The truth about high-protein diets- It can actually worsen your health.
The Hidden Dangers of Too Much Protein
While protein is essential, consuming too much—especially from animal sources (such as meat and dairy- milk, eggs, cheese, yogurt, ice cream, etc)—can damage your health. And it's not just due to saturated fat and cholesterol, this includes lean sources as well. Animal proteins are particularly concerning due to their high levels of certain amino acids like methionine and leucine, which are linked to chronic diseases. If a majority of our protein comes from animal sources, then we get an excess of those two amino acids, more than the body actually needs, and that leads to health consequences. Plant protein has much less methionine and leucine compared to animal- but just because it has less, doesn't mean that it's insufficient for the body, and it was due to that very assumption in the 1950's that spread the false belief that animal protein is necessary to eat on a regular basis for optimal health, on the assumption that "more is better", for amino acids. Thus the false idea came up that just because animal protein has more of something compared to plant protein, that that must be the optimal amount.
Many people today assume that plants don't even have enough protein to be sufficient but that's actually not true. Most people eat 2-3 times their daily need for protein and don't even know it. Thankfully, there have been plenty of scientific studies since then, that prove the optimum amount of those amino acids and the damages that come when consumed in excess. Human evolution adapted to needing less of those two amino acids because finding meat was difficult for the first 99% of human evolution, and dairy is also new to evolution. Eating meat and dairy on a daily is new to human evolution- and the human body has yet to adapt to the excess of the two amino acids that animal protein brings- this includes milk, eggs, cheese, yogurt, etc.
But it's not just meat and dairy: even plant-based protein powders, when consumed in excess, can cause serious issues. If your body only needs, for example, 50 grams of protein per day, but you already consumed 40 grams of animal protein in a day but then still add an additional 60 or more grams of plant-based protein per day (such as protein powders/shakes), it can still add up to being an excess of certain amino acids that the body actually needs. This section explores the specific risks of animal protein first, and then broadens the focus to the dangers of overdoing any type of protein.
So why isn't the government warning us about the dangers of too much protein, and especially animal? Why do they allow food manufacturers to sell protein shakes/bars that have 40 grams in one single item? Because their interests are more focused on protecting meat and dairy farmers, jobs at those places, and the economy. Plus they fear that most people will just come back with backlash- "stop telling me what to eat", for those who don't care about health and just want to eat what they want. However, I still don't believe that is a legitimate excuse to keep people in the dark. These facts should be taught in schools, and warnings should be put on food labels with a link to a webpage that explains the dangers.
Everyone should have the chance to know the facts, and then decide from there whether they want to be influenced by those facts. Meat and dairy has been a part of American culture and traditions for far too long that most people don't want to change their diet let alone hear about the dangers of it, even at the face of proof that it increases cancer, heart disease, inflammation, and all kinds of illnesses. The government simply leaves uncovering these scientifically-proven facts up to us- we are in charge of researching these studies. But not everyone has time to dig through every new scientific study on food. Plus, most people have no idea how to eat and cook plant-based foods because they grew up centering meals around meat and dairy. Hence why, we decided to spread this very important news.
Methionine and Homocysteine Levels
Animal products are rich in methionine, which, in high amounts, can raise homocysteine—a compound associated with increased cardiovascular risk. One study found that every 5 µmol/L increase in homocysteine raises heart disease risk by about 20%. (PMC4326479, scielo.br). Evolutionary history has proven that humans only ate animal protein less than 1 or 2 times per month, because of the difficulties in obtaining it, and instead relied on plants and bugs a majority of the time. So "too much" methionine in this case, is eating animal protein every single day, especially multiple times per day. Protein products high in carnitine, which comes from animal protein, have a lot of methionine.
Rather than summarize a recent breakthrough on protein and atherosclerosis risk, I'll just give you the article that explains the dangers of leucine here, for heart health.
Leucine and Insulin Sensitivity
Leucine, another amino acid found abundantly in animal protein, can not only cause atherosclerosis and arterial plaque (as mentioned above with the link to the study-backed article), but can also interfere with insulin signaling and glucose metabolism. Although it's sometimes marketed as helpful for muscle growth, excess leucine may lead to metabolic imbalance. (sciencedirect.com, frontiersin.org). This is one of the several different factors behind why people who eat more meat have more diabetes.
Soy protein is also very high in Leucine, and pea or legume protein is moderately high in Leucine, so it's not just milk-derived or carnitine products (protein powders and bars, for example). But as long as you don't consume more than the grams of daily protein your body needs based on your Basil Metabolic Rate (BMR), then soy and pea and legume protein is perfectly healthy- it's the milk-based or carnitine products that should be limited (no more than a quarter of your day's protein needs should come from animal sources to not get too much methionine and leucine). You can figure out your daily protein needs by multiplying between 0.36 and 0.45 grams per pound of body weight (based on activity level- if you are trying to build muscle and work out daily, stick to the upper end of 0.45). Any more protein than that will cause health problems.
IGF-1 and Cancer Risk
Animal protein consumption is closely linked to higher levels of IGF-1, a hormone that promotes cell growth—and when elevated, may accelerate aging and increase cancer risk. A major study found that adults aged 50-65 who ate high levels of animal protein had a 9% higher cancer mortality risk per 10 ng/mL increase in IGF-1. (PMC3988204) Animal protein also reduces protective IGF-binding proteins. (pubmed.ncbi.nlm.nih.gov)
Too Much Protein—Even From "Clean" Sources
Even when protein comes from "clean" protein sources such as protein powders or “clean” plant-based sources like soy or pea protein isolate, or farm-raised organic and lean meat, consuming too much is still harmful. Just as with animal protein, large amounts of isolated plant protein (eating more than your body actually needs) can strain the kidneys, exacberate any current kidney issues, contributes to dehydration, disrupts hormonal balance, may increase the risk of kidney stones and bone loss, and crowd out other essential nutrients from your diet. Powdered proteins are highly concentrated and easy to overconsume— making it easy to exceed healthy limits without realizing it. Your body only needs a moderate amount of protein to maintain health; the excess is either excreted or turned into fat, creating waste and metabolic stress.
High-protein diets often displace carbs and fiber-rich plant foods, which are essential for gut health, energy, and metabolic function. Without enough fiber, your "gut bugs" will starve off and then you'll have none to help keep your immunity as high as it should be, which is yet another reason for the increase in sickness in Western economies where plant foods are not prioritized in the diet. Gut bugs help create chemicals responsible for metabolic health. Your good gut bacteria does all kinds of magic to keep you healthy, and if you don't take care of them, they can't take care of you. Think about how you're not just feeding your stomach, you're also feeding the good bacteria (or bad/harmful gut bacteria with added sugar), depending on what you eat. Protein doesn't feed them. Processed fiber pills don't do them justice. It's the WHOLE PLANTS that keep them alive and flourishing. And they can't just eat one or two plants a day, they need more than that otherwise they will die off from starvation. Pure, natural, whole foods that humans have been eating for millenia: Apples, mandarins, berries, brocoli, kale, green peas, carrots, celery, edemane, whole (not flourized) grains, beans and lentils, and some nuts and seeds, are all high in fiber. This is a responsibility that's literally in your own hands, and yet most people don't think twice about what they eat. You can read more about this here, this diet change will increase your energy and elevate your mood as well.
The Benefits of Whole Plant-Based Protein
Instead of isolates and powders, the healthiest protein sources are whole plant foods like beans, lentils, whole grains, peas, and soy/edamame or tofu. These foods provide fiber, phytonutrients, antioxidants and anti-inflammatory compounds that support long-term health—unlike concentrated protein products. Plant-based diets have been shown to reduce inflammation, support kidney function, support healthier aging, and protect against chronic diseases.(PMC8621419, healthcare.utah.edu). Inflammation has been scientically proven time and time again to be the sole factor behind disease. And since antioxidants and anti-inflammatories are only found in whole plants and not isolated plant protein powders or animal protein, it's better to eat a bowl of natural whole grain cereal (the link is for a cereal made with 7 whole grains and 8 grams of protein in only a half cup), with organic soymilk that doesn't have added sugar and also provides calcium (adding yet another 8 grams of protein), a peanut butter and jelly sandwich on whole grain bread (not enriched bread, this one is one of the best), or beans/lentils to get your protein, than it is to consume a protein shake.
Bottom line: your body needs protein—but more is not better. Animal protein carries the highest risk, but even excess plant protein, especially from powders, can backfire. Focusing on whole, plant-based protein sources and avoiding excessive intake, especially from animal products and supplements, is key to protecting your long-term health.
If you are interested in learning how to cook delicious plant-based meals, check out this wonderful cook book by Dr. Michael Greger here. You can choose either the physical copy or the E-book download.