Last updated on June 2, 2025
In the strength-training world, it’s dogma. “Supplement with protein.” Some take it further, recommending the specific quantity, source, amino acid composition, and timing pre- and post-workout. But will it help you build bigger muscles? Will they develop faster? Will you gain any extra strength, at all?
A critical review published in the Journal of Nutrition examined these questions and others by analyzing the current body of research. The authors studied observational data, randomized controlled trials, crossover studies, and meta-analyses—studies that combine data from multiple experiments to generate broader insights—focusing on how protein and amino acid intake affect muscle growth during strength training.
Protein Can Enhance Muscle Growth and Repair
Let’s start with the basics. Your muscles are the largest reservoir of protein in your body. Constant cycles of protein synthesis and breakdown occur within your muscle cells. Strength training tips the balance, promoting net muscle protein synthesis, which results in hypertrophy (muscle growth) and improved strength.
The key to optimizing muscle protein synthesis (MPS) lies in providing the body with adequate, digestible amino acids. Among these, leucine, a branched-chain amino acid (BCAA), plays a critical role in activating the mTOR pathway, one of the key metabolic signals that drive MPS. Supplementing with protein after strength training, especially one that includes leucine-rich sources like whey, can therefore accelerate the muscle-building process, particularly for beginners or those returning to training after a break.
Protein Helps Preserve Muscle During Weight Loss
Weight loss often comes at a cost—lean muscle loss. This is problematic not only for aesthetics but also for long-term metabolic health. Muscle helps maintain a higher resting metabolic rate and supports physical function, particularly in older adults.
Several studies have shown that consuming more high-quality protein during caloric restriction helps preserve muscle mass. In a 2016 study published in Obesity, adults who consumed more protein while dieting lost more fat and retained more muscle compared to those who consumed lower amounts. This has crucial implications for aging populations, who are more vulnerable to sarcopenia (muscle loss associated with aging). By incorporating adequate protein, individuals can improve physical resilience and reduce the risk of falls and functional decline.
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What’s the Right Amount—and Type—of Protein?
The debate continues about how much protein is enough, but most experts agree that active individuals need more than the standard Recommended Daily Allowance (RDA) of 0.8 grams per kilogram of body weight. The International Society of Sports Nutrition recommends 1.4–2.0 g/kg/day for physically active people. But quality matters as much as quantity. Protein quality refers to the amino acid composition and digestibility of the protein. Animal-based proteins (e.g., whey, eggs, meat) generally have a complete profile of essential amino acids, including leucine, while many plant-based proteins are incomplete.
That said, plant-based options like pea, soy, and rice protein can still be effective if consumed in sufficient quantities or blended to create a complete amino acid profile. A study published in Nutrients in 2019 found that pea protein was just as effective as whey for muscle growth when consumed post-workout by resistance-trained men.
Adaptation Diminishes the Protein Effect
Here’s a lesser-known truth: the anabolic (muscle-building) response to protein supplementation may diminish over time. The reason? Adaptation.
Your body becomes less sensitive to amino acid intake with consistent training. Studies have shown that muscle protein synthesis declines as training age increases. In fact, the enhanced response seen in beginners or detrained individuals may fade after 3–6 weeks of consistent training. This doesn’t mean protein is useless—but it does suggest that once you’ve met your daily needs for essential amino acids, additional protein may not provide added benefits for strength or hypertrophy.
What about long-term performance? Meta-analyses suggest that while protein may enhance short-term muscle gain, it doesn’t provide significant additional strength increases over time beyond the gains made through training alone.
Individual Variability and the Role of Personalization
One of the more fascinating findings from the Journal of Nutrition review is the wide variation in how individuals respond to protein intake. Roughly 25% of people may be “non-responders,” meaning they see little or no benefit from protein supplementation post-exercise. The reasons for this variability remain unclear but could be related to genetics, microbiome diversity, baseline protein status, or training history.
Personalized nutrition, which is tailoring recommendations based on an individual’s biomarkers, lifestyle, and goals, is gaining momentum. While generalized guidelines provide a helpful baseline, individual testing and tracking may be the future of optimizing protein intake and supplementation strategies.
Protein: More Than Just Muscle
Beyond hypertrophy and strength, protein plays other important roles:
- It contributes to satiety and appetite regulation.
- It supports immune function and cellular repair.
- It may help improve glycemic control in those with insulin resistance.
Research continues to uncover new benefits and contexts in which protein can optimize health outcomes. For example, higher-protein diets have been linked to better weight maintenance post-weight loss and improved body composition in middle-aged adults.
Make Protein Work for You
So, what should you do with all this information? Here are a few key points:
- Get Enough Protein: Aim for at least 1.4–2.0 g/kg/day if you’re active, distributed evenly across meals.
- Prioritize Quality: Choose complete proteins or combine complementary plant-based options.
- Consider Timing: Post-workout protein can be helpful—especially for beginners or those returning to training.
- Track Your Response: Not everyone responds the same; personalize your approach over time.
Ultimately, protein supplementation can be a useful tool in your fitness toolbox—but it’s not a magic bullet. Combine it with structured resistance training, good sleep, and a balanced diet to get the best results.
Source: Reidy PT, Rasmussen BB. Role of Ingested Amino Acids and Protein in the Promotion of Resistance Exercise–Induced Muscle Protein Anabolism. The Journal of Nutrition. 2016;146(2):155-183. [DOI:10.3945/jn.114.203208](https://doi.org/10.3945/jn.114.203208)
Author:
Brian Bender, PhD is a biomedical engineer that works in the field of data-driven nutrition with the mission of improving global dietary eating patterns and helping you reach your dietary goals. Learn more about how to easily personalize your diet using more accurate dietary intake data. Brian can be contacted at brian@myintakepro.com.
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