126: Plant Protein vs Animal Protein - What the Science Really Says with Dr. Ben Bikman

Are plant proteins the same as animal proteins? Not exactly, and here's why it matters. Animal proteins like meat, eggs and dairy give you all the essential amino acids your body needs and you absorb them easily. That means more muscle support and better metabolic benefits per serving. Plant proteins can still work, but they're missing some amino acids and they're harder to digest. Because of that, you often need more plant protein to get the same effect. But plan also contain natural antinutrients that can compromise digestion, and plant protein powders are more likely to contain heavy metals from the soil. Bottom line, both can be part of a healthy diet. Just remember they are not one to one. If you rely on plants, aim for more total protein. This is lecture 126 of the metabolic Classroom. Looking to improve your own metabolic health? Visit insuliniq.com for courses, coaching, consultations and attend 10 day free community membership trial to dive deep into the science behind metabolic health. Become an insider@Benbickman.com where you'll enjoy my exclusive content ad, free podcasts, live stream, Q and A access and more. Welcome to the Metabolic Classroom. I'm Professor Benjamin Bickman, biomedical scientist and professor of Cell biology. Today we are addressing one of the most debated topics in nutrition, plant versus animal, and that's protein. Of course, with the rising popularity of plant based diets driven by environmental concerns or ethics or health claims, it's more important than ever to understand what the science actually tells us about these two protein sources. Now, please note that this mini lecture is not intended to address the views on ones I just mentioned, like environment and ethics, although those are very important and I would say very misunderstood today. Nevertheless, we are examining the fundamental differences between plant and animal proteins, but focusing on the biochemistry and the physiology, not those competing ideologies when it comes to the environment and ethics. As we go through the mini lecture, we're going to start with an overview of the amino acid profiles and then we'll get into digestibility and bioavailability and then also some factors that get overlooked but actually influence the ones I just mentioned, like antinutrients and even heavy metal contamination in plant proteins. By the end you'll have a clear evidence based understanding of how these protein sources differ at a level of human metabolism and what that means in turn for human health. Now, as I noted, I know this topic is very passionately debated and my mini lecture is not about ideologies, but simply the biochemistry and the physiology of what happens when we consume these very different protein sources. So let's start with the fundamentals all proteins are made of amino acids in some mix. There's 20 of them. To be precise, nine of these are essential, meaning our bodies cannot synthesize them and we must obtain them from food. The remaining 11 are non essential, not because they're unimportant, but because our bodies can manufacture them from other compounds. Now, here is where the first major distinction emerges. Animal proteins, any of them meat, fish, eggs, dairy, contain all nine essential amino acids in amounts that align well with human requirements. Because of this, they're commonly called complete proteins. Plant proteins, on the other hand, are often incomplete. In fact, very often, most plant sources are deficient in at least one. Often more of these essential amino acids, particularly this is us going to be lysine and methionine. Take legumes as an example. While beans and lentils certainly do provide some decent protein content, they're typically very low in methionine. Conversely, grains tend to be low in lysine. But there's one amino acid among all of them that deserves special attention, and that is leucine. Leucine is the primary signal for muscle protein synthesis, the process by which our bodies build and maintain muscle tissue. It activates a critical pathway called mtor, which essentially tells muscle cells to start building new proteins. Animal proteins are notably rich in leucine. A serving of whey protein might contain around 3 grams of leucine, whereas the same amount of protein from the best plant source, namely soy, might provide half of that. This difference in leucine content has real consequences. Research consistently shows that when adults, especially older adults, consume plant proteins compared to animal proteins at equivalent doses, the muscle protein synthesis response is lower with plant sources. When scientists fortify plant proteins with additional leucine to match the leucine content of whey protein, however, the muscle building response becomes equivalent. And this tells us something important. It's not that plant proteins can't support muscle synthesis. They can, but they need to be consumed in higher amounts and ideally with attention to their amino acid profiles. But as you'll see in a moment, there are consequences to eating more plant protein that are not good. Nevertheless, for most people eating a varied diet, combining different plant proteins throughout the day, say from beans with rice, can provide a complete amino acid profile. But this requires knowledge and planning. That isn't necessary with animal protein, which deliver complete profiles in a single and much smaller serving. Now, moving on. Even if a protein source contains adequate amino acids on paper, that what matters ultimately is how much of those amino acids actually make it into your bloodstream and tissues this is where digestibility and bioavailability come into play. And here we see another significant divergence between plant and animal proteins. Digestibility refers to how well the protein is broken down in the gastrointestinal tract. Animal proteins have digestibility scores around the mid or even high 90 percents. Plant proteins, by contrast, typically range from 70 to 80. This means if you eat 100 grams of plant protein with 75% digestibility, you're effectively getting only 75 grams worth of amino acids into circulation. With animal protein at, say, 93% digestibility, that same 100 grams yields 93 grams of bioavailable amino acids. The scientific community has developed scoring systems to account for these differences. The older system called Protein Digestibility Corrected Amino Acid score, or PDCAAs, has largely been replaced by a more sophisticated measure called DIAAs, or digestible indispensable Amino Acid Score. The DIAAS measures the digestibility of individual amino acids at the end of the small intestine, giving us a more accurate picture of what's actually absorbed. When we look at DIAAS scores, animal proteins consistently rank as high quality, in fact typically scoring well above 100. Plant proteins do have a much higher degree of variability. Soy protein isolate, perhaps the best of the plant proteins, scores around in the 90s, approaching animal protein quality. But remember, the score actually goes above 100. This is why I somewhat resent this scoring system. But even still other animal other plant proteins fall short. For example, wheat protein scores around 40, and several legume proteins are in the 70s. Recent human studies using stable isotope tracers have directly measured amino acid appearance in the blood after consuming equivalent portions of animal versus plant proteins. In one particularly well designed crossover trial, young and older adults consumed 2 ounce equivalents of either pork eggs, black beans or almonds. The results were striking. Both pork and eggs resulted in significantly higher circulating essential amino acid levels compared to black beans, which in turn were higher than the almonds. For the plant sources to achieve similar amino acid availability, subjects would need to consume considerably larger portions. Part of this digestibility difference comes down to structure. Plant proteins are embedded in cell walls made of cellulose and other fibers that our digestive enzymes cannot fully break down even with cooking, which helps. Some of the protein remains trapped within these structures, passing through the digestive system without being absorbed. Animal proteins lacking cell walls are more accessible to our digestive enzymes from the start. There's also a phenomenon called splanchnic extraction, essentially the liver and intestines taking their cut of amino acids before those amino acids make it to the general circulation in muscle tissue Studies using tracer techniques show that plant proteins undergo greater splanchnic extraction than animal proteins. More of the amino acids from plant proteins are diverted to the liver and intestines, where they're often oxidized for energy or or used for urea synthesis or simply extracted rather than being delivered to the muscle for muscle protein synthesis. Now, I've been touching on this, but this is a topic that's often downplayed in discussions about plant proteins, namely antinutrients. These are naturally occurring compounds in plant foods that interfere with nutrient absorption or digestion. They're not overtly or immediately harmful in the way a toxin might be, but they do reduce the nutritional value of plant proteins, sometimes significantly. But to be clear, some of these have been implicated in exacerbating autoimmune disorders. More on that in a moment. Now, let's start with just as let's just discuss some examples and starting with protease inhibitors, particularly trypsin inhibitors. Trypsin inhibitors are relevant here because trypsin is one of the key enzymes your pancreas secretes to digest protein. Trypsin inhibitors, abundant in legumes like soybeans, kidney beans and chickpeas, bind to and inactivate trypsin. The result? Reduced protein digestion. Studies in both animals and humans show that high levels of trypsin inhibitors can reduce protein digestibility by up to 50%. Even the normally encountered levels in cooked legumes can reduce digestibility by 10%. These inhibitors also have downstream effects. When trypsin is inhibited, the pancreas responds by secreting more trypsin, which over time can lead to a pancreatic hyperplasia, an enlargement of the pancreas. In animal studies, chronic exposure to high levels of trypsin inhibitors has been associated with pancreatic stress and in some cases, increased pancreatic cancer rates. In humans eating typical amounts of legumes, this isn't a major concern, but it does illustrate that these compounds have real biological effects. Then there's phytic acid, or phytate, found in high concentrations in grains, legumes, nuts and seeds. Phytate is a powerful mineral binder. It chelates, meaning it grabs onto minerals like iron, zinc, calcium and magnesium, forming insoluble complexes that pass through the digestive tract. Unabsorbed for populations heavily reliant on grains and legumes, phytate induced mineral deficiencies are a documented problem, particularly iron and zinc deficiency. Phytate also directly inhibits the digestive enzyme pepsin this is in the stomach and several enzymes in the intestines, further reducing protein digestibility. Research indicates that typical phytate levels in plant based diets can reduce protein and amino acid digestibility by about 10%. Lectins represent another class of antinutrients. These are carbohydrate binding proteins that can resist digestion passing through the gut intact. Some lectins, particularly phytohemaglutinin in raw or undercooked kidney beans, can cause severe GI distress, nausea, vomiting, diarrhea, even in properly cooked legumes. Residual lectins can bind to the cells lining intestines, potentially increasing intestinal permeability and inter nutrient absorption. One additional remarkable aspect of lectins that I simply had to include here is their ability to bind to and activate the insulin receptor. This means that if someone's consuming high levels of lectins, those high levels of lectins can be artificially stimulating the insulin receptors, potentially driving insulin resistance. Before moving on, let's come back to the role of antinutrients in autoimmune disorders. One of the more common reasons people adopt plant free or carnivore diets is to in fact help control autoimmune disorders. Indeed, a 2021 study surveyed over 2,000 adults following a carnivore diet, an all animal product diet. The Researchers found that 56% of participants cited autoimmune disorders, allergies or skin conditions as their primary reason for adopting this dietary approach. Of those with autoimmune conditions, about 90% reported improvement or complete resolution of their symptoms. While this was a survey study, not a controlled trial, the sheer number of people seeking relief from autoimmune diseases by eliminating plant proteins speaks to the clinical reality of many individuals experience. Now how can this be? The mechanism is multifaceted, involving both intestinal barrier disruption and a phenomenon called molecular mimicry. Let's just review each of these briefly. Let's start with intestinal permeability or leaky gut. Lectins in particular can bind to and damage the walls lining the intestine. This can disrupt what's called tight junctions or the cell's ability to be adhered to one another to prevent things from slipping through. When these barriers or the tight junctions break down, lectins not only themselves are able to pass through, but anything else is able to as well. And then once in circulation, these molecules can promote systemic inflammation and stimulate the immune system to such a degree that it begins to forget what it's attacking from the perspective of a foreign molecule. And then Begin attacking itself. But there's a second mechanism here, equally important Molecular mimicry. Some of these antinutrients, once again, like lectins, share amino acid sequences that are similar to human proteins. When the immune system produces antibodies against lectins that have crossed into the bloodstream, those same antibodies can mistakenly target the body's own structurally similar proteins. Research has documented this cross reactivity extensively. In one comprehensive study, antibodies against wheat germ agglutinin, that's the lectin in wheat, reacted with 37 different human tissue types. Antibodies against red kidney bean lectin reacted with 20 tissues, and soybean agglutinin with another 20. These are not trivial reactions. These represent real immune cross reactivity between food proteins, plant proteins specifically, and human tissue. Now, with all of this in mind, naturally, we want to have ways to reduce the presence of these antinutrients. And of all the methods humans have developed to reduce anti nutrients, fermentation stands out as particularly effective. This ancient food preservation technique employs beneficial bacteria and yeasts that produce enzymes capable of breaking down antinutrients. The microbial enzymes produced during fermentation, particularly phytase, systemically degrade phytic acid. Studies show that fermenting legumes and grains can reduce phytate content by up to 80%, far more than soaking or cooking alone. Fermentation also substantially decreases lectins and tannins and reduces trypsin inhibitor activity. The result is dramatically improved protein digestibility and mineral bioavailability. In some fermented soy products, like tempeh, the protein digestibility approaches that of animal proteins. Beyond fermentation, other preparation methods can help reduce antinutrients, though generally less effectively. Soaking legumes for 12 hours can reduce phytate by up to 9% in peas and more in some other legumes. Pressure cooking and boiling can also help reducing lectins and trypsin inhibitors. But even with these methods, antinutrients are rarely eliminated completely, and they continue to exert some effect on protein and mineral bioavailability. Animal proteins, for the most part, contain none of these compounds. There are no protease inhibitors in beef, no phytates in eggs, no lectins in fish. The protein in animal foods is presented to our digestive systems without these interfering substances. Here's something as we move on that doesn't get enough attention in the plant versus animal protein debate, Although I've alluded to it, which is heavy metal contamination. This has recently been making some of the headlines again, but it might surprise you to learn that plant proteins, particularly the concentrated plant protein powders, can contain significantly higher levels of heavy metals than their animal based counterparts. Why? It comes down to how plants interact with soil. Certain crop plants are particularly efficient at absorbing heavy metals like lead, cadmium, arsenic and mercury. These are absorbed from the soil and then concentrated in the parts we eat. This is particularly true when these plants are processed into protein concentrates or they're concentrated to con to get the protein powder. When you concentrate the proteins in order to get all of those amino acids, you inadvertently also concentrate the heavy metals with them. Animal sources, of course, typically show much lower heavy metal contamination than their plant sourced equivalents. The animals themselves consume feed that might contain heavy metals, but their digestive systems and organs filter out much of it. What ends up in the muscle tissue, which is the main part of the animals we eat, is typically low to the point of undetectable. To be clear, the levels found in most plant proteins are not immediately dangerous. You're not going to eat a bowl of lentils or even take a single scoop of plant based protein powder and then suffer from acute lead poisoning. But we are thinking about chronic, long term and cumulative exposure. Heavy metals do accumulate in the body over time. So for people consuming plant protein powders daily, or relying heavily on legumes and grains as their protein sources, this cumulative exposure may add up. So where does all this leave us? What are the practical takeaways for someone trying to make informed decisions about proteins? First, let's acknowledge that plant proteins can support human health and muscle maintenance. But and this is important, they are not nutritionally equivalent to animal proteins gram for gram. And to say that more succinctly, they are inferior. If you're relying primarily on plant proteins, you need to consume more total protein to achieve the same effect. The same muscle protein synthesis response, for example, as you would from animal proteins. This is due to the lower digestibility, lower leucine content, and again, the presence of antinutrients. And remember, the more plant protein you eat, the more unwelcome guests like those antinutrients and heavy metals, you're getting along with it. The antinutrients and heavy metal considerations also matter more for certain populations. Pregnant women, young children and individuals with marginal nutrient status are more vulnerable to the mineral binding effects of phytates and to heavy metal exposure. For these groups, ensuring adequate intake of highly bioavailable protein and minerals from animal sources, I would submit is particularly important. Also for older adults, the differences are more relevant. Aging is associated with anabolic resistance, something I have addressed previously, the muscles become less responsive to the signal from protein and amino acids. Older individuals, to put it bluntly, need more protein and specifically more leucine to stimulate muscle protein synthesis at the same rate as their younger individuals or younger selves. Several studies have shown that older adults consuming plant proteins show blunted muscle protein synthesis responses compared to animal proteins at equivalent doses. Now, none of this means plant proteins need to be avoided. Legumes, nuts, seeds and whole grains may offer compounds that are considered healthy like fiber or polyphenols or various vitamins and minerals. For most people, a diet that includes both plant and animal proteins is fine, but if you choose to rely exclusively on your to get your proteins from plant sources, you need very careful planning. If you're using plant protein powders, the data on heavy metals suggests that whey and other animal based protein powders are safe, safer and much more effective choices. If you do prefer plant based powders, not only look for third party testing that includes heavy metal content, but also avoid the I would try to avoid taking them daily, frankly. And then in conclusion, when it comes to protein, there is a clear winner in every metric. Animal sourced protein outperforms all plant source proteins. Unfortunately, various ideologies tend to muddy what should be a very Conclusion I hope you have found this information helpful and that you're able to make prudent and healthy decisions accordingly. Class dismissed. Until next time. More Knowledge Better Health Looking to improve your own metabolic health? Visit insuliniq.com for courses, coaching, consultations and a 10 day free community membership trial to dive deep into the science behind metabolic health. Become an insider@Benbickman.com, where you'll enjoy my exclusive content ad, free podcasts, livestream, Q and A access and more.