Protein requirements and nitrogen balance were initially developed for animal growth, not for non-growing adults.

“so that that's sort of the definition um where does the Rd come from I think it's useful to go back in history just a little bit then on protein um how did we begin to evaluate protein needs well it all came out of animal Sciences uh back in the early 1900s before we even knew the essential all the essential amino acids uh farmers were trying to say how do I get animals to grow best you know and different kinds of proteins and things like that and they develop protein quality scores and things like that so how much growth did I get for what I fed uh how much Nitro that I deposit for how much I fed so these were all rapidly growing animals and we developed this concept really of nitrogen retention um that basically uh We've now translated into what's called nitrogen balance and that's how we determine the protein requirement basically what's important in all of that discussion that long- winded explanation is that all of the concepts were developed for growth where nitrogen balance was positive you could measure a change over time and as we've now tried to start applying that to non-growing adults it gets a lot more vague so it's important to recognize that what we think about protein requirements is a developed from nitrogen balance where you measure all of the nitrogen you're eating which you can do pretty good but then you have to measure all of the nitrogen you're losing which were really bad at and we call that nitrogen balance can you explain how that's done Don that's this is I think we're going to talk so much about it that I think it's it's worth getting into the details of how nitrogen balance is calculated and let's do it in a human so if if I came into your lab how would you do this uhuh so so let's start with the front end let's start with nitrogen in so that's basically you just take a a bunch of food and you do an chemical analysis and you measure the nitrogen and you multiply it by a factor of 6. 25 so a you're measuring nitrogen it's not really protein it could be nucleic acids it could be anything with nitrogen you're calling it protein and then you're multiplying it by 6.25 which says I believe that protein contains 16% nitrogen which also isn't always true so now we've got this error on the front end and now on the back end we're going to try and measure losses so the primary loss of of nitrogen in the body is in the urine Ura so that's pretty easy to measure you can collect that second would be the stool uh so you can collect that but then you get into things like sweat and skin loss and hair loss and respiratory nitrogen ammonia and the breath and those are all incredibly vague so everyone who knows nitrogen balance says that nitrogen balance underestimates requirement everybody uniform but that is where the RDA comes from and it it when you do short-term studies what you find is most people young adult and again all these studies were done with college age students so they're kind of right at the end of their growth uh and basically in a short-term 7-Day study they look okay so that's s where we're at”