When many people think of protein-rich foods, they typically think of meat. Many people also think that if they only ate plants, they would become weak or protein deficient. So, if you are considering eating a more plant-based diet, you might be worried about getting enough protein. Do plants have any protein? In fact, most of the amino acids in the animal products we consume originally came from plants. Most of the protein that the world consumes comes directly from plants, however, plants are a more diluted source of protein than animal foods.1 So eating animal products does make it a bit easier for us to get more protein. However, if we decide we want to cut down on animal products for animal welfare, environmental, or health reasons, can we still get enough? Whether you’re an an athlete, someone who wants to build muscle, an older individual or anyone in between, in this post I will discuss how to get enough protein with a plant-based diet.
What is protein?
Protein is an important macronutrient. Proteins have many roles in the body. For example, they form tissues such as skin, muscle, and bone, they can be metabolised for energy, they can becomes enzymes that accelerate chemical reactions in the body, they form some hormones, and they transport other nutrients.2 Proteins are comprised of amino acid building blocks. There are twenty common amino acids. Out of these twenty amino acids, our bodies cannot directly synthesise nine of them, so we have to consume them directly via our diets.3 These nine are referred to as essential amino acids. When we eat a protein containing meal, our body releases enzymes that break down the proteins into smaller peptides and amino acids. Our small intestine can then absorb these peptides and amino acids.4
Do plants have enough protein?
Before we can answer this question, we must first define human protein requirements. Adults should consume at least 0.83 g of protein per kilogram of body weight per day.5 At this dose, the protein consumed matches the amount of nitrogen leaving our bodies via urine, which is enough to prevent deficiency. A 60 kg adult should then consume at least 48 g of protein per day. If a person is consuming a plant-based diet, they should consume about 10-20% more than this to account for the incomplete absorption of plant-based proteins, but more on this later. So in that case, eating about 58 g of protein per day would be sufficient. We can easily achieve this dose by eating plants. There is also no need to eat a tonne of calories in order to achieve this protein target. For example, tofu, seitan, tempeh, edamame, soy milk, lentils, chickpeas, meat alternatives, fungi, and other legume-based foods, are high in protein. Whole grains generally have more protein than refined grains. We can also now buy a variety of blended plant based protein powders supplements. For example, soy, pea, and brown rice protein powder supplements are common.
Depending on age and sex, children require between 0.84-1.31 g of protein per kilogram of body weight per day. Pregnant women should eat 1-31 g of extra protein per day depending on their stage of pregnancy. Breastfeeding women should also consume 13-19 g of extra protein per day.5 If children do not consume enough protein, their growth may be limited.5 However, this is typically only an issue in developing regions where access to sufficient food or a wide variety of food is limited. In contrast, in the developed world where we have access to a sufficient quantity of food and wide variety of food, this is generally not a concern. If a child eats enough calories for growth, then they are generally consuming enough protein at the same time.6
So, if you eat a plant-based diet, should you count how much protein you eat? It is good to develop a sense about how much protein we are eating. However, if you eat a few servings of the protein rich plant foods mentioned above every day and eat a variety of plants, you can easily consume enough protein without counting. When starting a new diet, it can be useful to count the amount of protein you consume for few weeks, to develop an intuitive sense for the protein content of different foods. However, if you don’t have a specific workout-related goal, there is no need to count every day.
Importantly, these dietary recommendations are the minimum amount we should eat. Depending on a person’s age and health goals, they may need more protein than this. I will explain these more specific circumstances in more detail in later sections.
Do plant proteins have all of the amino acids?
Even if we can eat enough total protein from plants, can we get all the necessary amino acids at the same time? Plants have all twenty amino acids, including the essential ones. However, depending on the plant, the amino acids are present in varying concentrations. For example, in general, grains do not contain high concentrations of the amino acid lysine, but they do contain higher concentrations of the amino acid methionine. On the other hand, in general, legumes do not have as much methionine, but they do contain more lysine. So, if you eat a variety of grains and legumes together, you can get all of these amino acids. Even if we don’t eat grains and legumes together at the exact same time, but at different meals every day, it will still have the same effect. Overall, if we eat enough plant protein, and if we eat a variety of plants, we will easily intake enough of the essential amino acids.7
Can humans digest and absorb plant proteins very well?
The quality of a protein is usually measured by considering two factors. This includes the concentration of each amino acid within a protein and the digestibility of the protein. The Protein Digestibility Corrected Amino Acid Score (PDCAAS) attempts to quantify the quality of proteins. To measure the PDCAAS, researchers feed a food to rats and the amount of protein in that food is compared to the protein in the rat’s faeces. The difference between these measures is considered to be the amount of absorbed protein. However, this score has some shortcomings. For example, the bacteria and other microorganisms within the colon, also known as the microbiome, also digest proteins. Therefore, the amount of protein in the faeces may not be representative of the actual protein digested by us.8
So, in order to solve these problems, researchers developed the Digestible Indispensable Amino Acid Score (DIAAS). This score measures the amount of protein digested at the end of a pig’s small intestine, known as the ileum.9 Surgery must first be performed on pigs in order to measure this.10 In general, this score shows that animal proteins are more completely and better absorbed than plant proteins.9
DIAAS is better than the PDCAAS, but it is still often interpreted and used incorrectly. For example, in general, this score is not measured in humans. The digestive systems of pigs and humans are more similar compared to mice, but they are still different. Additionally, published DIAAS scores are generally for raw foods. The DIAAS of raw plants is significantly lower than animal foods. This is because plants contain fibre and other nutrients that lower the absorption of protein.11 However, in general, we cook grains and legumes before we eat them, hence a lot more protein can be absorbed. When researchers fed cooked tofu, soy milk, peas, or seitan (wheat gluten) to pigs, 92-97 % of amino acids were absorbed and hence a high DIAAS score was observed.10 Moreover, it is not useful to focus on a single plant’s DIAAS score. In general, we eat several foods in one meal, so the total of DIASS score of our daily meals is much more important. Overall, if we eat enough plant-based protein, or if we eat protein from a variety of plants, we can overcome the problems associated with the slightly lower quality of plant-based protein.12
If you live in a food desert, if you are in a low socioeconomic status, if you do not have access to a variety of foods, or if your appetite reduces as you age, protein quality becomes a more important consideration. However, it is rare for vegans and vegetarians living in developed countries to develop protein deficiencies.6 If you do not eat enough calories, consume only foods within one category of plants, or do not eat legumes or nuts, you can develop a protein deficiency, but this situation is not common.
Can you build muscle on a plant-based diet?
Athletes, people who exercise, and people who want to build muscle should eat more protein than the minimum recommendations. Vegans have a stereotype of being weak and scrawny. However, there are vegan body builders out there. The person in the photo below has never eaten meat in their life. So how did they build muscle? Did they just take a lot of steroids? Well actually no. It is possible to build muscle by eating only plants and doing resistance exercise.
So, how much protein is enough to build muscle? A meta-analysis of randomised controlled trials found that people doing resistance training who ate more than 1.6 g of protein per kilogram of body weight per day did not gain any extra benefit.13 If we consider the quality of plant based protein, eating 1.7-1.8 g of protein per kg would be equivalent. Importantly, if we eat below this threshold and above the 0.8 g threshold, we can still build muscle, but we just won’t maximize our muscle gain. For example, if we eat 1.2 g per kilogram per day we can still achieve good muscle gain. Most people in developed countries already consume this dose via their everyday diet without trying.
So, what are the actual results in people who eat plant-based protein? Several randomised controlled trials and clinical trials compared vegan to non-vegan diets14, a vegan diet high in mycoprotein (fungi) to an omnivorous diet15, brown rice protein to whey protein16,17, soy protein to whey protein18, a vegan diet with soy protein supplementation to an omnivorous diet with whey protein supplementation19, and pea protein to whey protein.20,21 In these studies, people who ate plant-based protein gained muscle and strength to a similar degree, if they followed the same resistance training program and ate the same amount of protein. Longer trials will be needed to find if people can maintain this result in the long term. However, comparing plant and animal proteins over a 12 weeks period (as done in most of these studies) should be sufficient. Humans do not build muscle continuously forever, but we do build the largest amount of muscle during the initial period. So, there is little reason to expect that if a person continues to eat that amount of plant based protein, that it will make a big difference in the long term. After protein is broken down and the amino acids are absorbed, our muscles do not know if they came from an animal or a plant. Amino acids are just amino acids. Overall, whether we are vegan or non-vegan, if we eat around 1.6 g of protein per kilogram of body weight per day, we will gain approximately the same amount of muscle and strength. This is the only important result for us, because it focusses on overall outcomes rather than mechanisms.
What about leucine?
Leucine is an amino acid that stimulates muscle growth. So, can we get enough leucine on a plant-based diet? Seitan, legumes, and some seeds are high in leucine.22 There is also plant based protein powders with sufficient doses of leucine. Similar to the discussion about protein intake, whether we are a vegan or non-vegan, eating the same amount of leucine can help you gain the same amount of muscle and strength.23 Eating around 2-3 g of leucine per meal is enough.17 As long as we already eat around the 1.6 g per kilogram per day threshold, taking leucine supplements doesn’t provide any extra benefit.24
Do you need to build big muscles?
The 1.6 g per kilogram per day threshold is the amount of protein you should eat to maximise muscle growth. As previously mentioned, even if we eat less than this, we can still build muscle, but it will just not be maximised. Is this a problem? Not really. You don’t need to have big muscles to be healthy. However, it is healthy to build some muscle through resistance training and eating an intermediate amount of protein. Stimulating your muscles with resistance training is the most important thing. For example, moderate weight lifting or body weight exercises.
Caring about our appearance and muscles is not fundamentally a bad thing in and of itself. However, it is important to reflect on why we care about our appearance. Social media allows us to more easily compare our bodies to others and we may feel a need to conform to a certain standard.
Furthermore, are we justified in exploiting and killing animals for protein in order to achieve superficial goals? Even if researchers later discover that there is some significant benefit to building muscle by eating animal protein, is that benefit more important than the damage caused in order to produce that protein? If we can achieve a healthy amount of muscle with a plant-based diet, is it justifiable to try and achieve more than that by consuming animal protein? Caring about the optimal amount of protein is a privilege, not a necessity.
We can achieve large muscle gains through a plant-based diet, but we need to be aware of some of the information mentioned earlier. If you find it difficult to achieve your high protein goals through food alone, don’t want to eat a lot of tofu or legumes , or don’t want to eat a large volume of food, you may want to include more protein supplement. In general, we can pretty much always achieve our goals without exploiting animals. Another consideration is that the more muscle we build, the more calories and protein we need. Therefore, our individual effect on the environment is greater. However, if we eat plant based protein, this effect is less serious.
Do we need more protein as we age?
Sarcopenia is the gradual decline in muscle mass as we age. The more a person suffers from sarcopenia, the more likely they are to fall, their quality of life decreases, and their ability to perform daily tasks decreases. Even if sarcopenia is inevitable, the more protein you eat as you age, the slower this process may be. Our appetites tend to reduce as we age, so it is important to eat protein-dense foods.25 It is also important to eat more leucine as we age.26 Additionally, older individuals generally digest and absorb protein less effectively.27 So, in the case of older individuals, targeting a minimum of 1.2 g per kilogram of body weight per day may be more appropriate. It is possible to achieve this goal with a plant-based diet. For example, you can also eat more legumes or plant-based protein supplements. Exercise is also really important to hold off sarcopenia.28 Eating protein alone won’t be very effective without the associated resistance exercise.
One epidemiological study showed that for people aged 65 years old or above, eating more protein led to decreased mortality. However, for people aged 65 years old or younger, eating more protein led to increased mortality. If the younger participants ate plant-based protein instead of animal protein, this effect was less severe.29 So, young people do not need to eat a high dose of protein for longevity, but if they do want to eat more protein, eating plant-based sources seems to be a better approach. However, this is only one study. Further research will be needed to draw stronger conclusions. In a future post, I will discuss the relationship between food and all cause mortality further.
Some argue that because falling is a major cause of death, older people need to eat more animal protein to improve longevity. However, this recommendation is based on misinformation. Among people over 65 in the United States, accidental deaths account for 2.9% of deaths. Out of this 2.9%, unintentional falls represent the largest cause. However, the more significant causes of death overall are heart disease, cancer, and Alzheimer’s disease.30 In future posts, I will discuss the relationship between animal foods and these chronic diseases. If a person eats more animal products to prevent falling, they may increase their chances of developing other, more common chronic diseases. So, the overall effect would likely be an increase the probability of death. A strategy to reduce the chances of developing chronic diseases and falling simultaneously is to eat more plant-based protein.
Conclusion
If we eat a plant-centered diet, will we inevitably become weak? Not necessarily. There are many plant foods that are high in protein. Overall, even though the quality of animal protein is a little better than plant protein, that does not matter in a lot of cases. If we don’t eat animal products and eat a variety of plants, we can still easily eat and absorb enough essential amino acids (0.8 g of protein per kg per day). Additionally, if we eat enough plant-based protein (1.6 g of protein per kg per day), we can still build the same muscle and strength as those eating animal protein. We do not need to build big muscles to be healthy, but it is healthy to do regular resistance training and eat an intermediate dose of protein. Older people especially need to focus more on protein and resistance exercise.
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