Plant Protein: How Much and From Where

Plant-based protein is not a single number. It is a set of numbers that depend on the person, the food, and the goal. The two real differences from animal protein are lower digestibility and incomplete amino acid profiles in single sources. Both are manageable. The rest is noise.

This page gives figures in grams per kilogram of body weight. A protein target in grams alone is meaningless without the person it belongs to. The RDA is a minimum to prevent deficiency. A target for someone in a calorie deficit trying to keep muscle is a different number. That distinction is the one most of this cluster exists to resolve.

The RDA Is a Floor, Not a Target

The RDA for protein is 0.8 g per kilogram of body weight per day. This comes from the Institute of Medicine (now the National Academies) 2005 report. It is set to cover the needs of 97.5% of healthy adults. It is a minimum to prevent deficiency, not a target for muscle retention or satiety.

For a 70 kg adult, the RDA is:

0.8 g/kg × 70 kg = 56 g/day

That is the floor. If you are in a calorie deficit, the floor is not enough. The evidence for muscle retention during weight loss points to a higher intake. A 2014 review by Helms et al. in the Journal of the International Society of Sports Nutrition suggests 1.6–2.4 g/kg for lean, resistance-trained individuals in a deficit. That is a range, not a single number. The lower end is for those with more body fat; the upper end is for leaner individuals.

For a 70 kg person, that range is:

1.6 g/kg × 70 kg = 112 g/day
2.4 g/kg × 70 kg = 168 g/day

These figures are for animal protein. Plant protein requires a modest adjustment.

Two Real Differences

Digestibility

Plant proteins are less digestible than animal proteins. The DIAAS (Digestible Indispensable Amino Acid Score) is the current standard. It measures how much of each essential amino acid is absorbed. Animal proteins like whey, casein, and egg score above 1.0. Most single plant proteins score below 0.9. For example, wheat gluten has a DIAAS of around 0.45, pea protein isolate around 0.70, and soy protein isolate around 0.90. These values come from a 2013 FAO report and subsequent studies.

A DIAAS of 0.70 means that for every gram of protein consumed, only 0.70 grams of the limiting amino acid is absorbed. To compensate, you need more total protein. A common adjustment is 10–20% more. That is not a precise figure. It depends on the specific plant foods and the rest of the diet.

Amino Acid Profile

Most single plant sources are incomplete. They are low in one or more essential amino acids. Grains are low in lysine. Legumes are low in methionine. This is not a problem if you eat a variety of plant proteins across the day. The old idea of protein combining at every meal is unnecessary. A 2016 position paper from the Academy of Nutrition and Dietetics states that plant proteins can meet requirements when a variety is eaten over the day.

The Practical Consequence

If you are in a deficit and want to keep muscle, and you are eating only plant protein, the target is higher. Start with the range for animal protein and add 10–20%.

For a 70 kg person:

Lower end: 1.6 g/kg × 70 kg = 112 g/day
Add 10%: 112 g × 1.10 = 123 g/day

Upper end: 2.4 g/kg × 70 kg = 168 g/day
Add 20%: 168 g × 1.20 = 202 g/day

So the range is roughly 123–202 g/day. That is a wide range. It reflects the uncertainty in the evidence. The 10–20% adjustment is a rule of thumb, not a precise correction. It is wrong in both directions: it may overestimate for someone eating well-combined plant proteins with high DIAAS, and underestimate for someone eating mostly low-DIAAS grains.

Table: Protein Targets by Condition

Highest Protein Plant Foods

Per 100 g cooked or prepared:

• Seitan: 25 g
• Tempeh: 20 g
• Lentils: 9 g
• Tofu: 8 g
• Chickpeas: 7 g
• Quinoa: 4 g

These figures come from the USDA FoodData Central database. They are averages. Actual values vary by brand and preparation.

What People Get Wrong

The most common mistake is treating the RDA as a target. The RDA is a floor. If you are active or in a deficit, you need more. This mistake is natural because the RDA is the only protein number most people ever see. It is on food labels. It is in dietary guidelines. It is presented as the answer, not the minimum.

The second mistake is assuming plant protein is inferior. It is not. It is different. The differences are digestibility and amino acid profile. Both are manageable with a higher total intake and variety. A 2019 review by Mariotti and Gardner in Nutrients concluded that plant-based diets can meet protein needs if planned well.

The third mistake is overcomplicating amino acid combining. You do not need to combine rice and beans at every meal. Your body maintains a pool of amino acids. Eating a variety over the day is enough.

What the Evidence Does Not Say

There is no evidence that plant protein is superior to animal protein for muscle growth or strength. There is also no evidence that it is inferior when total intake is matched and adjusted for digestibility. The trials that matched calories and protein found small differences, and adherence dominates. If you prefer plant protein and eat enough, you will get similar results.

There is uncertainty about the exact adjustment for DIAAS. The 10–20% figure is a common recommendation, but it is not derived from a single study. It comes from comparing DIAAS scores and estimating the extra intake needed. Individual variation is large.

A Note on Safety

This page provides general information, not medical advice. If you have a medical condition, are pregnant, or are taking medication, consult a healthcare provider before changing your diet.

If you struggle with disordered eating, help is available. In the United States, the National Eating Disorders Association (NEDA) helpline is 1-800-931-2237. In the UK, Beat’s helpline is 0808 801 0677. These are free and confidential.

FAQ

Q: How much plant protein do I need per day? A: It depends on your weight and goal. The RDA is 0.8 g/kg. For muscle retention in a deficit, aim for 1.6–2.4 g/kg if eating animal protein, or 10–20% more if eating only plant protein. For a 70 kg person, that is roughly 123–202 g/day.

Q: Is plant protein as good as animal protein? A: It is different, not inferior. Plant proteins are less digestible and often incomplete, but these are manageable with a higher total intake and variety. When total intake is matched and adjusted, outcomes are similar.

Q: Do I need to combine plant proteins at every meal? A: No. Your body maintains an amino acid pool. Eating a variety of plant proteins over the day is enough. The old rule of combining at every meal is outdated.

Q: What are the highest protein plant foods? A: Seitan (25 g per 100 g), tempeh (20 g), lentils (9 g), tofu (8 g), and chickpeas (7 g). These values are from USDA FoodData Central and vary by preparation.

Q: Can a vegan diet meet protein needs? A: Yes, with planning. A 2016 position paper from the Academy of Nutrition and Dietetics states that well-planned vegan diets can meet protein needs. The key is eating enough total protein and a variety of sources.