Does the Source of Your Protein Matter?

Proteins are essential for a vast array of functions in living organisms.  They provide structure for cells.  They allow muscles to contract.  They are a part of our skin and our connective tissues. Antibodies, a feature of our immune system that protects us from diseases, are proteins.  The hemoglobin that transports oxygen in our blood is a protein.  Hormones are proteins.  Enzymes that are vital for biochemical reactions involved in body processes such as metabolism are proteins.  And there are many other roles that protein plays in our bodies. (2)

Where do we get our protein?  It comes in the food that we eat, of course.  Everybody knows that animal-sourced foods are a good way to get protein.  But not everyone realizes that all plants contain a significant amount of protein too. Many people think that eating a plant-based diet means that they’ll have trouble getting enough protein but this couldn’t be further from the truth.  Both plants and animals contain quantities of proteins more than sufficient for keeping our bodies alive and healthy.

Proteins are made up of various combinations of twenty amino acid building blocks.   These same twenty amino acids are present in the proteins of all living species. Our human bodies can produce eleven of these amino acids.  The other nine are called “essential” amino acids because they must be obtained from the diet.  This, however, is not a big deal at all.  Both protein sources, animal and plant, can supply all the essential amino acids we need for building our proteins.  (1,2)

 

It is important to understand

that the source of protein that you choose to eat

is a significant decision

and one much more crucial to your health

than you might presently think

 

Animals and plants are very different creatures and it’s not surprising that the “package” that their protein comes in is also dissimilar.  When we eat a food, we are not acquiring just protein, but other nutrients, both good and bad, that are part of that particular “package”. (1,2)

For example, meats are a great source of protein but, in the same “package” come detrimental nutrients such as saturated fat, cholesterol, hormones and, if the meat is processed, excess sodium.  On the other hand, beans and lentils are also excellent sources of protein but their “packages” contain valuable nutrients like fiber, a crucial nutrient for health that is completely missing in animal-sourced foods, and phytochemicals like antioxidants and polyphenols that offer a myriad of remarkable healthy effects that include the prevention of cancer and diabetes, the reduction of atherosclerosis within arteries and the lowering of body inflammation.  In addition, plant “packages” contain no sodium, hormones, cholesterol or saturated fat.  (3,4)

There now exists a wealth of evidence indicating that the source of dietary protein (its “package”) plays a key role in either improving or deteriorating health.  (5)

A study from Harvard followed over 100,000 men and women over decades to uncover the association between the consumption of animal and plant protein with early death.  Its results showed that high animal protein intake was linked to a greater risk of death from cardiovascular disease while high plant protein intake was linked to lower risk of death from all causes put together.  In addition, replacing just 3% of animal protein in a diet with plant protein was associated with lower risk of death, especially if the animal protein being replaced was meat or eggs. (6)

What mechanisms may be causing these effects?

Research from 2018 reveals that one such protective process may be the effect of plant protein on levels of the cancer-promoting growth hormone, IGF-1 (Insulin-like Growth Factor-1).  Animal-sourced protein intake boosts IGF-1 levels but plant-sourced protein intake does not and is in fact associated with decreased risks of cancer.  (7)

A 2015 review and meta-analysis of randomized controlled trials demonstrated that replacing one-third of animal protein with plant protein resulted in significant improvements in blood sugar control, fasting blood sugars and insulin levels.  (8)

Another review and meta-analysis from 2018 of randomized controlled trials observed that substituting plant protein for animal protein decreased LDL-cholesterol levels.  These researchers did not find a significant difference between the effects of whole plant foods and of isolated plant proteins such as soy which suggests that the cholesterol-lowering effects can be at least partly attributed to the plant protein itself and not just to the associated nutrients from the plant “package” (9).

Multiple other studies have linked the consumption of plant protein to other healthy effects like drops in blood pressure, reduced LDL-cholesterol levels, lower incidence of cardiovascular disease, improved insulin sensitivity and a lessening of the risk of type-2 diabetes.  (6,10)

All this is a strong indication that the source of dietary protein is an important variable for achieving optimal health.

A trial from 2018 sums this all up nicely (11).  The dietary habits of the over 81,000 participants were followed for 6 to 12 years.  Researchers looked at the percentages of the protein intake of each participant that originated in an animal or in a plant.  Their results illustrate that the risk of early death from cardiovascular disease rose steadily as more meat protein was consumed and conversely fell with higher intake of protein from plant-sourced foods such as nuts and seeds.

• Those eating the highest amount of meat had a 60% higher risk of dying from cardiovascular disease compared to those eating the lowest amount of meat.
• Those eating the highest amount of nuts and seeds had a 40% lower risk of dying from cardiovascular disease compared to those eating the lowest amount of nuts and seeds.

The message is clear.  When it comes to choosing where our protein is going to come from, we need to turn our thoughts to foods like beans, peas, lentils, whole grains, nuts and seeds and back off on meats, eggs and dairy products.

 

 SOURCES:

1  McDougall, J.  Plant foods have a complete amino acid composition.  Circulation. 2002 Jun 25; 105(25):e197.

2  https://rwu.pressbooks.pub/bio103/chapter/amino-acids-and-proteins/

3  Salehi, B., Quispe, C., Sharifi-Rad, J., Cruz-Martins, N., Nigam, M., Mishra, A.P., Konovalovm, D.A. et al.  Phytosterols: From Preclinical Evidence to Potential Clinical Applications. Front Pharmacol. 2021 Jan 14;11:599959. Doi: 10.3389/fphar.2020.599959. PMID: 33519459; PMCID: PMC7841260.

4  https://nutritionsource.hsph.harvard.edu/what-should-you-eat/protein/

5  https://www.health.harvard.edu/nutrition/high-protein-foods-the-best-protein-sources-to-include-in-a-healthy-diet

6   Song, M., Fung, T.T., Hu, F.B., et al. Association of Animal and Plant Protein Intake With All-Cause and Cause-Specific Mortality. JAMA Intern Med. 2016;176(10):1453-63.

7  Messina, M., Magee, P. Does soy protein affect circulating levels of unbound IGF-1?. Eur J Nutr. 2018;57(2):423-32.

8   Viguiliouk, E., Stewart, S.E., Jayalath, V.H., et al. Effect of Replacing Animal Protein with Plant Protein on Glycemic Control in Diabetes: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Nutrients. 2015;7(12):9804-24.

9  Li, S., Blanco Mejia,  D., Lytvyn, L., et al. Effect of Plant Protein on Blood Lipids: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. J Am Heart Assoc. 2017;6(12):e006659.

10  Ye, J., Yu, Q., Mai, W., Liang, P., Liu, X., Wang, Y. Dietary protein intake and subsequent risk of type 2 diabetes: a dose-response meta-analysis of prospective cohort studies. Acta Diabetol. 2019;56(8):851-70.

11  Tharrey, M., Mariotti, F., Mashchak, A., Barbillon, P., Delattre, M., Fraser, G.E. Patterns of plant and animal protein intake are strongly associated with cardiovascular mortality: the Adventist Health Study-2 cohort. Int J Epidemiol. 2018 Oct 1;47(5):1603-1612. Doi: 10.1093/ije/dyy030. PMID: 29618018; PMCID: PMC6658814.