Eating blueberries, grapes, apples and pears cuts the risk of type 2 diabetes but drinking fruit juice can increase it, a large study has found.
Researchers including a team from Harvard School of Public Health in the US examined whether certain fruits impact on type 2 diabetes, which affects more than 3 million Britons.
People who ate three standard servings a week of blueberries had a 26% lower chance of developing the disease, they found. Those eating grapes and raisins had a 12% reduced risk and apples and pears cut the chances by 7%. Prunes also had a protective effect, giving an 11% drop in the risk of developing type 2 diabetes.
Other fruits such as bananas, plums, peaches and apricots had a negligible impact but drinking fruit juice increased the risk by 8%, according to the study.
People who replaced all fruit juice with eating whole fruits could expect a 7% drop in their risk of developing type 2 diabetes.
For individual fruits, replacing three servings a week of fruit juice with blueberries cut the risk by 33% while replacing juice with grapes and raisins cut the risk by 19%. The risk was also 14% lower if juice was replaced with apples and pears, 13% lower if replaced with bananas and 12% lower if replaced with grapefruit.
The research, published in the British Medical Journal, includes data on 187,382 people taken from three separate studies, of whom 12,198 developed type 2 diabetes.
Food questionnaires were used every four years to assess diet and asked how often, on average, people consumed each food in a standard portion size.
The relatively high glycaemic load of fruit juice along with "reduced levels of beneficial nutrients through juicing processes" may explain why juice increases the risk of type 2 diabetes, the authors suggest. "Fluids pass through the stomach to the intestine more rapidly than solids even if nutritional content is similar. For example, fruit juices lead to more rapid and larger changes in serum levels of glucose and insulin than whole fruits," they said.
More research was needed, they added, but concluded: "Greater consumption of specific whole fruits, particularly blueberries, grapes and apples, is significantly associated with a lower risk of type 2 diabetes, whereas greater consumption of fruit juice is associated with a higher risk."
About 2.7 million people in the UK are diagnosed with type 2 diabetes and a further 850,000 are thought to have it but not know. Another 7 million people are estimated to be at high risk of developing the disease, which is linked to obesity and inactive lifestyle.
Complications of type 2 diabetes include limb amputation, blindness, kidney failure, heart disease and stroke.
Dr Matthew Hobbs, head of research for Diabetes UK, said: "The best way to reduce your risk of developing type 2 diabetes is to eat a balanced, healthy diet that includes a variety of fruits and vegetables and to be as physically active as possible.
"This research provides further evidence that eating plenty of whole fruit is a key part of the balanced diet that will help you to achieve a healthy weight and so minimise your risk of developing type 2 diabetes.
"However, the associations between type 2 diabetes and specific types or fruit or fruit drinks must be treated with much more caution. Some of the findings are based on a number of assumptions and models which may have distorted the results significantly.
"For example, the researchers used surveys to ask participants how often they ate certain foods. This type of survey can often be unreliable as people are more likely to remember certain types of food."
