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. Here I review the 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? To evaluate these possibilities, here I review what is known about the effects of starvation on the body, particularly the skeleton, and the mechanisms involved in storing and metabolizing BMAT during negative energy balance.

Bone Remodeling and Energy Metabolism: New Perspectives

“…When osteoblast-HSC contact is lost, the HSCs progress to form myeloid and lymphoid progenitors (103). The lymphoid lineage produces B, T and NK cells, whereas the myeloid lineage produces granulocytes, erythrocytes and platelets (101). By age 20, the appendicular skeleton is nearly all converted from red to fatty yellow marrow.…”

“…In another study, the investigation of the hormonal/ metabolic profile of patients with anorexia nervosa showed normal insulin sensitivity and increased levels of serum adiponectin in relation to normal weight control women (100). The relevance of marrow fat expansion in conditions of negative caloric balance still is speculative; a comprehensive discussion has been recently published by Devlin (2010) (101).…”

“…By age 20, the appendicular skeleton is nearly all converted from red to fatty yellow marrow. In the axial skeleton, hematopoiesis continues into adulthood, but there is fatty infiltration of the vertebral bodies with aging (101). Changes in mammalian HSCs may affect the progression of MSCs into osteoblasts or adipocytes (104,105,106).…”

Chronic hip pain

“…The pathophysiology of GMT is not well understood. In the early stages of starvation, bone marrow fat paradoxically increases even as other fat stores are being mobilized [7]. Lipolysis of bone marrow adipose tissue does not occur until end-stage starvation, when the body begins breaking down muscle tissue.…”

“…Lipolysis of bone marrow adipose tissue does not occur until end-stage starvation, when the body begins breaking down muscle tissue. This is the final stage in which protein wasting can result in death [7]; therefore, when GMT is present, it is indicative of advanced underlying disease.…”