How we ended up with the wrong number

The 0.8 g/kg/day RDA was set in the 1968 National Academy of Sciences review of nitrogen-balance studies. Nitrogen balance is the difference between protein intake and protein loss; "balance" was treated as the criterion of adequacy. The studies the RDA was derived from were nearly all conducted in young men, over short timeframes (days to weeks), with sedentary controls, and with a "minimum to not visibly degrade" criterion rather than "optimum for healthspan".

Subsequent generations of evidence have pulled in three directions:

Older adults have anabolic resistance. The same dose of protein triggers less muscle protein synthesis in older adults than in younger adults. The Volpi 2013 work (and downstream replications) showed that older muscle requires roughly 30-40g of high-quality protein per meal to maximally stimulate MPS, vs ~20-25g in young adults [1]. The RDA distributes ~0.8 g/kg/day across whatever meal pattern; for older adults that distribution is often sub-threshold at multiple meals.

Sarcopenia is a real and modifiable disease. Sedentary adults lose 3-8% of lean muscle mass per decade after 30, accelerating to 10-15%/decade after 60. Sarcopenia (the clinical late-stage) is one of the leading proximate causes of loss of independent living. Adequate protein intake is one of the most-evidenced modifiable risk factors. See our strength-training piece for the resistance-training side; protein intake is the dietary complement [2].

Trained athletes need more. Resistance-trained adults benefit from intakes up to ~1.6 g/kg/day for muscle gain, with diminishing returns above that. Morton et al. 2018 (British Journal of Sports Medicine) meta-analysed 49 RCTs and pegged the plateau at 1.62 g/kg/day for protein supplementation's effect on lean mass during resistance training [3].

The PROT-AGE consensus (Bauer et al. 2013) was the moment the geriatric-nutrition field formally re-set the recommendation [1]: 1.0-1.2 g/kg/day for healthy older adults, 1.2-1.5 for those with acute/chronic disease, 1.5-2.0+ for severely ill or injured. Most longevity-oriented adults sit at the upper end of "healthy": 1.2 to 1.6 g/kg/day.

The leucine threshold + meal distribution

Total daily protein is the most-cited number, but the meal-level distribution matters substantially.

Muscle protein synthesis (MPS) is triggered by exceeding a leucine threshold of approximately 2.5-3g of leucine per meal - which corresponds to roughly 25-40g of high-quality protein (lower end for young adults; upper end for older adults due to anabolic resistance). Once MPS is triggered, it runs for ~2-3 hours then returns to baseline regardless of additional intake within that window - the "muscle full" effect [4].

Mamerow et al. 2014 ran the controlled comparison directly [4]: same total daily protein (~90g), one group distributed evenly across breakfast/lunch/dinner (~30g each), the other skewed (10g breakfast, 16g lunch, 63g dinner). The even-distribution group had 25% higher 24-hour MPS over the 7-day trial.

The practical implication: hitting 100g of total daily protein matters, but eating it as 30g + 30g + 30g + (10g snack) is meaningfully better than 10g + 20g + 70g. For most adults, breakfast is the bottleneck - the typical Western breakfast (toast, cereal, fruit) is usually below the leucine threshold. Adding 2 eggs + Greek yogurt + nuts (~30g protein) is the single highest-leverage protein-distribution change most people can make.

Animal vs plant protein

Animal protein has higher concentrations of all essential amino acids per gram + a higher leucine content per gram than most plant proteins. This means hitting the leucine threshold from plant sources requires a meaningfully larger total-protein dose per meal - roughly 35-45g of plant protein vs 25-35g of animal protein.

This doesn't mean plant-based protein is inadequate. It means plant-based diets need more deliberate planning to hit per-meal MPS thresholds. Combining plant proteins (e.g., legumes + grains) raises the leucine density. Pea-protein isolate (the highest-leucine plant source commercially available) gets to within ~85% of whey's per-gram MPS effect per the Pinckaers 2024 work [5].

The cohort data on animal vs plant protein mortality is more nuanced than the popular framing suggests. Plant protein substitution for animal protein is associated with modestly lower all-cause and cardiovascular mortality in observational cohorts (Song et al. 2016, JAMA Internal Medicine, 130,000 participants over 32 years) [6]. The effect is driven primarily by the displacement of processed meat + saturated fat, not by plant protein being intrinsically better at the amino-acid level.

What about the Longo paper?

The 2014 Longo et al. paper (Cell Metabolism) is the most-cited piece of pop-science evidence for low-protein diets [7]. The finding: 50-65 year olds eating "high-protein" diets (≥20% of calories from protein) had a 75% increase in overall mortality + a 4× increase in cancer mortality over the 18-year follow-up vs low-protein eaters. The effect flipped after age 65: high-protein post-65 was associated with lower mortality.

The paper aged poorly under reanalysis. The "high protein" group in NHANES was eating significantly more red meat, processed meat, and saturated fat - and the mortality signal mostly disappeared once diet quality was adjusted for properly. The Levine et al. 2014 follow-up paper (from the same authorship group, on the same dataset) found that animal-protein intake correlated with most of the original mortality signal but plant-protein did not [7]. Subsequent meta-analyses (Banaszek 2019, multiple others) found no association between total protein intake and cancer mortality once whole-diet patterns were controlled for [8].

The IGF-1 / mTOR mechanism is theoretically interesting and animal models do show life-extension on protein restriction. But the human cohort signal hasn't held up under careful confounding control, and the mechanistic IGF-1 case has to compete with the substantial sarcopenia + metabolic costs of under-eating protein at older ages. The honest read: total protein intake is not the variable that the cancer-mortality cohort data lights up on once diet quality is properly adjusted.

The kidney myth

"High protein is bad for your kidneys" is a widely repeated worry that doesn't survive a careful read of the literature.

The worry's origin: people with existing chronic kidney disease (CKD) are advised to moderate protein as part of disease management, because the diseased kidney has reduced capacity to clear urea and other nitrogen byproducts. This is correct for CKD patients. It does not generalise to healthy adults.

The Devries 2018 meta-analysis (28 RCTs, 1,358 healthy adults) found high-protein diets (>1.5 g/kg/day) had no adverse effect on glomerular filtration rate, urinary albumin excretion, or blood pressure compared to lower-protein controls [9]. The hyperfiltration that happens after a high-protein meal is a normal, adaptive physiological response - not a sign of kidney damage. If you have known CKD, talk to your nephrologist; if you don't, the kidney concern is unfounded.

The dose, in practical food terms

For a 70 kg adult targeting 1.4 g/kg/day = ~100g of protein daily, distributed across 3-4 meals:

  • Breakfast (~30g): 2 eggs (12g) + 200g Greek yogurt (18g). Or 200g cottage cheese (24g) + 30g almonds (6g).
  • Lunch (~30g): 100g chicken breast (30g). Or 150g salmon (30g). Or 1 tin tuna (25g) + 1 egg (6g).
  • Dinner (~35g): 120g lean beef (30g) + side. Or 150g cod (30g) + lentils (12g). Or 200g tofu (~20g) + tempeh (~14g).
  • Snack (~10-15g): 30g cheese, or a small protein bar, or a glass of milk + nuts.

Hitting 100g/day from whole food is a planning problem, not a chemistry problem. The breakfast row is usually the highest-leverage change - most people undershoot at breakfast and overshoot at dinner.

Whey protein supplementation is useful when (a) you've just trained and your appetite is suppressed, (b) your morning meal is genuinely light and you can't make eggs work, or (c) you're travelling. The meta-analyses show no advantage of whey over equivalent whole-food protein at matched dose; the "you must drink three shakes" framing is supplement-industry marketing.

What the evidence does not support

Three claims that don't survive a careful read.

  • "Protein restriction extends lifespan." Animal models show this; human cohorts do not, once diet-quality confounders are adjusted for. The Longo paper's headline effect was a diet-quality story dressed up as a protein-quantity story.
  • "You can only absorb 30g of protein per meal." This conflates two distinct ideas. Beyond ~40g per meal, additional protein doesn't drive additional MPS within the 2-3 hour window (the "muscle full" effect). But absorption of dietary protein into amino acids continues regardless; the extra protein is used for other purposes (oxidised for energy, nitrogen-cleared, etc). Eating 60g at one sitting doesn't mean 30g is wasted - it means only ~30g of it contributes maximally to acute MPS, which is a different statement.
  • "High protein is bad for your kidneys." See above. Not in healthy adults; the meta-analysis evidence is unambiguous.

The takeaway

The 0.8 g/kg/day RDA was set in 1968 against young adults; the modern evidence base for healthy aging puts the actual number at 1.2-1.6 g/kg/day. The meal-level distribution matters: hitting the leucine threshold (roughly 25-40g of high-quality protein per meal) at 3-4 meals per day drives substantially more cumulative MPS than the same total skewed toward dinner. Animal protein is denser per gram; plant protein works with deliberate planning. The Longo cancer-mortality finding has aged poorly. The kidney worry is unfounded in healthy adults. Most people's highest-leverage change is the breakfast row.

If you want protein intake, lean-mass-index trends, sarcopenia-risk markers, and the rest of your body-composition domain tracked together as part of a coherent bio-age picture, have a look at Thier.

Frequently asked questions

How much protein per day for healthy aging?

The PROT-AGE international consensus (Bauer et al. 2013) recommends 1.0-1.2 g/kg/day for healthy older adults, climbing to 1.2-1.5 g/kg/day for those with acute or chronic disease, and even higher (1.5-2.0+) for severely ill or injured older adults. The longevity-oriented healthy adult sits at the upper end of healthy: 1.2-1.6 g/kg/day. For a 70kg person, that's 84-112g protein per day. The 1968-era RDA of 0.8 g/kg/day was set against nitrogen-balance studies in young adults and is now broadly recognised as inadequate for healthy aging.

Does the meal distribution matter?

Yes, substantially. Muscle protein synthesis (MPS) is triggered by hitting a leucine threshold of roughly 2.5-3g of leucine per meal, which corresponds to about 25-40g of high-quality protein (the lower end for young adults, the upper end for older adults due to anabolic resistance). MPS plateaus within 2-3 hours of a meal. Distributing 100g of daily protein across 3-4 meals each above the leucine threshold drives substantially more cumulative MPS than the same 100g eaten as 70g at dinner + 30g grazed across the day. The Mamerow 2014 RCT showed that even-distribution increased 24-hour MPS by 25% vs skewed distribution at matched total intake.

Is high-protein bad for your kidneys?

Not in healthy adults. The "protein damages kidneys" worry comes from the renal-disease literature, where existing kidney impairment requires protein moderation as part of management. For healthy adults, no published study has shown high-protein diets cause kidney damage. The Devries 2018 meta-analysis (28 trials, 1,358 participants) found high-protein diets had no adverse effect on glomerular filtration rate, urinary albumin excretion, or blood pressure vs lower-protein controls. If you have known CKD, talk to your nephrologist; if you don't, the kidney worry is unfounded.

Do I need supplements, or is food enough?

Food is enough for nearly everyone who's not a competitive athlete. A 30g protein serving is one 100g chicken breast, or one tin of tuna, or 3 large eggs, or 200g Greek yogurt + 30g almonds, or 200g cottage cheese, or 150g salmon. Hitting 100g/day from whole food is a planning problem, not a chemistry problem. Whey protein supplementation is useful when (a) you've trained within 2 hours and your appetite is suppressed, (b) your morning meal is light, or (c) you can't realistically hit 30g of protein at breakfast from food alone. The "must drink three shakes" framing is supplement-industry marketing; the meta-analysis evidence shows no advantage to whey over equivalent whole-food protein at matched dose.

Doesn't high protein increase cancer risk per the Longo work?

The Longo 2014 paper (Cell Metabolism) reported a 75% increase in overall mortality + a 4× increase in cancer mortality for high-protein vs low-protein diets in 50-65 year olds. The finding flipped after age 65 (high-protein associated with lower mortality). The original analysis has aged poorly - subsequent reanalyses found the effect was driven primarily by animal-protein intake correlation with overall diet quality (red meat + processed meat + saturated fat), not protein per se. Multiple follow-ups (Levine 2014; meta-analyses 2018+) found no association between total protein intake and cancer mortality once diet quality was adjusted for. The IGF-1 / mTOR mechanism remains theoretically interesting but the human cohort signal didn't hold up.

References

  1. Bauer J, Biolo G, Cederholm T, et al. Evidence-based recommendations for optimal dietary protein intake in older people: a position paper from the PROT-AGE Study Group. Journal of the American Medical Directors Association. 2013;14(8):542-559. PubMed
  2. Cruz-Jentoft AJ, Bahat G, Bauer J, et al. Sarcopenia: revised European consensus on definition and diagnosis. Age and Ageing. 2019;48(1):16-31. PubMed
  3. Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine. 2018;52(6):376-384. PubMed
  4. Mamerow MM, Mettler JA, English KL, et al. Dietary protein distribution positively influences 24-h muscle protein synthesis in healthy adults. Journal of Nutrition. 2014;144(6):876-880. PubMed
  5. Pinckaers PJM, Hendriks FK, Hermans WJH, et al. Potato protein ingestion increases muscle protein synthesis rates at rest and during recovery from exercise in humans. Medicine & Science in Sports & Exercise. 2024;56(2):265-279. PubMed
  6. Song M, Fung TT, Hu FB, et al. Association of animal and plant protein intake with all-cause and cause-specific mortality. JAMA Internal Medicine. 2016;176(10):1453-1463. PubMed
  7. Levine ME, Suarez JA, Brandhorst S, et al. Low protein intake is associated with a major reduction in IGF-1, cancer, and overall mortality in the 65 and younger but not older population. Cell Metabolism. 2014;19(3):407-417. PubMed
  8. Banaszek A, Townsend JR, Bender D, et al. The Effects of Whey vs. Pea Protein on Physical Adaptations Following 8-Weeks of High-Intensity Functional Training: A Pilot Study. Sports. 2019;7(1):12. PubMed
  9. Devries MC, Sithamparapillai A, Brimble KS, et al. Changes in Kidney Function Do Not Differ between Healthy Adults Consuming Higher- Compared with Lower- or Normal-Protein Diets: A Systematic Review and Meta-Analysis. Journal of Nutrition. 2018;148(11):1760-1775. PubMed