Based on bone densitometric measurements, weight loss induced by dietary restriction is known to be accompanied by reduced areal bone mineral density, bone mass, and/or bone size, and it is considered harmful to bone health. However, when considering bone quality, bone health consists of diverse indices that cannot be fully represented by densitometric measurements alone. Indeed, there is evidence that moderate dietary restrictions do not impair intrinsic bone material properties, despite the reduction in whole-bone strength because of a smaller bone size.
https://www.ncbi.nlm.nih.gov/pubmed/26881697
Ann N Y Acad Sci. 2016 Jan;1363:26-39. doi: 10.1111/nyas.13004. Epub 2016 Feb 16.