Plant vs Animal Proteins: Which One’s Better?
I’ve been very clear about the importance of muscle mass and aging. Gaining or maintaining muscle requires resistance training, a caloric intake above your basal metabolic rate, and adequate protein. That last piece, protein, tends to generate a lot of debate. I was recently reading through a few papers, and as expected, there’s plenty of back and forth on which type of protein is “better”: plant or animal.
The answer, like most things in nutrition, is it depends. So, this week I’m breaking down the key differences between plant and animal proteins, how we measure protein quality, and how to think through goals when choosing sources.
What Are Proteins and Amino Acids?
Proteins, made by different combinations of amino acids, are the cornerstone of the structure and function of the human body.1 Amino acids are organic compounds containing both a carboxyl group (made of carbon, oxygen, and hydrogen) and an amino group (made of nitrogen and hydrogen). There are 20 amino acids in total, and your body uses them in various combinations to build every protein it needs.
Nine of these are considered essential amino acids, meaning the human body can’t synthesize them, so they must come from food. Five of them are conditional, meaning the body can synthesize them under normal conditions but requires dietary intake during times of rapid growth or stress. Without adequate intake of all essential amino acids, our body can’t effectively build and repair muscle tissue or perform countless other metabolic functions.
The following chart is a list of the 20 amino acids with their functions.
Amino Acid | Essential? | Key Functions & Contributions |
Alanine | No | Energy source for muscles; helps convert glucose for energy2,3 |
Arginine | Cond. | Supports immune function, wound healing, blood flow (via nitric oxide), growth2-7 |
Asparagine | No | Important for brain development and function; helps make proteins2,3 |
Aspartate | No | Energy for cells; major excitatory neurotransmitter in the brain2,3,8 |
Cysteine | Cond. | Antioxidant (glutathione production); supports immune system; made from methionine2,3,5 |
Glutamate | No | Major excitatory neurotransmitter; energy for intestine; helps make other amino acids2-4,8 |
Glutamine | Cond. | Maintains gut health; supports immune system; energy for the intestine; helps muscle recovery2-7 |
Glycine | No | Inhibitory neurotransmitter; helps with sleep, collagen, and detoxification2-4,8,9 |
Histidine | Yes | Makes histamine (immune response, digestion); needed for growth and tissue repair3,10,11 |
Isoleucine | Yes | Muscle repair; energy regulation; blood sugar control; branched-chain amino acid (BCAA)3,6,9,12,13 |
Leucine | Yes | Stimulates muscle protein synthesis (mTOR pathway); energy; BCAA2-7,9,12,13 |
Lysine | Yes | Needed for growth, tissue repair, immune function; helps absorb calcium3,10,11 |
Methionine | Yes | Antioxidant; helps make cysteine; supports liver health and metabolism3,10,11 |
Phenylalanine | Yes | Makes tyrosine (for dopamine, norepinephrine); supports brain function3,8,10,11 |
Proline | Cond. | Collagen production (skin, joints); wound healing; supports gut health2,3,5,7 |
Serine | No | Brain function; helps make other amino acids and cell membranes2,3,11 |
Threonine | Yes | Collagen and tooth enamel formation; supports gut health3,10,11 |
Tryptophan | Yes | Makes serotonin and melatonin (mood, sleep); supports immune function2-5,7,8,10,13 |
Tyrosine | Cond. | Makes dopamine, norepinephrine, thyroid hormones; made from phenylalanine3,8,11 |
Valine | Yes | Muscle growth and repair; energy; BCAA3,6,9,12,13 |
Complete vs. Incomplete Proteins
One of the fundamental differences between protein sources is whether they’re “complete” or “incomplete.”
A complete protein contains all nine essential amino acids in sufficient amounts to support the body’s needs. Most animal proteins fall into this category, including meat, poultry, fish, eggs, and dairy. There are a few plant-based exceptions, including soy, quinoa, buckwheat, and amaranth.1
An incomplete protein lacks one or more essential amino acids. Many plant proteins fall into this group because their amino acid profiles are limited. For example, grains are often low in lysine, while legumes are typically low in methionine.14
The traditional thinking has been that plant proteins must be combined with other complementary plant proteins at each meal to provide the full complement of essential amino acids. This has since been debunked. While complementary pairing is still recommended, it can be done throughout the day, rather than at each meal.15
How Protein Quality is Measured (PDCAAS vs. DIAAS)
Not all proteins are created equal when it comes to how well your body can digest, absorb, and use them. There are two separate scores that have been developed to incorporate these aspects of protein quality.
The PDCAAS (Protein Digestibility-Corrected Amino Acid Score) considers amino acid content and digestibility. Proteins with the full complement of essential amino acids that are also highly digestible are given a score of 100%. Examples are casein, whey, milk, and eggs. Plant proteins, with the exception of soy isolates, are below 100%. Wheat gluten has a PDCAAS of 25% because of its low digestibility.16 However, this score does not take into account the digestibility of each individual amino acid, which ignores how well each amino acid is absorbed.
The newer method is the DIAAS (Digestible Indispensable Amino Acid Score) which accounts for this factor as well. Scores can be over 100, as is the case with milk and eggs. However, plant proteins tend to score lower than animal proteins with this scoring system as well.16
One of the main issues with plant protein digestibility is that there are a lot of other nutrients and vitamins in plants that are harder to digest, such as fiber. So while they may not offer a complete essential amino acid profile, they do provide many other required nutrients. It is also important to note that proteins with low scores do not mean they are “bad” foods. It just means they need to be paired with other protein containing foods for a balanced amino acid profile.
Leucine: The Key Amino Acid for Muscle Growth
When it comes to stimulating muscle protein synthesis, the process by which your body builds new muscle tissue, one amino acid stands out: leucine. Leucine acts like a molecular “on switch” for MPS through the mTOR pathway.17-19
Research demonstrates that hitting a necessary daily leucine threshold will stimulate muscle growth, but that value varies based on goals, age, and sex.18,20-22 Animal proteins, especially whey, are naturally rich in leucine, making it easier to reach that threshold with smaller amounts.17
Plant proteins often have lower leucine content, which means larger portions or strategic combinations may be needed to hit the same anabolic signal. For example, a modest serving of whey can hit the leucine threshold, whereas it may take a significantly larger serving of rice or pea protein to match it. For people following plant-based diets, this isn’t a dealbreaker, it just requires awareness and planning.
Health, Goals, and Medical Considerations for Protein Choice
Your protein choices should ultimately align with your goals and health status. Someone trying to build muscle aggressively may prioritize high-leucine, highly digestible sources. Someone managing dyslipidemia or atherosclerosis might choose leaner animal sources or more plant-based options to keep saturated fat low.
I’ll use myself as an example. I recently found out that my Lp(a) is extremely high, which means I need to reduce every other risk factor for heart disease. I now limit saturated fat intake to less than 6% of my daily calories. I still include animal protein, but I’m very deliberate about the sources I choose. At the same time, I’m focused on maintaining and increasing muscle mass, so quality and leucine content remain top of mind.
Ethical and Environmental Considerations in Animal Proteins
For some people, the choice between plant and animal proteins isn’t primarily about nutrition. It’s about ethics or sustainability. Plant-based proteins generally have a lower environmental footprint, and some individuals avoid animal products entirely for ethical reasons.
These are valid considerations. From a strictly nutritional standpoint, if you choose plant proteins exclusively, you just need to be intentional about variety and total intake to cover all essential amino acids.
How to Choose the Right Protein for Your Goals
There isn’t a single “best” protein source for everyone. Instead, ask yourself a few questions:
- What are your health and fitness goals—muscle maintenance, muscle gain, metabolic health, or disease risk reduction?
- Do you have any medical conditions that affect your dietary choices (e.g., dyslipidemia, kidney disease, elevated Lp(a))?
- Do you have ethical or environmental considerations guiding your diet?
- How much effort are you willing to put into planning complementary proteins if you choose a plant-based pattern?
If your goal is to build or maintain muscle mass, you’ll want to ensure you’re hitting your total daily protein needs, getting adequate leucine at each meal, and choosing sources that are digestible, complete, or strategically combined if plant based.
Bottom Line: Plant vs. Animal Proteins in a Healthy Diet
The plant vs. animal protein debate isn’t black and white. It’s very grey. The “better” source depends on your goals, your health, and your values. Both can fit into a healthy, muscle-supporting diet when chosen thoughtfully.
Whether you reach for salmon, lentils, tofu, or whey, understanding amino acids, leucine, and protein quality gives you the tools to build a diet that supports your long-term health and strength.
Disclaimer: Even though I’m a doctor, I’m not your doctor—and reading this blog does not establish a doctor–patient relationship. This information is intended for general educational purposes only and should not be taken as personalized medical advice. Always speak with your own healthcare provider before making decisions about your health.
References
- Heymsfield SB, Shapses SA. Guidance on energy and macronutrients across the life span. New England Journal of Medicine. 2024;390(14):1299-1310.
- Wu G. Functional Amino Acids in Growth, Reproduction, and Health. Advances in Nutrition (Bethesda, Md). 2010;1(1):31-37. doi:10.3945/an.110.1008
- Heymsfield SB, Shapses SA. Guidance on Energy and Macronutrients across the Life Span. The New England Journal of Medicine. 2024;390(14):1299-1310. doi:10.1056/NEJMra2214275
- Wu G. Amino Acids: Metabolism, Functions, and Nutrition. Amino Acids. 2009;37(1):1-17. doi:10.1007/s00726-009-0269-0
- Flynn NE, Shaw MH, Becker JT. Amino Acids in Health and Endocrine Function. Advances in Experimental Medicine and Biology. 2020:97-109.
- Wu G. Functional Amino Acids in Nutrition and Health. Amino Acids. 2013;45(3):407-411. doi:10.1007/s00726-013-1500-6
- He W, Wu G. Metabolism of Amino Acids in the Brain and Their Roles in Regulating Food Intake. Advances in Experimental Medicine and Biology. 2020:167-185.
- Watford M, Wu G. Protein. Advances in Nutrition (Bethesda, Md). 2018;9(5):651-653. doi:10.1093/advances/nmy027
- Hou Y, Wu G. Nutritionally Essential Amino Acids. Advances in Nutrition (Bethesda, Md). 2018;9(6):849-851. doi:10.1093/advances/nmy054
- Furuya S, Fukuwatari T. Physiological Functions of Proteinogenic Amino Acid. Journal of Nutritional Science and Vitaminology. 2022;68(Supplement):S28-S30. doi:10.3177/jnsv.68.S28
- Posey EA, Bazer FW, Wu G. Amino Acids and Their Metabolites for Improving Human Exercising Performance. Advances in Experimental Medicine and Biology. 2021:151-166.
- Paudel S, Wu G, Wang X. Amino Acids in Cell Signaling: Regulation and Function. Advances in Experimental Medicine and Biology. 2021:17-33.
- Uneyama H, Kobayashi H, Tonouchi N. New Functions and Potential Applications of Amino Acids. Advances in Biochemical Engineering/Biotechnology. 2017:273-287.
- Soh BXP, Smith NW, von Hurst PR, McNabb WC. Achieving High Protein Quality Is a Challenge in Vegan Diets: A Narrative Review. Nutr Rev. Jul 1 2025;83(7):e2063-e2081. doi:10.1093/nutrit/nuae176
- Marsh KA, Munn EA, Baines SK. Protein and vegetarian diets. Med J Aust. Aug 19 2013;199(S4):S7-s10. doi:10.5694/mja11.11492
- Berrazaga I, Micard V, Gueugneau M, Walrand S. The role of the anabolic properties of plant-versus animal-based protein sources in supporting muscle mass maintenance: a critical review. Nutrients. 2019;11(8):1825.
- Thomas DT, Erdman KA, Burke LM. Nutrition and Athletic Performance. Medicine & Science in Sports & Exercise. 2016;48(3)
- Ely IA, Phillips BE, Smith K. A Focus on Leucine in the Nutritional Regulation of Human Skeletal Muscle Metabolism in Ageing, Exercise and Unloading States. Clinical Nutrition (Edinburgh, Scotland). 2023;42(10):1849-1865. doi:10.1016/j.clnu.2023.08.010
- Anthony JC, Anthony TG, Kimball SR, Jefferson LS. Signaling Pathways Involved in Translational Control of Protein Synthesis in Skeletal Muscle by Leucine. The Journal of Nutrition. 2001;131(3):856S-860S. doi:10.1093/jn/131.3.856S
- Glynn EL, Fry CS, Drummond MJ. Excess Leucine Intake Enhances Muscle Anabolic Signaling but Not Net Protein Anabolism in Young Men and Women. The Journal of Nutrition. 2010;140(11):1970-1976. doi:10.3945/jn.110.127647
- Jäger R, Kerksick CM, Campbell BI. International Society of Sports Nutrition Position Stand: Protein and Exercise. Journal of the International Society of Sports Nutrition. 2017;14:20. doi:10.1186/s12970-017-0177-8
- Lixandrão ME, Longobardi I, Leitão AE. Daily Leucine Intake Is Positively Associated With Lower Limb Skeletal Muscle Mass and Strength in the Elderly. Nutrients. 2021;13(10):3536. doi:10.3390/nu13103536
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