 For most of the last century, a prevailing theory within the field of nutrition was that by eating acid-forming foods, such as meat, we were in essence at risk of peeing our bones down the toilet. And no wonder experiments dating back to 1920 showed over and over that if you add meat to the diet, you get a big spike in the amount of calcium being lost in the urine. And so this made total sense. We had known since 1912 that meat was acid-forming within the body, and how do you buffer acid? What are in antacid pills? Antia acid pills like Tums? Calcium. Meat and eggs have a lot of sulfur-containing amino acids, two to five times more than grains and beans, that are metabolized into sulfuric acid, which the body buffers with calcium. That's why the antacids like Tums are made out of calcium. Calcium can buffer acid. And where is calcium stored in the body? The skeleton. So the thinking was that every time we ate a steak, our body would pull calcium from our bones bit by bit, and over time this could lead to osteoporosis. Based on 26 such studies, every 40 grams of protein we add to our daily diet, we pee out an extra 50 milligrams of calcium. And look, we only have about 2 pounds of calcium in our skeleton, so the loss of 50 a day would mean losing close to 2% of our bone calcium every year. And so by the end of the 20th century, there was little doubt that acid-forming diets would dissolve our bones away. But if you actually look at all the studies done on protein intake and bone health, that's not what you find. So where is the flaw in our logic? Meat leads to acid, which leads to calcium loss, which leads to bone loss, right? Well, it's uncontroversial that protein results in greater calcium excretion. But we've just been assuming it's coming from the bone. I mean, where else could the extra calcium dumped in our urine be coming from, but from our bones? This is the study that appeared to solve the mystery. An intrepid group of researchers tried feeding a bunch of volunteers radioactive calcium and then putting them on a high protein diet. What happens when you put people on a high protein diet? The amount of calcium in their urine shoots up. And indeed, that's just what happened. But here's the big question. Was that extra calcium in their urine radioactive or not? And to everyone's surprise, it was radioactive, meaning that the excess calcium in the urine was coming from their diet. Remember, they're feeding them radioactive calcium. So the excess calcium in their urine wasn't coming from their bones, but from what they were eating. What seemed to be happening is that the excess protein consumption boosted calcium absorption from down around 19% up to 26%. So all of a sudden, there was all this extra calcium in the blood, so presumably the kidneys are like, whoa, what are we going to do with it all, so they dump it in the urine. 90% of the extra calcium in the urine after eating a steak doesn't appear to be coming from our bones, but from our diet. We're not sure why protein boosts calcium absorption. Probably the protein increases the solubility of calcium by stimulating stomach acid production. Whatever the reason, yes, more calcium lost, but more calcium gained such that in the end, most of that extra calcium is accounted for. Soon effect more calcium is lost in the urine stream, but may be compensated by less loss of calcium through the fecal stream. This was repeated with even more extreme diets, an acid-forming 5 burgers a day worth of animal protein diet that limited fruit and vegetables, versus an alkaline diet emphasizing fruits and vegetables. More calcium in the urine on burgers, but significantly greater calcium absorption such that at the end, it was pretty much a wash. Other studies have also since supported this interpretation. Here's an ingenious one. Feed people a high animal protein diet, but with an alkali salt to neutralize the acid. The old thinking would predict that there would be no calcium loss since there was no excess acid to buffer. But no, even though the acid load was neutralized, there was still the excess urinary calcium consistent with the radioactive isotope study. Challenging this long-standing dogma, the animal protein consumption results in an acidosis that promotes the excess excretion of calcium. So if our body isn't buffering the acid formed from our diet with our bones, how is it neutralizing the acid? Maybe with our muscles. Alkaline diets may protect our muscle mass, all covered in my next video, entitled Testing Your Diet with Pea and Purple Cabbage. Stay tuned.