They discovered that animal products such as meat, cheese and egg yolks trigger stomach acids linked to the killer disease.
But most fruits, including lemons and oranges which are widely perceived as acidic, effectively knock out these acids before they can have a harmful effect on the body’s metabolism.
Study leader Dr Francoise Clavel-Chapelon said: “A diet rich in animal protein may favour net acid intake, while most fruits and vegetables form alkaline precursors that neutralise the acidity.
“Contrary to what is generally believed, most fruits such as peaches, apples, pears, bananas and even lemons and oranges actually reduce dietary acid load once the body has processed them.”
Acid load, or excess acid, can spark serious complications with the metabolic system. This in turn reduces the body’s ability to regulate its insulin levels, leading to diabetes.
Dr Clavel-Chapelon’s team at the Centre for Research in Epidemiology and Population Health in Paris studied tens of thousands of women volunteers over 14 years.
They found those with the most acidic diets were more likely to develop type 2 diabetes.
And, alarmingly, women whose potential renal acid load (Pral) scores were in the top 25 per cent had a 56 per cent greater risk of getting diabetes than those in the bottom 25 per cent.
Pral refers to the potential impact of certain foods on kidney and urine acid levels. Meats can have a Pral value as high as 13.2, cheeses 26.8 and fish 10.8.