Eating 125g (less than one cup) of raspberries every morning can reduce the chances of developing diabetes, even in people who are already at risk, such as those who are overweight or obese and are already showing signs of insulin resistance.
The berries can also lower blood sugar levels in diabetics after they've eaten a meal, a second research paper has established.
Raspberries are rich in polyphenols, antioxidants that also protect against cancers, heart disease and general inflammation.
The two new studies focused on the fruit's impact on diabetes. The first tested a group of 32 people who were pre-diabetic and gave them either 125g or 250g of red raspberries for three days along with a high-carbohydrate breakfast, which usually causes the body to release more insulin to break down the sugars. As a control, a group of healthy people were just given the breakfast without any raspberries.
Both amounts of raspberries "significantly reduced" insulin levels, researchers from the Illinois Institute of Technology concluded.
In a separate trial, the fruit was tested on people who already had diabetes. Their blood glucose was "significantly lower" after they had eaten the raspberries for a month. The berries reduced hyperglycaemia (high blood sugar) and inflammation markers, say researchers from Oklahoma State University.