Uploaded August 2026 | Updated September 2026, 2 weeks ago
We rarely measure kidney filtration directly. We estimate it from creatinine, a breakdown product of muscle. It goes up when you carry more muscle, and it goes up for a day or two after you eat a big steak or start taking creatine. So a lean, muscular person, or anyone who ate meat before their blood draw, can show a lower estimated GFR and look like their kidneys are failing when nothing has actually changed. Part of the 'protein wrecks your kidneys' signal is that measurement quirk, not real damage.
We rarely measure kidney filtration directly. We estimate it from creatinine, a breakdown product of muscle. It goes up when you carry more muscle, and it goes up for a day or two after you eat a big steak or start taking creatine. So a lean, muscular person, or anyone who ate meat before their blood draw, can show a lower estimated GFR and look like their kidneys are failing when nothing has actually changed. Part of the 'protein wrecks your kidneys' signal is that measurement quirk, not real damage.
