Ask whether plant or animal protein is “better” and you can quickly
end up answering two quite different questions.
One is about muscle. Animal proteins are often described as higher
quality because they tend to be highly digestible and provide
substantial amounts of all the essential amino acids, including
leucine.
The other is about long-term health. There, the comparison becomes
much more complicated. We don’t eat amino acids in isolation. We eat
beans, lentils, tofu, yoghurt, eggs, fish, chicken, nuts, cheese, beef
and many other foods that happen to contain protein.
Protein source can matter, but its importance depends on what you’re
trying to achieve, which foods or proteins you’re comparing, how much
protein you eat and what the rest of your diet looks like.
Start with what
dietary protein has to do
Protein provides amino acids that the body uses to build and maintain
tissues and support many other biological functions.
Nine amino acids are considered essential because the body cannot
produce enough of them on its own and therefore needs to obtain them
from food.
Foods differ in how much of these amino acids they provide, their
proportions and how well their protein is digested and absorbed. These
differences contribute to what researchers call protein
quality.
Animal-derived proteins generally score highly on measures of
digestibility and indispensable amino-acid content. Plant proteins are
more variable. Soy is different from wheat; pea is different from rice;
potato protein is different again.
Protein-quality scoring systems are useful for characterising
individual proteins, but they don’t reproduce everything that happens
when people eat mixed meals and varied diets.
“Plant protein” is therefore a broad category, and so is “animal
protein.”
Why
some animal proteins can produce a stronger short-term muscle
response
Muscle is constantly breaking down and rebuilding proteins.
Eating protein supplies amino acids that can stimulate muscle
protein synthesis, the process through which new muscle
proteins are produced. Resistance exercise also stimulates this process
and makes muscle more responsive to protein.
The amount and composition of essential amino acids reaching the
circulation influence that response. Leucine appears to have an
important signalling role, while the other essential amino acids provide
material needed to build new protein.
Many animal-derived proteins provide relatively high concentrations
of essential amino acids and leucine and are highly digestible. Some
plant proteins provide less of one or more essential amino acids or are
digested less efficiently. Equal gram amounts of different proteins
therefore don’t necessarily produce identical short-term responses.
A recent systematic review and meta-analysis directly comparing
plant- and animal-based proteins found that estimates for muscle protein
synthesis tended to favour animal proteins overall. A modest advantage
was also reported in adults aged 65 and older, but that age analysis
rested on only a small number of older-adult studies within an evidence
base of just 12 studies overall.
There is another important limitation: the underlying studies
included male participants only. We therefore cannot assume the size of
these acute differences would be identical in women.
The estimates were also imprecise. Most of the animal-protein
evidence came from milk-based proteins, while the plant sources varied
considerably.
Taken together, the findings support the possibility of
source-dependent differences in acute muscle protein synthesis. They do
not establish that animal protein is always superior to plant
protein.
An
acute muscle response is not the same as gaining more strength
A short-term muscle-protein-synthesis experiment can tell us
something about the body’s response to a meal. It cannot, by itself,
tell us how much muscle or strength someone will gain over months.
For that question, longer randomized trials are more useful.
A 2025 systematic review identified 43 randomized controlled trials
comparing plant and animal protein for muscle-related outcomes. Thirty
were included in the muscle-mass meta-analysis.
Animal protein showed a small overall advantage for muscle mass.
There was no significant pooled difference, however, between soy
and milk protein. The animal-protein advantage was more
apparent when animal proteins were compared with non-soy plant proteins
or plant-based diets.
The review also found no significant difference between plant
and animal protein for muscle strength or physical performance.
No included trial directly measured sarcopenia as an outcome.
A small difference in one body-composition measure therefore
shouldn’t become the much larger claim that people who rely on plant
protein cannot become strong or maintain useful physical function.
What about older adults?
Age makes the question more relevant, but the comparative evidence
remains limited.
Older muscle can become less responsive to the anabolic effects of
protein, which is one reason adequate protein and resistance training
become particularly relevant with ageing.
Current evidence still doesn’t justify telling older adults that
plant protein simply “doesn’t work.”
In the 2025 meta-analysis, the overall animal-protein advantage for
muscle mass was driven more clearly by adults under 60. Among adults
aged 60 and older, the pooled difference in muscle mass was not
statistically significant.
A separate systematic review of plant-protein interventions in adults
aged at least 60 found broadly comparable results for body composition,
strength and physical function. All the included studies used soy,
however, so those findings should not be extended automatically to every
plant protein.
A 2026 meta-analysis of 29 randomized trials involving 2,363 adults
aged 50 or older likewise found generally similar effects of plant- and
animal-derived protein interventions on body composition, handgrip
strength and most cardiometabolic measures.
Again, the details matter. Twenty-five of those 29 trials used soy as
the plant source, and 23 studied purified protein isolates or
isolate-based products rather than whole foods.
The evidence is therefore more informative about soy-based
protein interventions compared largely with dairy-based
interventions than about every possible plant-based diet
compared with every possible animal-based diet.
For an older adult, adequacy still matters, as do appetite, total
protein intake, the foods providing it and resistance exercise.
Plant
proteins don’t have to be perfectly matched at every meal
Plant proteins are sometimes described as “incomplete,” which can
give the impression that a plant-based meal fails unless every essential
amino acid is perfectly balanced at that sitting.
That description is too crude.
Individual plant foods can provide lower amounts of particular
essential amino acids, but people normally eat different foods over the
course of a day. Plant sources can complement one another; legumes, for
example, tend to have a different amino-acid profile from grains.
A varied diet can therefore provide all the essential amino acids
without requiring animal protein or deliberate protein pairing at every
meal.
Quantity still matters. If total protein intake is relatively low,
someone relies heavily on a narrow range of protein sources, or
maximising muscle adaptation is a priority, differences in protein
quality may become more relevant. In some circumstances, consuming a
larger amount of a plant protein can also help compensate for a lower
amount of particular essential amino acids per gram, although the effect
depends on the specific protein.
For people who prefer mostly plant-based eating, useful protein foods
include soy foods, legumes, lentils, beans, peas, nuts, seeds and whole
grains. The aim is an adequately protein-rich diet built from foods you
can eat consistently, rather than an amino-acid calculation at every
meal.
Protein
quality isn’t a health score for the food
A protein-quality score tells us about characteristics of the
protein. It doesn’t provide a complete health rating
for the food carrying it.
Foods with protein can also differ in fibre, saturated fat, sodium,
micronutrients, phytochemicals, degree of processing and the other foods
they tend to accompany.
Plant protein foods often provide fibre and a variety of
micronutrients and phytochemicals. Animal foods are also nutritionally
diverse. Fish, yoghurt, eggs, poultry, cheese and processed meat
shouldn’t be treated as though their only meaningful difference is the
amount of protein they contain.
This is particularly important when acute muscle research is used to
make claims about cardiovascular health or longevity. A protein can
perform well in a muscle-protein-synthesis experiment without that
experiment telling us whether eating more of the food reduces heart
attacks, extends life or improves someone’s overall diet.
Those questions require different evidence.
For long-term
health, what you replace matters
Observational research often finds that diets containing more
plant-derived protein are associated with favourable long-term health
outcomes.
A 2026 meta-analysis of nine cohort studies involving more than one
million participants found that substituting some dietary energy from
animal protein with plant protein was associated with lower all-cause
and cardiovascular mortality.
Because these were observational studies, the result cannot establish
that making a particular substitution will cause an individual to live
longer.
The foods involved also matter. Replacing processed meat with beans
isn’t nutritionally equivalent to replacing fish with a highly processed
plant-protein product, even though both could loosely be described as
replacing animal protein with plant protein.
This is why food-based interpretation is more useful than declaring
one broad protein category healthier than the other. Which food supplied
the protein, what replaced what, and the quality of the overall diet all
contribute to the answer.
What does this mean for
everyday eating?
Most people don’t need to build their diet around allegiance to one
protein source.
If you eat animal foods, protein can come from fish, eggs, dairy,
poultry and meat alongside beans, lentils, soy foods, nuts, seeds and
grains.
If you eat mostly or entirely plant-based, protein quality deserves
some consideration, particularly when total intake is low, appetite is
limited or maintaining muscle is a priority. A varied diet with adequate
protein and useful higher-protein plant foods can do much of the
practical work without requiring amino-acid calculations.
If building or preserving muscle is the goal, resistance training
remains important too. Choosing a theoretically superior protein cannot
reproduce the training stimulus.
Source becomes more relevant when protein intake is marginal, food
choices are narrow, appetite limits how much someone can eat, or someone
is trying to obtain a strong muscle-protein response from a relatively
small amount of food.
When total protein intake is already adequate and comes from a varied
diet, differences between individual sources may carry less practical
weight. The foods themselves still matter because protein is only one
part of what they contribute to the diet.
The bottom line
Plant and animal proteins aren’t nutritionally identical. Some animal
proteins have advantages in digestibility and essential-amino-acid
composition, and this can affect short-term muscle protein
synthesis.
Longer-term evidence is less clear-cut. Comparative trials show a
small overall animal-protein advantage for muscle mass in some analyses,
but soy and milk have performed similarly for some muscle outcomes,
while pooled differences in strength and physical performance have not
been significant.
Meanwhile, long-term health questions depend on much more than
protein quality. The particular foods, what they replace and the wider
dietary pattern all matter.
For ordinary eating, the plant-versus-animal label tells you
something. It doesn’t tell you everything you need to know.
Sources & Further Reading
- Effects of Plant- vs Animal-Based Proteins on Muscle Protein
Synthesis: A Systematic Review With Meta-Analysis — Journal
of the Academy of Nutrition and Dietetics, 2026 - Effect of Plant Versus Animal Protein on Muscle Mass,
Strength, Physical Performance, and Sarcopenia: A Systematic Review and
Meta-analysis of Randomized Controlled Trials — Nutrition
Reviews, 2025 - Effects of Plant-Based Protein Interventions, with and
without an Exercise Component, on Body Composition, Strength and
Physical Function in Older Adults: A Systematic Review and Meta-Analysis
of Randomized Controlled Trials — Nutrients, 2023 - Plant-versus animal-derived protein and nutritional,
cardiometabolic, and inflammatory outcomes in middle-aged and older
adults: A systematic review and meta-analysis of randomized controlled
trials — Clinical Nutrition ESPEN, 2026 - Comprehensive overview of the quality of plant- and
animal-sourced proteins based on the digestible indispensable amino acid
score — Food Science & Nutrition, 2020 - Limitations with the Digestible Indispensable Amino Acid
Score (DIAAS) with Special Attention to Plant-Based Diets: a
Review — Current Nutrition Reports, 2021 - Isocaloric substitution of animal protein with plant protein
and its impact on all-cause, cardiovascular, and cancer mortality: A
systematic review and meta-analysis — Clinical Nutrition,
2026