Animal Protein and Osteoporosis
At least one study has linked higher animal protein intake with loss of bone density, but it is important to note the reasons why animal protein is associated with greater risk and plant-based protein is not. When we digest protein, the sulfur-containing amino acids in that protein are converted by our body into sulfuric acid, which acidify our blood. To buffer the effects of the acidic blood, our body has a number of defenses, one of which is to use calcium to counteract the acid. If our body requires more calcium than is available in our blood, it draws extra calcium from our bones. Thus, a diet chronically high in animal-based proteins is often associated with increased loss of bone-density, the result of our bones losing calcium to buffer the acidic blood.
This is not the case with plant-based proteins because most fruits and vegetables contain alkaline compounds as well, which effectively buffer the increased acidity caused by protein. With extra buffering capability built-in, no calcium is needed to buffer the acid, and our bones remain intact. Unfortunately, most Americans eat more animal protein at the expense of vegetables, which is a dangerous combination capable of leading to osteopenia and osteoporosis.
Animal protein does not need to cause loss of bone density, just make sure that every meal which contains animal protein also contains a healthy load of vegetables as well. By providing your body with a buffer to the acidifying effects of protein, you ensure your bones will never suffer as a result.
Animal Protein and Cancer
Like osteoporosis, animal protein has been linked numerous times to cancer, especially red meats like beef and lamb. The mechanisms for why this may be are not fully clear, but the links are strongest when the following factors are all found together: high animal protein intake, higher fat intake, and low fiber intake. When lower-fat meats like fish or chicken are consumed, they were inversely related to cancer risk. Similarly, in diets high in fiber, cancer risk was lower as well.
Whether it is animal protein itself which causes cancer is uncertain, and a much stronger link can be made between diets low in fruits and vegetables and cancer. In many of the studies on animal protein and cancer risk, the common denominator is a diet lower in plant-based foods. As total calories consumed from animal products goes up, total calories consumed from plant products goes down. Most fruits and vegetables have numerous phytochemicals which offer anti-inflammatory and anti-cancer effects, and without these nutrients our body does a much poorer job of fending off chronic diseases like cancer. If you always ensure your vegetable intake is high, the risks associated with animal protein are low.