Researchers discover genetic basis for body fat

An international consortium has discovered specific genes and genome sites in the human body that are linked to weight-distribution, and have thereby claimed that fat distribution is partly biologically driven.

A meta-analysis involving the results of 46 different studies identified 18 new weight-related genomic regions linked to increased Body Mass Index (BMI). This brings the total of known BMI-related genomic regions to 32.

The genes appeared to act in the brain and therefore researchers speculate that they are controlled through appetite. A total of over 120,00 people took part in the study.

A second study discovered 13 gene variants that appeared to influence body fat distributions and specifically the waist-to-hip ratio (WHR).

Dr Ruth Loos, group leader in the Genetic Aetiology of Obesity Program at the Institute of the Metabolic Science in Cambridge, clarified that “A high WHR corresponds to fat deposition on the waist, a low WHR (which is better) corresponds to fat deposition on the hips”.

Thus these gene variants can influence a person to become apple-shaped, with extra weight in the abdomen, or pear-shaped people, with extra weight in the hips and thighs. Seven of these gene variants had a stronger effect on women than on men.

Dr Loos explained, “This reflects the difference in physiology between men and women. Women have a greater propensity to store fat on the hips, whereas men easier store fat on the waist.”

In the second study, it was found that fat metabolism, rather than appetite, influenced the distribution of fat. The 13 genes were found to explain only one per cent of a person’s body-fat distribution, and therefore that the genetic information alone cannot determine whether a newborn infant will store fat in the hips or waist and whether the infant will become overweight.

However, researchers maintained that an increase in weight-related genes positively correlates with an increase in weight.

Dr Jim Wilson, a Royal Society University Research Fellow from the University of Edinburgh's Centre for Population Health Sciences, explained: “Comparing the two per cent of people with the most obesity risk variants against the two per cent of the population with the least risk variants showed that about seven kilograms of weight could be explained by the genes alone. There is thus the opportunity to target vigorous interventions to this subgroup who need them most.

“Body weight is a result of an interplay of environmental and genetic factors, that remains the case, but the exact relationship can be different for different people.”

A Scottish Health Survey in 2008 found that 66.4 per cent of men and almost 60 per cent of women were overweight.

The studies involved 400 scientists from 280 research institutions from around the world, including the University of Edinburgh, the Medical Research Council Human Genetics Unit in Edinburgh, Oxford University, and Cambridge University.

The full article regarding the studies appeared in the 10 October online issue of Nature Genetics.