With more people than ever buzzing about the benefits of plant-based diets and opting for animal-free alternatives to the traditional burger, plant protein is earning its place at the kitchen table right alongside its animal-derived counterpart. Which might have you wondering: When it comes to plant and animal protein, is one healthier than the other?
Like so many questions in nutrition science, the answer here is more complicated (and more interesting!) than you might expect. Here’s what you should know about plant vs. animal protein.
What protein actually is
Let’s start by looking at protein on the most basic level. This macronutrient is an integral part of every cell in the human body. (Btw, a macronutrient is one of three nutrients that the body needs in large quantities; carbs and fat are the other two.) Protein plays a crucial role in growth and development by building and repairing the body’s various cells and tissues (including your muscles, bones, organs, and skin), as the Food and Drug Administration (FDA) explains. It’s also necessary for various body functions from blood clotting and hormone production to immune system response. So yeah, this stuff is super important.
On a molecular level, all dietary protein is made up of tiny organic compounds called amino acids—hundreds or thousands of them linked together, the FDA explains. There are 20 different kinds. Whenever we eat protein, it gets broken back down into these singular amino acid building blocks, and then recombined (or, put back together in different arrangements) as necessary and dispatched to perform those various jobs throughout the body, as SELF previously explained.
So while, say, a chicken breast and bowl of lentils might look (and taste) very different, the protein they each provide is made of the same exact basic units. “On a chemical level, by the time you’ve eaten and absorbed and utilized one of those amino acids, it doesn’t matter…if it came from a plant or animal,” Christopher Gardner, Ph.D., research professor of medicine at the Stanford Prevention Research Center, tells SELF.
The deal with complete vs. incomplete proteins
The 20 different amino acids can be divided into two main groups: essential and non-essential. The nine essential amino acids are the ones that the body cannot make on its own, so it’s essential that we get them from the food we eat, the U.S. National Library of Medicine explains. The other 11, the nonessential ones, our body can produce.
When a protein source contains an adequate supply of all nine essential amino acids, it’s dubbed with the honorific title of complete protein. When it’s low or lacking in one or more, it’s classified as incomplete, the FDA explains. (Kind of harsh.)
This is where the composition of plant and animal proteins begins to look distinct. All animal proteins are complete proteins. This includes both muscle tissue from animals (beef from cows, bacon and ham from pigs, breasts from chickens, filets of fish, etc.), as well as the products derived from them (eggs and dairy products, like milk and yogurt). Plant proteins, on the other hand—including beans, legumes (lentils, peas), nuts, seeds, and whole grains—are almost all incomplete. Only a couple lucky plant proteins are complete, like soy products (e.g. edamame, tofu, and soy milk) and quinoa.
Therefore, “Strictly in terms of nutritional adequacy, it is easier to ensure you have consumed the essential amino acids by consuming animal protein,” Whitney Linsenmeyer, Ph.D., R.D., nutrition and dietetics instructor in the Doisy College of Health Sciences at Saint Louis University and spokesperson for the Academy of Nutrition and Dietetics, tells SELF. Including adequate amounts of animal proteins in your diet pretty much guarantees that you won’t miss out on any of the essential amino acids.
However, this complete vs. incomplete distinction is not as big a deal as we used to think. In fact, the Academy of Nutrition and Dietetics goes so far as to call the complete vs. incomplete distinction “misleading” in its 2016 position paper on vegetarian diets.
First of all, most plant proteins are lacking in just one or two essential amino acids, Gardner points out. And because “plant-based food groups tend to be lacking in different amino acids,” Linsenmeyer says, they are often complementary—meaning that together, they form a complete amino acid profile. Kind of cute, right? For example, grains are low in lysine, while beans and nuts are low in methionine, the FDA says. But a classic PB&J on whole wheat toast gives you all nine essential amino acids—dare we say, in a jiffy.
We used to believe that it was important to consume these complementary proteins in pairs at a single meal, like a bowl of rice and beans, for instance. But science has since indicated that this is not necessary after all, according to the U.S. National Library of Medicine, and that what actually counts is your whole diet over the course of the day. “The total amount of protein consumed and the variety of sources throughout the day is much more important than the timing of those foods,” Linsenmeyer says. Therefore, it’s typically not too tricky for people who rely on plants for protein (i.e. vegans and vegetarians) to get a good supply of all the essential amino acids if they eat a reasonably diverse and balanced diet, Gardner says. (So just don’t go on an all-bean diet, or anything.)
How much protein you’re actually getting and using
So far, we’ve been comparing plant and animal protein on a pretty microscopic level, solely in terms of their amino acid profiles. But let’s pull back and look at how much protein each type of source offers, and how well it gets used by our bodies.
Animal proteins generally offer a greater concentration of protein, but not always, Beth Kitchin, Ph.D., R.D.N., assistant professor in the UAB Department of Nutrition Sciences, tells SELF. For instance, take the average serving sizes of a few different protein sources. A 100 g serving of chicken breast meat (an average portion) has 20 grams of protein; a 100 g serving of eggs (a little more than two eggs) has 13.6 grams; a 100 g serving (½ cup) of black beans has 22 grams; and a 100 g (½ cup) serving of lentils has nine grams of protein.
Something else to consider is how much of that protein actually gets used for growth by the body. “The rate of body protein synthesis appears to be lower when plant-based proteins are consumed versus animal-based proteins,” Linsenmeyer says, meaning that a lower proportion of the amino acids in plants get digested, absorbed, and utilized for things like muscle tissue-building.
This means that animal protein may have a slight edge when it comes to muscle repair and growth. “When you look at protein quality in terms of its digestibility, its ability to provide you with all the essential amino acids, and how well it’s absorbed into the muscle, we find in general that animal protein does those things a little better,” Kitchin explains. Animal proteins are also higher than plant proteins in one particular amino acid, leucine, which is thought to be key to muscle protein synthesis.
But honestly, we don’t have quite enough research yet on plant protein synthesis to know how much better animal proteins may be for muscle building and why. And the research we do have is mostly conducted using protein powders, not whole foods, and has yielded mixed results. While some studies find animal-based protein powders are better at building muscle than plant-based protein powders, others find no difference. But scientists are still investigating this complicated issue. “What kinds of proteins are going to be incorporated into the muscle most efficiently? That’s a really interesting area of research right now,” Kitchin says.
Here’s the other thing. It’s also not clear how much the rate of protein synthesis ultimately matters overall. According to the Academy of Nutrition and Dietetics, people on vegetarian and vegan diets get enough or more than enough protein when they’re eating enough calories. (So anyone still asking these people, “But WHERE do you get your protein?!” can just, um, not.) And even if animal protein is technically better-utilized than plant protein, this probably doesn’t make a big difference to the average person who exercises regularly but isn’t an athlete or strength-trainer, Kitchin points out.
Consider this paper published in the American Journal of Clinical Nutrition in 2017 analyzing data about the dietary patterns and body composition of 2,986 men and women (aged 19 to 72, all non-Hispanic white) over the course of three years. They put people in six groups based on whether they got most of their protein from one of various animal sources (fish, chicken, red meat, etc.) or plants (legumes, nuts and seeds, fruit and vegetables, and cereals and grains). They found that where people mainly got their protein made no difference in their lean muscle mass or quadriceps strength.
So if your only dietary goal, desire, or requirement is to make sure you’re hitting your protein needs as efficiently as possible, animal proteins are probably the way to go. And for someone who grew up with a diet heavy in hamburgers and chicken fingers, like so many of us here in the U.S., getting your protein from plants instead does require a conscious effort. But for someone who’s generally cool with nomming on plants, it’s no big thing.
What else you’re getting when you eat plant vs. animal protein
We’ve compared plant and animal proteins in terms of their molecular composition and protein content. But let’s zoom out again and look at the whole food packages that these proteins are actually coming in. The question is, “What else are you getting when you eat that protein?” Gardner says. And from this point-of-view, “Plant and animal sources both have pros and cons,” Linsenmeyer says.
Animal products, for instance, are the richest natural sources of some vital micronutrients. One is vitamin D, which is found in eggs, cheese, and ocean fish like salmon and tuna, per the U.S. National Library of Medicine. (Dairy milk and plant-based foods like cereal, orange juice, and soy milk are often fortified with vitamin D.) In the case of vitamin B12, animal proteins are its only natural source, according to the U.S. National Library of Medicine (although it commonly found in fortified cereals and nutritional yeast).
But wait! Plant proteins also offer their own unique advantages. Perhaps the biggest one is fiber (which is only naturally sourced from plants), Gardner says. Plant foods like beans and whole grains are a double-whammy in this sense, offering sizable hits of fiber and protein, so you can basically maximize your pecs and your poops in one go. Plants also contain a variety of phytochemicals—bioactive compounds including flavonoids, carotenoids, and polyphenols that, some studies suggest, may be linked to lower risk of chronic diseases like cancer and cardiovascular disease. (But these preventive effects are speculative, and the potential mechanisms are not understood.)
Another major difference? The rest of the stuff that typically makes up plant and animal protein sources. When it comes to carbs, all plant proteins contain some, from just a few grams in something like almonds (6 g in a standard 1 oz serving) to a higher amount in something like canned chickpeas (19 g in a standard ½ cup serving). With animal protein, meat, poultry, and fish are virtually carb-free, while dairy products contain some carbs in the form of lactose, or dairy sugars.
Then there’s fat, both the type and amount. Almost all animal proteins contain saturated fat, although the quantity varies widely, from none in fat-free dairy to lower amounts in seafood to higher amounts in lusciously fatty cuts of red meat.
Now, there’s nothing inherently good or bad about these various nutritional differences between animal and plant proteins, because we all have different dietary needs and health profiles. For instance, someone who’s trying to eat lower-carb for whatever reason (say, someone with type 2 diabetes who wants to manage their blood sugar levels) might opt for animal protein, while somebody trying to include more fiber or complex carbs in their diet may prefer plant proteins. There are plenty of reasons someone might make either choice.
Another reason someone might turn to plant protein is if they’re trying to eat a more plant-based diet in general. As SELF covered previously, there is a decent amount of research associating red meat consumption with a range of negative health outcomes. And while the research on this link has its limitations, several major medical organizations like the American Cancer Society and the American Heart Association recommend limiting red meat consumption.