Diets in Western nations typically contain more animal protein than the body needs, and as the excess amino acids are broken down and excreted, the sulfurous amino acids (typically derived from animal rather than vegetarian foods) cause calcium to be excreted in the urine; calcium is one component of the most common type of human kidney stones, calcium oxalate.
Red meat also contains acids that need to be excreted and this acidity constitutes another risk factor for kidney stones. High intake of animal protein also presents a greater uric acid load to be excreted by the kidney. This in turn acidifies the urine, increasing the risk of uric acid stones. In either case, the body often balances this acidic urinary pH by leaching calcium from the bones.