Protein: how much, and from where

Two different questions get asked with the same words. The first is whether a plant-based diet supplies enough protein at all. The second is whether the protein it supplies is as useful as the protein in meat, milk or eggs. They have different answers, and the second one is where the argument actually lives.

A review of protein and amino acids in vegetarian diets concluded that protein-rich foods such as traditional legumes, nuts and seeds are sufficient to reach full protein adequacy in adults eating vegetarian or vegan diets, and that the question of amino acid deficiency has been substantially overstated. [1]

The caveat the same review attaches is the one that matters most for anyone making the comparison at a particular age.

The same review reports that protein adequacy is more complex in older adults, and that there are no specific protein-adequacy concerns in children because their energy requirements are very high relative to their protein needs. [1]

The quality question is real, and the review literature does not soften it.

A review of plant protein quality states plainly that the nutritional quality of plant proteins may be inferior in some respects relative to animal proteins, while setting out how to combine them to meet amino acid requirements. [2]

It is also measurable in the shops. A Dutch group bought forty vegan meat and dairy analogues and analysed them, rather than analysing the plants they are made from.

A survey of 40 vegan meat and dairy analogues sold in the Netherlands found total protein was lower than in the animal products they replace in 80% of meat analogues, 100% of lunch meats and cheese analogues, and 90% of milk and yoghurt analogues, with lower essential amino acid contents alongside. [3]

In the same survey the total essential amino acid content was adequate in all but one analogue, but every analogue was short in one or more specific essential amino acid: methionine in 39 of 40 (98%) and lysine in 11 (28%). [3]

So the plants are, on paper, the weaker protein. Then the same group measured what happens inside people, which is the only test that settles it. Thirty grams of protein, given once, with muscle protein synthesis measured over the next five hours.

In a randomised trial of 24 young men, 30 grams of a blend of wheat, corn and pea protein raised muscle protein synthesis rates no differently from 30 grams of milk protein (0.064 against 0.053% per hour, P = 0.08), even though the milk protein raised plasma essential amino acid concentrations more. [4] [4]

Two further trials from the same group found no difference in muscle protein synthesis between 30 grams of pea protein and 30 grams of milk protein (P = 0.96), or between 30 grams of potato protein and 30 grams of milk protein (P = 0.54), with the milk protein again raising plasma essential amino acids more. [5] [6]

Read that pair together and the shape of the answer appears. The plant proteins put less amino acid into the blood and still produced the same short-term muscle response at that dose — but a single 30-gram serving in a 24-year-old is not the same question as a whole diet in a 76-year-old.

That second question has been asked directly, and the answers are less comfortable. Requirements rise with age in every set of guidance, including the one written for older adults specifically.

A position paper from the PROT-AGE study group recommends that people over 65 take at least 1.0 to 1.2 grams of protein per kilogram of body weight a day, and 1.2 to 1.5 grams for those with acute or chronic disease, with severe kidney disease as an exception. [7] [7]

The same paper states that older people with severe kidney disease who are not on dialysis are an exception, and may need to limit protein intake. [7]

The same research group that found no difference in young men has argued that older adults are the case where a vegan diet is hardest to get right.

A perspective from the same research group argues that a vegan diet raises the risk of inadequate protein intake in older age, on the grounds of lower bioavailability and functionality of proteins in a vegan diet, lower essential amino acid content, and specific essential amino acid shortfalls in plant proteins. [8] [8]

And when older adults who had eaten this way for decades were actually measured, the shortfalls were not theoretical.

In a cross-sectional study of 26 Dutch adults aged 72 to 80 who had followed vegetarian or vegan diets for decades, protein intake below the recommended daily allowance occurred in 83% of vegans, 40% of vegetarians and 25% of omnivores. [9]

The same study found protein quality across the day was below the reference in every vegan and in 83% of the vegetarians, and that both plant-based groups fell short of recommended intakes for calcium, zinc, vitamin B12 and vitamin D. [9] [9]

Their sample was small — twenty vegetarians and six vegans — and the same paper says what can be done about it.

That study's authors note the sample was 20 vegetarians and 6 vegans, and that well-composed plant-based meals can provide adequate protein quality. [9] [9]

The population-level version of the question has been modelled twice on Dutch national diet data, by replacing meat with meat alternatives rather than by asking people to change.

In a model of the Dutch diet, replacing all animal meat gram for gram with plant-based meat alternatives lowered median total protein intake from 1.14 to 1.09 grams per kilogram a day, lowered utilizable protein from 0.94 to 0.86 grams per kilogram a day, and lowered the share of the adult population with adequate protein intake from 93% to 86%. [10]

The same modelling study reports that protein adequacy was mostly affected by the total protein content, the lysine content and the digestibility of the alternatives, and concludes that protein intake remained adequate for the majority of the population. [10] [10]

The second model split the population by age and looked at everything else in the diet at the same time.

A simulation of two plant-based substitution scenarios in the Dutch national food consumption survey found total protein intake fell in both, with the largest falls in people aged 71 to 79, and that intakes of calcium, iron, iodine, selenium and zinc also fell, especially among women and adolescents. [11] [11]

The same simulation reports that vitamin intake, particularly B vitamins and vitamin A, declined in most age groups, and that vitamin D remained chronically low. [11]

The protein picture, then, is not that plant protein fails. It is that total amount, the amino acid that happens to be short, and the age of the person eating it do most of the work, and that the same diet can be adequate in aggregate and inadequate for a particular person.

What this section does not show

Adequacy depends on the person

A diet can be adequate in aggregate and inadequate for one person. The measured shortfall in long-term older vegetarians and vegans was in protein amount and quality as well as calcium, zinc, vitamin B12 and vitamin D.

The nutrients at issue are named

Protein amount, protein quality, lysine, vitamin B12, iodine, iron, zinc, calcium, vitamin D, and omega-3 EPA and DHA. This section refuses any adequacy claim that does not name them.

Who is not covered

Pregnancy, infancy and childhood are outside what this entry can support. The sources retrieved for it do not cover them, and the Commission's own caveat on bioavailability for children and women of reproductive age is quoted in the last section.

The muscle studies are small

Three of the trials here measured a short-term marker in 24 healthy young men each, over five hours. That is not muscle mass, strength or health, and the section says so where it uses them.

All twelve elements

The entry's full limits block covers the dates, the study designs, who was and was not studied, the comparators, the adjustment sets, the uncertainty, the counter-signals and what we did not check. Read it on the entry's first page.

This page is general information about published research. It is not medical advice, and it is not a substitute for advice from a qualified health professional. No clinician-patient relationship exists, and we do not know your diet, your medications, your test results, your medical conditions or your history. Talk to a health professional before changing your diet if you are pregnant or breastfeeding, feeding an infant or child, over 65, taking medication, living with a medical condition, or if you have been diagnosed with a nutrient deficiency or have a history of disordered eating. The evidence described is about groups and diets, not about you, and not about any product listed on this site. If you are unwell, contact a health professional; in an emergency, call 911. No clinician reviewed this entry. It is a compilation of published sources by this site.

Sources for this section

Every numbered sentence above was checked against the source with that number on the date shown. The number links to the entry in this list, and the entry's first page lists every source it cites.

1. Dietary Protein and Amino Acids in Vegetarian Diets-A Review. Nutrients. narrative review. Open the source ↗
   Checked 19 September 2026. Backs 2 sentences in this section.
2. Plant Proteins: Assessing Their Nutritional Quality and Effects on Health and Physical Function. Nutrients. review. Open the source ↗
   Checked 19 September 2026. Backs 1 sentence in this section.
3. The amino acid composition of commercially available vegan meat and dairy analogues. British Journal of Nutrition. product analysis. Open the source ↗
   Checked 19 September 2026. Backs 2 sentences in this section.
4. The Muscle Protein Synthetic Response to the Ingestion of a Plant-Derived Protein Blend Does Not Differ from an Equivalent Amount of Milk Protein in Healthy Young Males. The Journal of Nutrition. randomised trial. Open the source ↗
   Checked 19 September 2026. Backs 1 sentence in this section.
5. Post-prandial muscle protein synthesis rates following the ingestion of pea-derived protein do not differ from ingesting an equivalent amount of milk-derived protein in healthy, young males. European Journal of Nutrition. randomised trial. Open the source ↗
   Checked 19 September 2026. Backs 1 sentence in this section.
6. Potato Protein Ingestion Increases Muscle Protein Synthesis Rates at Rest and during Recovery from Exercise in Humans. Medicine & Science in Sports & Exercise. randomised trial. Open the source ↗
   Checked 19 September 2026. Backs 1 sentence in this section.
7. Evidence-based recommendations for optimal dietary protein intake in older people: a position paper from the PROT-AGE Study Group. JAMDA. position paper. Open the source ↗
   Checked 19 September 2026. Backs 2 sentences in this section.
8. Perspective: Vegan Diets for Older Adults? A Perspective On the Potential Impact On Muscle Mass and Strength. Advances in Nutrition. perspective. Open the source ↗
   Checked 19 September 2026. Backs 1 sentence in this section.
9. Long-Term Vegetarian and Vegan Diets in Older Adults Are Associated With Inadequate Intakes of Protein and Micronutrients. The Journal of Nutrition. cohort analysis. Open the source ↗
   Checked 19 September 2026. Backs 3 sentences in this section.
10. Replacing Animal Meat with Plant-Based Meat Alternatives: The Impact of Protein Quality on Protein Adequacy in the Dutch Diet. Current Developments in Nutrition. modelling study. Open the source ↗
    Checked 19 September 2026. Backs 2 sentences in this section.
11. Shifting to Plant-Based Protein Diets Alters Nutrient Adequacy Across Age Groups: A Dutch Dietary Modeling Study. Nutrients. modelling study. Open the source ↗
    Checked 19 September 2026. Backs 2 sentences in this section.