Remember that friend who brought you so much joy in the beginning, but who you needed to say goodbye to many years later when your relationship turned toxic? If you’ve shared this common experience, you may have been left wondering how the friend you thought you knew so well could have turned out to be so two-faced.
It’s kind of like that with protein.
We all know the arguments for a protein-rich diet. Higher-than-recommended amounts of protein are helpful for elderly folks, and they help control appetite and can contribute to a weight loss goal. If you’ve worked in the health care or exercise fields, you’ve recommended higher protein diets for sick patients or fitness buffs to help them recover from surgery or hard workouts.
Protein-rich foods also help us grow when we’re young, so our parents feed us milk or eggs in the morning, pack us off to school with a meat or cheese sandwich for lunch (or the school cafeteria provides much the same) and serve us beef, chicken, pork, lamb, veal, or fish for dinner. As teens and young adults, we continue to eat this way, for the sake of putting on muscle or the belief that eating carbs will cause weight gain, while proteins will do no such thing. And we’ve passed this way of eating down through the generations to our own families. The unspoken national viewpoint thus became “there’s no such thing as too much protein.” Just like there’s no such thing as having too many friends. (Until you remember the relationships with friends that became toxic.) The data on protein toxicity may cause your thinking on this nutrient to change as well.
This is a multi-faceted topic. Two of the viewpoints that have emerged for a restraint on protein intake deal with the issue of quality and quantity. The issue of quality comes from data on the effects of plant-based protein compared with animal protein. So far, studies have been published on how these protein sources differ in their effects on the risks for mortality, diabetes, cardiovascular disease, metabolic syndrome, weight gain, and dementia (among others).
The data doesn’t look so good for lovers of animal protein.
Higher intakes have been linked with greater risk for dying from any and all causes (“all-cause” mortality) while plant protein was linked with a lower risk.1 Higher intakes of animal protein were found to increase the risk for diabetes, while moderate plant protein intakes reduced the risk,2-3 and similar results were found for the metabolic syndrome.4 Dietary patterns characterized by low animal protein and high plant protein intakes are also associated with a lower risk for dementia.5 In studies where people’s eating habits were looked at in relation to body weight, excess weight gain has been closely related to the intake of animal protein, while those eating plant protein experience either little or no weight gain.6
The issue of protein quality also involves the differences in saturated fat and cholesterol that exist between animal and plant protein, and how these are responsible for greater disease risk. The best example is evidence that red meat is the worst type of animal protein, from a health viewpoint.
As to why plant protein protects us from disease better, we could start with the idea that these proteins, in addition to having little to zero saturated fat and cholesterol respectively, also lower cholesterol levels. This explains the lower risk for cardiovascular disease, but what about the other ailments?
One way to address all of these in one fell swoop would be to say that plant proteins also contain far greater amounts of fiber, vitamins, minerals, and protective plant chemicals compared to animal proteins. These nutrients are well-known to protect against common chronic diseases in general. Plant foods are generally lower in energy density and higher in fiber than animal foods, which would help protect against excess weight gain and obesity-related diseases like those mentioned above. Other explanations are beyond the scope of this article.7
This should be enough to convince anyone to start replacing animal protein with plant protein.
If it’s not enough, consider the aging problem. We have a rapidly-expanding aging population that is living longer, but not healthier, so it needs more care. This will certainly put even more of a strain on our health system than what we have now.
The experts in anti-aging research have come to a consensus on how the average person can slow the aging process. Although for many years it was thought that a barely-tolerable level of calorie restriction would be necessary, the evidence now points to restricting animal protein as having the same effect.8
Houston (and other places where cattle and hogs are raised) do we ever have a problem! Americans are not just “in love”, they’re in thrall to their meat, eggs, and cheese consumption. Unless they’re advised to do so willingly, voluntarily and gradually, they probably will resist a change to a diet higher in plant and lower in animal protein. It’s up to us to make this transition easier for those who want to understand why and how to undertake this journey.
“Simplified diagram of the metabolic impact of protein restriction. From Green CL, Lamming DW. Regulation of metabolic health by essential dietary amino acids. Mech Ageing Dev. 2019 Jan;177:186-200.
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Chen Z et al. Dietary protein intake and all-cause and cause-specific mortality: results from the Rotterdam Study and a meta-analysis of prospective cohort studies. Eur J Epidemiol. 2020 Feb 19. doi: 10.1007/s10654-020-00607-6.
Ye J et al. Dietary protein intake and subsequent risk of type 2 diabetes: a dose-response meta-analysis of prospective cohort studies. Acta Diabetol. 2019 Aug;56(8):851-870.
Zhao LG et al. Dietary protein intake and risk of type 2 diabetes: a dose-response meta-analysis of prospective studies. Eur J Nutr. 2019 Jun;58(4):1351-1367.
Shang X et al. Dietary protein from different food sources, incident metabolic syndrome and changes in its components: An 11-year longitudinal study in healthy community-dwelling adults. Clin Nutr. 2017 Dec;36(6):1540-1548.
Pistollato F et al. Nutritional patterns associated with the maintenance of neurocognitive functions and the risk of dementia and Alzheimer’s disease: A focus on human studies. Pharmacol Res. 2018 May;131:32-43.
van Baak MA et al. Dietary Intake of Protein from Different Sources and Weight Regain, Changes in Body Composition and Cardiometabolic Risk Factors after Weight Loss: The DIOGenes Study. Nutrients. 2017 Dec 6;9(12). pii: E1326.
The other explanations include the dangers associated with toxic compounds found in animal protein, including advanced glycation end products and oxysterols, and the ability of an excess of essential amino acids to activate the mTOR pathway, a central pathway in most chronic diseases.
Kitada M et al. The impact of dietary protein intake on longevity and metabolic health. EBioMedicine. 2019 May; 43: 632–640.