The thin-fat phenotype and global metabolic disease risk

There has been a great deal of interest in the thin-fat phenotype evident in Asian Indians and its risk associations in the epidemic of noncommunicable chronic disease associated with it. The cause of this phenotype is probably related to lifestyle and environment; however, genotypic and epigenetic modifications in utero also have been considered.

The thin-fat phenotype occurs when fat is added to an already thin frame. This may occur with rural-urban migration, when positive energy balance occurs in a migrating population who were predominantly thin and physically active to begin with. The role of the pre-existing skeletal muscle mass and its interaction with newly deposited fat must be considered. The thin-fat phenotype may be programmed during fetal growth, but the evidence for this phenomenon is still not completely clear. Finally, although there is increased chronic disease morbidity at lower BMI and younger age in south Asian populations, BMI-related mortality does not appear to follow this trend.

At present, the weight of evidence appears to link the thin-fat phenotype to an environmental and lifestyle phenomenon occurring in previously thin people. This is particularly relevant in India, given the pace of transition over the last two decades.