If you’ve ever wondered whether plants can really “measure up” when it comes to protein, you’re not alone. You might be wondering whether you can get enough protein from plants, whether the plant protein you’re consuming is ‘complete’ enough, or if it’s even good for you to rely solely on plants at all.
The truth? Plants are more powerful than they get credit for. In this post, we unpack the science behind plant protein: how it supports your health, your muscles, and even the planet. Plus, why making the switch might be easier (and more impactful) than you think.
Protein is one of our macronutrients, along with carbohydrates and fats. You probably already know that protein is required for building and maintaining muscle, but it is also critical for your immune function (which is responsible for fighting illness and regulating inflammation), the production of hormones such as insulin, oestrogen and cortisol, the creation of neurotransmitters that are crucial for memory and movement, and for repairing your cells following damage.
But when it comes to plant-based or vegan diets in particular, concerns are regularly raised about protein quality, completeness, and timing. Could vegans be at risk?
Let’s kick off by addressing a very common question straight on…
Amino acids are the building blocks of protein and there are 20 different ones available. You can think of these as the individual beads of a beaded necklace, with 20 different colours. Out of these 20, 9 are known as ‘essential amino acids’, termed ‘essential’ because our bodies cannot make them and so we must get them from food.
You might have heard animal proteins being referred to as “complete,” as well as the accompanying explanation that this is because they contain all 9 essential amino acids.. That makes sense, since animal flesh is made of pretty much the same stuff as our own flesh, so it generally matches our requirements.
This is where the myth about plant protein comes in. Many people believe that plant proteins are “incomplete” or missing one or more of our 9 essential amino acids. In reality, all plants contain all amino acids, including the 9 essential ones (1). Let’s say that again more clearly: all plants contain all essential amino acids. The only difference is the proportions they come in. The “incomplete” concern comes from historical research, before we understood how the body pools amino acids from different foods eaten across the day.
“All plant proteins contain all 9 essential amino acids.”
Figure 1. below illustrates the amino acid content of a range of plant and animal foods, with essential amino acids outlined, demonstrating the adequacy of consuming a variety of plant proteins (1).
An easy way to understand how the body uses amino acids from food is to think of foods as scrabble bags, with the letters inside being our individual amino acids. These letters build different words and sentences, just like amino acids build different proteins that adopt different roles and functions in our body. Animal-based foods are bags that have all the letters we need in roughly the right proportions for the English language, with proportionally more ‘A’ and ‘S’ tiles and fewer ‘Z’ and ‘X’ tiles.
Plant-based bags, just like different plant foods, are all varied in their content. One bag might have fewer ‘A’ tiles, but another might have more. And here’s the other important thing: we don’t just eat one food or have just one Scrabble bag. In reality, we’re eating a mix of plant foods every day, which means we have a whole collection of Scrabble bags! When you combine these different bags, we can find all the letters we need to build full words and sentences. Plus, if we did stick to eating just one food, we would be missing out on a whole lot more than just amino acids.
Some plant proteins, like soy, quinoa, buckwheat and hemp, have amino acid profiles similar to animal proteins. However, grains tend to be lower in lysine (the first blue in figure 1), while legumes tend to be lower in methionine (the pink in figure 1), but if you eat them both in your daily diet, they combine beautifully to provide everything we need (1). In fact, many traditional dishes appear to have this nutritional wisdom woven in, for example with dishes such as rice and peas, black beans and corn tortilla or dahl with rice.
As long as your diet includes a basic variety of plant foods and you are eating enough to meet your energy needs, you can easily meet your essential amino acid requirements entirely from plants (1,2).
You might hear that plant proteins are less “bioavailable” than animal proteins, meaning the body absorbs and uses them less efficiently. Concerns surrounding bioavailability are based on outdated studies that used isolated proteins in raw form, tested in pigs or rats rather than humans. Not only do I condone the use of animal testing, these studies don’t actually reflect how humans eat protein, as part of cooked, mixed meals. In reality, when you eat a variety of plant foods in adequate amounts, your body gets all the essential amino acids it needs and uses them efficiently. Modern research shows that, within a well-planned plant-based diet, protein bioavailability is not a meaningful limitation (3).
Protein needs are based on body weight. For healthy adults, the European Food Safety Authority (EFSA) recommends 0.83 grams of protein per kilogram of body weight per day (4). So, for someone who weighs 75 kilograms, that works out to around 62 grams of protein per day (75 × 0.83 = 62.25g).
Most people in high-income countries already eat well above this amount; the average protein intake in many Western countries is at least 150% of recommended values (5). In places like the UK and US, adults typically get between 1.1 and 1.3 grams per kilogram per day, mainly because of higher intakes of animal-based foods (6).
Aside from those who may be experiencing food insecurity, illness, or any other form of calorie insufficiency, protein deficiency is rare. That said, population groups such as older adults, athletes, and pregnant or lactating women are likely to benefit from getting a bit more protein to help muscle maintenance, growth and recovery. The following is a guide for these groups:
Recent research shows that when you eat protein is just as important as how much you eat. Your muscles repair and grow through a process called muscle protein synthesis (MPS), which works best when you spread your protein intake evenly throughout the day (8).
In everyday life, many people tend to eat most of their protein at dinner, with very little at breakfast and lunch. This uneven pattern can make it harder for the body to build and repair muscle, especially in older adults (60+) (8,9).
Plant-based diets can support muscle growth just as well as animal-based diets, as long as you get enough total protein and the amino acid leucine, which helps trigger MPS. Plant based sources of leucine include soya (tofu and tempeh), beans and lentils. A 2023 study showed that high‑protein vegan and meat-containing diets yield the same MPS and gains in muscle volume and strength after resistance training in young adults, indicating that there are no compromises in muscle with sufficient protein on a vegan diet (10).
“Plant-based diets can support muscle growth just as well as animal-based diets.”
Eating a diet rich in plant foods is linked to a lower risk of heart disease, high blood pressure, type 2 diabetes, obesity, and some cancers; in other words, that’s most of our most prevalent diseases in the western world (11). These benefits come from including more of the good stuff from plants, like fibre and antioxidants, and less of the not-so-good stuff from animal protein, like saturated fat, haem iron, TMAO (trimethylamine-N-oxide), and certain cooking by-products such as heterocyclic amines (HCAs), polycyclic aromatic hydrocarbons (PAHs), and advanced glycation end products (AGEs).
Animal agriculture, particularly those that produce meat and dairy, is an inefficient way to produce food and a major driver of environmental harm. Animal farming uses about 83% of the world’s farmland but only produces 18% of our calories and 37% of our protein (12). Raising livestock, including fish and laying hens, also contributes heavily to deforestation, soil and water pollution, biodiversity loss and the greenhouse gas emissions that drive climate change.
“Animal farming uses about 83% of the world’s farmland but only produces 18% of our calories and 37% of our protein.”
In contrast, plant proteins are much more efficient with the resources they use, enabling us to grow more food for more people. Legumes use less water and land and produce far fewer emissions for every gram of protein compared to animal sources..
Shifting just a small part of our protein intake from animals to plants can have a big positive impact on conserving the natural world. Even in the absence of veganism, small, consistent changes toward more plant protein and less animal protein in the general population can add up to huge progress… we just need more people on board.
The below table (figure 2.) provides an overview of some of our top sources of plant protein and how much they contain per 100 grams or milliliters. These foods also offer complex carbohydrates, fibre, minerals (like iron and zinc), and healthy fats, making them powerful staples in a nutritious diet.
Plants are not “incomplete” or “inferior” sources of protein. In fact, as part of a healthy diet, plant proteins can even be considered superior due to their association with improved health and environmental outcomes. Plant proteins can fully meet human nutritional needs, support muscle growth and repair, reduce the risk of chronic disease, and contribute to a more sustainable food system… without the cruelty of animal agriculture, which, in my view, is its most undeniable and meaningful advantage.
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