People carrying excess weight who aim to ward off diabetes should try to lose the pounds before they reach middle age, Australian researchers suggest.

A woman's body mass index (BMI) in her late 40s was the strongest predictor of her risk of developing diabetes over the next eight years, Dr. Gita D. Mishra of the University of Queensland and her colleagues found.

On the other hand, there was no link between weight change in subsequent years and the likelihood of becoming diabetic.

While excess weight is understood to boost the risk of developing type 2 diabetes, the effects of shorter-term weight gain or loss are not as clear, Mishra and her team note in the journal Diabetes Care. To investigate, the researchers followed 7,239 women for 8 years. Study participants were 45 to 50 years old when the study began, and they completed surveys on their health at the study's outset in 1996 and in 1998, 2001 and 2004.

Those with BMIs of 25 or greater, indicating they were overweight or obese, in 1996 were at the highest risk of developing type 2 diabetes by 2004, the researchers found. Very obese women with BMIs of 35 or above were 12 times more likely than their normal-weight peers to become diabetic.

Weight gain or loss during the course of the study had no influence on a woman's risk of developing diabetes, while physical activity only reduced risk for the most active women.

"Because women's risk of developing type 2 diabetes in midlife is more closely related to their initial BMI (when aged 45-50 years) than to subsequent short-term weight-change, public health initiatives should target the prevention of weight gain before and during early adulthood," the researchers conclude.

They note that only small changes in physical activity and calorie intake are needed to stop from becoming overweight or obese, and that it is particularly important to "inspire people" to make those changes while they are young adults.