In healthy adults, [[bone]] is undergoing constant repair and renewal. New bone is deposited by [[osteoblast]] cells and resorbed or destroyed by [[osteoclast]] cells. This addition and subtraction of bone usually yields no net change in the overall mass of the skeleton, but the turnover process can be significantly affected by pH.<ref name="Barzel Review"/>
===Bone Mineralmineral Densitydensity===
[[Bone density|Bone Mineralmineral Densitydensity]] (BMD) is a measure commonly used to quantify bone health. A lower BMD value indicates an increased risk of an [[osteoporosis]] or a fracture.<ref>{{cite journal|last=Lips|first=P|title=Epidemiology and predictors of fractures associated with osteoporosis.|journal=The American Journal of Medicine|date=Aug 18, 1997|volume=103|issue=2A|pages=3S–8S; discussion 8S–11S|pmid=9302892|doi=10.1016/s0002-9343(97)90021-8 }}</ref> There is a large range of factors influencing BMD. Protein consumption has shown to be beneficial for bone density by providing amino acid substrates necessary for bone matrix formation. It is also thought that blood concentration of the bone formation stimulant, [[Insulin-like growth factor 1|Insulin-like Growth Factor-I]] (IGF-I), is increased from high protein consumption and [[parathyroid hormone]] (PTH), a bone resorption stimulant, is decreased.<ref name="cao review" /> Although protein has shown to be beneficial for increasing bone mass, or bone mineral density, there is no significant association between protein intake and fracture incidence.<ref>{{cite journal|last=Kerstetter|first=JE|title=Dietary protein and bone: a new approach to an old question.|journal=The American Journal of Clinical Nutrition|date=December 2009|volume=90|issue=6|pages=1451–52|pmid=19864406|doi=10.3945/ajcn.2009.28812|doi-access=free}}</ref> In other words, a low BMD can be predictive of osteoporosis and increased fracture risk, but a higher BMD does not necessarily mean better bone health. High BMD is also correlated with other health issues.<ref>{{cite journal|last=Gregson|first=CL|author2=Hardcastle, SA |author3=Cooper, C |author4= Tobias, JH |title=Friend or foe: high bone mineral density on routine bone density scanning, a review of causes and management.|journal=Rheumatology (Oxford, England)|date=June 2013|volume=52|issue=6|pages=968–85|pmid=23445662|doi=10.1093/rheumatology/ket007 |pmc=3651616}}</ref> For example, a higher BMD has also been associated with increased risk of breast cancer.<ref>{{cite journal|last=Lucas|first=FL|author2=Cauley, JA |author3=Stone, RA |author4=Cummings, SR |author5=Vogt, MT |author6=Weissfeld, JL |author7= Kuller, LH |title=Bone mineral density and risk of breast cancer: differences by family history of breast cancer. Study of Osteoporotic Fractures Research Group.|journal=American Journal of Epidemiology|date=Jul 1, 1998|volume=148|issue=1|pages=22–29|pmid=9663400|doi=10.1093/oxfordjournals.aje.a009554|doi-access=free}}</ref>
