Protein is one of nutrition’s most essential and debated topics. It goes far beyond its reputation as the building block of muscle, playing a crucial role in metabolism, insulin sensitivity, and the prevention of diseases like type 2 diabetes and sarcopenia. But questions abound: How much protein is enough, and can too much, particularly from animal sources, be harmful?
Protein intake, paired with resistance training, drives muscle repair and growth, enhancing athletic performance, improving metabolic health, and promoting longevity by protecting against age-related frailty. Research suggests that higher protein intakes—ranging from 1.2 to 1.6 grams per kilogram of body weight—are more beneficial than the standard RDA of 0.8 grams, with even higher amounts being optimal for body recomposition.
Despite concerns about the links between high-protein diets and health risks like cancer, heart disease, or kidney dysfunction, lifestyle factors such as physical activity profoundly influence these outcomes. Exercise can redirect growth factors like IGF-1 towards muscle and brain repair, potentially mitigating risks in other tissues. Differences between animal and plant proteins also play a role in muscle protein synthesis, with strategies available for vegetarians and vegans to meet their needs through varied sources, higher intake, and plant-based protein concentrates.
Timing and distribution of protein matter, too. Evenly spaced protein intake across meals optimizes muscle protein synthesis, while the once-emphasized “post-exercise anabolic window” may be more flexible than previously thought. The amino acid leucine also emerges as a key player, activating muscle-building pathways and informing considerations around protein quality.
Protein is more than a macronutrient—it’s a tool for building muscle, enhancing performance, and promoting longevity, offering a path to a stronger, healthier, and frailty-free future.
Muscle mass and strength decline significantly with age. Starting at 50, the average person loses about 1% of their muscle mass each year, and strength declines even faster—by approximately 3% annually. Without regular strength training, this rate accelerates to a 4% loss of strength annually by age 75. This decline contributes to frailty and increases the risk of falls and fractures, including hip fractures, which are often fatal. Research shows that individuals who experience fragility fractures have double the mortality risk, with 22–58% of those with hip fractures dying within 12 months.
Strength training is the cornerstone for preventing muscle loss and building reserves for later life. Combining resistance training with adequate protein intake amplifies these benefits. A meta-analysis led by Dr. Stuart Phillips found that individuals consuming 1.6 grams of protein per kilogram of body weight daily while engaging in resistance training increased their muscle mass by 27% and their strength by 10%, compared to those who trained without extra protein. Optimizing protein intake, particularly for older adults, is essential to maintaining muscle mass and strength.
Muscle accounts for 30–40% of lean body mass, providing far-reaching benefits beyond strength. More muscle enhances metabolism, improves insulin sensitivity, and protects against type 2 diabetes. It also reduces the risk of frailty, falls, and fractures, which can dramatically improve quality of life in older adults. Importantly, higher muscle mass is associated with a 30% reduction in early mortality risk, whereas higher fat mass increases that risk by 56%.
Anabolic resistance, a reduced muscle anabolic response to protein intake, is a major factor in muscle loss as we age. Older individuals require nearly double the protein per meal to achieve the same muscle-building effect as younger people. This means that older adults should aim for 0.4g of protein per kilogram of body weight per meal—equivalent to 32 g for an 80 kg person—to stimulate muscle protein synthesis.
However, physical inactivity exacerbates anabolic resistance, reducing insulin sensitivity and worsening muscle loss. The good news is that exercise reverses these effects. When older adults exercise before consuming protein, their muscle anabolic response mirrors that of younger adults. Active older individuals experience less anabolic resistance, underscoring the importance of regular physical activity alongside higher protein intake.
Muscle strength and size can increase at any age with consistent training. A study involving adults aged 90 and older showed that 8 weeks of high-intensity strength training resulted in a 174% increase in muscle strength and a 48% increase in leg muscle size. These results demonstrate that even individuals in their ninth decade of life can achieve substantial improvements in muscle health, challenging the notion that aging must be synonymous with frailty.
Protein needs vary based on individual goals, such as building muscle, maintaining it, or improving body composition. Calculating protein intake based on lean body mass or an adjusted ideal body weight is preferred to avoid unrealistic targets for individuals with higher body fat percentages. While the Recommended Dietary Allowance (RDA) for protein is 0.8 grams per kilogram of body weight per day, this amount is widely considered inadequate for optimal health. The RDA is based on nitrogen balance studies, which have significant limitations.
Stable isotope studies suggest that the optimal protein intake is closer to 1.2 to 1.6 grams per kilogram of body weight daily (0.54 to 0.72 grams per pound). Evidence supports this higher intake, particularly in older adults, where consuming at least 1.2g/kg per day can prevent lean mass loss and reduce frailty by 30%. For those engaged in resistance training, 1.6g/kg per day has been shown to maximize gains in lean mass, with a 27% increase compared to a 1.2g/kg intake.
Higher protein intake offers several benefits for those aiming to lose fat while maintaining or gaining muscle. Protein improves satiety, helping control hunger, and supports fat loss by preserving lean body mass during calorie restriction. Combined with resistance training, a high-protein diet ensures more weight loss comes from fat rather than muscle. For body recomposition, a protein intake above 1.6g/kg per day may provide additional advantages.
Professional or high-level athletes may benefit from even higher protein intakes to gain a marginal edge in muscle protein synthesis. For these individuals, intakes as high as 2.2g/kg (1g per pound) daily can be advantageous.
The belief that high protein diets harm kidney health is unfounded for individuals without pre-existing kidney conditions. While a higher protein intake increases kidney filtration rates, this is a normal adaptive response and not indicative of kidney damage. Research shows that protein intakes as high as 3.2 to 4.5g/kg daily for up to one year are safe and cause no adverse effects on kidney function, even in populations at risk, such as individuals with obesity or diabetes. Emerging studies suggest that a higher protein intake may reduce mortality risk in people with chronic kidney disease, challenging traditional protein restriction guidelines.
How we distribute our daily protein intake has long been debated, but emerging evidence shows that the body can effectively utilize even large doses of protein.
While spreading protein intake evenly across 3–4 meals is ideal for maximizing muscle protein synthesis, consuming fewer, higher-protein meals is not ineffective. For instance, studies by Dr. Luc van Loon and colleagues found that consuming 100 grams of protein after exercise elicited a robust and prolonged anabolic response, dispelling the myth that the body cannot use more than 20–25 grams of protein in one sitting. This suggests that focusing on total daily protein intake is more critical than worrying about precise distribution.
The anabolic window, traditionally defined as the 30-minute to 2-hour post-exercise period, has been re-evaluated by recent research. While muscle protein synthesis is elevated during this time, it remains significantly heightened for up to 24 hours after exercise. Additionally, studies show no meaningful difference between pre- and post-exercise protein intake regarding effects on muscle growth and strength, so the timing of protein relative to exercise is flexible. However, consuming protein immediately after a workout can be beneficial for those seeking marginal gains in muscle mass or strength, particularly for fasted exercisers.
Consuming protein before bed is an effective strategy for increasing total daily intake and enhancing overnight muscle recovery. Studies by Dr. Luc van Loon demonstrate that protein consumed before sleep is digested and absorbed overnight, increasing muscle protein synthesis rates and improving net protein balance. This strategy is particularly beneficial for those engaging in resistance exercise earlier in the day. A nightly pre-sleep intake of about 30 grams of protein during training can improve muscle mass and strength without suppressing morning appetite or muscle protein synthesis. However, those not actively training should consider the potential impact of reduced insulin sensitivity near bedtime.
High-quality proteins are efficiently digested and utilized to maximize muscle protein synthesis. Factors such as digestibility, whether the protein is plant- or animal-based, and its amino acid composition all contribute to its quality. A key determinant is the presence of leucine, a branched-chain amino acid that acts as the primary driver of muscle protein synthesis by activating the mTOR pathway.
Leucine thresholds, around 2–3 grams per meal, must be met to stimulate muscle protein synthesis effectively. This can be obtained by consuming 20 grams of a high-quality protein such as whey protein. While leucine triggers this process, all essential amino acids are needed to sustain it for 4–6 hours. Aging increases the leucine threshold, but regular exercise improves muscle sensitivity to leucine, helping older adults overcome this challenge.
From the perspective of muscle protein synthesis, animal-based proteins are superior. They are denser in protein, more digestible, and contain a complete amino acid profile, including essential amino acids like leucine. In contrast, plant-based proteins often have lower protein density, reduced digestibility due to fiber, and incomplete amino acid profiles, making it harder to stimulate a robust anabolic response.
That said, plant-based eaters can optimize their protein intake by:
Despite these differences, studies show that vegetarian and vegan diets can support muscle protein synthesis and strength gains if total daily protein intake is sufficiently high.
Protein supplements like whey and casein provide convenient, high-quality options. Whey protein, rich in leucine and rapidly digested, is particularly effective for stimulating muscle protein synthesis at rest and after exercise. Casein, on the other hand, digests more slowly, offering a prolonged release of amino acids that can sustain muscle protein synthesis over time. In contrast, collagen protein, while rich in glycine and proline, lacks essential amino acids like leucine. As such, it is suboptimal for enhancing muscle protein synthesis and building muscle. However, collagen may have specific benefits for joint and connective tissue health.
Some researchers argue that a high protein intake, particularly from animal sources, may increase cancer risk and accelerate aging. This hypothesis is based on laboratory studies in animals and observational studies in humans. For instance, one study found that middle-aged adults consuming high-protein diets (20% of daily calories) were 75% more likely to die from any cause and four times more likely to die from cancer. However, these risks often disappear when accounting for other lifestyle factors such as obesity, smoking, heavy drinking, or sedentary behavior. Among healthy individuals, high-protein diets do not show the same associations with mortality, suggesting that lifestyle context is crucial.
Protein-rich diets, especially those high in animal protein, increase IGF-1 levels. IGF-1 supports muscle growth, repair, and brain health but may also promote the survival of precancerous cells, potentially raising cancer risk. However, overly low IGF-1 levels have their own risks, such as impaired brain health, as evidenced by studies showing brain matter loss with extreme calorie restriction.
Recent research highlights a U-shaped relationship between IGF-1 levels and mortality, with both very high and very low levels linked to increased death rates. For most people, an optimal range of IGF-1 (120–160 ng/mL) may balance these risks, though these recommendations are often aimed at sedentary individuals, not active ones.
Exercise fundamentally alters how IGF-1 behaves in the body. It reduces circulating IGF-1 levels, redirecting them to where they’re most beneficial: muscle and the brain. In muscles, IGF-1 supports repair and growth by increasing receptor density and sensitivity. In the brain, IGF-1 promotes neurogenesis, particularly in memory-critical areas like the hippocampus. Exercise also binds IGF-1 to protective proteins, reducing its availability to precancerous cells.
Furthermore, consuming protein after exercise does not elevate IGF-1 levels in the same way as consuming protein in a sedentary state, further demonstrating the protective effects of physical activity. Exercise enhances immune surveillance, reduces chronic inflammation, and improves insulin sensitivity, all of which lower cancer risk and enhance longevity.
If protein and IGF-1 were inherently harmful, athletes—who consume higher protein diets and have elevated IGF-1 levels—should experience shorter lifespans. Yet, the opposite is true. Athletes consistently live 2–8 years longer than the general population and have lower rates of cancer and cardiovascular disease. Regular physical activity ensures that dietary protein and IGF-1 are used for repair and growth, not pathways associated with disease.
Leucine is essential for activating mTOR, the pathway responsible for muscle protein synthesis and growth. However, mTOR activation in peripheral tissues, such as the vascular system, has been linked to atherosclerosis and cancer. Exercise resolves this issue by directing leucine toward muscle tissue, ensuring mTOR activation occurs where it’s beneficial. For sedentary individuals, leucine and mTOR activation may pose greater risks.