“People of South Asian origin are more prone to diabetes because of the way their muscles burn fat,” BBC News reported.
This news story is based on research looking at the rates of fat metabolism in 20 men of South Asian origin and 20 white European men. The findings suggest that South Asian men have a lower rate of fat metabolism during exercise than European men. During resting states, fat metabolism was the same. The South Asian men also had a reduced sensitivity to insulin compared with the European group. This indicates a possible tendency towards glucose intolerance and type 2 diabetes.
This was a small preliminary study and much further research is needed to confirm this association, and to determine how differences in fat metabolism may contribute to the risk of type 2 diabetes.
The study was carried out by researchers from Glasgow University, the MRC Epidemiology Unit and Pfizer Global Research and Development in the US. The researchers were supported by funding from Diabetes UK, the Translational Medicine Research Collaboration, the four associated NHS Health Boards, Scottish Enterprise and Pfizer. The study was published in the peer-reviewed medical journal PLoS One.
The research was covered well by the BBC.
South Asians have a higher risk of type 2 diabetes than other ethnic groups, particularly when they migrate away from the Indian subcontinent. The researchers say that a high BMI is a risk factor for type 2 diabetes; however, analyses have shown that when weight and BMI are taken into account, the South Asian population is still at greater risk than other groups. They say this suggests that the high rate cannot be explained by differences in the amount of body fat people have.
The researchers wanted to explore whether differences between South Asians and white Europeans could explain this increased risk. This was an experimental study that compared 20 men of South Asian origin with 20 men of white European descent. The researchers focused on whether there were biochemical differences in the way the two ethnic groups metabolised their fat stores.
The study recruited 20 men of South Asian origin and 20 men of white European descent who were currently living in Glasgow. Of these, 18 Europeans and four South Asians had lived in the UK all of their lives. Of the South Asians born outside the UK, the average time they had lived in the UK was two and a half years.
The participants were between 18 and 40 years of age, non-smokers and reported low to moderate physical activity (less than two hours of planned exercise a week and a physically inactive job). They also had no known history of diabetes or cardiovascular disease.
The participants performed exercise tests following a 12-hour overnight fast to look at fat and carbohydrate metabolism (use of fat or carbohydrate as energy sources during exercise). They measured insulin sensitivity by looking at glucose and insulin responses to an oral glucose tolerance test. The patients’ glucose and insulin levels were measured after fasting and after they had been given glucose, to see how well their body responded to and managed glucose levels.
The researchers took a blood sample and a muscle and fat biopsy from each participant’s thigh to search for genes that may be involved in fat metabolism or the insulin system.
The South Asian group and the European group had similar typical activity levels and had a similar daily intake of calories from foods containing similar amounts of fat, carbohydrate and protein. The Europeans reported drinking more alcohol than the South Asian group (approximately seven times more on average).
All of the analyses were adjusted for age, BMI and fat mass. During the exercise tests, the South Asian men had a lower rate of fat metabolism during submaximal exercise (just under the limit of what they could do) than the European men. Compared with Europeans, the South Asians had less HDL-cholesterol (good-cholesterol) and a reduced sensitivity to insulin (26% difference; p=0.010). The researchers found there was an association between fat metabolism during exercise and insulin sensitivity, so people who metabolised more fat had a greater sensitivity to insulin and vice versa. The resting metabolic rate and rate of fat metabolism during rest did not differ between groups. During rest there was no association between fat metabolism rate and insulin sensitivity.
The muscle samples indicated the South Asians had reduced expression of some genes involved in insulin signalling. However, once BMI and fat mass were taken into account, these differences were not significant.
The researchers said that “South Asians oxidised less fat during submaximal exercise than Europeans”, and that this correlated with insulin sensitivity.
They said that South Asian men used about 40% less fat than Europeans during exercise and the rate of fat metabolism was not different between the two groups when resting.
These findings suggest that there may be differences in fat metabolism during exercise between South Asian and European men. These differences were associated with a reduced sensitivity to insulin, which may contribute to the higher risk of type 2 diabetes in the South Asian population.
However, this is preliminary research carried out in a very small number of people – only 20 people were included in each group. The results ideally need to be confirmed in a larger number of people. In particular, a larger study is needed to investigate whether there are ethnic differences in the activity of the genes and proteins involved in fat metabolism and insulin signalling.