The protein myth

September 22, 2021

Newsflash: all plants contain protein and all nine amino acids. Chances are, you’re meeting or exceeding your protein needs on a plant-based diet.

Protein is made up of amino acids, which are often called the building blocks of life. When we consume protein, our digestive system breaks the protein molecules down into their constituent amino acids, which are then absorbed by our bodies and used to create over 30,000 different proteins, from antibodies to hormones to enzymes to transport molecules, and much more, that are essential to our bodies’ functioning. Proteins are defined by the amino acids that they contain and the sequence in which the acids occur.


There are two major classes of amino acids: essential amino acids (EAAs) and non-essential amino acids (NEAAs). Like essential and non-essential nutrients, NEAAs are those our bodies can manufacture on their own, and therefore we do not require them in our diet. EAAs, on the other hand, cannot be produced by our bodies, so we must obtain them from the food we eat. If we supply our body with sufficient EAAs, they will work together with the NEAAs to manufacture all of the protein molecules we require.

EAAs are found in different concentrations in plant and animal foods, which leads to these foods sometimes being described as ‘incomplete’ and ‘complete’ proteins. These terms would make most people think that plant foods are missing certain EAAs, but that is not true – all plants contain all nine EAAs.

The term ‘incomplete’ only means that the quantity of one or more of the EAAs in a particular plant food is lower than what is considered optimal. The problem with this narrow view of protein consumption is that, instead of looking at the overall dietary pattern, it judges a single food in isolation.

The only way this could ever be a problem is if you only ate a single source of protein, such as rice or nuts, as your sole source of calories – and even then, if you were consuming adequate calories, you would still easily be getting all EAAs in the required amounts, except lysine, which would just fall short of the daily recommendations. Fortunately, this is not how we eat and there are plenty of plant foods that are bursting with lysine – beans, lentils, tempeh, and tofu, to name just a few.

You may be wondering whether this means you need to make sure you are eating ‘complementary’ protein sources of amino acids in each and every meal you have. Fortunately, there is no need to become hyper-focused on your amino acid intake, especially if you are eating a diverse range of plant foods. Your body has a constant pool of amino acids from the food you consume across the day.


While it’s clear that people eating a wholefood, plant-based (WFPB) diet can easily get enough protein, the other aspect of protein quality that should be considered is its digestibility. You may have even heard someone say that plant protein is less digestible than animal protein. This belief comes from various studies that use one or both of the two main evaluation methods that rate protein digestibility, the PDCAAS and DIAAS. While these scoring systems are somewhat helpful in assessing protein quality, they are far from perfect.

Fortunately, as science advances, we are beginning to see more precise studies conducted in humans and, so far, animal and plant protein digestibility only differ by a few percent. It’s for these reasons that global protein recommendations are not any higher for vegetarians or vegans than others.

Even if we assumed that on average plant protein was around 10 percent less digestible than animal protein (to play it safe), increasing our protein intake by 10 percent above the recommendations as an insurance policy is easily achieved on a WFPB diet. For most people, this is only around five to 10 grams of protein more per day – equivalent to that found in two to three tablespoons of hemp seeds.


The US Academy of Nutrition and Dietetics 2016 position paper emphasised that “vegetarian, including vegan, diets typically meet or exceed recommended protein intakes, when caloric intakes are adequate”, a finding supported by multiple studies that have analysed the protein intakes of vegetarian and vegan populations across the world.

The National Health and Medical Research Council (NHMRC) protein recommendations for the average adult are set out as grams per kilogram of body weight. Men require slightly more protein than women, and the recommended dietary intake (RDI) increases slightly for people 70 and older, due to their increased risk of muscle loss and frailty. Protein requirements are also higher during pregnancy and lactation to help promote healthy growth and development of a baby.


It’s important to note that the protein recommendations are based on the amount of protein required to meet basic nutritional needs and prevent deficiency, and have not been tailored for people following a WFPB diet. To illustrate what this looks like in terms of protein per day, let’s go through an example using a 35-year-old woman who weighs 65 kilograms, spends a large percentage of their day sitting, and doesn’t perform intensive exercise. Working from the NHMRC protein recommendations, this woman’s recommended daily protein intake is approximately 49 grams (65 kilograms x 0.75 grams). If we were to add an extra 10 percent as an insurance policy, to factor in the slightly lower digestibility of plant protein, it would increase her daily requirement to approximately 54 grams.

What about someone who is more physically active: how much protein do they require? There is a good amount of science to suggest that increasing protein intake is beneficial to those seeking improved muscle recovery, strength, growth, and body composition. If this is you, my general recommendation is for plant-powered endurance athletes to aim for around 1.5 grams per kilogram per day, and strength athletes to aim for around 1.8 grams per kilogram per day, which is at a level that will maximise muscle growth and recovery while still allowing sufficient room to consume all food groups.

These ranges are based on the best science available today, including a 2018 meta-analysis that looked at all of the science on optimal protein consumption for muscle repair and growth. Many of these studies looking at protein consumption and muscle growth are based on people consuming animal protein as part of an omnivorous diet. I’ve accounted for the slightly lower bioavailability of plant protein in my recommendations, along with the fact that there is an upper limit of protein set by the NHMRC of 25 percent of total calories. Above this level, there is the potential for calories from protein to displace calories from other healthful food groups.


While all plants contain protein, legumes are going to provide most of your protein when you eat a healthy WFPB diet. I really cannot think of a healthier substitute for animal products! They contain all EAAs in health-promoting ratios and are incredibly rich in fibre, vitamins, minerals, and phytonutrients, while being naturally low in saturated fats and free from cholesterol.

This article is an edited extract from The Proof is in the Plants by Simon Hill. Published by Penguin Life.

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