But how can you make the difference between one type of fat and another? Sorting out all the different factors that bring about obesity, and defining subgroups to which people belong would offer the possibility of more personalized interventions. Scientists from the University of Regensburg and Zoltán Kutalik, SIB Group Leader (Institute of Social and Preventive Medicine, Lausanne University Hospital) describe a first important step towards this goal in a paper that has just been published in Nature Communications.

Genetic markers and body location

Obesity is a very complex state of affairs, involving many factors of a different nature. It has a strong genetic determinant (40%). Genetic markers directly linked to diabetes and hypertension, for example, are now known and, not so long ago, markers linked to the recently unveiled “favourable fat” were also discovered.

But adipose tissue is not worn in the same way by all: it can gather around our hips, or thicken our waist, or it can surround our internal organs or accumulate beneath our skin. In this study, Kutalik et al. identified different subgroups of obesity, taking into account how the genetic markers influence the location of the fat.

Four major obesity subgroups

They did this by combining data from over 300,000 subjects, and classifying signals associated with body-mass-index (BMI) and waist-to-hip ratio (WHR). In this way, the researchers were able to identify four major subgroups of obesity, which then formed a basis for investigating their impact in terms of anthropometry, fat depots and metabolic health.

One of these subgroups describes a metabolically favourable form of obesity: one extra kg of this uncommon fat type could indeed reduce the risk of coronary artery disease by ~6% for example. Another subgroup seems to implicate genes whose expression is particularly high in the digestive system - a fact that is quite new to obesity genetics.

Favourable fat: carried by one in eight people

"Our study is a first step towards potential personalization of obesity interventions," says Zoltan Kutalik. "As an example, we estimate that one in eight people who are overweight could be classified in the subgroup whose fat is metabolically favourable, despite an elevated BMI."

Further studies are necessary however he adds, to identify more accurately this particular subgroup based on genetic and clinical biomarkers.

This work has been carried out in close collaboration between the University of Regensburg (Thomas Winkler and Iris Heid), and the Lausanne University Hospital (CHUV).

Winkler T W et al. A joint view on genetic variants for adiposity differentiates subtypes with distinct metabolic implications. Nature Communications 2018. doi:10.1038/s41467-018-04124-9