The War on Protein: How Much You Actually Need, Where to Get It, and Why None of It Matters Without the Weights
A 35-year-old man presented to the Emergency Department with crampy abdominal pain of two to three days duration. Vital signs were within normal limits. Abdominal examination revealed generalised tenderness with specific localisation to the left lower quadrant. Laboratory investigations were notable for a mild leucocytosis; computed tomography confirmed uncomplicated sigmoid diverticulitis.
Following counselling on the natural history of uncomplicated diverticulitis, current evidence around selective antibiotic use, and the role of a short-term low-residue diet in the acute phase, I proceeded to my standard downstream preventive counselling — a transition to a plant-forward dietary pattern, with plants occupying approximately 80% of the plate and a target of 30 to 40 unique plant species per week.
At this point in the conversation, the patient disclosed that he had recently adopted a high-protein dietary pattern at approximately 2.2 g/kg/day, sourced predominantly from beef, chicken, and eggs. This intake target had been adopted verbatim from a podcast, without individualised clinical indication, and without concurrent resistance training. The consequence: displacement of fibre-rich plant foods in favour of animal protein sources, in a patient whose presenting diagnosis was causally linked to low dietary fibre intake.
This case is a microcosm of a much larger phenomenon — the translation of nuanced protein science, across populations with wildly different needs, into a single decontextualised number, shouted from a podcast, and acted upon by patients who were never the intended audience.
The Evidence
Where the RDA Came From — and What It Was Designed to Do
The current Recommended Dietary Allowance for protein in adults — 0.8 g/kg/day — is derived from the 2003 meta-analysis by Rand and colleagues, published in the American Journal of Clinical Nutrition.¹ Pooling data from 235 subjects across 19 nitrogen balance studies, the authors estimated a population RDA of 0.83 g/kg/day — defined as the intake at which approximately 97.5% of healthy adults would maintain nitrogen equilibrium.
Two features of this number warrant emphasis. First, it is a floor — designed to prevent deficiency, not to optimise health. Second, the Dietary Reference Intakes document itself acknowledges that the nitrogen balance methodology has substantial limitations and should no longer be regarded as the gold standard for determining protein requirements.¹
Optimising, Not Just Preventing Deficiency
Phillips, Chevalier, and Leidy's 2016 review in Applied Physiology, Nutrition and Metabolism argued that the current RDA — while adequate to prevent frank deficiency — is insufficient for optimising muscle mass, preventing age-related sarcopenia, and supporting body composition goals.² Synthesising the available evidence from indicator amino acid oxidation studies and dose-response trials, they concluded that high-quality protein intakes in the range of 1.2 to 1.6 g/kg/day represent a more reasonable target for optimising health outcomes in adults.
Tagawa and colleagues provided the clearest dose-response evidence in their 2022 meta-analysis published in Sports Medicine Open.³ Across randomised controlled trials of resistance-trained adults, they demonstrated a dose-response relationship between total protein intake and changes in muscle strength, with the curve plateauing at approximately 1.5 g/kg/day. Nunes and colleagues, in a 2022 systematic review published in the Journal of Cachexia, Sarcopenia and Muscle, reached a similar ceiling at approximately 1.3 g/kg/day.⁴
Protein Source and Long-Term Cardiovascular Risk
In 2024, Glenn and colleagues published a landmark analysis in the American Journal of Clinical Nutrition, pooling data from three of the largest prospective cohorts in nutrition science — the Nurses' Health Study, Nurses' Health Study II, and the Health Professionals Follow-up Study.⁵ Substitution of plant protein for animal protein was associated with statistically significant reductions in the risk of cardiovascular disease and coronary heart disease. This epidemiologic signal aligns with the mechanistic reality that animal protein sources typically co-deliver saturated fat, heme iron, and other atherogenic compounds, whereas plant protein sources co-deliver fibre, polyphenols, and a broader micronutrient profile.
The Plant-versus-Animal Protein Question in Resistance Training
Hevia-Larraín and colleagues, publishing in Sports Medicine in 2021, conducted a controlled trial comparing habitual vegans and habitual omnivores undertaking identical resistance training programmes with protein intakes matched at 1.6 g/kg/day.⁶ After twelve weeks, there were no statistically significant differences between groups in muscle hypertrophy or strength gains. This finding has since been reinforced by Santini and colleagues in a 2025 randomised clinical trial published in the Journal of the International Society of Sports Nutrition.⁷ When total protein intake is matched and resistance training stimulus is provided, protein source — animal versus plant — does not appear to meaningfully alter resistance training adaptations.
The Critical Caveat in Older Adults
Zhang and colleagues published a 2025 systematic review and meta-analysis in BMC Geriatrics examining protein supplementation in older adults with physical inactivity.⁸ The finding was unambiguous: in the absence of concurrent resistance training, protein supplementation alone did not meaningfully improve muscle mass, muscle strength, or physical performance.
This is arguably the most important finding in the contemporary protein literature for the general public. Adequate protein intake is necessary but not sufficient for the prevention of sarcopenia. Without the anabolic stimulus of resistance training, dietary protein will not preserve lean mass. The ESPEN expert group recommendation of 1.0 to 1.2 g/kg/day in healthy older adults, with escalation to 1.2 to 1.5 g/kg/day in the context of illness or injury, presupposes the presence of resistance exercise as a concurrent intervention.⁹
Protein Quality — PDCAAS, DIAAS, and Their Clinical Relevance
The Protein Digestibility Corrected Amino Acid Score (PDCAAS) and the newer Digestible Indispensable Amino Acid Score (DIAAS) quantify the extent to which a given food provides the nine essential amino acids relative to human requirements, corrected for digestibility.¹⁰ Animal proteins systematically score higher on both metrics. This technical distinction, however, is frequently weaponised in public-facing communication in ways the underlying science does not support.
Three considerations warrant emphasis. First, these scoring systems were developed to identify single-source proteins in contexts of food insecurity — not to guide dietary choice in well-fed adults in high-income countries. Second, scores are typically calculated on raw, minimally processed foods; real-world preparation (cooking, soaking, fermenting) substantially improves the bioavailability of plant protein. Third — and most consequentially — when protein intake is adequate and the diet is varied, the composite amino acid profile of a plant-based diet is sufficient to support the full range of physiological functions, including resistance training adaptation, as demonstrated by Hevia-Larraín and colleagues.⁶
How Should This Modify Your Practice?
For clinicians engaging patients on dietary protein:
• Screen for the decontextualised target. Patients who report specific, aggressive protein targets (e.g., 2.0–2.2 g/kg/day) should be asked where the recommendation originated and whether it is accompanied by resistance training. In the absence of the latter, the former is rarely indicated.
• Quantify before prescribing. Most adults in the United States and Australia are already consuming 0.9 to 1.3 g/kg/day without intervention.¹¹,¹² Before recommending increased protein intake, establish current intake — ideally via a validated dietary tracking approach.
• Frame the intervention as protein plus resistance training, never protein alone. The Zhang 2025 meta-analysis provides the cleanest evidence that protein supplementation in the absence of resistance training does not meaningfully affect muscle mass or function in older adults.⁸
• Counsel on source, not just quantity. The Harvard cohort data supports partial substitution of plant for animal protein as a cardiovascular risk-reduction strategy.⁵ For patients with colonic disease, cardiovascular disease, or type 2 diabetes, this substitution also aligns with the broader dietary pattern evidence.
• Individualise for comorbidity. Patients with chronic kidney disease, a history of gout, or on certain pharmacologic regimens may require tailored protein recommendations that differ from the general population target.
For patients, the translation of this evidence into actionable behaviour is straightforward:
• Adults maintaining muscle and general health: 1.0 to 1.2 g/kg/day.
• Adults actively resistance training for hypertrophy or strength: 1.2 to 1.6 g/kg/day.
• Adults over 65: 1.0 to 1.2 g/kg/day baseline, 1.2 to 1.5 g/kg/day in the context of illness or injury, always with resistance training.
• Prioritise plant sources; use animal sources as complements rather than the dietary foundation.
• Track current intake before assuming a deficit exists. Most patients discover they are already meeting their target.
About the Author
Dr. Adrian Cois is an Emergency Medicine physician, health educator, and the creator of DrCois.com and the Overheard in the Emergency Room podcast. His clinical interests span emergency medicine, exercise physiology, and preventive health, with a focus on translating clinical evidence into practical, patient-centred guidance. He is committed to evidence-based medicine for everyday people — fewer bad days, more good decades.
References
1. Rand WM, Pellett PL, Young VR. Meta-analysis of nitrogen balance studies for estimating protein requirements in healthy adults. Am J Clin Nutr. 2003;77(1):109–127. doi:10.1093/ajcn/77.1.109
2. Phillips SM, Chevalier S, Leidy HJ. Protein “requirements” beyond the RDA: implications for optimizing health. Appl Physiol Nutr Metab. 2016;41(5):565–572. doi:10.1139/apnm-2015-0550
3. Tagawa R, Watanabe D, Ito K, et al. Synergistic effect of increased total protein intake and strength training on muscle strength: a dose-response meta-analysis of randomized controlled trials. Sports Med Open. 2022;8:110. doi:10.1186/s40798-022-00508-w
4. Nunes EA, Colenso-Semple L, McKellar SR, et al. Systematic review and meta-analysis of protein intake to support muscle mass and function in healthy adults. J Cachexia Sarcopenia Muscle. 2022;13(2):795–810. doi:10.1002/jcsm.12922
5. Glenn AJ, Wang F, Tessier AJ, et al. Dietary plant-to-animal protein ratio and risk of cardiovascular disease in 3 prospective cohorts. Am J Clin Nutr. 2024;120(6):1373–1386. doi:10.1016/j.ajcnut.2024.09.006
6. Hevia-Larraín V, Gualano B, Longobardi I, et al. High-protein plant-based diet versus a protein-matched omnivorous diet to support resistance training adaptations: a comparison between habitual vegans and omnivores. Sports Med. 2021;51(6):1317–1330. doi:10.1007/s40279-021-01434-9
7. Santini MH, Erwig Leitão A, Mazzolani BC, et al. Similar effects between animal-based and plant-based protein blend as complementary dietary protein on muscle adaptations to resistance training: findings from a randomized clinical trial. J Int Soc Sports Nutr. 2025;22(1):2568047. doi:10.1080/15502783.2025.2568047
8. Zhang L, Liu G, Huang X, He F. Effects of protein supplementation on muscle mass, muscle strength, and physical performance in older adults with physical inactivity: a systematic review and meta-analysis. BMC Geriatr. 2025;25:228. doi:10.1186/s12877-025-05885-x
9. Deutz NEP, Bauer JM, Barazzoni R, et al. Protein intake and exercise for optimal muscle function with aging: recommendations from the ESPEN expert group. Clin Nutr. 2014;33(6):929–936. doi:10.1016/j.clnu.2014.04.007 *
10. Mathai JK, Liu Y, Stein HH. Values for digestible indispensable amino acid scores (DIAAS) for some dairy and plant proteins may better describe protein quality than values calculated using the concept for protein digestibility-corrected amino acid scores (PDCAAS). Nutr Rev. 2017;75(8):658–667. doi:10.1093/nutrit/nux025 *
11. Centers for Disease Control and Prevention. Nutrition — Health, United States. CDC/NCHS. Updated August 2024. Accessed April 16, 2026. https://www.cdc.gov/nchs/hus/topics/nutrition.htm
12. Australian Bureau of Statistics. Usual nutrient intakes, 2023. Accessed April 16, 2026. https://www.abs.gov.au/statistics/health/food-and-nutrition/usual-nutrient-intakes/latest-release
