Do muscles grow more with animal or plant proteins?

The ultimate guide! Also includes a list of the best protein foods to grow your muscles

 

In this guide, we will analyze the latest studies and research to understand together how proteins, and especially amino acids (you will understand what I'm talking about later), make muscles grow, to answer the question we posed: do muscles grow more with animal or vegetable proteins?

 

Let's immediately clarify a few things. Today we will understand together what the anabolic response of muscles is when you eat vegetable proteins, which translated means: which proteins are best from a dietary perspective, both for protein intake and for essential amino acid intake.

 

Essential amino acids are called that because they are necessary for our lives (and therefore also for muscle growth), but our body is unable to synthesize them in sufficient quantities, so we must obtain them through diet.

 

We can state right now that vegetable proteins are attracting great interest, both clinically and from common users who often prefer them for muscle mass gain or maintenance programs.

 

Do vegetable proteins have the same anabolic effect as animal proteins on muscle growth?

 

Recent studies and research have shown that the ingestion of plant-based proteins from soy and wheat results in a lower response from our muscles compared to several animal-derived protein sources.

 

Are animal proteins still superior?

 

The apparently inferior anabolic properties of plant protein sources can be attributed to two well-defined reasons:

 

• Lower digestibility
• Lack of some essential amino acids

 

In addition to these two reasons, there is also, still related to amino acids, a lower leucine content in most plant-based protein sources, which, for our goal of increasing muscle mass, translates into a reduction in the anabolic effect derived from their ingestion.

 

Given this overview, you might think there's little doubt about which proteins to choose, but I ask you not to jump to conclusions and to continue reading to understand if: do muscles grow more with animal or vegetable proteins?

 

Muscle growth with plant proteins: a paradigm shift

 

Despite the inferior anabolic properties of plant proteins compared to animal ones, we can apply various strategies to increase these properties and, consequently, the growth of our muscles, placing animal and plant proteins on the same level, at least "on paper". These strategies are threefold:

 

1. fortification of plant-based protein sources with amino acids
2. selecting various plant sources to improve amino acid profiles
3. consuming larger quantities of plant-based protein sources

 

However, the effectiveness of these strategies, especially the second and third, on postprandial muscle protein synthesis (i.e., immediately after meals) still needs to be studied and tested. Don't worry, as soon as there are updates, we will immediately update this section with new discoveries or scientific studies.

 

Why is the peak of essential amino acids after a meal so important?

 

The answer, though simple, is not obvious: the increase in postprandial essential amino acid (EAA) concentrations modulates our protein synthesis rates within our muscles, causing them to increase.

 

In this situation, if we ingest a lower content of essential amino acids or if there is a specific lack of some of them (such as leucine, lysine, and/or methionine), a lower anabolic capacity can occur, and this, as we said before, is much more common when we eat plant-based proteins.

 

What influences postprandial essential amino acid availability?

 

The availability of essential amino acids in our body after a meal is regulated by a series of physiological processes, among the most important of which we can mention:

 

• Protein digestion
• The interpersonal ability of each of us to absorb them
• The intestinal microbiota, i.e., the billions of good bacteria that contribute to our intestinal function
• Amino acid composition
• Essential amino acid content
• The presence or absence of anti-nutritional factors, i.e., substances present in foods that interfere with the absorption of essential nutrients for our body

 

Let's admit it, animal proteins generally contain more essential amino acids

 

In the chart below, we find the essential amino acid (EAA) composition of various animal and plant protein sources compared to human skeletal muscle proteins.

 

Specifically, the composition of the following foods was analyzed:

 

• Oats
• Lupin
• Wheat
• Hemp
• Algae
• Soy
• Brown rice
• Peas
• Corn
• Potatoes
• Milk
• Whey
• Calcium caseinate
• Casein
• Eggs

 

The result of this comparison was what we already expected, i.e., the essential amino acid content in plant proteins like oats (21%), lupin (21%), and wheat (22%) was lower than in animal-derived proteins (whey 43%, milk 39%, casein 34%, and eggs 32%) and human muscle protein (38%).

 

Amino acids and leucine: their content varies greatly in plant proteins

 

Now let's address another point of our comparison that will help us answer our initial question: Do muscles grow more with animal or plant proteins?

 

Let's consider the amino acid profile of the protein sources we just analyzed (if you haven't realized it yet, essential amino acids are the "balancing act" to answer the question we posed today). In the case of plant proteins, the leucine content varies widely, and in some cases, the content is higher than that of animal proteins.

 

Delving a little deeper, in animal proteins, the leucine content varies from 7% (in eggs) to 9% (in milk), human muscle protein stands at 7.6%, while the most incredible data is that of plant proteins, which varies from 5.1% (in hemp) up to 13.5% (in corn).

 

The opposite case concerns methionine and lysine, where the content is typically lower in all plant-based protein sources compared to animal and muscle ones.

 

We can, definitively, state with absolute certainty that there are large differences in the content and composition of essential amino acids found in plant proteins.

 

Therefore, choose plant protein sources very carefully, also considering the ratio between amino acids and not just the protein intake.

 

 

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A useful alternative for vegetarians and vegans who want to eliminate animal proteins from their diet, while still ensuring an excellent amino acid ratio.

 

 

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Essential amino acids are primarily responsible for our muscle growth

 

You understood correctly, we have dwelled on understanding the amino acid composition of the protein sources we ingest precisely for this reason, because essential amino acids are primarily responsible for the growth of our muscles.

 

There is, in fact, a relationship between the dose of essential amino acids we ingest and the stimulation of protein synthesis we activate. Therefore, to promote the growth of our muscles or prevent their loss, it is important to consider the essential amino acid content of the dietary protein source we eat.

 

Now we come to the reason why you have come this far, why you are reading this article, the question that has plagued us from the beginning, we are ready to answer:

 

Do muscles grow more with animal or vegetable proteins?

 

The answer is that animal protein sources are not always the most effective (compared to plant-based ones), although we have observed that the average essential amino acid content of plant proteins is generally lower than that of animal-derived and human skeletal muscle proteins, some plant proteins have a higher essential amino acid content than others.

 

Specifically, soy, brown rice, peas, corn, and potato proteins have an essential amino acid content that meets the requirements recommended by: WHO, FAO, and UNU.

 

Furthermore, the essential amino acid content of potato protein (37%) is indeed higher than casein (34%) and egg (32%).

 

Does aging decrease the ability to utilize proteins?

With aging, does our body maintain the same ability to convert food proteins into available amino acids in the blood? And most importantly: is there a significant difference between eating whole proteins and taking free amino acids from a supplement? Recent research (2024-2026) provides surprising and clinically relevant answers.

 

Dietary Proteins in the Elderly: What Changes with Age

Protein Digestion Becomes More Complex

According to a study published in Amino Acids in 2021 DOI: 10.1007/s00726-021-03000-z, which used isotopic tracers to study protein absorption in healthy elderly individuals (>65 years), significant differences emerge in the kinetics of dietary protein digestion:

• Require prolonged gastric digestion
• Amino acid absorption is gradual and sustained over time
• The plasma peak is reached more slowly (>2-3 hours)
• Amino acid availability is distributed within a 5-hour window

Processed Proteins (minced meat):

• Slightly faster digestion compared to whole meat
• Intermediate absorption between intact and hydrolyzed proteins
• The plasma peak remains relatively slow

Hydrolyzed Proteins (predigested):

• Significantly faster absorption in the first 2 hours
• Earlier and more pronounced plasma peak
• Immediate availability for protein synthesis

The Problem of Reduced Digestive Capacity

As we age, physiological changes occur that impact protein digestion:

1. Reduced gastric secretion (hydrochloric acid, pepsin)
2. Decreased pancreatic enzymes (trypsin, chymotrypsin)
3. Slowed gastric emptying
4. Alterations in intestinal motility

These factors mean that intact dietary proteins require greater digestive effort and may not be completely digested, reducing the effective availability of amino acids.

Free Amino Acids from Supplements: The Metabolic Advantage

Direct and Immediate Absorption

A 2025 study published in Nutrients DOI: 10.3390/nu17162671 directly compared the absorption of free amino acids versus intact proteins (casein) in healthy volunteers:

Key results:

• Free amino acids (L-AA) show faster absorption compared to casein
• The area under the curve (AUC) for total amino acids and BCAAs is significantly greater for L-AA vs casein (p < 0.008)
• Peak plasma concentration is reached much more quickly
• No digestion required: amino acids begin to be absorbed as early as the oral tract and proximal small intestine

The Difference in Leucine Peak

The 2025 study in European Journal of Nutrition DOI: 10.1007/s00394-025-03605-0 specifically examined middle-aged and older adults (50-75 years):

Whey Protein vs Pea Protein:

• Whey protein generates a 32% higher plasma leucine peak compared to pea protein (p = 0.032)
• The area under the curve (iAUC) for leucine is 20% greater with whey (p = 0.012)
• This demonstrates that even among fast-digesting proteins, quality and digestibility significantly influence the plasma peak

Implication: If "fast" proteins like whey already show these differences, free amino acids (which require no digestion) offer an even greater advantage, especially in older adults with reduced digestive capacity.

The Phenomenon of "Anabolic Resistance": A Myth Debunked

Healthy Older Adults: No Resistance if the Stimulus is Adequate

A groundbreaking 2024 study in Journal of Cachexia, Sarcopenia and Muscle DOI: 10.1002/jcsm.13613 demonstrated that healthy, lean older adults do NOT exhibit anabolic resistance when receiving essential amino acids:

Key findings:

• Muscle protein synthesis (MPS) increases identically between young (22±3 years) and older adults (70±3 years)
• Older adults show higher basal levels of proteins involved in amino acid sensing (LAT1 +31%, Rheb +45%, Rag B +31%)
• This represents a compensatory mechanism that maintains anabolic sensitivity

Study conclusion: "Age per se does not cause anabolic resistance in human skeletal muscle" when amino acids are available in optimal form.

The Real Problem: Amino Acid Availability

If healthy older adults do not have intrinsic anabolic resistance, why does sarcopenia occur? The answer lies in amino acid availability, not the ability to utilize them:

1. With dietary proteins: Reduced digestion leads to an insufficient plasma amino acid peak to fully activate mTORC1 (the main anabolic pathway)
2. With free amino acids: The rapid and significant peak ensures a strong anabolic signal that exceeds the activation threshold even with reduced digestive capacity

Dietary Proteins vs. Free Amino Acids: The Direct Comparison

Comparative Table

Experimental Evidence: Hydrolyzed vs. Intact Proteins

Agergaard et al.'s (2021) study showed that even simply pre-digesting proteins (hydrolysis) significantly improves kinetics in older adults:

• Labeled phenylalanine appears in plasma much more quickly with hydrolyzed proteins
• The time to reach peak is reduced by over 40%
• Maximum concentration is reached before that of intact proteins begins to rise

Interpretation: If simple hydrolysis of proteins (which produces small peptides, not free amino acids) already offers this advantage, completely free amino acids offer the maximum possible benefit.

BCAAs and Leucine: The Critical Anabolic Signal

Leucine as an "Anabolic Switch"

A 2025 review in Frontiers in Nutrition DOI: 10.3389/fnut.2025.1709867 highlights the crucial role of leucine as the primary anabolic signal:

Mechanism:

• Leucine directly activates mTORC1 (via Sestrin2 and TSC complex)
• A plasma leucine concentration of >120 μM is necessary to fully activate protein synthesis
• This "leucinemic threshold" is more difficult to reach in older adults with intact dietary proteins

With dietary proteins:

• The leucine peak is gradual and may not exceed the optimal threshold
• The high concentration window is short

With free amino acids (rich in leucine):

• The peak significantly exceeds the threshold
• The anabolic window is maximized

Optimal Metabolic Profiles in Responsive Older Adults

A 2026 metabolomic study in GeroScience DOI: 10.1007/s11357-025-02074-x identified that older adults with better hypertrophic response show:

• Upregulation of leucine, isoleucine, and valine (BCAAs) in muscle
• Absence of catabolites of these amino acids (indicating optimal utilization)
• Enrichment of the urea cycle (efficient amino acid metabolism)

This profile is more easily achievable with free amino acid supplementation, which ensures constant and optimal availability.

The Importance of Exercise and the Role of Immobilization

Exercise: The Multiplier of the Anabolic Effect

The study in Journal of Cachexia, Sarcopenia and Muscle DOI: 10.1002/jcsm.70114 demonstrated that:

• Immobilization completely abolishes anabolic effects, even with optimal amino acid peaks
• Net amino acid balance deteriorates by -261% in the immobilized leg
• Resistance exercise sensitizes muscle to the action of amino acids

Practical implication:

• Dietary proteins + sedentary lifestyle = poor protein synthesis
• Free amino acids + exercise = maximized protein synthesis
• The amino acid-exercise combination is synergistic, not additive

Conclusion: In older adults with metabolic alterations, providing free amino acids may not be sufficient if there are downstream metabolic blocks. An integrated approach (exercise + nutrition + metabolic management) is essential.

Practical Answer to the Initial Question

For Dietary Proteins in Older Adults:

PROS:

• Provide complete nutrients (not just amino acids)
• Gradual and sustained release
• Satiating and nutritious
• Cost-effective

CONS:

• Require optimal digestive capacity (which declines with age)
• Lower and delayed plasma amino acid peak
• May not reach the necessary leucinemic threshold
• Less effective in the post-exercise window (too slow)
• High digestive load (can cause discomfort in elderly with hypochlorhydria)

For Free Amino Acids from Supplements:

PROS:

• Immediate absorption (no digestion required)
• High and rapid plasma peak (30-60 minutes)
• Ensure optimal leucinemic threshold
• Ideal post-exercise (maximum anabolic window)
• No digestive load
• Effective even with reduced digestive capacity
• Precise and controlled dosage

CONS:

• Do not provide accessory nutrients (unless they are in a food matrix)

Conclusions

Based on the latest scientific evidence published between 2024 and 2026:

1. The amino acid peak in the blood does NOT necessarily decrease with age

But the source of amino acids makes a crucial difference:

• Intact dietary proteins: Reduced and delayed peak in elderly due to reduced digestive capacity
• Free amino acids (supplements): High and rapid peak, independent of digestive capacity

2. Healthy elderly individuals do NOT have intrinsic anabolic resistance

The problem is to ensure optimal availability of amino acids:

• With dietary proteins: the peak may be insufficient
• With free amino acids: the peak always exceeds the anabolic threshold

3. Amino acids from plant fermentation offer unique advantages

• Free form (L-amino acids) = optimal absorption
• No digestion required = effectiveness even with hypochlorhydria
• Rapid and marked peak = maximum mTORC1 activation
• Ideal in combination with resistance exercise

Final Recommendation

For the elderly, the combination of quality dietary proteins and targeted supplementation with free essential amino acids represents the optimal approach to:

• Ensure adequate plasma peaks even with reduced digestion
• Maximize muscle protein synthesis
• Preserve muscle mass and function
• Maintain independence and quality of life

Free amino acids from plant fermentation do not replace nutrition but strategically complement it at key moments, bypassing the digestive limitations of aging.

Bibliography

1. Agergaard J, Hansen ET, van Hall G, Holm L. Postprandial amino acid availability after intake of intact or hydrolyzed meat protein in a mixed meal in healthy elderly subjects: a randomized, single blind crossover trial. Amino Acids. 2021;53(6):951-959. DOI: 10.1007/s00726-021-03000-z
2. Daly A, Pinto A, Evans S, et al. Protein Substitute Absorption: A Randomised Controlled Trial Comparing CGMP vs. Amino Acids vs. Micellar Casein in Healthy Volunteers. Nutrients. 2025;17(16):2671. DOI: 10.3390/nu17162671
3. Korzepa M, Marshall RN, Rogers LM, et al. Postprandial plasma amino acid and appetite responses to a low protein breakfast supplemented with whey or pea protein in middle-to-older aged adults. European Journal of Nutrition. 2025;64(2):86. DOI: 10.1007/s00394-025-03605-0
4. Horwath O, Moberg M, Hodson N, et al. Anabolic Sensitivity in Healthy, Lean, Older Men Is Associated With Higher Expression of Amino Acid Sensors and mTORC1 Activators Compared to Young. Journal of Cachexia, Sarcopenia and Muscle. 2024;16(1):e13613. DOI: 10.1002/jcsm.13613
5. Wu J. Effects of branched-chain amino acids on the muscle-brain metabolic axis: enhancing energy metabolism and neurological functions, and endurance exercise in aging-related conditions. Frontiers in Nutrition. 2025;12:1709867. DOI: 10.3389/fnut.2025.1709867
6. de Jong JCBC, Jameson TSO, Andrews RC, et al. Anabolic Effects of Salbutamol Are Lost Upon Immobilization. Journal of Cachexia, Sarcopenia and Muscle. 2025;16(6):e70114. DOI: 10.1002/jcsm.70114
7. Lim C, Lixandrão M, Trivedi D, et al. Skeletal muscle metabolomic markers underlying the enhanced exercise-induced hypertrophy response to resistance training in older adults. GeroScience. 2026;Jan 5. DOI: 10.1007/s11357-025-02074-x
8. Kheirandish M, Cheraghloo N, Tavasoli N, et al. Amino acid metabolic signatures of dynapenic obesity in older adults: a (principal component analysis) PCA-based sex-stratified analysis in the Bushehr elderly health program. Journal of Diabetes and Metabolic Disorders. 2025;24(2):218. DOI: 10.1007/s40200-025-01746-x