In a recent interview I was pressed on the topic of protein for overall vitality, for peak physical performance, for satiety and weight control.
When I answered regarding how protein quality is and should be defined, regarding the prevailing fallacies that more is better and that the best quality protein must be sourced from meat (more on these below), I was pushed further: what about protein to preserve function into older and overtly old age?
I at first doubled down on my initial answers, when a far more decisive response occurred to me. Without question or debate, the single most important means of preserving lean body mass, stamina, strength, and muscle function into older and old age- is to use those muscles routinely. The best remedy by far for the muscle loss of senescence- sarcopenia- is physical activity.
But that just shifts the same question further upstream: how best to preserve the capacity for routine physical activity into older and genuinely old age? That answer, also indisputably, is to protect general health and vitality.
Which, obviously again pushes the question further upstream still: how best to preserve vitality into old age? That answer spans the domains of lifestyle as medicine, but with particular regard to diet, it is clear: food, not too much, mostly plants. The basic dietary theme that best promotes and protects the vitality of Homo sapiens is decisively established across a vast expanse of evidence of every conceivable methodology. Our muscles are best nourished, our coronaries most pristine, and our minds most acute when we prioritize whole vegetables, fruits, legumes, grains, nuts, seeds, and plain water to quench our quotidian thirst.
This answer has taken us some distance from the provocation about protein, so let’s circle back now to that.
That we have canonized the virtues of protein- and let’s face it, we have- is perhaps all but inevitable. In our ongoing societal boondoggles where basic sense about feeding ourselves ought to be, we sequentially vilified two macronutrient classes out of three: first fat in the 1980s, and then carbohydrate in the 1990s. Interest in, and marketing of, both generally fat-restricted and carbohydrate-restricted diets have long outlasted whatever scientific support either had, if any- but persist, they do. Had we moved on to vilify protein as well, our only recourse would have been to clamp our lips together and hope to master photosynthesis. There are just three macronutrients; all food is made of one or more in their many iterations, and the rest is air, water, and…sunlight.
To be clear, there was a case for vilifying protein, too- made with scientific acumen and a bracing dose of passion by T. Colin Campbell in The China Study. But we went the other way.
Every villain calls out for a hero, every action calls out for an equal and opposite reaction, and fatuous pop culture conceptions of diet favor both scapegoats and silver bullets. Accordingly, we anointed protein as the virtuous counterweight to the menace of carbohydrate and fat.
A great deal of nonsense detrimental to public health- and now, even more importantly, planetary health- inevitably ensued. We adopted and promulgated the notion that because some protein is good, more is better- neglecting the simple, established fact of metabolism that excess calories from any source are stored as fat. Yes, to be clear: overfeed humans protein, and expressly protein - and we do not grow enviable muscles as a result. We grow all the protuberances we wish we didn’t have, where adipose tissue accumulates.
Outside of intensive care and burn units, and perhaps among the desperately disadvantaged and homeless, protein deficiency is all but unknown in the United States. It does still exist in those countries prone to famine, alas, but it is simply not a public health problem in the industrialized world.
Protein greatly in excess of biological need tends to prevail, and protein commensurate with that need is readily sourced not only from conventional diets, but also from plant-exclusive diets practiced with a modicum of sense and balance. Of note, this issue is rather misrepresented in media coverage of a recent U.N. report on global nutrition. Of course, it is true that if any foods, including animal foods, are removed from already very marginal diets and replaced by nothing- those diets will devolve from marginality to insufficiency. The question “what happens to marginal diets if we take away any of their current nutrient sources?” anticipates the inevitable answer: they deteriorate. This could be used to argue that animal foods are important to human nutriture.
There is, however, another and far better question: “what are the best ways to address nutritional marginality and nutrient insufficiency around the globe?” That answer, serving both public and planetary health, and the urgent concern of sustainability, would emphasize improved, global access to a wide variety of nutrient-rich plant foods, with much less emphasis on animal foods. Animal foods are essential to optimal human nutrition only where optimized access to diverse plant foods is not achieved.
As for protein, plant exclusive diets can, and do, deliver the protein needed even for the outer limits of human performance not only in the realm of stamina, but also strength. That should come as no great surprise; the greatest muscles on land belong to herbivores.
That comment deserves a bit more consideration: when we source protein from animals as food, they, in turn, have sourced it ultimately (and more often than not directly, as we eat herbivorous animals preferentially, although not exclusively) from plants. In biology, “alchemy” of a sort is a practical reality: horse biology turns oats, grass, and hay into… horse. Our muscles are dwarfed by those of a horse, to say nothing of a buffalo, hippo, rhino, or elephant- and those mighty muscles are powered entirely by plants.
The question, then, is not whether plants can deliver all the protein mighty muscles require, but simply- are humans among the animals that can run exclusively on plant-sourced protein? The answer is clearly yes, as whole populations and elite athletes do just that. The details are there to validate why: we have an omnivore’s physiology, capable of processing either plant or animal food; and all essential amino acids are present in all plant foods, varying only in concentration.
Concentration does matter, of course; so much so that the hoary but still-used definition of protein quality is predicated on it directly. While the Protein Digestibility Corrected Amino Acid Score (PDCAAS) has been supplanted by the Digestible Indispensable Amino Acid Score (DIAAS) – in both cases, the concentration of select amino acids, rather than any net effects of eating the food in which they reside, is emphasized.
That’s a problem, because quality implies “better” in some way that matters. Higher concentrations of select amino acids in meat might indeed be better in a population prone to deficiency, but quite the contrary for populations far more prone to excess. Further, protein molecules specific to animal foods have been implicated in potential harms. More importantly, diets excessive in animal foods and relatively deficient in whole plant foods are implicated in nearly all major chronic diseases, and the overall risk of premature death.
Even these concerns neglect the great and universal threat of our time: mass production of animal food is devastating the planet. If we bequeath our children a world without lions, tigers, and bears; if we pass on a planet stripped of the Amazon rainforest and ice in the Arctic - hamburgers will have much to do with our blighted legacy.
Finally, the concentrations of amino acids that best fuel rapid, neonatal growth (in rats, or humans) are scarcely a mark of “quality” where children are prone far less to famine than to obesity, fatty liver, and type 2 diabetes.
In sum, high quality protein sources should deliver high quality outcomes that matter (e.g., years in life, life in years, sustainable biodiversity, and a vital planet), or we are forced to wonder: what, exactly, does “quality” mean?
With a sensible, modernized definition of protein quality taking into account the known and net effects of eating the food delivering it- beans would readily displace beef atop the marquee. (Note that alternative definitions of protein quality might be invoked based on epidemiologic context; what is helpful in alleviating famine and kwashiorkor only makes obesity and cardiometabolic disease worse.)
Our obsolete-in-this-part-of-the-world definition of protein quality invites our society to persist in the misguided view that protein is synonymous with meat. To wit, not all that long ago, I was asked by a server if I wanted “protein” with my quinoa salad.
I did; it was in the quinoa.
David L. Katz, MD, MPH, FACPM, FACP, FACLM, is the Founding Director (1998) of Yale University’s Yale-Griffin Prevention Research Center, and former President of the American College of Lifestyle Medicine. He has published roughly 200 scientific articles and textbook chapters, and 15 books to date, including multiple editions of leading textbooks in both preventive medicine, and nutrition. He has made important contributions in the areas of lifestyle interventions for health promotion; nutrient profiling; behavior modification; holistic care; and evidence-based medicine. David earned his BA degree from Dartmouth College (1984); his MD from the Albert Einstein College of Medicine (1988); and his MPH from the Yale University School of Public Health (1993). He completed sequential residency training in Internal Medicine, and Preventive Medicine/Public Health. He is a two-time diplomate of the American Board of Internal Medicine, and a board-certified specialist in Preventive Medicine/Public Health. He has received two Honorary Doctorates.