt , “Protein concerns,” Vegetarian News., November 3, 2003 Article by Tremble: Protein concerns is no longer active.  

Wikipedia, Healthy diet:  

Wikipedia Human nutrition: