Ectopic fat

Ectopic fat is lipid stored within or around organs that normally contain little adipose tissue — liver, skeletal muscle, pancreas, heart, and pericardium — distinct from subcutaneous or visceral depots. When energy intake chronically exceeds subcutaneous storage capacity, fatty acids and triglycerides spill into these organs, generating lipotoxic intermediates (diacylglycerol, DAG; ceramides) that impair insulin signalling. DAG activates PKC-ε in the liver — blunting insulin receptor substrate phosphorylation and driving hepatic glucose overproduction — and PKC-θ in skeletal muscle, reducing glucose uptake; in β-cells, lipid accumulation suppresses first-phase insulin secretion. Roy Taylor formalised the personal fat threshold: each individual has a genetically determined subcutaneous storage limit beyond which ectopic deposition begins, independent of body weight. The 2023 Clinical Science ReTUNE study, in normal-BMI individuals with type 2 diabetes, showed that a median 6.5% weight loss normalised liver fat and restored β-cell function, achieving remission in 70% of participants. Shulman's 2014 NEJM review established the mechanistic framework linking ectopic lipid to insulin resistance in humans via MR spectroscopy; causal direction is supported by intervention and Mendelian randomisation studies, though some observational associations remain confounded. Measurement via MRI, MR spectroscopy, or CT provides cardiometabolic and age-related disease risk information beyond BMI or waist circumference, even at a metabolically normal body weight.