Plant vs. Animal Proteins

I’m often asked my opinion about a diet or a disease is. Who cares what my or anyone else’s opinion is? All we should care about is what the science says. What does the best available balance of evidence published in the peer-reviewed medical literature have to say right now?

Welcome to the NutritionFacts Podcast – I’m your host Dr. Michael Greger.

There has been a history of enthusiasm for protein in the nutrition world. In fact – a century ago, the protein recommendations were more than twice what they are today. Let’s start with a public health case for modernizing the definition of protein quality.

In 2019, Dr. David Katz and colleagues, including one of my favorite researchers, David Jenkins, published a public health case for modernizing the definition of protein quality. The prevailing definition seems to have more to do with biochemistry than the net effects on human health. The popular concept that protein is good, and the more the better, coupled with a protein quality definition that favors animal protein, fosters the impression that eating more meat, eggs, and dairy is desirable and preferable. But this is directly opposed to nutrition guidelines that are instead trying to push more plants. Although protein malnutrition is still prevalent in many areas of the world, it is exceedingly rare in the industrialized world, where the most formidable public health threat is not something like kwashiorkor—protein/calorie malnutrition—but from chronic diseases.
And in 2016, a landmark study was published out of Harvard, involving more than 100,000 people that found that replacing animal protein with plant protein was associated with lower risk of dying prematurely. The worst seemed to be processed meat like bacon, as well as egg protein (the egg whites), but swapping in even just 3 percent plant protein for any of the animal proteins: processed meat, unprocessed meat, chicken, fish, eggs, or dairy was associated with a significantly lower risk of arguably the most important endpoint of all, death.
Yeah, but how do we know it’s the protein? The researchers adjusted for factors such as saturated fat intake, which suggested it wasn’t just the animal fat. Okay, but how does your body even know the difference between protein from a plant and protein from an animal? Isn’t protein, protein? No, unlike animal protein, plant protein is generally low in branched-chain amino acids, for example, and decreased consumption of branched-chain amino acids improves metabolic health. It could be the IGF-1, a cancer-promoting growth hormone that is boosted by so-called high-quality animal protein intake though. We suspect the IGF-1 connection is cause and effect, since people who are just born to have higher IGF-1 levels, regardless of what they eat, do appear to suffer higher rates of killers like type 2 diabetes and heart disease.
Or, it could be something the Harvard researchers didn’t control for, such as toxic pollutants, such as dioxins and PBCs, since they tend to accumulate up the food chain into cattle, pigs, chickens, and fish––and therefore end up on our plates. So, plant-based protein also stands as an important step to lower the body burden of harmful pollutants.
If you don’t think 100,000 people are enough, how about 400,000 people? The NIH-AARP study is the largest diet cohort study in history. And again, simply swapping 3 percent of calories from various animal protein sources with plant protein was associated with 10 percent decreased overall mortality. And you get even twice that benefit if you get rid of eggs, too. That’s not a surprise, since egg consumption is associated with a higher risk of developing cardiovascular disease.
Put all the studies together on dietary protein intake and mortality, and people who eat more protein tend to live shorter lives. But this is mainly driven by a harmful association of animal protein. Plant protein intake is inversely associated with mortality––meaning those who eat more plant protein tend to live longer lives. More animal protein may mean more mortality, whereas more plant protein is correlated with less mortality. So, the best of both worlds would be to increase the intake of plant protein in place of animal protein. In other words, as another 2020 meta-analysis concluded, “Persons should be encouraged to increase their plant protein intake to potentially decrease their risk of death.”

Do vegetarians and vegans get enough protein? Let’s find out.

The largest study in history of those eating plant-based diets recently compared the nutrient profiles of about 30,000 non-vegetarians to 20,000 vegetarians, and about 5,000 vegans, flexitarians, and no meat except fish-eaters, allowing us to finally put to rest the perennial question, “Do vegetarians get enough protein?” The average requirement is 42 grams of protein a day. Non-vegetarians get way more than they need, and so does everyone else. On average, vegetarians and vegans get 70% more protein than they need every day.
Surprising that there’s so much fuss about protein in this country when less than 3% of adults don’t make the cut—presumably folks on extreme calorie-restricted diets who just aren’t eating enough food, period. But 97% of Americans get enough protein.
There is a nutrient, though, for which 97% of Americans are deficient. Now, that’s a problem nutrient. That’s something we really have to work on. Less than 3% of Americans get even the recommended minimum adequate intake of fiber. So, the question isn’t “Where do you get your protein?” but “Where do you get your fiber?” We only get about 15 grams a day. The minimum daily requirement is 31.5, so we get less than half the minimum. If you break it down by age and gender, after studying the diets of 12,761 Americans, the percentage of men between ages 14 and 50 getting the minimum adequate intake? Zero.
“This deficit is stunning in that dietary fiber has been [protectively] associated…with the risk of diabetes, metabolic syndrome, cardiovascular disease…, obesity, and various cancers as well as…high cholesterol, blood pressure, and blood [sugars]. Therefore, it is not surprising that fiber is [now] listed as a nutrient of concern in the…Dietary Guidelines…” Protein is not.
“One problem is that most people have no idea what’s in their food; more than half of Americans think steak is a significant fiber source.”
By definition, fiber is only found in plants. There is no fiber in meat, dairy, or eggs, and little or no fiber in junk food. Therein lies the problem. Americans should be eating more beans, vegetables, fruits, whole grains—how are we doing on that? Well, 96% of Americans don’t eat the minimum recommended daily amount of beans, 96% don’t eat the measly minimum for greens. 99% don’t get enough whole grains. Look at these numbers. Nearly the entire U.S. population fails to eat enough whole plant foods. And, it’s not getting any better; a “lack of progress [that’s] disappointing.”
Even semi-vegetarians, though, make the minimum for fiber. And those eating completely plant-based diets triple the average American intake. Now, when closing the fiber gap, you’ll want to do it gradually, no more than about five extra grams of fiber a day each week, until you can work your way up.
But it’s worth it. “Plant-derived diets tend to contribute significantly less fat, saturated fat, cholesterol, and [foodborne pathogens], while at the same time offering more fiber, folate, vitamin C, and phytochemicals…all essential factors for disease prevention, and optimal health and well-being.”
And, the more whole plant foods, the better. If you compare the nutritional quality of “vegan [vs.] vegetarian, semi-vegetarian, pesco-vegetarian and omnivorous diets, traditional healthy diet-indexing systems, like compliance with the dietary guidelines, consistently indicate the most plant-based diet as “the most healthy one.”

Finally today – we examine the myth that plant proteins are incomplete.

All nutrients come from the sun or the soil. Vitamin D, the “sunshine vitamin,” is created when skin is exposed to sunlight. Everything else comes from the ground. Minerals originate from the earth, and vitamins from the plants and micro-organisms that grow from it.
The calcium in a cow’s milk (and her 200-pound skeleton) came from all the plants she ate, which drew it up from the soil. We can cut out the middle-moo, though, and get calcium from the plants directly.
Where do you get your protein? Protein contains essential amino acids, meaning our bodies can’t make them; and so, they are essential to get from our diet. But other animals don’t make them either. All essential amino acids originate from plants (and microbes), and all plant proteins have all essential amino acids. The only truly “incomplete” protein in the food supply is gelatin, which is missing the amino acid tryptophan. So, the only protein source that you couldn’t live on is Jell-O.
As I covered previously, those eating plant-based diets average about twice the estimated average daily protein requirement. Those who don’t know where to get protein on a plant-based diet don’t know beans! Get it? That’s protein quantity, though, but what about protein quality?
The concept that plant protein was inferior to animal protein arose from studies performed on rodents more than a century ago. Scientists found that infant rats don’t grow as well on plants. But infant rats don’t grow as well on human breast milk either; so, does that mean we shouldn’t breastfeed our babies? Ridiculous! They’re rats. Rat milk has ten times more protein than human milk, because rats grow about ten times faster than human infants.
It is true that some plant proteins are relatively low in certain essential amino acids. So, about 40 years ago, the myth of “protein combining” came into vogue—literally, the February ‘75 issue of Vogue magazine. The concept was that we needed to eat “complementary proteins” together, for example, rice and beans, to make up for their relative shortfalls. This fallacy was refuted decades ago. The myth that plant proteins are incomplete, that plant proteins aren’t as good, that one has to combine proteins at meals—these have all been dismissed by the nutrition community as myths decades ago, but many in medicine evidently didn’t get the memo. Dr. John McDougall called out the American Heart Association for a 2001 publication that questioned the completeness of plant proteins. Thankfully though, they’ve changed and acknowledged that, “Plant proteins can provide all the essential amino acids, no need to combine complementary proteins.”
It turns out our body is not stupid. It maintains pools of free amino acids that it can used to do all the complementing for us, not to mention the massive protein recycling program our body has. Some 90 grams of protein are dumped into the digestive tract every day from our own body to get broken back down and reassembled, and so our body can mix and match amino acids to whatever proportions we need, whatever we eat, making it practically impossible to even design a diet of whole plant foods that’s sufficient in calories, but deficient in protein. Thus, plant-based consumers do not need to be at all concerned about amino acid imbalances from the plant proteins that make up our usual diets.
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