Vegan and Plant Protein: Sources, How to Combine Them and How Much You Need

Plant protein has an undeserved bad reputation. It is true that it tends to be a little less dense and that varying sources helps, but with minimal planning it covers anyone's needs, including people who train hard. The position paper of the Academy of Nutrition and Dietetics (2016) puts it this way: well-planned vegetarian and vegan diets are nutritionally adequate at every stage of life, athletes included.

Best vegan protein sources: table per 100 g and per serving

The figures come from USDA FoodData Central. Check two things before comparing: whether the food is dry or cooked, and which tofu you buy. Firm tofu set with calcium sulphate has almost twice the protein of tofu set with nigari, and the gap between seitan brands is even bigger.

What is a "complete" protein? Limiting amino acids

There are nine essential amino acids your body cannot make: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Plant proteins contain all of them, but not always in the ideal proportion, and the one that falls shortest is called the limiting amino acid. In grains it is lysine; in legumes, the sulphur amino acids (methionine and cysteine), which according to Mariotti and Gardner (2019) are only slightly below optimal. That is why legumes and grains complement each other: what one lacks, the other provides. Young and Pellett already summed it up in 1994: mixtures of plant proteins can be a complete and well-balanced source of amino acids.

PDCAAS and DIAAS: how protein quality is measured

For years the standard was the PDCAAS, which corrects the amino acid profile for digestibility measured in rat faeces and is capped at 1. In 2013 an FAO expert consultation recommended replacing it with the DIAAS, which uses the digestibility of each amino acid at the end of the small intestine, and proposed indicative cut-offs: 100 or more, "excellent" quality; 75 to 99, "good"; below 75, no quality claim. When both are calculated for the same foods, the PDCAAS tends to score higher, especially for lower-quality proteins (Rutherfurd et al., 2015; Mathai et al., 2017).

Two important caveats. First, the DIAAS scores a single food, and nobody eats only rice: in a mix, the lysine in legumes makes up for what grains lack, and the review by Herreman et al. (2020) calculated that soy, pea and potato proteins raise the score of many other plant proteins when combined. Second, in humans the digestibility of soy protein, pea protein or wheat flour measured at the end of the small intestine is around 89-92%, similar to egg (91%) or meat (90-94%), according to Mariotti and Gardner (2019). The difference from animal protein is more about the amino acid profile than about digestion.

Do you have to combine proteins on the same plate?

No. The idea of always eating rice and lentils together at the same meal has been revised: the review by Mariotti and Gardner (2019) concludes that there is no evidence that a plant protein needs to be complemented by another at the same meal, and that a reasonable variety of sources over the day is enough. Mixing them on the same plate is simply a practical way to secure the profile when your total protein intake is low. Traditional pairings are still the easiest way to do it:

• Lentils with rice, as in Middle Eastern mujaddara or Indian dal with rice
• Hummus with wholegrain bread
• Beans with corn tortillas
• Wholewheat pasta with peas or lentils
• Couscous with chickpeas
• Stir-fried tofu with brown rice

Do you need to eat more protein if you are vegan?

For general health, it does not seem necessary. A meta-analysis of nitrogen balance studies (Rand et al., cited by Mariotti and Gardner) found no difference in requirements between diets based on animal, plant or mixed protein, and the authors consider it over-cautious to ask vegetarians for more protein than the reference when the diet is at least slightly varied. The adult reference is the same for everyone: 0.83 g per kg of body weight per day according to EFSA, about 58 g for a 70 kg person.

For building muscle there is a nuance. In studies lasting a few hours, the same dose of plant protein stimulates muscle protein synthesis slightly less than animal protein, because it contains less of some essential amino acids and somewhat less leucine (on average 8 g per 100 g of protein versus 9.5 g in animal protein, according to Mariotti and Gardner). Among the strategies proposed by van Vliet et al. (2015) and Pinckaers et al. (2021) is precisely eating a little more plant protein or mixing sources; in older adults, who respond less to protein, the review by Berrazaga et al. (2019) points in the same direction. In practice: if you do strength training, aim for the middle or upper part of the ISSN range (1.4-2.0 g/kg) and split it into doses of 20-40 g, the per-meal amount that society proposes. Work out your own figure with the protein calculator.

Building muscle on plant protein: what the studies say

The honest reading: if the total amount is sufficient, the source matters little for building muscle. The advantages of animal protein that do show up are small and appear mainly in short-term muscle protein synthesis and in younger adults. Soy is the plant source with the most evidence, and varying legumes, grains and seeds over the day makes up for the profile of the rest.

A vegan day with 111 g of protein (with the maths)

Example for a 70 kg person who does strength training: 1.6 g/kg is about 112 g. Amounts are ready-to-eat food, and the grams of protein come from the USDA data in the table (plus oats, 173904, and cooked brown rice, 169704):

• Breakfast: 60 g rolled oats (7.9 g) + 250 g (one glass) unsweetened soy drink (7.2 g) + 30 g hemp seeds (9.5 g) = 24.6 g
• Lunch: 250 g cooked lentils (22.6 g) + 150 g cooked brown rice (4.1 g) = 26.7 g
• Snack: 150 g edamame (17.9 g) + 30 g peanuts (7.7 g) = 25.6 g
• Dinner: 150 g firm tofu set with calcium sulphate (26.0 g) + 185 g cooked quinoa (8.1 g) = 34.1 g
• Total: 111.0 g of protein and about 1,740 kcal, not counting oil, vegetables or fruit

If you want the whole week already organised, there is a weekly vegan meal plan with breakfasts, lunches and dinners.

Common mistakes when switching to plant protein

• Removing meat and putting nothing in its place: the plate ends up as pasta or rice with vegetables. Every main meal needs its protein source: legumes, tofu, tempeh, seitan or textured soy.
• Counting low-protein foods as the main source: cooked quinoa has 4.4 g per 100 g and cooked brown rice 2.7 g. They add up, but they cannot carry a meal.
• Assuming all tofu is the same: depending on the coagulant, 125 g of firm tofu gives 11 or 22 g of protein. Check the label.
• Forgetting B12: it has nothing to do with protein, but it is the one supplement a vegan diet cannot skip.

Eating vegan and hitting your protein are not in conflict: they just need variety and a little planning. Log your meals with Renzy to check that your plant-based diet reaches your target (and do not forget B12).