尿液是人体主要代谢途径之一，尿液中通常含有来自各种食品、饮料、药物、环境污染物、内源性废物代谢物和细菌副产物的代谢分解产物。在这些看似“废物”的物质中，恰恰隐藏着被机体排出的各种变化，所以尿液是被大家忽略的、可以挖掘外周生物标志物的“金矿”。
【摘要】Total and per capita protein consumption rates in US diets， whether from plant or animal sources， rank among the highest in the world. When protein consumption outpaces physiologic protein demands， excess amino acids are degraded in the human body and nitrogen is excreted and released to the environment， mainly in the form of urea. Such excess reactive N can enter downstream environments， thereby impairing human and ecosystem health as well as contributing to economic losses. We show that matching protein consumption with physiologic requirements would reduce US hydrologic N losses to aquatic ecosystems by 12% and overall N losses to ecosystems by 4%. Were US citizens to consume protein at recommended rates， projected N excretion rates in 2055 would be 27% less than they are today， despite population growth. Optimizing US protein consumption to levels that meet human health standards has environmental benefits on par with improving wastewater treatment using existing technology， while also generating impactful economic benefits.
至于为什么匪夷所思地选择了尿液，据说是因为他觉得人体本身就很神奇，从嘴巴吃进去的跟排泄出来的物质完全不一样，而尿作为人体液的一种，颜色又和黄金有那么点接近，没准就是成功的关键呢。The Alchemist Discovering Phosphorus by Joseph Wright 。
