Why does starvation make bones fat?

Abstract

Body fat, or adipose tissue, is a crucial energetic buffer against starvation in humans and other mammals, and reserves of white adipose tissue (WAT) rise and fall in parallel with food intake. Much less is known about the function of bone marrow adipose tissue (BMAT), which are fat cells found in bone marrow. BMAT mass actually increases during starvation, even as other fat depots are being mobilized for energy. This review considers several possible reasons for this poorly understood phenomenon. Is BMAT a passive filler that occupies spaces left by dying bone cells, a pathological consequence of suppressed bone formation, or potentially an adaptation for surviving starvation? These possibilities are evaluated in terms of the effects of starvation on the body, particularly the skeleton, and the mechanisms involved in storing and metabolizing BMAT during negative energy balance.

Figure 1

Starvation-induced physiological changes associated with increased adipogenesis, decreased osteogenesis, and suppression of hematopoiesis in bone marrow. Fuel sources shown in gray. Boxes indicate association with increased BMAT; italics indicate association with decreased osteogenesis. WAT, white adipose tissue. FFAs, free fatty acids. PPAR, peroxisome proliferator-activated receptor. FGF, fibroblast growth factor. PGC, peroxisome proliferator-activated receptor gamma coactivator protein. STAT5, signal transducer and activator of transcription. GH, growth hormone. IGF, insulin-like growth factor.