Quick answer

Protein supplies the amino acids your body uses to build and repair muscle. Adults need at least 0.8 g per kg of body weight a day, and people who train are advised to get 1.4 to 2.0 g. Over weeks of training, pea and other plant proteins came close to whey in trials when total protein was enough.^1,2,3,4

Key facts

Nine of the amino acids in protein are essential, so they have to come from food.¹
Protein supplements stopped adding lean mass in trials once total intake reached about 1.6 g per kg a day.⁵
American men already eat about 100 g of protein a day on average, and women about 69 g.¹
No upper limit is set for protein, and NIH reports no safety concerns up to about 2.0 g per kg a day.¹

What protein does

Protein is necessary to build, maintain and repair muscle, and muscle builds protein faster for up to a day or two after exercise.¹

Digestion breaks the protein in food into amino acids. Your body uses them to repair cells and make new ones, and protein matters for growth in children, teens and pregnant women.⁶

Nine amino acids are essential and must come from food: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.¹

Most complete proteins are about 40 percent essential amino acids, so 25 g of protein supplies about 10 g of them.¹

Proteins from different foods differ in how much of each essential amino acid they carry and in how fast they are digested. Leucine matters most: it is the amino acid that switches on muscle protein building.^2,7

Dairy proteins are about 9 to 11 percent leucine, egg about 8.6 percent and meat about 8 percent; plant proteins are generally lower.^2,7

What the evidence shows

Each claim below carries a grade for how much human research there is and how well it agrees, with the amounts the studies used beside it. The third claim mentions the fava bean and yeast protein in our own Plant Protein, which has not been tested in a training trial.

Protein contributes to the growth and maintenance of muscle*¹

Moderate evidence

This is a well-established nutrient function: the NIH describes protein as necessary to build, maintain and repair muscle, and the essential amino acids it supplies must come from the diet. One serving of our Plant Protein provides 20 g (vanilla) or 21 g (chocolate) of protein.

Amount studied: The RDA of 0.8 g per kg of body weight a day from all foods, and more for people who train

Extra protein supports small added gains in strength and lean mass from resistance training when your usual intake is below about 1.6 g per kg of body weight a day*⁵

Moderate evidence

A meta-analysis of 49 randomized trials (1,863 people) found protein supplements added about 2.5 kg to one-rep-max strength and 0.3 kg of fat-free mass over training alone, with no further gain above about 1.6 g of protein per kg a day in total. The trials averaged 36 g of supplement a day (range 4 to 106 g) and mostly used whey or milk protein, so 20 or 21 g of a fava and yeast blend is only a partial match; hence moderate, not strong.

Amount studied: 4 to 106 g of supplemental protein a day (36 g on average) during 6 to 52 weeks of resistance training

Plant proteins can support training gains close to those of animal proteins when total protein intake is adequate; this fava and yeast blend is untested*^3,8,9

Early evidence

A meta-analysis of 16 trials found no difference between plant and animal protein for gains in absolute lean mass or strength, though animal protein did slightly better for percent lean mass and in adults under 50; the plant proteins were soy, pea and rice, not fava or yeast. In the one fava trial, about 23 g did not raise muscle protein synthesis above a control drink of non-essential amino acids in 16 adults, and a 6-month trial of yeast protein in 92 older adults found no change in muscle mass or grip strength.

Amount studied: Soy, pea or rice protein in diets with total protein generally above the RDA

In pooled training trials, the extra lean mass from protein supplements got smaller with age and was larger in people who already trained.⁵

Training is still the main driver. In the pooled trials, resistance training on its own added about 1.1 kg of fat-free mass, and protein added about 0.3 kg on top.⁵

How much protein you need

The Recommended Dietary Allowance (RDA) for protein is 0.8 g per kg of body weight a day for healthy adults and 0.85 g per kg for teens. The ISSN says this amount is not enough for people in regular training.^1,2

The International Society of Sports Nutrition says 1.4 to 2.0 g of protein per kg of body weight a day is enough for most people who exercise to build and keep muscle. NIH gives a similar range for athletes, 1.2 to 2.0 g per kg.^1,2

In national survey data from 2007 to 2008, American men ate about 100 g of protein a day on average and women about 69 g.¹

For comparison, 0.8 g per kg comes to 56 g a day for a 70 kg adult, less than either average. A shake is most useful when food alone falls short of your own target; the dosage guide sets out amounts by body weight.¹

Pea, plant or whey

Whey is one of the complete proteins in milk and is the protein in most powders and drinks. It is digested quickly.^1,2

Pea protein isolates are about 80 percent protein, rich in lysine and low in methionine. They hold less leucine than whey, so about 38 g of pea protein supplies the leucine in 25 g of whey.⁷

Combining plant proteins, or plant with animal proteins, can give an amino acid profile closer to animal protein than a single plant protein.⁷

Over weeks of training the source mattered less than the amount. Pea and whey gave similar results in the largest head-to-head trial, and soy matched animal proteins in pooled trials; the comparison page has the details.^4,10

Food first

One ounce of meat, fish or poultry, 1 large egg, a quarter cup of tofu, or half a cup of cooked beans or lentils each gives about 7 g of protein.⁶

Meat, poultry, fish, eggs and dairy foods contain all the essential amino acids. Grains and legumes each contain different ones, so eating a mix of plant foods is one way to get them all.¹¹

NIH says most athletes can probably get enough protein from food, and that protein powders and protein-fortified foods can help when they cannot. It sees no benefit in eating more than the recommended amounts.¹¹

What's in ours

What’s in ours

Collagen Peptides: Protein, 18 g per serving, from the label
Collagen Peptides: Protein, 18 g per serving, from the label
Plant Protein: Protein, 20 g per serving, from the label
Plant Protein: Protein, 21 g per serving, from the label

Our Plant Protein is made from fava bean protein isolate with fermented yeast protein, not pea. Collagen Peptides list 18 g of protein per serving, but collagen lacks tryptophan and scores zero on the standard protein-quality scale, so it does not stand in for complete protein.^12,13

Side effects, medicines and who should ask first

NIH lists no known side effects of protein and reports no safety concerns at intakes up to about 2.0 g per kg of body weight a day.¹

No tolerable upper intake level has been set for protein, because the risk of harm from protein in food is very low. NIH still advises caution with high intakes from foods and supplements combined, since data are limited, and reports no safety concerns up to about 2.0 g per kg a day.¹

Allergic reactions can occur. Milk, soy and peanuts are major food allergens, and peas, lentils, lupin and other legumes can also cause reactions, sometimes severe and sometimes in people already allergic to peanut.^14,15

Fava beans contain vicine and convicine, which make red blood cells break down in people with G6PD deficiency. Nursing babies with the condition have been harmed after their mothers ate fava beans.¹⁶

Ask your pharmacist or doctor first

Protein can lower how much levodopa is absorbed. The carbidopa and levodopa label says levodopa competes with certain amino acids to cross the gut wall, so a high-protein diet may delay its absorption and reduce the amount that reaches the blood.¹⁷

On the medicine's label

Ask your pharmacist or doctor first

The label of phenelzine, an MAO inhibitor, tells people to avoid high-protein foods that have been aged, fermented, pickled or smoked, along with yeast extract and fava bean pods, because of the tyramine or dopamine they can contain. Ask before using a protein powder made with fermented yeast or fava bean protein.¹⁸

On the medicine's label

Plants can take up lead from the environment. In a 2026 study of 30 protein supplements, plant-based products averaged about three times the lead of dairy-based ones (0.18 against 0.06 mg per kg).^19,20

Do not use fava bean protein if you have G6PD deficiency (favism), unless your doctor says it is safe¹⁶
Ask first if you have kidney disease or have been told to limit protein
Ask first if you are pregnant or nursing, or under 18
Ask first if you are allergic to milk, soy, peanuts, peas, lupin or other legumes, or to yeast
Ask first if you take levodopa or an MAO inhibitor

Questions people ask

Is pea protein a complete protein?

Pea protein contains all nine essential amino acids and met the requirement for them as a whole in a laboratory analysis, but it is low in methionine. Combining it with a grain protein such as brown rice, which carries more methionine, gives a profile closer to animal protein.⁷

Is plant protein as good as whey?

Over weeks of training it came close. Pooled trials found no difference between plant and animal protein in strength or absolute lean mass, with a small edge for animal protein in percent lean mass and in adults under 50. Gram for gram, plant proteins carry less leucine, which a larger serving can make up.^3,7

Is a high-protein diet hard on the kidneys?

Not in healthy people, according to NIH: diets with two to three times the RDA do not appear to harm kidney function. If you have kidney disease, protein limits may be part of your care, so ask your doctor first.^1,21

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Sources

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.