Study explains South Asian predisposition to diabetes

A new study has shown how lower amounts of brown adipose tissue (BAT, or ‘brown fat’) could help explain why South Asians have an exceptionally high susceptibility to developing metabolic problems such as obesity and type 2 diabetes. BAT has shown beneficial effects on glucose tolerance, lipid metabolism and body weight in pre-clinical studies. The findings, published in The Lancet Diabetes and Endocrinology, could lead to new ways of preventing diabetes.

Unlike white fat cells, which store the body’s surplus energy as fat, brown fat cells in BAT can convert some of this energy (lipids and glucose) into large amounts of heat when the body is exposed to cold, thus burning the energy surplus rather than storing it. It is estimated that fully activated BAT contributes up to 20% of total energy expenditure. Earlier studies have shown that BAT activity is reduced in obese adults.

South Asians have a much greater risk than white Caucasians of developing type 2 diabetes. Moreover, the condition develops in South Asians at a far younger age and at much lower body mass index (BMI). But until now little was known about the causes underlying these differences.

In this study, researchers from the Netherlands compared resting energy expenditure and BAT volume and activity in 12 healthy lean South Asian men, aged about 25 years, and 12 matched white Caucasian men after exposure to cold, using 18F-fluorodeoxyglucose positron emission tomography and computed tomography (18F-FDG-PET-CT) scans. The effect of cold exposure on non-shivering thermogenesis and plasma lipid levels was also measured.

Strikingly, results showed that resting energy expenditure was 32% lower in South Asian participants than in Caucasians, as was the volume of metabolically active BAT (minus 34%). These findings were in line with the significantly higher shiver temperature noted in South Asians upon cold exposure, despite their higher total fat mass. They also had lower cold-induced non-shivering thermogenesis compared with Caucasians.

A linked comment by Michael Symonds from The University of Nottingham in the UK points out: ‘As South Asians are much more susceptible to metabolic disturbances, it is important to establish whether these individuals are resistant to established stimulators of BAT thermogenesis such as chronic cold exposure or dietary stimulants.

‘This group is now the ideal target for new pharmacological interventions that might offer proof-of-principle that enhanced BAT volume or function can have long-term health benefits against metabolic disease.’