Lifestyle choices, such as diet and exercise, may have more influence on the development of insulin resistance than heredity, suggests new research.

Insulin resistance occurs when the body produces too little of the hormone insulin and fails to effectively regulate the metabolism of fats, proteins and sugars. The condition can lead to diabetes.

The study, published online Wednesday in the American Journal of Physiology Endocrinology and Metabolism, was conducted by researchers at the Helsinki University Central Hospital and the University of Helsinki.

They studied identical twins born between 1975 and 1979 to determine the impact of lifestyle choices on their genes.

Fourteen pairs of the twins had radically differing body weights, with one twin obese and the other a normal weight.

All were measured for body insulin sensitivity, body composition and heart fitness levels. The obese twins had lower insulin sensitivity and poorer fitness levels than their leaner siblings.

Researchers also found that the expression of genes that help cells in the body produce energy were impaired in those who did not exercise regularly and were obese. This condition in turn made it more difficult to lose weight, leading to additional weight gain.

"The study shows that independent of genetic factors, obesity is associated with poor fitness, low insulin sensitivity and decreased transcript levels of genes involved in mitochondrial oxidative phosphoration," the process by which gene expression is altered, write the authors.

The authors do not rule out the role of genetic factors in altering gene expression. They say that more study is needed.