"When protein intake exceeds about 95 grams per day, the body goes into negative mineral balance because of high acidity. With an intake of 140 gm, there is a mean loss of 60 mg of calcium per day, regardless of the amount of calcium ingested." Horne, Chapter 15, Diet and Nutrition.

So if u eat nothing else all day, a 12 oz steak, some mashed potatoes and asparagus in just 1 typical, unhealthy meal would exceed that 95g protein/day threshold and cause bone resorption.