Published in Diabetologia, the research team analysed data from more than 60,000 women over 14 years in order to assess whether dietary acid load impacted later risk of type 2 diabetes.
Led by Dr Guy Fagherazzi from the Gustave Roussy Institute, France, the researchers reported that a higher overall acidity of diet was linked to increases in the incidence of type 2 diabetes - regardless of the individual foods making up that diet.
"We have demonstrated for the first time in a large prospective study that dietary acid load was positively associated with type 2 diabetes risk, independently of other known risk factors for diabetes," said Fagherazzi and his colleagues.
"Our results need to be validated in other populations, and may lead to promotion of diets with a low acid load for the prevention of diabetes," they said - noting that further research that focuses on the underlying mechanism is needed.
The team investigated data from a total of 66,485 women from the E3N study (the French Centre of the European Prospective Investigation into Cancer and Nutrition, a well-known ongoing epidemiological study). The women were followed for new diabetes cases over 14 years, and dietary acid load was calculated from their potential renal acid load (PRAL) and their net endogenous acid production (NEAP) scores - both of which are standard techniques for assessing dietary acid consumption from nutrient intake.
During the 14 year follow-up, Fagherazzi and his colleagues observed 1,372 new cases of type 2 diabetes.
In the overall population, those in the top 25% (quartile) for PRAL had a 56% 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% for top quartile versus bottom) while overweight women (BMI 25 and over) had only a 28% increased risk (top quartile versus bottom). NEAP scores showed a similar increased risk for higher acid load.
"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," said Fagherazzi and his colleagues.
"A diet rich in animal protein may favour net acid intake, while most fruits and vegetables form alkaline precursors that neutralise the acidity," they explained. "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."
Published online ahead of print, doi: 10.1007/s00125-013-3100-0
"Dietary acid load and risk of type 2 diabetes: the E3N-EPIC cohort study"
Authors: Guy Fagherazzi, Alice Vilier, Fabrice Bonnet et al