Is Protein Good or Bad for Bones?

One of the most hotly debated controversies in clinical nutrition today is whether a diet higher in protein has a positive or negative effective on bone strength and bone mineral density (BMD).Those who are against protein point to the fact that vegetarians tend to have stronger bones than people who eat more meat and the clinical trials showing increased loss of calcium in the urine when meat or protein intake is increased.

On the other hand, those who believe more protein is beneficial to bone strength point to clinical trials in which children who consume more protein tend to build stronger bones than those who consume less.In some studies of older Americans who consumed more protein, the risk of bone fracture was reduced.Our Ancient Ancestors Had Strong BonesIf we look at this problem from an evolutionary perspective, two things are clear.First, from the fossils of our ancient ancestors, it is clear that their bones were far stronger on average than those of Americans today.Second, our ancient ancestors were for the most part hunter-gatherers and ate a diet that was likely considerably higher in protein than the diet of most Americans.The bones of our closest “relatives”, the great apes, consume a much more vegetarian diet than our ancestors did and yet their bones are stronger still.Our ancient ancestors had stronger bones in part because they were much more physically active than modern people today. Also their diets differed in many other ways which impact bone strength than simply being higher in protein.A recent study examined the long-term impact of dietary protein and other factors on bone development in children from 6 to 18 years. It showed that while higher protein intake was generally associated with stronger bones, the beneficial impact of more protein in the diet was greatly diminished if the diet had relatively little alkalinizing minerals (calcium, potassium, magnesium).1Fruits and vegetables are very high in potassium and also can have a lot of calcium and/or magnesium.These minerals oppose the acids that form from the metabolism of protein-rich foods that are high in phosphorus and sulfur. These are metabolized to sulfate and phosphates, which make the urine more acid. In addition these foods can generate more uric acid.Normal metabolism generates lactic acid and other organic acids that tend to acidify the urine.Grains also on balance tend to result in more acid that alkaline in the blood and urine when metabolized, although not as much as most animal products. Potatoes and yams have more of an alkalizing effect than grains, even when those grains are whole.Most high protein foods of animal origin such as cheese, meat, fish, poultry and eggs generate more acidity in the body.Increased dietary salt is known to increase the loss of calcium in the urine even though its impact on the acid-base balance in the body is neutral because sodium is a strong base but chloride is a strong acid. One way to cut the net acid load on the body is to replace added salt in the diet with MSG. Research has shown that replacing sodium from salt with MSG results in far less acidic urine and also cuts the loss of calcium in the urine, which should reduce not only the risk of osteoporosis but also most kidney stones.Bottom line:While research now shows that diets with more protein do help strengthen bones, it is also very important to get enough calcium, potassium and magnesium by eating more fruits and vegetables. It is also important to minimize the foods that tend to generate excess acidity like refined grains, processed meats, and cheeses. Reducing salt helps reduce calcium excretion and replacing it with MSG alkalanizes the urine, which should help strengthen bones A diet low in meat, cheese, eggs, salt and refined grains and much higher in fruits, vegetables, and with MSG in place of salt, can be used to alkalinize the urine and reduce the risk of osteoporosis and most kidney stones.By James J. Kenney, PhD, RD, FACN.References:1 Am J Clin Nutr 2005;82:1107-14