WHAT IS THE REAL “HIGH QUALITY” PROTEIN?
Sometimes erroneous beliefs can become repeated, accepted and eventually acculturated. And there are several popular ideas about one nutrient in particular – protein – that certainly exemplify this.
Specifically, there are some oft-repeated but inaccurate beliefs about protein that are perpetuated by popular culture, the media, and even some within the medical establishment. Although we need many nutrients for our various complex physiologic functions, we seem singularly obsessed with protein. Even the term itself comes from the Greek word “proteius,” meaning “the important one.”
Further, we call animal protein “high quality protein” while we refer to plant protein as “low quality protein”. What is the meaning and relevance of these terms? Does “high quality” mean healthier or more nutritious, and “low quality” the opposite?
DEFINING PROTEIN
First, let’s define exactly what a protein is. It’s simply a chain of amino acids joined together by a peptide bond. When we eat food, our bodies digest the protein in the food, breaking the bonds that link the amino acids together. We then store the individual amino acids in a “pool,” from which our bodies later draw to make brand new proteins for various functions (like cell regeneration or repair, creating enzymes, building muscle, etc.).
The term “essential amino acids” refers to nine particular amino acids that our bodies do not synthesize and we therefore need to get from food. Today, we know that, with few exceptions such as gelatin (which is an animal protein), most proteins from both animal and plant foods are “complete proteins” – meaning they contain all of the essential amino acids our bodies need.[1]
WHY IS ANIMAL PROTEIN CALLED “HIGH QUALITY”?
Are we understanding this term correctly?
Protein was discovered in the early 1800s, by a Dutch chemist. He isolated protein from meat, and therefore it was initially (but incorrectly) thought that protein was exclusively in animal foods. In the late 1800s, however, it was discovered that plants contained protein too. However, plant proteins were labeled “incomplete”, as it was believed (again incorrectly) that they lacked all of the essential amino acids.
Today, of course, we know that most proteins from both plants and animals are “complete proteins” (meaning they contain all of the essential amino acids we need).[1] However, the term “low quality” is still used to refer to plant proteins because they typically have a lower proportion of these essential amino acids as compared to animal proteins.
But it’s important to understand that having a higher proportion of essential amino acids, as animal protein does, is actually problematic (not advantageous) for our health, as are many other attributes of the animal foods with which animal proteins are packaged.
SEVEN SERIOUS PROBLEMS WITH ANIMAL PROTEIN
1. Animal Protein and IGF-1 / Increased Cancer Risk
When we ingest proteins that have a higher proportion of the essential amino acids (which is a characteristic of animal protein), it results in our bodies producing higher levels of the hormone IGF-1 (insulin-like growth factor-1).[2 – 8]
This hormone stimulates cell division and growth (in both healthy and cancer cells), and for this reason, having higher circulating levels of IGF-1 has been consistently associated with increased cancer risk, proliferation and malignancy.[2 – 8]
2. Animal Protein and TMAO
Consuming animal protein also results in us having higher circulating levels of trimethylamine N-oxide, or TMAO.
TMAO is a substance that injures the lining of our vessels, creates inflammation, and facilitates the formation of cholesterol plaques in our blood vessels. And that, of course, is highly problematic for cardiovascular health.[9 – 10]
TMAO is created by complex interactions involving our gut flora and the nutrients in the food we eat. And when we eat animal foods, it alters our gut flora in such a way that facilitates the creation of TMAO.[9 – 10]
So, consuming animal foods result in higher TMAO levels, which is damaging to our vessels. Even without all of the other problematic aspects of animal foods, this one issue involving TMAO is, according to the recent president of the American College of Cardiology Dr. Kim A. Williams, sufficient by itself for people to vigorously avoid animal foods.[11]
3. Animal Protein and Phosphorus
Animal protein contains high levels of phosphorus. And when we consume high amounts of phosphorus, one of the ways our bodies normalize the level of phosphorus is with a hormone called FGF23 (fibroblast growth factor 23).
FGF23 has been found to be harmful to our blood vessels. It can also lead to hypertrophy of the cardiac ventricle (abnormal enlargement of our cardiac muscle), and is associated with heart attacks, sudden death and heart failure.[12 – 13] So eating animal protein with its high concentration of phosphorus can result in increased levels of this hormone in our bodies, which in turn is highly problematic for our health.
4. Animal Protein, Heme Iron and Free Radicals
Iron is the most abundant metal in the human body. We can consume it in two forms: (a) heme iron, found widely in animal foods like meat, poultry and fish, and (b) non-heme iron found widely in plant foods.
One of the problems with heme iron is that it can convert less reactive oxidants into highly reactive free radicals.[14] And free radicals can damage different cell structures like proteins, membranes and DNA.[14 – 15]
Heme iron can also catalyze the formation of N-nitroso compounds in our body, which are potent carcinogens. So, not surprisingly, high intake of heme iron has been associated with many kinds of gastro-intestinal cancers as well as other pathologies.[15]
It is true that heme iron has higher absorption rates and bio-availability than non-heme iron. However, iron itself can cause oxidative stress and DNA damage, so with iron generally, it’s not always a situation where “more is better.”[15]
While we definitely need iron, the absorption and bioavailability of iron from a well-rounded plant-based diet is generally adequate, and we may avoid the problems associated with heme iron and other negative health attributes of animal foods.[16 – 17]
5. Higher Sulfur-Containing Amino Acids and Bone Health Problems
Animal proteins also have, in general, higher concentrations of sulfur-containing amino acids, which can induce a subtle state of acidosis when we metabolize them in our body.[18] One of the mechanisms our body uses to compensate for this acidosis is leaching calcium from our bones to help neutralize the increased acidity. Over time, this can have a detrimental effect on bone health.[19 – 24]
This is thought to be one of the reasons why some studies have found that populations with higher dairy consumption, as well as higher consumption of animal protein in general, also have a higher incidence of bone fractures.[18 – 30]
6. Animal Protein and Cholesterol
Most animal foods contain saturated fat and cholesterol (this is true for even so-called “lean” meats like chicken, turkey and salmon, regardless of how they are cooked or prepared – even if boiled, baked or steamed).
As humans, we do not need to consume any cholesterol, since our bodies synthesize all the cholesterol we need for our physiologic functions.
Eating cholesterol despite this fact is problematic for our health, as it increases our risk of developing heart disease – currently the number one cause of death for both men and women in the US.[31 – 37]
Atherosclerosis, or plaques of cholesterol that accumulate in the lining of our vessels, is exquisitely less common on a plant-based vegan diet devoid of animal products. And, some studies have found that eating this way can even reverse atherosclerosis.[32 – 37]
7. Animal Protein and Fiber (or total lack thereof)
Unlike plant protein, which comes packaged with fiber, antioxidants and phytonutrients, animal protein comes with exactly none of the foregoing. To this point, meat, eggs, poultry, dairy, fish and other animal foods have absolutely no fiber whatsoever.
Many people, in their effort to “get enough” protein, tend to eat large amounts of animal foods, which displaces plant foods that have these important nutrients. Fiber deficiencies, in particular, are far more common than not.
For example, The Institute of Medicine recommends that men consume 38 grams of fiber, but the average adult only eats about 15 grams per day – less than half the recommended amount. In fact, according to the USDA, almost all Americans (~95%) do not get an adequate amount of dietary fiber.[38 – 39]
High fiber intake is associated with decreased cancer risk, specifically colon and breast cancers, as well as lower risk of ulcerative colitis, Crohn’s disease, constipation and diverticulitis. It may also reduce the risk of stroke, high cholesterol and heart disease.[40 – 41]
CONCLUSION
Given all the issues, the “high quality” aspect of animal protein might be more appropriately described as “high risk” instead.
And there’s no need to obsess about getting enough protein either. If you are eating a sensible variety of plant foods (vegetables, fruits, legumes, grains, roots, nuts and seeds), and you are eating enough calories (you feel satisfied), there is no need to worry about protein adequacy.
The amino acids we need are structurally identical regardless of the source. However, as discussed above, there are serious health implications depending on whether the amino acids are packaged with animal or plant foods. Dr. Walter Willett, the chair of Harvard’s Department of Nutrition, said it well:
“To the metabolic systems engaged in protein production and repair, it is immaterial whether amino acids come from animal or plant protein. However, protein is not consumed in isolation. Instead, it is packaged with a host of other nutrients.”[42]
He therefore recommends that you “[p]ick the best protein packages by emphasizing plant sources of protein rather than animal sources[.]”[42]
In the end, plant foods are the real “high quality” foods that we should be eating for optimal health.
(Please select the “Sources” tab above to view the footnotes.)
[1] VR Young and PL Pellett. Plant proteins in relation to human protein and amino acid nutrition. Am J Clin Nutr. 1994 May; 59(5 Suppl): 1203S-1212S. Available here (accessed Jan. 16, 2017).
[2] GE Dunaif and TC Campbell. Relative Contribution of Dietary Protein Level and Aflatoxin B1 Dose in Generation of Presumptive Preneoplastic Foci in Rat Liver. J Natl Cancer Inst. 1987 Feb; 78(2):365-9. Available here (accessed Jan. 16, 2017).
[3] LD Youngman and TC Campbell. Inhibition of Aflatoxin B1-Induced Gamma-Glutamyltranspeptidase Positive (GGT+) Hepatic Preneoplastic Foci and Tumors by Low Protein Diets: Evidence that Altered GGT+ Foci Indicate Neoplastic Potential. Carcinogenesis. 1992 Sep; 13(9):1607-13. Available here (accessed Jan. 16, 2017).
[4] TC Campbell. Dietary Protein, Growth Factors, and Cancer. Am J Clin Nutr. 2007; 85:1667. Available here (accessed Jan. 16, 2017).
[5] D Ornish, G Weidner, WR Fair, R Marlin and EB Pettengill, CJ Raisin, S Dunn-Emke, L Crutchfield, FN Jacobs, RJ Barnard, WJ Aronson, P McCormac, DJ McKnight, JD Fein, AM Dnistrian, J Weinstein, TH Ngo, NR Mendell, PR Carroll. Intensive Lifestyle Changes May Affect the Progression of Prostate Cancer. J Urol. 2005 Sep; 174(3):1065-9. Available here (accessed Jan. 16, 2017).
[6] DL Kleinberg, TL Wood, PA Furth and AV Lee. Growth Hormone and Insulin-Like Growth Factor-I in the Transition from Normal Mammary Development to Preneoplastic Mammary Lesions. Endocr Rev. 2009 Feb; 30(1):51-74. Available here (accessed Jan. 16, 2017).
[7] NE Allen, PN Appleby, GK Davey, R Kaaks, S Rinaldi and TJ Key. The Associations of Diet with Serum Insulin-Like Growth Factor I and its Main Binding Proteins in 292 Women Meat-Eaters, Vegetarians, and Vegans. Cancer Epidemiol Biomarkers Prev. 2002 Nov; 11(11):1441-8. Available here (accessed Jan. 16, 2017).
[8] MF McCarty. Vegan Proteins May Reduce Risk of Cancer, Obesity, and Cardiovascular Disease by Promoting Increased Glucagon Activity. Med Hypotheses. 1999 Dec; 53(6):459-85. Available here (accessed Jan. 16, 2017).
[9] WH Tang, Z Wang, BS Levison, RA Koeth, EB Britt, X Fu, Y Wu and SL Hazen. Intestinal Microbial Metabolism of Phosphatidylcholine and Cardiovascular Risk. N Engl J Med. 2013; 2013 Apr 25; 368(17):1575-84. Available here (accessed Jan. 16, 2017).
[10] RA Koeth, Z Wang, BS Levison, JA Buffa, E Org, BT Sheehy, EB Britt, X Fu, Y Wu, L Li, JD Smith, JA DiDonato, J Chen, H Li, GD Wu, JD Lewis, M Warrier, JM Brown, RM Krauss, WH Tang, FD Bushman, AJ Lusis and SL Hazen. Intestinal Microbiota Metabolism of L-carnitine, a Nutrient in Red Meat, Promotes Atherosclerosis. Nat Med. 2013 May; 19(5):576-85. Available here (accessed Jan. 16, 2017).
[11] Interview with Kim. A Williams, Sr., MD, President of the America College of Cardiology (August 25, 2015; Chicago). Recording and transcript available on file with author and here (accessed Jan. 17, 2017).
[12] Y Xiao, C Peng, W Huang, J Zhang, M Xia, Y Zhang and W Ling. Circulating Fibroblast Growth Factor 23 is Associated with Angiographic Severity and Extent of Coronary Artery Disease. PLoS One. 2013 Aug 28; 8(8):e72545. Available here (accessed Jan. 16, 2017).
[13] A Ozkok, C Kekik, GE Karahan, T Sakaci, A Ozel, A Unsal and A Yildiz. FGF-23 Associated with the Progression of Coronary Artery Calcification in Hemodialysis Patients. BMC Nephrol. 2013 Nov. 1; 14: 241. Available here (accessed Jan. 16, 2017).
[14] H Atamna. Heme, Iron, and the Mitochondrial Decay of Ageing. Ageing Res Rev. 2004 Jul; 3(3):303-18. Available here (accessed Jan. 16, 2017).
[15] MH Ward, AJ Cross, CC Abnet, R Sinha, RS Markin and DD Weisenburger. Heme Iron from Meat and Risk of Adenocarcinoma of the Esophagus and Stomach. Eur J Cancer Prev. 2012 Mar; 21(2):134-8. Available here (accessed Jan. 16, 2017).
[16] PJ Tuso, MH Ismail, BP Ha and C Bartolotto. Nutritional Update for Physicians: Plant-Based Diets. Perm J. 2013 Spring; 17(2): 61-66. Available here (Accessed Jan. 16, 2017).
[17] WJ Craig and AR Mangels; American Dietetic Association. Position of the American Dietetic Association: Vegetarian Diets. J Am Diet Assoc. 2009 Jul; 109(7): 1266–82. Available here (Accessed Jan. 16, 2017).
[18] E Giovannucci. Dietary Influences of 1,25(OH)2 Vitamin D in Relation to Prostate Cancer: A hypothesis. Cancer Causes Control. 1998 Dec; 9(6):567-82. Available here (accessed Jan. 16, 2017).
[19] Harvard T.H. Chan, School of Public Health website: The Nutrition Source – Calcium and Milk: What’s Best for Your Bones and Health? Available here (accessed Jan. 16, 2017).
[20] HC Sherman and AO Gettler. The Balance of Acid-Forming and Base-Forming Elements in Foods, and its Relation to Ammonia Metabolism. J Biol Chem. 1912 11: 323-338. Available here (accessed Jan. 16, 2017).
[21] D Feskanich, WC Willett, MJ Stampfer, GA Colditz. Protein Consumption and Bone Fractures in Women. Am J Epidemiol. 1996 Mar 1; 143(5):472-9. Available here (accessed Jan. 16, 2017).
[22] LA Frassetto, RC Morris Jr., DE Sellmeyer, A Sebastian. Adverse Effects of Sodium Chloride on Bone in the Aging Human Population Resulting from Habitual Consumption of Typical American Diets. J Nutr. 2008 Feb; 138(2):419S-422S. Available here (accessed Jan. 16, 2017).
[23] MM Adeva, G Souto. Diet-induced Metabolic Acidosis. Clin Nutr. 2011 Aug; 30(4):416-21. Available here (accessed Jan. 16, 2017).
[24] US Barzel, LK Massey. Excess Dietary Protein can Adversely Affect Bone. J Nutr. 1998 Jun; 128(6):1051-3. Available here (accessed Jan. 16, 2017).
[25] DM Hegsted. Calcium and Osteoporosis. J Nutr. 1986 Nov; 116(11): 2316-9. Available here (accessed Jan. 16, 2017).
[26] K Michaëlsson, A Wolk, S Langenskiöld, S Basu, EW Lemming, H Melhus and L Byberg. Milk Intake and Risk of Mortality and Fractures in Women and Men: Cohort Studies. BMJ. 2014; 349: g6015. Available here (accessed Jan. 16, 2017).
[27] D Feskanich, HA Bischoff-Ferrari, L Frazier and WC Willett. Milk Consumption During Teenage Years and Risk of Hip Fractures in Older Adults. JAMA Pediatr. 2014 Jan; 168(1): 54–60. Available here (accessed Jan. 16, 2017).
[28] HC Sherman, AR Rose and MS Rose. Calcium Requirement of Maintenance in Man. J. Biol. Chem. 1920 44: 21-27. Available here (accessed Jan. 16, 2017).
[29] BJ Abelow, TR Holford and KL Insogna. Cross-cultural Association between Dietary Animal Protein and Hip Fracture: A hypothesis. Calcif Tissue Int. 1992 Jan; 50(1):14-8. Available here (accessed Jan. 16, 2017).
[30] LM Ausman, LM Oliver, BR Goldin, MN Woods, SL Gorbach and JT Dwyer. Estimated Net Acid Excretion Inversely Correlates with Urine pH in Vegans, Lacto-ovo Vegetarians, and Omnivores. J Ren Nutr. 2008 Sep; 18(5):456-65. Available here (accessed Jan. 16, 2017).
[31] Centers for Disease Control and Prevention website: Life Stages and Populations – Deaths – Leading Causes of Death. Available here (accessed Jan. 16, 2017).
[32] CB Esselstyn Jr. Updating a 12-year Experience with Arrest and Reversal Therapy for Coronary Heart Disease (An Overdue Requiem for Palliative Cardiology). Am J Cardiol. 1999 Aug 1;84(3): 339-41, A8. Available here (accessed Jan. 16, 2017).
[33] CB Esselstyn Jr, G Gendy, J Doyle, M Golubic and MF Roizen. A Way to Reverse CAD? J Fam Pract. 2014 Jul; 63(7):356-364b. Available here (accessed Jan. 16, 2017).
[34] D Ornish, SE Brown, LW Scherwitz, JH Billings, WT Armstrong, TA Ports, SM McLanahan, RL Kirkeeide, RJ Brand and KL Gould. Can Lifestyle Changes Reverse Coronary Heart Disease? The Lifestyle Heart Trial. Lancet. 1990 Jul 21; 336(8708):129-33. Available here (accessed Jan. 16, 2017).
[35] CB Esselstyn Jr, SG Ellis, SV Medendorp and TD Crowe. A Strategy to Arrest and Reverse Coronary Artery Disease: A 5-year Longitudinal Study of a Single Physician’s Practice. J Fam Pract. 1995 Dec; 41(6):560-8. Available here (accessed Jan. 16, 2017).
[36] TC Campbell, B Parpia and J Chen. Diet, Lifestyle, and the Etiology of Coronary Artery Disease: the Cornell China Study. Am J Cardiol. 1998 Nov 26; 82(10B):18T-21T. Available here (accessed Jan. 16, 2017).
[37] CB Esselstyn Jr. Resolving the Coronary Artery Disease Epidemic Through Plant-Based Nutrition. Prev Cardiol. 2001 Autumn; 4(4):171-177. Available here (accessed Jan. 16, 2017).
[38] Usual Intake from Food and Beverages 2007-2010 Compared To Dietary Reference Intakes; Part E. Section 2: Supplementary Documentation to the 2015 DGAC Report. Scientific Report of the 2015 Dietary Guidelines Advisory Committee. 2015. Available here (accessed Jan. 16, 2017).
[39] NS Rizzo, K Jaceldo-Siegl, J Sabate and GE Fraser. Nutrient Profiles of Vegetarian and Nonvegetarian Dietary Patterns. J Acad Nutr Diet. 2013 Dec; 113(12):1610-9. Available here (accessed Jan. 16, 2017).
[40] JY Wick. Diverticular disease: Eat your fiber! Consult Pharm. 2012 Sep; 27(9): 613-8. Available here (accessed Jan. 16, 2017).
[41] A Dilzer, JM Jones and ME Latulippe. The Family of Dietary Fibers: Dietary Variety for Maximum Health Benefit. Nutrition Today. 2013 May/June; 48(3):108-118. Available here (accessed Jan. 16, 2017).
[42] PJ Skerrett and WC Willett. Essentials of healthy eating: a guide. J Midwifery Womens Health. 2010 Nov-Dec; 55(6): 492-501. Available here (accessed Jan. 16, 2017).
This article was written by Sofia Pineda Ochoa, MD, and an alternate version of this article is also available on the Forks Over Knives website.