New research published this week looking at body fat in identical twins has shown that a higher body mass index (BMI) is associated with a greater risk of developing type 2 diabetes but not with a higher risk of heart attack.

The study, carried out by a team from Umeå University, Sweden, set out to look at the effect of BMI -- a measure of obesity -- on an increased risk of heart attack, mortality, and diabetes using data from the Swedish Twin Registry, the largest of its kind in the world.

The study was conducted between 1998 and 2003 and looked at 4,046 genetically identical twin pairs aged between 42 and 92 who had different levels of body fat, as measured by their BMI, enabling the team to look at obesity-related health risks that are independent of genetic factors.

Follow-ups to look at the rate of mortality, heart attack and diabetes were also carried out until 2013 for a period of 12.4 years on average.

Perhaps surprisingly, the results clearly showed that the twins with a higher BMI did not have an increased risk of heart attack or mortality when compared to the thinner siblings, with the team finding that among twin siblings with a higher BMI (mean value 25.1), there were 203 heart attacks (5%) and 550 deaths (13.6%) during the follow-up period, but among twin siblings with a lower BMI (mean value 23.9), there were 209 heart attacks (5.2%) and 633 deaths (15.6%) during the same period.

However the team did find that those with a higher BMI did have an increased risk of type 2 diabetes.

Peter Nordström, one of the study's co-authors outlined that although the study suggests that lifestyle changes which reduce levels of obesity may not have an effect on the risk of death and heart attack, "What the study does show is that there's a strong association between obesity and diabetes, which leads us to conclude that weight reduction interventions can be more effective against diabetes than when it comes to reducing the risk of heart attack and mortality."

The findings were published in the journal JAMA Internal Medicine.