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Reviewed by CalculatorApp.me Health Team
Daily protein requirements, optimal intake by goal, protein timing, amino acid science, and food sources.
0.8 g/kg
RDA minimum
1.6-2.2
g/kg for muscle gain
20-30g
Per-meal target
20-35%
Thermic effect
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Protein is a macronutrient composed of amino acids — the building blocks of muscle, bone, skin, enzymes, and hormones. Of the 20 amino acids, 9 are essential (must come from food): histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine.
Protein is critical for muscle protein synthesis (building/repairing muscle), immune function, enzyme production, hormone regulation, and satiety. It has the highest thermic effect of food (TEF) — your body uses 20-35% of protein calories just to digest it, compared to 5-15% for carbs and 0-5% for fat.
The RDA of 0.8 g/kg body weight is the minimum to prevent deficiency — not the optimal amount. Research consistently shows higher intakes (1.2-2.2 g/kg) benefit muscle retention during weight loss, muscle building, bone health, and appetite control.
Daily Protein = Body Weight (kg) × Target (g/kg) Targets by goal: Sedentary adult: 0.8 g/kg Active adult: 1.2-1.4 g/kg Endurance athlete: 1.2-1.6 g/kg Strength/muscle gain: 1.6-2.2 g/kg Weight loss (preserve muscle): 1.2-1.6 g/kg Elderly (60+): 1.0-1.2 g/kg Example (80 kg, muscle gain): 80 × 1.8 = 144g protein/day = 576 calories from protein
Use lean body mass instead of total weight if obese — otherwise protein targets become unrealistically high.
Daily Protein = Lean Mass (kg) × 2.2-3.1 g/kg Lean Mass = Weight × (1 − Body Fat %) Example (80 kg, 20% body fat): Lean mass = 80 × 0.80 = 64 kg Protein = 64 × 2.5 = 160g/day This method is more accurate for: • Overweight individuals • Very lean individuals • Bodybuilders/athletes
Using lean mass normalizes protein targets across different body compositions — equally useful for all body types.
Optimal per-meal dose: 0.4-0.55 g/kg Example (80 kg, 160g/day target): 4 meals × 40g = 160g ✓ 3 meals × 53g = 160g ✓ Muscle Protein Synthesis (MPS): Threshold: ~20g high-quality protein Ceiling: ~40g per meal Leucine trigger: 2.5-3g per meal High-leucine foods per 30g protein: Whey protein: 3.4g leucine Chicken breast: 2.4g leucine Eggs (5 large): 2.5g leucine Greek yogurt: 1.8g leucine
| Food | Serving | Protein (g) | Calories | PDCAAS | Leucine (g) |
|---|---|---|---|---|---|
| Chicken breast | 100g | 31g | 165 | 1.00 | 2.4 |
| Whey protein isolate | 1 scoop (30g) | 25g | 110 | 1.00 | 2.7 |
| Eggs | 3 large | 18g | 210 | 1.00 | 1.5 |
| Greek yogurt | 200g | 20g | 130 | 1.00 | 1.6 |
| Salmon |
Dutch chemist Gerardus Johannes Mulder, at the suggestion of Jöns Jacob Berzelius, coined the term 'protein' from the Greek 'proteios' (primary/first). Berzelius wrote: 'The name protein that I propose seems to me very appropriate because this substance appears to be the primitive or principal substance of animal nutrition.'
Emil Fischer and Franz Hofmeister independently proposed the peptide bond theory — that proteins are chains of amino acids linked by peptide bonds. Fischer went on to synthesize the first true peptide in 1901 and won the Nobel Prize in 1902.
The first US Recommended Dietary Allowances (RDAs) were published, including 70g protein/day for men. This was set during WWII to ensure military and civilian nutritional adequacy during rationing.
The Protein Efficiency Ratio (PER) was replaced by PDCAAS (Protein Digestibility Corrected Amino Acid Score) as the standard for protein quality. PDCAAS scores range from 0-1.0, with animal proteins scoring 1.0 and most plant proteins 0.4-0.7.
British Journal of Sports Medicine
Meta-analysis of 49 studies (1,863 participants): protein supplementation significantly increased muscle mass and strength gains during resistance training. Optimal intake: 1.6 g/kg/day. Benefits plateaued above 1.62 g/kg/day.
American Journal of Clinical Nutrition
Evenly distributing protein across 3 meals (30g each) stimulated 25% more 24-hour muscle protein synthesis than skewing intake to dinner (10g/15g/65g), despite identical total protein intake.
Journal of the Academy of Nutrition
Athletes in caloric deficit who consumed 2.3 g/kg protein preserved significantly more lean mass than those consuming 1.0 g/kg. The high-protein group lost 1.3 kg less muscle — despite identical calorie deficits.
Annals of Internal Medicine
High protein intake damages your kidneys.
No evidence supports this in healthy adults. A comprehensive review found protein up to 2.2 g/kg is safe for healthy kidneys. The restriction applies only to people with pre-existing kidney disease. Hydrate well and you're fine.
You can only absorb 30g of protein per meal.
Your body can digest and absorb virtually unlimited protein. The '30g limit' refers to the muscle protein synthesis ceiling — MPS maxes out at ~40g per meal. Excess protein is used for other functions (enzymes, hormones, energy).
Plant protein is inferior to animal protein.
Individual plant proteins may lack some amino acids, but combining sources (rice + beans, for example) provides complete amino acid profiles. PDCAAS of soy = 1.0 (equal to animal protein). Plant-based athletes can thrive with proper planning.
You need protein immediately after a workout.
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MPS peaks at 20-40g per meal. The 'muscle full' effect means eating 100g in one meal won't build more muscle than 40g.
Higher protein preserves muscle during deficit: Study (Mettler et al., 2010): Group 1: 1.0 g/kg → lost 1.6 kg muscle Group 2: 2.3 g/kg → lost 0.3 kg muscle Both groups: same calorie deficit! Recommendation during cut: Mild deficit (250 cal): 1.2-1.6 g/kg Moderate deficit (500): 1.6-2.0 g/kg Aggressive deficit (750+): 2.0-2.4 g/kg The leaner you are, the more protein you need to preserve muscle
Higher protein during calorie restriction is the #1 strategy for preserving lean mass. It also increases satiety, reducing hunger.
| 100g |
| 25g |
| 208 |
| 1.00 |
| 1.8 |
| Tofu (firm) | 150g | 15g | 130 | 0.56 | 1.1 |
| Lentils | 1 cup cooked | 18g | 230 | 0.52 | 1.3 |
| Almonds | 30g | 6g | 170 | 0.40 | 0.5 |
Research by Layman et al. identified leucine as the key amino acid triggering muscle protein synthesis. The threshold dose (~2.5g leucine per meal, found in ~25-30g quality protein) established the modern per-meal protein recommendation.
The International Society of Sports Nutrition published their position: athletes and exercisers need 1.4-2.0 g/kg/day protein — nearly 2-3× the RDA. For muscle gain during resistance training, 1.6-2.2 g/kg was optimal.
A systematic review found no evidence that high protein intake (up to 2.2 g/kg) damages kidneys in healthy adults. The myth originated from clinical guidelines for people with existing kidney disease — not healthy individuals.
The 'anabolic window' is wider than once thought — 4-6 hours, not 30 minutes. Total daily protein intake matters far more than timing. That said, a protein-rich meal within 2 hours post-workout is a good practice.