Optimal Protein Intake: Guide, Science & Foods
Protein is an essential component for building lean muscle mass, supporting metabolism, weight loss, and recovery. The optimal protein intake depends on numerous factors, with needs increasing with strength training, typically within a higher range of 1.4-2.4 g/kg daily.
What is Protein?
Proteins are complex molecules composed of amino acid chains connected by peptide bonds, serving as the body’s fundamental building blocks. Among the 20 amino acids, nine are classified as essential and must be obtained through diet since the body cannot synthesize them. (1) (2)
Essential vs. Non-essential Amino Acid
| Essential | Conditionally Essential | Non-essential |
|---|---|---|
| Histidine (H) | Arginine (R) | Alanine (A) |
| Isoleucine (I) | Cysteine (C) | Aspartic acid (D) |
| Leucine (L) | Glutamine (Q) | Asparagine (N) |
| Lysine (K) | Glycine (G) | Glutamic acid (E) |
| Methionine (M) | Proline (P) | Serine (S) |
| Phenylalanine (F) | Tyrosine (Y) | Selenocysteine (U) |
| Threonine (T) | ||
| Tryptophan (W) | ||
| Valine (V) |
These molecules perform crucial functions including:
- building muscle tissue (5) and providing structural support for tissues and organs. (6) (7)
- promoting regeneration, recovery, and growth
- catalyzing biochemical reactions as enzymes (8) (9)
- transporting molecules like oxygen (hemoglobin) (10)
- supporting immunity and fighting infections
The body constantly undergoes protein turnover—a dynamic process of protein breakdown and synthesis that enables adaptation to changing conditions, particularly during growth, recovery, and as a response to exercise. (11) Protein’s importance extends beyond muscle development to virtually every biological function, including immune function.
How much protein do I need daily?
Protein recommendations vary widely depending on individual factors, such as activity level, height, goals, BMR, sex, etc. (13) (14)
The Recommended Dietary Allowance (RDA) for protein is 0.8 grams per kg of bodyweight daily. (15) This is the minimum amount needed to prevent deficiency, mostly a suboptimal amount for health, with further evidence suggesting an increase to 1.0 g/kg/d. (16)
Recommended Dietary Allowance (RDA)
The standard Recommended Dietary Allowance (RDA) for protein is 0.8 g/kg/d. (15) This recommendation represents the minimum amount needed to prevent deficiency in sedentary adults, not necessarily the optimal amount for health. (15)
For a 165-pound (75 kg) person, this translates to about 60 grams of protein daily. However, this baseline recommendation has several important limitations:
- It’s derived from nitrogen balance studies, which may not account for all routes of nitrogen input and output (17)
- It represents the minimum to prevent deficiency rather than the amount needed for optimal health (18)
- It doesn’t account for differences in age, activity level, or health goals (19) (18)
Further evidence shows the minimal RDA has been underestimated, recommending an increase to 1.0 g/kg/d, more specifically 0.93 g/kg/d or 1.2 g/kg/d for men. (16)
Optimal Protein Intake for Muscle Mass
Optimal protein intake can differ depending on the goals.
For increasing muscle mass, the range of optimal protein intake sits between 1.6 g/kg/d to 2.2 g/kg/d. (29) (38) Consuming more protein beyond this level does not result in significant gains in muscle mass, with numerous meta-analysis showing small increase in muscle mass from 0.3-0.6 kg. (29) (38)
High-protein diets effectively improve and support both goals of increasing or preserving lean muscle mass, as well as losing fat. Via various mechanisms like increased thermogenic effect of food (TEF), preserving higher metabolic rate due to muscle mass, and reducing appetite or increasing satiety, high-protein intake helps attenuate both goals, burning fat and preserving or gaining muscle.
Optimal Protein Intake for Older Adults (Aging)
As we age, especially past 40-50 years, our protein needs increase due to sarcopenia (age-related muscle loss). (19) Older adults tend to lose muscle mass and strength at rates of 0.5-1% and 1-3% respectively. (20) Their bodies are also less responsive to protein, meaning less MPS is stimulated per the same amount of protein ingested, driving the need for protein intake up. (21)
Research indicates that the close-to-ideal protein intake for older adults is around:
- Sedentary adults over 40-50 years: 1.0-1.2 g/kg body weight daily (19) (22)
- Adults over 65 years: 1.0-1.2 g/kg body weight daily according to European Society for Clinical Nutrition and Metabolism (ESPEN) (17)
- Older adults with certain acute or chronic illnesses: 1.2–1.5 g protein/kg/bw and up to 2.0 g/kg/bw in cases of severe illnesses, injuries, or malnutrition (23) (24)
- Highly active older adults training to lose weight or gain muscle may additionally increase, aiming at 1.6-2.4 g/kg/d (22)
These higher recommendations help maintain muscle mass, strength, and overall functionality with aging.
Optimal Protein Intake for Athletes
Physical activity significantly increases protein requirements
- Minimal physical activity: 0.8-1.0 g/kg/day (25) (26)
- Moderate physical activity: 1.3 g/kg/day (25) (26)
- Intense physical activity: 1.6 g/kg/day (25) (26)
- Athletes (depending on sport type): 1.2-2.0 g/kg/day according to American College of Sports Medicine and other organizations (18)
For professional athletes, training at higher volumes and competing, the ACSM recommends 1.2-2.0 g/kg/d (27) close to the estimation of the ISSN, at 1.4-2.0 g/kg/d. (28)
For athletes engaged in strength training or high-intensity activities, requirements can range up to 2.2 g/kg/day or even higher during specific training phases (18).
Generally, an intake of 1.6-2.2 g/kg/d is the close to optimal range for many athletes, to preserve lean mass or gain muscle. (29) In some instances, moving up to the range of higher protein intake at 2.2 – 2.7 g/kg/d seems to provide additional benefit for resistance trained and endurance athletes. (30) (31) (32)
Optimal Protein Intake for Fat Loss
Eating a hypocaloric diet (~300-500 calories less than burned) is effective for fat loss. (33) (34) Being at a deficit can cause muscle loss (35) at instances of low protein intake and training volume.
Consuming more protein is essential to preserve lean muscle mass, particularly during a calorie deficit which decreases MPS. Even in athletes consuming hypocaloric diets, a higher protein intake of 1.6-2.0 g/kg/d is shown to preserve or increase lean muscle mass, (36) suggesting that the optimal intake sits at 1.6-2.4 g/kg/d for people who want to lose weight, but preserve muscle. (37)
High-protein diets effectively improve and support both goals of increasing or preserving lean muscle mass, as well as losing fat. Via various mechanisms like increased thermogenic effect of food (TEF), preserving higher metabolic rate due to muscle mass, and reducing appetite or increasing satiety, high-protein intake helps attenuate both goals, burning fat and preserving or gaining muscle.
How much protein do I need to maximize anabolism?
To maximize anabolism (muscle protein synthesis), consume 1.6-2.2g of protein per kg of bodyweight daily, distributed across 3-5 meals containing 0.3-0.4g/kg per meal (typically 20-40g per meal for most people).
Leucine content is particularly important, with a threshold of ~2-3g of leucine per meal needed to optimally trigger muscle protein synthesis.
Is there a limit to how much protein one can consume in a single meal?
Research indicates there’s no strict limit on protein absorption, but there is a limit to how much protein can effectively stimulate muscle protein synthesis in a single meal.
Studies suggest diminishing returns beyond 0.4g/kg bodyweight (about 25-40g for most people) in a single meal, with additional protein being used for other bodily functions or energy.
Typically, having digestive issues after eating a large portion of protein suggests potential problems with absorption, which can be improved by taking digestive enzymes or distributing protein more evenly.
Should we limit protein to 40 grams per meal?
The 40 grams guideline isn’t a strict limit but rather a point of diminishing returns for muscle protein synthesis for most people. Larger individuals may benefit from slightly more (0.4g/kg per meal), while consuming more than this threshold doesn’t harm health but provides minimal additional anabolic benefit.
Do I need more protein if I exercise regularly?
Yes, regular exercise increases protein requirements significantly. While sedentary individuals need 0.8-1.0g/kg daily, those with moderate physical activity require around 1.3g/kg, and those with intense regular exercise need approximately 1.6g/kg or more to support recovery, adaptation, and performance.
Do endurance athletes need additional protein?
Yes, endurance athletes need more protein than sedentary individuals, though typically less than strength athletes. Research recommends 1.2-1.6g/kg bodyweight daily for endurance athletes to support recovery, repair muscle damage from prolonged exercise, and maintain performance. During periods of intensified training or racing, requirements may increase to 1.6-2.0g/kg.
How much protein do older adults need?
Older adults (40-50+ years) need more protein than younger adults due to age-related anabolic resistance.
Recommended intake is
1.0-1.2g/kg daily for sedentary older adults
1.2-1.5g/kg for those with illness or conditions
1.6-2.4g/kg for active older adults training to maintain muscle mass.
Distribution across meals is important, with 25-40g of high-quality protein per meal being optimal.
Benefits of Increasing Protein Intake
Beyond providing structural support to tissues, proteins are important for immunity, cellular health, and brain function. Sufficient levels of protein prevent excess catabolism (breakdown) keeping various organs—muscles, skin, and bones— intact, functional, and in good shape.
Additionally, amino acids serve as key messengers and precursors for certain neurotransmitters (dopamine, serotonin) that enable numerous vital functions in the body.
Muscle Growth and Repair
Protein intake dictates muscle maintenance, growth, and regeneration. Beyond mechanical load which covers the training part, for muscle growth to occur muscle protein synthesis (MPS) needs to be net positive, i.e., higher than muscle protein breakdown (MPB). Studies generally suggest ∼20-25 g of a high-quality protein maximizes MPS response after resistance training. (39)
When muscles experience damage from exercise or injury, they initiate repair processes that depend on protein availability. The process involves amino acids serving as both building materials and signaling molecules that activate repair processes. (40) (41)
A meta-analysis including data from 74 RCTs showed increasing daily protein intake enhances muscle mass gains, when combined with resistance exercise. (42)
Post-exercise protein feeding elevates muscle protein synthesis and activates satellite cells—stem cell populations orchestrating muscle repair. (43) The amino acid composition significantly influences repair efficacy, with leucine-enriched essential amino acids particularly important in supporting muscle growth. (44) (45) (46)
Protein intake also significantly influences hormonal signaling, particularly growth hormone (GH) activity. GH functions beyond height regulation, increasing fat burning and muscle growth. (47) GH-responsive neurons throughout the brain, enable GH to serve as a messenger that impacts metabolism, food intake, energy expenditure, and glucose levels. Protein provides essential amino acids that modify both GH secretion and tissue sensitivity. (47)
Weight Management and Appetite
Higher protein diets offer significant metabolic advantages for weight management through multiple mechanisms:
- increased feelings of fullness or satiety to a greater extent than carbohydrates (48) (49)
- higher thermogenic effect of food, increasing energy expenditure (burning more calories to digest protein) (48) (49)
- maintenance of lean muscle mass, improving metabolic profile (48) (49)
Multiple studies indicate that higher protein diets at 25-30% protein (50) (51) (52) or 1.36 g/kg of bodyweight (53) enhance weight loss outcomes in overweight and obese individuals compared to low-protein diets.
The ACOORH trial incorporated protein-rich meal replacement which was associated with weight loss in 12 weeks. (54)
Perhaps most importantly, higher protein intake during weight reduction preserves lean body mass, which is critical for maintaining a higher metabolic rate, as muscle tissue is more metabolically active than fat. (48) (55) The evidence collectively suggests that strategic protein intake is a valuable approach to weight management through its effects on satiety, energy expenditure, and body composition.
Metabolic Rate
Higher protein consumption can increase resting metabolic rate (RMR), particularly when combined with resistance training. (56) Additionally, high protein combined with resistance training aids in preserving muscle mass and maximizing fat loss, (57) which can theoretically increase metabolic rate, as muscle is more metabolically active tissue compared to fat.
The TEF of protein is also higher, making high-protein diets more effective at raising metabolic rate, as more energy is being used to digest proteins.
High-protein diets consistently show greater thermogenic responses compared to high-carbohydrate or high-fat diets, which may contribute to their effectiveness in weight management programs. (60) (58)
Immune System
Protein plays a crucial role in immune function by providing essential materials for immune proteins like antibodies and cytokines that mediate immune responses. (61) (62)
Research shows that cysteine-rich protein sources may support immune responses to antigens by increasing liver glutathione concentrations (as cysteine is the precursor of the master antioxidant in the body, GSH) responsible for the activation of antioxidant defense systems. (63) (64) (65)
Protein’s immune benefits extend to the gut-brain-immune axis, where dietary proteins and their metabolites regulate gut barrier function and immune homeostasis. (66) The intestinal microbiota, significantly influenced by protein intake, affects host metabolism by regulating energy absorption and modulating endocrine functions. (66) Certain amino acids and fiber may increase the production of short-chain fatty acids in the gut (67) (68) that play an important role in immunity and mediate inflammation. (69) (70) (71)
Amino acids are also key in repairing muscle from the micro injuries that occur daily, whether one exercises or not.
What are the benefits of consuming protein for my health?
Protein provides essential amino acids that support tissue growth and repair, enzyme and hormone production, immune function, and metabolic health. It increases thermogenesis (calorie burning), promotes satiety, stabilizes blood sugar, preserves lean muscle mass during aging and weight loss, enhances recovery from exercise, and supports bone health.
How does protein contribute to muscle growth and repair?
Protein supplies amino acids (particularly leucine) that stimulate muscle protein synthesis (MPS), the process where muscles build new tissue. After exercise creates micro-damage in muscle fibers, dietary protein provides the building blocks needed for repair and adaptation. Consistent protein intake (1.6-2.2g/kg daily) optimizes this process.
Is protein harmful to your kidneys?
For individuals with healthy kidney function, even higher protein intakes (up to 2.2-2.7g/kg) have not been shown to cause kidney damage. However, those with existing kidney disease should consult healthcare providers, as they may need to moderate protein intake based on their specific condition and kidney function.
Does consuming “excess” protein increase fat mass?
No, consuming more protein than needed for muscle building doesn’t automatically convert to fat. While protein can be converted to glucose through gluconeogenesis or used for energy, this is metabolically inefficient. High protein intake typically reduces overall calorie intake due to increased satiety and has a higher thermic effect (20-30% of calories burned during digestion) compared to fats and carbs.
Does more protein consumption mean more muscle gain?
Only up to a point. Research shows diminishing returns beyond 1.6-2.8 g/kg daily. Consuming more protein beyond this range provides minimal additional muscle-building benefits. Muscle growth ultimately depends on a combination of adequate protein intake, progressive resistance training, sufficient calories, and recovery factors like sleep and stress management.
Can protein help with weight loss and appetite control?
Yes, higher protein intake (1.6-2.4g/kg daily) during caloric restriction helps preserve muscle mass while promoting fat loss. Protein increases satiety hormones (GLP-1, PYY) and reduces hunger hormone (ghrelin) levels, helping control appetite. The higher thermic effect of protein (20-30%) means more calories are burned during digestion compared to carbs (5-10%) and fats (0-3%), creating a metabolic advantage for weight management.
Best Sources of Protein
The quality of dietary protein is determined by its amino acid composition, digestibility, and bioavailability – essentially how well your body can use the protein you consume. Protein sources are mainly divided into two categories: animal-based and plant-based.
The gold standard for assessing protein quality (digestibility, or protein-derived amino acids for protein synthesis) is DIAAS. (72) (73) The score is typically between 50-150%, with 100% being considered complete protein, providing adequate amounts of EAA.
Comparing by the DIAAS score of foods assessing protein quality or digestibility, animal proteins like beef, casein, eggs, and milk show higher scores (>100%) compared to plant-proteins like rice, peas, wheat, and pasta (<75%).
Generally, the best protein sources with higher digestibility and “complete” EAA profile include animal sources of protein like red meat, chicken, fish, eggs, cottage cheese, casein, whey, and tuna – all ≥100% in DIAAS score.
DIAAS score of Foods
| Food | DIAAS (%) |
|---|---|
| Casein | 117.0 |
| Milk | 116.0 |
| Eggs | 113.0 |
| Beef | 112.0 |
| Whey Protein | 109.0 |
| Tuna | 100.0 |
| Soy | 90.0 |
| Peas | 65.0 |
| Rice | 60.0 |
| Pasta | 41.0 |
| Wheat | 40.0 |
Animal Proteins
Plant Proteins
Plant-based proteins (legumes, grains, nuts, and seeds) have historically been considered “incomplete” as individual sources often lack optimal amounts of one or more essential amino acids. New technology emerges to increase plant-protein bioavailability and functionality. (77)
Getting sufficient EAA (essential amino acids) from plant sources is possible by combining specific foods, but less convenient. For instance, combining beans (high in lysine) with rice (high in methionine) creates a complementary amino acid profile more similar to animal proteins.
Maximize the Anabolic Properties of Plant-Based Protein
One strategy to maximize the anabolic properties of plant-based proteins is to:
- consume higher total amounts of protein,
- combine foods with complementary amino acids, and
- supplement specific amino acids that support muscle protein synthesis but are often lacking in typical plant-based diets like Leucine
Protein Supplementation
Protein is an essential nutrient that can be supplemented if insufficient levels are consumed through diet. Due to its wide-reaching effects and supportive role in muscle protein synthesis, supplementing protein is not exclusive to athletes or bodybuilders, but desired in non-athletes with lower than optimal levels.
Whey Protein
Whey protein, derived from cow’s milk during cheese production, is among the most used forms of protein supplement. It contains all essential amino acids and is rich in branched-chain amino acids (BCAAs), particularly leucine, which stimulates muscle protein synthesis. The three main types of whey protein include: isolate, concentrate, and hydrolysate.
Due to its EAA rich profile and quick-digestion properties, whey is an ideal option for stimulating MPS and supporting muscle growth. (78) (79) Research shows whey supplementation can improve muscle mass (80) and function, particularly in older adults at risk of sarcopenia (age-related muscle loss) and in combination with resistance training. (81)
Plant-Based Proteins
Plant-based protein supplements are derived from sources like pea, rice, hemp, and soy, serving as alternatives to animal-derived proteins. While individual plant proteins may have lower leucine content than whey, well-formulated blends can achieve comparable amino acid profiles. (82)
Other food sources of plant-protein that are more complete (containing higher levels of EAA) include quinoa, buckwheat, soybeans, hemp seeds, tofu, and amaranth. Supplementing with proteins from these sources may yield a greater amino-acid profile.
The digestibility of plant proteins has improved through processing techniques like fermentation and enzymatic treatment, making them more effective. Research shows that combining plant protein with probiotics may improve amino acid absorption, essentially helping the digestive system extract more nutrition from plant proteins. (83)
Amino-Acids
Supplementing with individual amino acids can cover specific needs or deficiencies, or complement proteins lacking in one’s diet. Individual amino acids serve specific functions, being different than having all EAAs in a pool, such as in a whey protein powder.
Here are the most common individual AAs supplemented and the function they serve in the body:
| Amino Acid | Typical Supplement Dose | Main Functions/Benefits |
|---|---|---|
| Taurine | 500-1000 mg/day | Neuroprotective effects, supports brain development, and may prevent neuronal apoptosis |
| Leucine | 2-5 g/day | Important for muscle protein synthesis and metabolic health |
| Arginine | 3-6 g/day | Improves blood flow, supports immune function, and may enhance exercise performance |
| Methionine | 200-1000 mg/day | Supports liver function and detoxification processes, though excessive amounts can be harmful |
| Lysine | 1-3 g/day | Supports collagen formation, connective tissue regeneration, and immune function |
| Histidine | 500-1500 mg/day | Involved in histamine production, tissue repair, and red blood cell production |
| Tryptophan | 500-1000 mg/day | Precursor to serotonin, supports mood regulation and sleep quality |
| Phenylalanine | 500-1500 mg/day | Precursor to tyrosine and neurotransmitters like dopamine, epinephrine, and norepinephrine |
Leucine is by far the most important AA to support muscle protein synthesis (MPS) and prevent muscle breakdown. (44) (45) (84) This can be particularly helpful in people with insufficient protein levels, aging population, and under highly stressful (catabolic) states, to prevent muscle loss and provide anabolic support.
BCAAs
Branched-chain amino acids (BCAAs) are three essential amino acids—leucine, isoleucine, and valine—with a supportive role in muscle growth and recovery. BCAAs make up 35% of all essential amino acids in the muscle, being critical to growth and recovery.
Since they’re essential, the body doesn’t synthesize them, but they need to be obtained through diet. (85) Typically, animal sources of protein like eggs, meat, and dairy contain a solid amount of BCAAs.
BCAAs on their own are unlikely to significantly increase MPS, (86) however, they can help delay muscle fatigue and soreness, (87) support anabolic pathways, (88) and improve muscle performance during exercise. (89)
Does one need protein supplements to meet daily requirements?
No, protein supplements aren’t essential if you consume sufficient protein from whole foods. However, supplements can be beneficial when: convenience is needed, dietary preferences limit protein sources, higher protein needs exist (athletes, older adults), or during caloric restriction when maintaining muscle mass is a priority.
How do I use protein powder?
Mix protein powder with water, milk, or plant-based milk (1-2 scoops with 8-12 oz liquid) and shake thoroughly. You can also blend it into smoothies with fruits and vegetables, add it to oatmeal, yogurt, or baked goods to increase protein content.
What are BCAAs and what role do they play in protein supplements?
BCAAs (branched-chain amino acids) are three essential amino acids—leucine, isoleucine, and valine—that make up 35% of muscle essential amino acids. While they support muscle recovery and may reduce exercise fatigue, BCAAs alone aren’t as effective for muscle protein synthesis as complete proteins. Leucine is particularly important as the primary trigger for muscle protein synthesis, but all essential amino acids are needed for optimal results.
Do you need to consume protein within 1 hour following resistance training?
While the post-workout anabolic window isn’t as narrow as once thought, consuming protein within several hours of training is beneficial. Research indicates that protein consumed within 0-2 hours post-exercise may optimize recovery and adaptation, particularly if you haven’t consumed protein before training. However, total daily protein intake is ultimately more important than precise timing.
How should I spread my protein intake throughout the day?
Distribute protein evenly across 3-5 meals spaced 3-5 hours apart, with each meal containing 0.3-0.4g/kg bodyweight (20-40g for most people). This approach maintains elevated muscle protein synthesis throughout the day compared to consuming the same amount of protein in fewer, larger meals or many smaller meals.
