Have you ever stood in front of a shelf stacked with protein powders, feeling completely overwhelmed by the sheer number of options? Which protein source is actually the best? Whey, casein, soy, pea, rice, hemp, egg white, beef isolate—there’s even cricket protein now. And that’s just the powdered stuff. Then there’s the age-old question of whether we should be getting our protein from whole foods instead. Are we better off sticking to chicken, fish, eggs, and dairy? Or can a shake do the trick just as well?
This debate has been raging for years, dating back to the rise of bodybuilding culture in the mid-20th century, when whey protein first gained popularity, and even further to ancient times when societies debated the benefits of meat-heavy diets versus plant-based sustenance. Bodybuilders swear by whey protein, plant-based athletes champion pea and soy, and dietitians urge people to get their nutrients from real food. Everyone’s got an opinion, and if you’ve ever found yourself wondering which protein is actually best, you’re not alone.
Luckily, research is always ongoing, and a recent study tackled this very question, comparing plant and animal protein sources to see how they stack up for muscle mass, strength, and performance.
The Study: How It Was Done and What They Found
The study in question was a systematic review and meta-analysis of 43 randomised controlled trials, looking at how different protein sources impact muscle mass, strength, and physical performance. Meta-analyses are particularly valuable in research because they combine data from multiple studies, increasing statistical power and providing a more comprehensive view of a topic than a single study alone. The researchers pulled together data from over 1,500 participants and analysed whether plant or animal protein made a meaningful difference when it came to building muscle and maintaining strength.
Here’s what they found: overall, animal protein had a slight edge over plant protein for muscle mass, but there was no major difference in strength or physical performance between the two. Interestingly, the superiority of animal protein was more noticeable in younger adults under 60, while older adults didn’t seem to benefit as much from animal protein over plant-based sources.
However, not all plant proteins are created equal. Soy protein performed just as well as milk protein for muscle mass, but when it came to other plant proteins like rice, oat, chia, and potato, animal protein outperformed them.
Another key finding; resistance training mattered more than protein type. This means that if your goal is to build muscle, the most important factor isn’t just the protein source, but whether you’re engaging in resistance training. If you’re consuming plant protein, pairing it with a solid strength training routine can help compensate for any small differences in muscle growth compared to animal protein. On the other hand, if you’re not strength training, focusing on high-quality protein sources alone won’t yield the same muscle-building benefits. When people lifted weights, animal protein did have a stronger effect on muscle mass than plant protein, but without resistance training, the differences between the two shrank considerably.
Breaking Down the Key Findings
1. Soy Holds Its Own, but Other Plant Proteins Lag Behind
One of the most surprising results was that soy protein was just as effective as milk protein for maintaining and building muscle mass. That’s great news for vegetarians and vegans who want a plant-based option without compromising on muscle-building potential.
However, other plant proteins didn’t fare as well. Rice, oat, chia, and potato protein fell short when compared to animal-based proteins. That suggests that not all plant proteins are interchangeable, and some may require additional supplementation (like extra leucine) to match the muscle-building power of animal protein.
2. Younger Adults Respond Better to Animal Protein—But Why?
The study found that younger people under 60 had a stronger response to animal protein than plant protein when it came to muscle growth. This seems a little counterintuitive because older adults typically have a harder time maintaining muscle and might benefit from a more bioavailable protein source.
One possible explanation is that younger muscles are simply more responsive to protein overall and can make better use of higher-quality sources like meat and dairy. In contrast, older adults may experience anabolic resistance, where the body is less efficient at using protein to build muscle, making the source of protein less of a determining factor.
3. Resistance Training is the Real Game Changer
Regardless of whether participants consumed plant or animal protein, the biggest factor in muscle growth was resistance training. People who engaged in weight training while consuming animal protein saw better muscle gains than those who did the same with plant protein.
However, in people who weren’t lifting weights, there was little difference between protein types.
This reinforces the idea that diet alone isn’t enough—exercise plays a crucial role in muscle maintenance and growth. You can consume the highest-quality protein in the world, but if you’re not challenging your muscles, the impact is going to be limited.
4. Whole-Food Plant-Based Diets Had a Negative Effect on Muscle Mass
While supplementing with soy protein seemed fine, switching entirely to a plant-based diet led to a reduction in muscle mass compared to eating a mixed diet with animal protein. This could be due to the lower digestibility of some plant proteins, as well as differences in amino acid composition.
Many plant proteins contain anti-nutritional factors—compounds that interfere with digestion and absorption. For example, lectins and protease inhibitors, which are found in legumes, can make it harder for the body to break down and utilise protein.
That’s not to say you can’t build muscle on a plant-based diet, but it does suggest that careful planning is needed to ensure adequate protein intake from high-quality sources.
5. Non-Soy Plant Proteins Don’t Always Match Their Amino Acid Content
Another interesting takeaway was that even when non-soy plant proteins (like rice and potato) had comparable essential amino acid content to animal protein, they still didn’t perform as well for muscle growth.
This suggests that protein quality isn’t just about amino acid content—it’s also about digestibility and how well the body absorbs and utilises the protein. Some plant proteins may have a structure that makes them harder to break down, reducing their effectiveness compared to animal proteins.
6. More Muscle Mass Didn’t Mean Better Physical Performance
Perhaps the most unexpected finding was that neither plant nor animal protein had a major impact on physical performance. This suggests that other factors, such as neuromuscular coordination, endurance, and overall training methods, may play a larger role in determining functional ability. While protein contributes to muscle mass, aspects like agility, mobility, and cardiovascular fitness could be more influential in real-world physical performance outcomes. Despite differences in muscle mass and strength, measures like walking speed and balance didn’t improve significantly in either group.
This suggests that muscle mass alone doesn’t guarantee better movement or function—other factors like neuromuscular coordination, endurance, and joint health might play a bigger role in overall physical performance.
So, Which Protein is Best?
The takeaway? It depends on your goals.
- If you’re looking to build muscle and strength, both animal and plant proteins can do the job, but soy is the most reliable plant-based option.
- If you’re following a plant-based diet, you may need to be strategic about getting enough high-quality protein sources.
- If you’re not engaging in resistance training, the differences between protein sources matter much less.
- And if your focus is physical performance rather than muscle size, protein type isn’t the most important factor to worry about.
At the end of the day, the best protein is the one you can consistently eat and enjoy. Whether that’s a steak, a scoop of whey, or a plant-based shake, the key is making sure you get enough of it, especially if you’re working out.
Reference
Reid-McCann, R. J., Brennan, S. F., Ward, N. A., Logan, D., McKinley, M. C., & McEvoy, C. T. (2025). 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. Click here to review the full research article.
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