Protein

Your intake

What each level of protein does

Approximate dose-response bands. Individual response varies — these are starting points, not prescriptions.

1. Severely lowYOU ARE HERE

   0 g – 16.5 g

   Muscle loss, slow wound healing, immune dysfunction.

2. Insufficient

   16.5 g – 50 g

   RDA (~50 g) is a survival floor, not optimum. Active adults often need 1.2–2.0 g/kg.

3. Adequate

   50 g – 75 g

   FDA DV met. Supports basic enzymatic and structural needs.

4. Therapeutic

   75 g – 100 g

   Higher intake supports muscle protein synthesis in training adults and older people.

5. Diminishing returns

   100 g – +

   Past the point where extra intake typically helps. Evidence for further benefit is thin.

Overview

Macronutrient providing the 20 amino acids required for tissue synthesis, enzymes, hormones, immune molecules, and signalling. Adequate protein supports muscle maintenance, immune function, and satiety — especially relevant in aging (sarcopenia prevention requires 1.0–1.2 g/kg, well above the 0.8 RDA).

Functions

• ●Substrate for muscle, bone matrix, skin, hair, enzymes, hormones
• ●Triggers muscle protein synthesis (especially leucine)
• ●Highest thermic effect of feeding (~25%) — supports weight management
• ●Strongest satiety effect per calorie
• ●Acid-base buffer (sulfur amino acids contribute to acid load)

Mechanism

Dietary protein is hydrolysed to amino acids and small peptides. Leucine triggers mTORC1 signalling that initiates muscle protein synthesis — a ~3 g leucine 'threshold' per meal (~25–30 g high-quality protein) maximises MPS response in older adults. Protein turnover is continuous (~250 g/day in adults); inadequate intake forces net negative balance and tissue loss.

Benefits

• ●Prevents and treats sarcopenia (especially with resistance training)
• ●Improves body composition during weight loss (preserves lean mass)
• ●Increases satiety, supports weight management
• ●Supports immune function and wound healing
• ●Higher intake reduces fracture risk in older adults (modern view)
• ●Reduces all-cause mortality at adequate vs inadequate intake (older adults)

Deficiency

Rare in calorie-replete populations but functional inadequacy is common in older adults (sub-RDA + reduced anabolic response = ongoing muscle loss). Kwashiorkor (protein-calorie malnutrition) is a global pediatric issue.

Excess

Tolerated to ~3.5 g/kg/day in healthy kidneys. Older 'high protein causes kidney damage' claim is outdated — only relevant in pre-existing renal disease. Some hydration adjustment needed for nitrogen excretion.

Forms

• Whole-food protein (animal)
  Complete amino acid profile, high leucine, gold standard
• Whey isolate / concentrate
  Fastest digesting, highest leucine per gram; post-workout standard
• Casein
  Slow-digesting; bedtime use for overnight MPS support
• Plant blends (pea + rice)
  Combined to complete amino acid coverage; ~2× volume vs whey for equal effect
• Soy isolate
  Complete protein; modestly lower leucine than whey
• Collagen peptides
  Joint/skin focus; not a complete protein; do not use as MPS driver
• EAA / BCAA powders
  Free amino acids; expensive vs whole protein; niche use

Food sources

• Cooked chicken breast · 3 oz26 g
• Cooked salmon · 3 oz22 g
• Cooked beef · 3 oz25 g
• Greek yogurt (plain, nonfat) · 1 cup23 g
• Lentils (cooked) · 1 cup18 g
• Tofu (firm) · 1/2 cup20 g
• Whey protein · 1 scoop20–25 g

Supplement forms

Whole-food protein is the best baseline. Whey isolate has the highest leucine content per gram (best muscle protein synthesis trigger). Casein digests slowly and is good before sleep. Plant blends (pea + rice) provide complete amino acid coverage. Soy is a complete protein on its own.

Bioavailability

DIAAS / PDCAAS scores: whey ~1.09, milk ~1.0, egg ~1.0, soy ~0.91, beef ~0.92, pea ~0.65, wheat ~0.42. Older adults need higher per-meal doses (~0.4 g/kg per meal vs ~0.25 g/kg in young adults) due to anabolic resistance.

Longevity relevance

U-shaped relationship: low intake drives sarcopenia and fall/fracture risk in older adults — the dominant cost. Very high animal protein has weak association with cardiometabolic risk in some cohorts (mTOR signalling and IGF-1) but the benefit of preventing sarcopenia outweighs in most older adults. Spread intake across meals (~3 × 30 g) is more anabolic than back-loading.

Relationships

References

• Linus Pauling Institute — Proteinreview
• Bauer — PROT-AGE protein recommendations for older adults (JAMDA 2013)review
• Phillips — protein for older adults review (Nutrients 2016)review

About Protein

Amino acids for muscle protein synthesis, enzymes, hormones.

Role

Muscle · satiety

Daily target

50 g (DV)

Also called

protein, whey protein, casein, pea protein, collagen peptides, hydrolyzed collagen