Obesity - the most important cause of diabetes?

Elderly men and women with normal body weight still may be at risk for developing type 2 diabetes if they have large amounts of muscle fat or visceral abdominal fat, according to new study.

"Our study found that even though an elderly person may not be overweight, he or she might still be at risk for developing diabetes,"​ said Dr Bret H. Goodpaster from the University of Pittsburgh in the US and principal investigator of the study. "An important factor is where in the body their excess fat is stored."​

Although the prevalence of type 2 diabetes is highest among men and women over the age of 65, the prevalence of obesity in this group is only 14 per cent compared with 24 per cent for people in their 50s, said Dr Goodpaster.

"It appears that in elderly individuals, there might be some disassociation between obesity and the risk for insulin resistance and type 2 diabetes,"​ he added.

The study enrolled almost 3000 men and women, aged 74 years on average, who are participating in the Health ABC study. The group was 48.5 per cent male and 58.3 per cent white. Fifty-one per cent were classified as having normal glucose tolerance, 21 per cent had impaired glucose tolerance and 24 per cent had type 2 diabetes. Muscle and fat in the thigh and abdomen were determined using CT scans.

The researchers report in the February issue of Diabetes Care​ that prevalence of diabetes was higher among obese subjects than among overweight or normal weight subjects, with 30 per cent of obese men and 34 per cent of obese women having type 2 diabetes.

Despite similar amounts of thigh fat, the proportion of intermuscular fat was higher in subjects with type 2 diabetes and impaired glucose tolerance than in subjects with normal glucose tolerance. Also, the proportion of visceral abdominal fat was higher in men and women with type 2 diabetes and impaired glucose tolerance than in those with normal glucose tolerance.

The study showed that among those with type 2 diabetes, 22 per cent were normal-weight men and 12 per cent were normal-weight women. Another 14 per cent of men and 22 per cent of women had impaired glucose tolerance. This means that two thirds of men with type 2 diabetes were not obese. A similar pattern emerged for women.

"This suggests that obesity, per se, is not required for diabetes or glucose intolerance in elderly men and women,"​ Dr Goodpaster said. "Fat distribution is a key determination of insulin resistance and altered glucose homeostasis.​

"The concept of the metabolically obese normal-weight individual is likely to be of great importance in understanding risk factors that drive the heightened risk of type 2 diabetes in relation to ageing,"​ he added.