A new study has revealed that higher overall acidity of the diet, regardless of the individual foods making up that diet, increases the risk of type 2 diabetes.

The study of more than 60,000 women was conducted by Dr Guy Fagherazzi and Dr Francoise Clavel-Chapelon, Center for Research in Epidemiology and Population Health, INSERM, Paris, France, and colleagues, and is the first large prospective study to demonstrate these findings.

A western diet rich in animal products and other acidogenic foods can induce an acid load that is not compensated for by fruit and vegetables; this can cause chronic metabolic acidosis and lead to metabolic complications.

A total of 66,485 women from the E3N study (the French Centre of the European Prospective Investigation into Cancer and Nutrition were followed for new diabetes cases over 14 years.

Their dietary acid load was calculated from their potential renal acid load (PRAL) and their net endogenous acid production (NEAP) scores, both standard techniques for assessing dietary acid consumption from nutrient intake.

During follow-up, 1,372 new cases of incident type 2 diabetes occurred. In the overall population, those in the top 25 percent (quartile) for PRAL had a 56 percent increased risk of developing type 2 diabetes compared with the bottom quartile.

Women of normal weight, BMI of 25 and under, had the highest increased risk (96 percent for top quartile versus bottom) while overweight women (BMI 25 and over) had only a 28 percent increased risk (top quartile versus bottom). NEAP scores showed a similar increased risk for higher acid load.

"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," researchers said.

"In our study, the fact that the association between both PRAL and NEAP scores and the risk of incident type 2 diabetes persisted after adjustment for dietary patterns, meat consumption and intake of fruit, vegetables, coffee and sweetened beverages suggests that dietary acids may play a specific role in promoting the development of type 2 diabetes, irrespective of the foods or drinks that provide the acidic or alkaline components," they added.

The study is published in the journal Diabetologia.