You asked what past research we did on the maximum daily recommended protein, and what Peter Attia recommends. Here is the honest answer, assembled from the SmartStrongAlive project files and the central ResearchLibrary.

The short version: we never ran a dedicated "what is the upper limit" research pass. What we do have is the ceiling evidence gathered on July 10 and 11, 2026, while building the protein calculator, and it answers your question well. Every DOI below was verified against CrossRef at the time it was banked.

The three numbers that matter

There is no single maximum. There are three different ceilings, and they get confused with each other constantly.

For a 150 lb woman that is roughly 109 g, 136 to 150 g, and 225 g respectively.

Where Peter Attia's number comes from

Worth knowing up front: Attia's protein recommendations in our files come from the papers he cites, not from anything he said on tape. We checked. The MenopauseKnowledgeBase transcript corpus holds 26 Attia videos, and across all of them there is exactly one passing mention of protein, because that corpus was scoped to menopause. So there are no Attia quotes to pull, only his evidence base.

Three papers carry his argument, all banked on 2026-07-11:

Morton 2018, British Journal of Sports Medicine This is the ceiling paper. A systematic review and meta-analysis of protein plus resistance training, and the source of the finding that gains in muscle mass and strength plateau at roughly 1.6 g/kg/day. When Attia talks about a dose-response curve that flattens, this is the curve. It is also the single most useful citation you have for a "how much is too much" article, because it gives you a real number with real evidence behind it rather than a vibe.

Phillips, Chevalier and Leidy 2016, Applied Physiology, Nutrition and Metabolism Titled "Protein requirements beyond the RDA." This is his primary justification that 0.8 g/kg is a floor designed to prevent deficiency, not a target for health, and that 1.2 to 1.6 g/kg is the more defensible range.

Nowson and O'Connell 2015, Nutrients Protein requirements for older people. He cites this for anabolic resistance, the reason older muscle needs a bigger dose to respond at all.

Where the safety ceiling comes from

Three papers, banked 2026-07-10:

Antonio 2016, Journal of Nutrition and Metabolism A one-year crossover study in resistance-trained people eating 2.5 to 3.3 g/kg/day. No harm to kidney function, liver function, or blood lipids. This is the highest sustained intake in our library with safety data attached, and it is the reason the "protein wrecks your kidneys" worry does not hold up for healthy people.

Devries 2018, The Journal of Nutrition Meta-analysis, 28 studies, 1,358 people. Higher protein raises glomerular filtration rate, but the change in kidney function does not differ from normal or low protein diets in healthy adults. In plain terms: the kidneys work harder, which is not the same as being damaged.

Cheng 2024, Frontiers in Nutrition Meta-analysis of 148,051 people and 8,746 chronic kidney disease cases. Higher total, plant, and animal protein were each associated with lower CKD risk, not higher.

The caveat that travels with all three: this applies to people without pre-existing chronic kidney disease. Anyone with moderate to severe CKD needs clinician-guided protein restriction, and that framing is already on the live calculator page.

What the calculator actually does with this

The protein calculator caps at 2.0 g/kg. That was a deliberate call, not a default. The ceiling was raised to the ISSN 2.0 figure on 2026-07-11 specifically so muscle-focused midlife women would not be under-dosed by a tool built on sedentary-adult numbers.

The ranges it applies:

• Sedentary: 1.2 to 1.6 g/kg
• Strength training twice a week or more, losing weight, or on a GLP-1: 1.4 to 2.0 g/kg
• Age 65 and up: floor rises to 1.2 g/kg for anabolic resistance
• Mostly plant-based: final number multiplied by about 1.15
• Per meal: 25 to 40 g, three to four times a day

Gabrielle Lyon's widely quoted 1 g per pound of ideal body weight works out to about 2.2 g/kg, which sits just above the calculator's cap. It is documented as context on the page, not offered as the default. Stacy Sims and the ISSN 2023 position stand for female athletes put the lifespan range at 1.4 to 2.2 g/kg.

What is missing, and what I would do about it

We have never researched the actual upper limit as its own question. Everything above was collected to defend a minimum that is higher than the RDA. That is a different argument, and it means we have thin coverage on the things a "how much is too much" piece would need: nitrogen excretion limits, the protein leverage hypothesis, the mTOR and longevity tension (which is genuinely interesting given Attia's own position has shifted on it), and satiety ceilings.

There is a ready-made article sitting here. The Lyon, Sims and Attia deep dive, "the expert case for higher protein," has been researched and never drafted. It is open item #2 on the protein calculator's list. If you want a maximum-protein piece, most of the sourcing already exists and the honest angle is a good one: the ceiling is real, it is around 1.6 g/kg for muscle, and the reason to eat more than that is not more muscle but easier adherence, better satiety, and a margin for the days you fall short.

One framing to avoid, because it is false and it is already flagged in the project notes: do not say most women are deficient by the RDA. Only single-digit percentages miss that floor. The defensible line is the optimal gap, which is that roughly 82% of older adults miss the 1.2 g/kg that expert groups actually recommend.