Marrow Adipose Tissue
Bone marrow contains fat as well as blood-forming cells - it increases in obesity, harms bone-building, and changes in the first years after weight-loss surgery.
Plain English
Patient-Friendly Explanation
Bone marrow is best known as the factory that makes blood cells, but a large share of it in adults is fat - marrow adipose tissue. That fat is not simply filler. It sits inside the same space as the bone-building cells, and when it expands it does so at their expense, because fat cells and bone-forming cells come from the same parent cell and the body has to choose between them. Marrow fat also releases signals that slow bone formation and encourage bone breakdown, and it is affected by metabolic health: it increases with obesity and with type 2 diabetes, and it is linked with poorer bone quality even though bone density readings often look reassuringly high in heavier people. Losing weight changes it in a two-stage way - it rises in the first few months after weight-loss surgery, then falls again with continued loss over the following year or two. Measuring it needs magnetic resonance imaging rather than an ordinary bone scan, so it is a research and specialist tool rather than a routine test in Singapore.
Medical
Clinical Definition
Bone marrow adipose tissue (BMAT) is a distinct adipose depot that occupies a substantial and increasing proportion of marrow volume with age, accounting for as much as 50 to 70 per cent of marrow space in adult long bones. It is not inert: marrow adipocytes are metabolically active, secrete adiponectin, leptin, RANKL, interleukin-6 and other cytokines, and act as a local regulator of haematopoiesis and of skeletal remodelling. Adipocytes and osteoblasts share a common mesenchymal stromal cell precursor, and lineage allocation between adipogenesis and osteoblastogenesis is governed by competing signalling - PPAR-gamma and C/EBP-alpha favour adipogenesis while Wnt/beta-catenin and RUNX2 favour osteoblastogenesis - so expansion of the marrow adipocyte population occurs at the expense of osteoblast number and bone formation. BMAT is increased in obesity and further in obesity with type 2 diabetes, correlates with insulin resistance, HbA1c and visceral adiposity, and associates with reduced bone formation rate, trabecular microarchitectural deterioration and increased vertebral fracture risk independently of areal bone mineral density - an important point given that BMD is often relatively high in patients with obesity. Intentional weight loss has a biphasic effect: BMAT rises acutely after bariatric surgery and during rapid weight loss, then declines with continued weight loss over 12 to 24 months, alongside a 5 to 10 per cent fall in hip and femoral neck bone mineral density in the first one to two years. Quantification requires magnetic resonance spectroscopy or water-fat MRI, since DXA cannot separate marrow fat from other soft tissue and CT is limited by radiation and low contrast; proton density fat fraction MRI is the current reference approach. BMAT is an active research target as a mechanistic link between obesity, insulin resistance and skeletal fragility, with no established clinical reference range.
Key Insight
Why It Matters
Marrow fat is one reason we take bone health seriously in weight management - and one reason we push protein, calcium, vitamin D and strength training alongside steady loss rather than crash dieting. If you have had weight-loss surgery or a fracture from a minor fall, ask about a bone density scan.
Sources
Reviewed against standard medical references.
Medically reviewed by
Family Physician & Registered Acupuncturist, Accord Medical Clinic. MBBS (NUS), Graduate Diploma in Family Medicine (NUS), Graduate Diploma in Acupuncture (Singapore College of TCM).
Last reviewed: September 2026
This page is general health education, not medical advice. Whether any treatment is appropriate for you is a decision made in consultation after assessment.
