Place · Level 3
Protein & Amino Acids
20 个氨基酸 · 9 个必须吃来 · 一天的身体都在拆建 · 不同人群需求差很多
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Chapter 1
Complete vs incomplete
Complete vs incomplete
Protein quality has two dimensions: whether all 9 essential amino acids are present, and whether the ratio is close to body need.
Complete proteins contain all 9 EAAs at ratios near human requirement. Eggs are the gold-standard animal reference; milk, lean meat, fish, and poultry all qualify. Among plants only soy, quinoa, buckwheat, amaranth, and hemp seed count as complete — a small set.
Incomplete proteins typically run low on one or two EAAs — the 'limiting amino acid'. Grains (wheat, rice, corn) are short on lysine (Lys); legumes are short on methionine (Met) and cysteine (Cys); most nuts and seeds are short on Lys or Met; vegetables are mostly low across the board.
The complementation strategy is simple: pair grains with legumes; combining across a day is sufficient — you don't need every meal balanced (the 1970s theory has been overturned). Classic combinations: rice + beans (Latin America / India), bread + hummus (Middle East), corn tortilla + black beans (Mexico), oats + milk (Northern Europe), tofu + rice (East Asia).
Two scoring systems exist: PDCAAS (Protein Digestibility-Corrected Amino Acid Score) is the older standard, range 0–1; DIAAS (Digestible Indispensable Amino Acid Score) is the FAO 2013 newer, more precise standard. Egg = 100, milk protein ~100, soy ~90, wheat bran ~40.
TL;DR: with a varied diet plus some animal source or soy / quinoa, quality solves itself.
Complete proteins contain all 9 EAAs at ratios near human requirement. Eggs are the gold-standard animal reference; milk, lean meat, fish, and poultry all qualify. Among plants only soy, quinoa, buckwheat, amaranth, and hemp seed count as complete — a small set.
Incomplete proteins typically run low on one or two EAAs — the 'limiting amino acid'. Grains (wheat, rice, corn) are short on lysine (Lys); legumes are short on methionine (Met) and cysteine (Cys); most nuts and seeds are short on Lys or Met; vegetables are mostly low across the board.
The complementation strategy is simple: pair grains with legumes; combining across a day is sufficient — you don't need every meal balanced (the 1970s theory has been overturned). Classic combinations: rice + beans (Latin America / India), bread + hummus (Middle East), corn tortilla + black beans (Mexico), oats + milk (Northern Europe), tofu + rice (East Asia).
Two scoring systems exist: PDCAAS (Protein Digestibility-Corrected Amino Acid Score) is the older standard, range 0–1; DIAAS (Digestible Indispensable Amino Acid Score) is the FAO 2013 newer, more precise standard. Egg = 100, milk protein ~100, soy ~90, wheat bran ~40.
TL;DR: with a varied diet plus some animal source or soy / quinoa, quality solves itself.
Is plant protein enough?
The most common concern for vegans / near-vegans, which can be answered precisely.It's enough when several conditions hold simultaneously: total calories are sufficient (not in a cut or aggressive fat-loss phase); diet is varied, with legumes, whole grains, nuts/seeds, and soy products covered weekly; 30–45 g of plant protein per meal (slightly higher than animal's 25–40 g because of lower Leu content and lower DIAAS); and resistance training, with isolated soy or pea protein as needed.
Scenarios that often go wrong: cutting phase + vegan + no EAA supplement — total protein is often too low to preserve muscle, blunting training results; elderly + vegan + sedentary — anabolic resistance compounded by low Leu and chronic low energy accelerates sarcopenia; athletes relying solely on legumes — Met stays chronically low.
Two things have been re-understood since the 2010s. First, 'AA complementation must happen within every meal' — the old Frances Moore Lappé idea from the 1970s — has been overturned; the AA pool in blood and liver stays available for several hours, so same-day combining works. Second, 'plant protein = low quality' has been refined: soy and quinoa have DIAAS comparable to meat, and mixtures (rice + beans) approach meat; single plant sources are indeed lower.
Practical supplements for vegan hypertrophy: soy protein isolate (DIAAS ~90, decent Leu); pea + rice protein blend (complements Lys and Met, mimicking whey's AA profile); EAA powder (9-EAA mix, 5–10 g added to a main meal can amplify the response).
So 'vegetarians can't build muscle' is a debunked old claim. Hevia-Larraín 2021 RCT showed that, at matched total protein, pea protein matched whey for hypertrophy — but this requires deliberate planning, not casual eating.
Chapter 2
Stomach + pancreas · breakdown
Stomach + pancreas · breakdown
Protein from mouth to blood travels a breakdown chain.
Station 1, stomach (acid + pepsin). Gastric HCl (pH 1.5–2) denatures protein — once the tertiary structure unfolds, enzymes can reach the peptide bonds. Pepsin is activated at low pH and cuts protein into 10–50-AA fragments, preferentially at peptide bonds adjacent to aromatic AAs (Phe, Trp, Tyr).
Station 2, duodenum (pancreatic enzymes + alkalinization). Once chyme enters the duodenum, pancreatic bicarbonate neutralizes the acid, raising pH to 6.5–7.5. Trypsin cuts after Lys / Arg; chymotrypsin cuts at aromatic bonds; elastase cuts at small AAs; carboxypeptidase A/B trim single AAs from the C-terminus.
Station 3, small intestine (brush border + enterocyte). Aminopeptidases trim single AAs from the N-terminus; di- and tripeptidases reduce short peptides to free AAs or di/tripeptides. Absorption uses PEPT1 (di/tripeptide transporter) plus a panel of AA-specific transporters — neutral AAs, acidic AAs, basic AAs each have dedicated carriers. After entering enterocytes, AAs go via the portal vein to the liver as first stop.
The liver filters most AAs before releasing them into systemic circulation. The branched-chain AAs (BCAA: Leu, Ile, Val) are the exception — barely metabolized by liver, they head directly to muscle.
Two often-overlooked black boxes: first, insufficient gastric acid (elderly atrophic gastritis / long-term PPI use) quietly cuts protein digestion and also blocks B12 release; second, poor pancreatic function (chronic pancreatitis, cystic fibrosis) impairs both fat and protein digestion. In these cases 'eating more protein doesn't build muscle' — the absorption bottleneck is upstream.
Station 1, stomach (acid + pepsin). Gastric HCl (pH 1.5–2) denatures protein — once the tertiary structure unfolds, enzymes can reach the peptide bonds. Pepsin is activated at low pH and cuts protein into 10–50-AA fragments, preferentially at peptide bonds adjacent to aromatic AAs (Phe, Trp, Tyr).
Station 2, duodenum (pancreatic enzymes + alkalinization). Once chyme enters the duodenum, pancreatic bicarbonate neutralizes the acid, raising pH to 6.5–7.5. Trypsin cuts after Lys / Arg; chymotrypsin cuts at aromatic bonds; elastase cuts at small AAs; carboxypeptidase A/B trim single AAs from the C-terminus.
Station 3, small intestine (brush border + enterocyte). Aminopeptidases trim single AAs from the N-terminus; di- and tripeptidases reduce short peptides to free AAs or di/tripeptides. Absorption uses PEPT1 (di/tripeptide transporter) plus a panel of AA-specific transporters — neutral AAs, acidic AAs, basic AAs each have dedicated carriers. After entering enterocytes, AAs go via the portal vein to the liver as first stop.
The liver filters most AAs before releasing them into systemic circulation. The branched-chain AAs (BCAA: Leu, Ile, Val) are the exception — barely metabolized by liver, they head directly to muscle.
Two often-overlooked black boxes: first, insufficient gastric acid (elderly atrophic gastritis / long-term PPI use) quietly cuts protein digestion and also blocks B12 release; second, poor pancreatic function (chronic pancreatitis, cystic fibrosis) impairs both fat and protein digestion. In these cases 'eating more protein doesn't build muscle' — the absorption bottleneck is upstream.
Stomach acid myths
'Insufficient gastric acid causes poor digestion' is a common direct-sales + alternative-medicine narrative; the real picture is more complex.What stomach acid actually does: denatures protein so pepsin can cut peptide bonds; activates pepsin (only works at pH < 4); kills pathogens (partial inhibition of Salmonella / Campylobacter / H. pylori); releases B12 from food protein (prerequisite for intrinsic-factor binding); aids iron absorption (Fe³⁺ → Fe²⁺).
Real causes of hypochlorhydria are limited: elderly atrophic gastritis (~15–20% in 60+), long-term PPI / H2-blocker use, late-stage H. pylori infection, post-gastric-bypass surgery.
Symptoms are often misread. Early satiety, bloating, belching, dyspepsia, plus B12 / iron / calcium / magnesium deficiency — that's the picture of low acid. But 'acid reflux / heartburn' is mostly not excess acid; it's typically GERD (reflux) with a lax lower esophageal sphincter — PPI is symptomatic treatment, not just 'killing acid'.
'Betaine HCl supplements' is a direct-sales pitch. Real indications are narrow: patients with objectively confirmed low acid plus protein maldigestion may partly benefit. Most people with GERD / reflux / dyspepsia should not use it — it can worsen esophageal injury. Use under physician guidance, not as OTC trial and error.
In practice, people with true maldigestion + B12 / iron deficiency + elderly age should see a physician for assessment (endoscopy / serum pepsinogen); 'I feel like my digestion is bad so I bought betaine HCl' is not reasonable and is risky. Eating slowly, chewing thoroughly, and not over-diluting gastric juice with lots of water are the low-risk habits that actually help digestion.
Chapter 3
20 amino acids · 9 essential
20 amino acids · 9 essential
The body uses 20 standard amino acids, split into two classes by essentiality.
9 essential AAs (EAA) the body cannot synthesize — they must come from food. Three branched-chain AAs (BCAA): leucine (Leu), isoleucine (Ile), valine (Val); plus lysine (Lys), methionine (Met), phenylalanine (Phe), threonine (Thr), tryptophan (Trp), histidine (His) (more critical in infants and pregnancy).
11 non-essential AAs can be synthesized from other AAs / metabolic intermediates. But 'non-essential' does not mean 'unimportant' — it just means you don't theoretically need to eat them specifically. Six of these are conditionally essential — in severe illness / trauma / infancy they actually must be eaten: arginine, tyrosine, cysteine, glutamine, glycine, proline.
Protein synthesis follows an 'all-or-nothing' rule: when building a single protein chain, if any essential AA is short, the whole chain stops and the partial assembly is degraded back to free AAs. Like missing one letter and being unable to spell the whole word.
Leucine is the true star — the direct activation signal for the mTOR complex 1: The main working form of mTOR — the switch that directly drives protein synthesis. pathway (master switch for protein synthesis). Cytosolic Leu is sensed by Sestrin2 / Sar1 → mTORC1 complex activates → phosphorylates downstream S6K1 / 4E-BP1 → ribosomal translation begins.
For the Leu threshold, ~2.5–3 g of leucine per meal best activates mTORC1. In food terms that's roughly: 4 large eggs (~600 mg Leu each), 100 g chicken breast (~2.5 g Leu), 20–25 g whey protein, or 30 g soy protein (slightly lower Leu fraction).
So '25–40 g of quality protein per meal' beats 'one mega-meal + three half-hearted ones' — this is the practical corollary of the Leu threshold.
9 essential AAs (EAA) the body cannot synthesize — they must come from food. Three branched-chain AAs (BCAA): leucine (Leu), isoleucine (Ile), valine (Val); plus lysine (Lys), methionine (Met), phenylalanine (Phe), threonine (Thr), tryptophan (Trp), histidine (His) (more critical in infants and pregnancy).
11 non-essential AAs can be synthesized from other AAs / metabolic intermediates. But 'non-essential' does not mean 'unimportant' — it just means you don't theoretically need to eat them specifically. Six of these are conditionally essential — in severe illness / trauma / infancy they actually must be eaten: arginine, tyrosine, cysteine, glutamine, glycine, proline.
Protein synthesis follows an 'all-or-nothing' rule: when building a single protein chain, if any essential AA is short, the whole chain stops and the partial assembly is degraded back to free AAs. Like missing one letter and being unable to spell the whole word.
Leucine is the true star — the direct activation signal for the mTOR complex 1: The main working form of mTOR — the switch that directly drives protein synthesis. pathway (master switch for protein synthesis). Cytosolic Leu is sensed by Sestrin2 / Sar1 → mTORC1 complex activates → phosphorylates downstream S6K1 / 4E-BP1 → ribosomal translation begins.
For the Leu threshold, ~2.5–3 g of leucine per meal best activates mTORC1. In food terms that's roughly: 4 large eggs (~600 mg Leu each), 100 g chicken breast (~2.5 g Leu), 20–25 g whey protein, or 30 g soy protein (slightly lower Leu fraction).
So '25–40 g of quality protein per meal' beats 'one mega-meal + three half-hearted ones' — this is the practical corollary of the Leu threshold.
BCAA supplements: real evidence
BCAA (Leu + Ile + Val) supplements are one of the biggest single products in the fitness market — the evidence can be examined in tiers.Two theoretical anchors: Leu triggers mTOR complex 1: The main working form of mTOR — the switch that directly drives protein synthesis. to initiate protein synthesis; Ile + Val share a BCAA aminotransferase and compete for absorption.
Going through the RCT evidence point by point.
First, BCAA raising MPS. Jackman 2017 (*Frontiers Physiol*) showed post-workout BCAA 5.6 g vs placebo raised MPS by 22%, but the MPS response to BCAA alone is far below that of complete protein or EAA mixtures. Mechanistically, complete MPS requires all 9 EAAs to be present — BCAA provides only 3, starting the machine without raw material.
Second, BCAA reducing muscle damage. Some small RCTs show post-workout BCAA lowers subjective soreness (DOMS) and slightly reduces CK. But total effect is small, and most meta-analyses show no advantage over complete protein.
Third, BCAA reducing fatigue / boosting performance via the central-fatigue hypothesis. Theory says BCAA competes with tryptophan at the blood-brain barrier, reducing 5-HT entry and the sense of fatigue. RCT results are inconsistent — overall evidence is weak.
Practical conclusion per Volpi, Phillips 2018+ consensus: if complete protein intake is sufficient (1.6 g/kg/day spread across meals, each meal containing 25–40 g with 2.5+ g Leu), BCAA isn't needed. BCAA cannot replace complete protein. EAA (9-EAA mix) is slightly better than BCAA, but still inferior to real food or whey. Real benefit appears only in extreme low-protein diets combined with inability to eat — a clinical setting.
For comparison: 25 g whey contains ~2.5 g Leu and all 9 EAAs, 25 g total protein, costs less than BCAA, is nutritionally complete, and provides other AAs — in almost every situation, whey beats BCAA.
So BCAA is a 'precision-marketed but partly mechanistically valid' edge-case supplement, usually worth considering only when whey is unavailable; for most lifters, money on BCAA is wasted.
Chapter 4
Muscle protein synthesis
Muscle protein synthesis
Muscle protein synthesis (MPS) is ignited where two signals overlap.
Nutritional signal: amino acid arrival, especially leucine — Leu activates mTOR complex 1: The main working form of mTOR — the switch that directly drives protein synthesis., and insulin synergizes (so carbs + protein co-ingested have synergy).
Mechanical signal: muscle contraction / stretch, especially resistance training — mechanical tension activates FAK + Vinculin → mTORC1, and simultaneously raises myocyte sensitivity to Leu. This 'anabolic sensitivity' lets the same Leu dose roughly double its effect post-training.
Both together open the largest synthesis window. A single protein meal elevates MPS for 4–6 hours then returns to baseline; a single resistance session elevates MPS for 24–48 hours. Eating protein 0–2 h post-workout stacks ~30% more synthesis than training or eating alone.
On meal distribution vs one big bolus, Morton 2018 BJSM meta (49 RCTs, n=1,863) is clear: 3–4 meals/day × 25–40 g of quality protein each maximizes hypertrophy; above 1.6 g/kg/day, marginal returns approach zero; one huge meal (60+ g) plus three token meals actually underperforms equal distribution.
Why a threshold? MPS isn't 'more gas = more speed' — it's more like 'lighting a firework'. Past the Leu threshold, adding more Leu doesn't raise MPS further; excess AAs go to the liver, get deaminated, and are oxidized for energy (using protein as fuel).
Practical corollary: spread protein across 3–4 meals (25–40 g each); eat a high-protein meal within 0–2 h post-training; whey is the best post-training form due to highest Leu content and fastest digestion; casein releases slowly, suitable pre-sleep; plant proteins need slightly larger single-meal doses (35–45 g) due to lower Leu.
Nutritional signal: amino acid arrival, especially leucine — Leu activates mTOR complex 1: The main working form of mTOR — the switch that directly drives protein synthesis., and insulin synergizes (so carbs + protein co-ingested have synergy).
Mechanical signal: muscle contraction / stretch, especially resistance training — mechanical tension activates FAK + Vinculin → mTORC1, and simultaneously raises myocyte sensitivity to Leu. This 'anabolic sensitivity' lets the same Leu dose roughly double its effect post-training.
Both together open the largest synthesis window. A single protein meal elevates MPS for 4–6 hours then returns to baseline; a single resistance session elevates MPS for 24–48 hours. Eating protein 0–2 h post-workout stacks ~30% more synthesis than training or eating alone.
On meal distribution vs one big bolus, Morton 2018 BJSM meta (49 RCTs, n=1,863) is clear: 3–4 meals/day × 25–40 g of quality protein each maximizes hypertrophy; above 1.6 g/kg/day, marginal returns approach zero; one huge meal (60+ g) plus three token meals actually underperforms equal distribution.
Why a threshold? MPS isn't 'more gas = more speed' — it's more like 'lighting a firework'. Past the Leu threshold, adding more Leu doesn't raise MPS further; excess AAs go to the liver, get deaminated, and are oxidized for energy (using protein as fuel).
Practical corollary: spread protein across 3–4 meals (25–40 g each); eat a high-protein meal within 0–2 h post-training; whey is the best post-training form due to highest Leu content and fastest digestion; casein releases slowly, suitable pre-sleep; plant proteins need slightly larger single-meal doses (35–45 g) due to lower Leu.
Protein powder buyer's guide
Protein powder choice, mapped to budget and goal.Whey protein dominates. Concentrate (WPC, 70–80%) is the value champion, with a little lactose and fat, fine for most; isolate (WPI, 90%+) is low-lactose and low-fat, 30–50% more expensive, suited to lactose intolerance or cutting; hydrolysate (WPH) is pre-digested, absorbs fast but costs another 50–100% more — used mostly in clinical burn recovery, rarely in fitness. Whey's advantages are high Leu content (~11%), fast absorption (~2–3 h to complete), and the strongest MPS trigger.
Casein is slow-release, 6–8 h, suitable pre-sleep or for long inter-meal gaps. Leu content is slightly below whey, but long-term nitrogen balance is more stable. Choose micellar casein over calcium caseinate — the former has intact structure and releases more slowly.
Egg protein has DIAAS ~100 (top-tier) but typically costs more than whey. Useful for those allergic to dairy who don't accept plant protein.
Plant proteins each have a profile:
Soy: DIAAS ~90, complete, contains isoflavones (some men worry about estrogenic effects — evidence is weak)Pea: short on Met, DIAAS ~65, needs pairing with rice proteinRice: short on Lys, DIAAS ~60, needs pairing with peaHemp: contains ω-3 but lower Leu / total-protein ratioPea + rice blend (50:50): DIAAS ~85, close to whey — the practical first choice for plant-based hypertrophy
Common traps to avoid. Amino spiking (adding cheap AAs like glycine, taurine to inflate protein measurement) — third-party testing (Labdoor, ConsumerLab) filters these out; 'clinically proven 50% more muscle' is marketing; the simpler the formula the better — complex 'super-blends' just dilute.
For dose: 25–40 g post-training (~2.5 g Leu); optionally 25–30 g casein pre-sleep. Protein powder doesn't replace food — 1–2 scoops/day fill gaps, not the main source.
Chapter 5
Turnover, not just gains
Turnover, not just gains
Whole-body protein turnover synthesizes and breaks down ~250–300 g daily — far exceeding daily intake (60–100 g). It's recycling plus net balance: gross synthesis ~280 g/day (building protein from free AA pool), gross breakdown ~280 g/day (protein degraded back to AA pool), dietary intake ~70 g/day (replacement + loss), and net oxidation ~70 g/day (N-containing compounds excreted in urine).
Different tissues turn over at very different rates. Intestinal mucosal epithelium replaces every 2–5 days, liver protein every 10–14 days, skin / hair / nails over weeks, red blood cells every 120 days, muscle on the scale of months, and collagen the slowest, on the scale of years.
So 'is protein enough' is never just 'can I get jacked' — immunity (antibodies), wound healing, hair and nails, hormone synthesis (protein / peptide hormones), gut repair, and enzyme systems are all queued for amino acids.
Older adults show anabolic resistance. At the same protein dose, the elderly MPS rise is only about half that of the young. Mechanisms include declining insulin sensitivity, blunted myocyte response to Leu, and reduced digestion-absorption efficiency. The solution is raising per-meal Leu from 2.5 g to ~4 g (equivalent to 35–40 g of quality protein) plus resistance training.
That's why people over 65 are advised to push protein to 1.0–1.2 g/kg, well above the adult RDA of 0.8 — not 'extra doesn't hurt' but 'without extra you can't keep up'.
Sarcopenia is one of the largest single reversible causes of elderly disability — strength training plus high-protein diet is the only intervention with strong evidence.
Different tissues turn over at very different rates. Intestinal mucosal epithelium replaces every 2–5 days, liver protein every 10–14 days, skin / hair / nails over weeks, red blood cells every 120 days, muscle on the scale of months, and collagen the slowest, on the scale of years.
So 'is protein enough' is never just 'can I get jacked' — immunity (antibodies), wound healing, hair and nails, hormone synthesis (protein / peptide hormones), gut repair, and enzyme systems are all queued for amino acids.
Older adults show anabolic resistance. At the same protein dose, the elderly MPS rise is only about half that of the young. Mechanisms include declining insulin sensitivity, blunted myocyte response to Leu, and reduced digestion-absorption efficiency. The solution is raising per-meal Leu from 2.5 g to ~4 g (equivalent to 35–40 g of quality protein) plus resistance training.
That's why people over 65 are advised to push protein to 1.0–1.2 g/kg, well above the adult RDA of 0.8 — not 'extra doesn't hurt' but 'without extra you can't keep up'.
Sarcopenia is one of the largest single reversible causes of elderly disability — strength training plus high-protein diet is the only intervention with strong evidence.
'High protein hurts kidneys'
'High-protein diets damage the kidneys' is one of the most persistent nutrition misconceptions and needs careful stratification.The origin is the 1980s Brenner hypothesis: high protein → glomerular hyperfiltration → potential long-term glomerulosclerosis. This was confirmed in patients with existing kidney disease (CKD 3+) but was wrongly extended to everyone.
Real evidence in healthy kidneys runs the opposite way. **Devries 2018 *J Nutr*** meta (28 RCTs, n=1,358) showed 1.5–2 g/kg high-protein diets did not change eGFR or kidney function in healthy adults (this is *J Nutr*, not BJSM); **Antonio 2015 *JISSN* had resistance-trained men eat 3.4 g/kg/day for 8 weeks with kidney, liver, and lipids all normal; the Thomas / Erdman / Burke 2016** ACSM-AND-DC joint position sets the reasonable athlete range at 1.2–2.0 g/kg/day, with some sports-nutrition reviews extending the cap to 2.2.
Actual kidney patients require stage-based handling. CKD 1–2 (eGFR > 60): normal protein intake, no restriction needed; CKD 3–5 (eGFR < 60): restrict to 0.6–0.8 g/kg/day with high-biological-value protein (animal + soy) to slow progression; dialysis (HD/PD) actually needs more, 1.0–1.4 g/kg/day (because dialysis causes losses).
So healthy adults adding 1.6–2.4 g/kg protein with adequate water is safe; known kidney disease should restrict protein under medical guidance, not self-prescribe high protein; don't fall short of the RDA out of 'I heard it hurts kidneys' fear — elderly under-eating protein is far more common than 'eating too much hurts kidneys'.
For gout risk, high-purine proteins (organ meat, sardines, shellfish) should be controlled in those with gout; regular chicken breast / eggs / dairy / tofu carry low gout risk. This is a heads-up for gout-prone individuals, not a fear source for the general population.
Chapter 6
How much per day
How much per day
RDA of 0.8 g/kg/day is the 'avoid-deficiency floor', not the optimum.
Stratified by scenario:
Practical split for a 70 kg lifter targeting ~126 g/day.
Breakfast ~30 g could be: 2 eggs (12 g) + 100 g Greek yogurt (10 g) + 1 scoop whey (20 g), total 42 g; or oats + 200 mL milk (7 g) + 1 scoop protein powder, total 27 g.
Lunch ~35 g: 120 g chicken breast (32 g) + rice + vegetables; or 150 g salmon (32 g) + quinoa + salad.
Dinner ~35 g: 120 g beef (30 g) + beans + vegetables; or 200 g tofu (15 g) + 2 eggs (12 g) + mushrooms + rice.
Late snack ~25 g (post-training or pre-sleep): 100 g Greek yogurt + 1 scoop casein; or 1 cup milk and a handful of almonds.
Sources don't all need to be protein powder. 3–4 meals/day × 25–40 g of quality protein, plus resistance training 2–4×/week, plus a slight caloric surplus — that's the evidence-based hypertrophy prescription.
Stratified by scenario:
| Scenario | Recommended (g/kg/day) | Example (70 kg) |
|---|---|---|
| Sedentary adult (baseline) | 0.8 | 56 g |
| Generally active | 1.2–1.6 | 84–112 g |
| Strength training, building muscle | 1.6–2.2 | 112–154 g |
| Endurance athlete | 1.4–1.8 | 98–126 g |
| Cutting phase, preserving muscle | 1.8–2.4 | 126–168 g |
| ≥ 65 years old | ≥ 1.0–1.2 | 70–84 g |
| Severely ill / burn / post-major-surgery | 1.5–2.0 | clinical |
| Mid–late pregnancy | + 25 g/day | RDA + 25 g |
| Lactation | + 25 g/day | RDA + 25 g |
Practical split for a 70 kg lifter targeting ~126 g/day.
Breakfast ~30 g could be: 2 eggs (12 g) + 100 g Greek yogurt (10 g) + 1 scoop whey (20 g), total 42 g; or oats + 200 mL milk (7 g) + 1 scoop protein powder, total 27 g.
Lunch ~35 g: 120 g chicken breast (32 g) + rice + vegetables; or 150 g salmon (32 g) + quinoa + salad.
Dinner ~35 g: 120 g beef (30 g) + beans + vegetables; or 200 g tofu (15 g) + 2 eggs (12 g) + mushrooms + rice.
Late snack ~25 g (post-training or pre-sleep): 100 g Greek yogurt + 1 scoop casein; or 1 cup milk and a handful of almonds.
Sources don't all need to be protein powder. 3–4 meals/day × 25–40 g of quality protein, plus resistance training 2–4×/week, plus a slight caloric surplus — that's the evidence-based hypertrophy prescription.
Protein for height & fat loss
'Kids eating more protein grow taller' plus 'high-protein diet is best for fat loss' are two common misunderstandings — let's compare the evidence point by point.On height, genetics determines roughly 80% of final adult height; nutrition + sufficient sleep + activity affect the remaining 20%. Kids getting adequate protein (1.0–1.5 g/kg) is a necessary condition, but excess does not break the genetic ceiling. The real-world example is the 10–15 cm height gain in Korean / Japanese populations from the 1950s to 2000s, mostly from overall nutrition improvement (varied protein + calcium + D + total energy), not 'just eat more meat'. Excess protein doesn't make kids taller — it may make them fatter, and chronically elevated IGF-1 may affect adult chronic-disease risk.
On fat loss, high protein (1.6–2.4 g/kg) does have clear advantages in a cut. First, muscle preservation: a caloric deficit + high protein + resistance training drops body fat while preserving lean mass. Second, satiety: protein has a thermic effect (TEF) of 25–30%, far higher than carb's 5–10% and fat's 0–3%. Third, appetite regulation: high-protein meals suppress ghrelin more, reducing appetite. But the absolute 'caloric deficit' is still the core — high protein by itself doesn't create a deficit. 'Eat more protein and you'll lean out' is wrong; total calories are the foundation, protein only optimizes.
In practice, growing children and adolescents need 1.0–1.5 g/kg/day plus varied food plus sufficient sleep plus outdoor activity; adults cutting need 1.8–2.4 g/kg/day plus a caloric deficit (500–750 kcal/day) plus resistance training plus plenty of produce. 'More protein = leaner' and 'more carbs = fatter' are the same kind of oversimplification error.