Green tea also reduced cholesterol levels in the women.
"Green tea extract is a promising alternative for reducing Type 2 diabetes risk in overweight women" University of Goias scientists
The predominant active compounds in green tea are flavonoid monomers known as catechins, in particular epigallocatechin-3-gallate, which is the most abundant and most effective catechin in metabolic care, particularly among obese patients.
Writing in the journal Clinical Nutrition ESPEN, they said: "Green tea extract is a promising alternative for reducing Type 2 diabetes risk in overweight women."
Type 2 diabetes affects almost 1 in ten adults in the UK and costs the NHS around £14billion a year to treat.
More than four million Britons have Type 2 diabetes and another 12 million are at risk of developing the condition.