Type 2 diabetes - which is most affected by lifestyle choices such as obesity, smoking and exercise - has had another risk factor identified: too much meat.
Scientists who studied a group of 66,485 women found that those with the most acidic diets were more likely to develop type 2 diabetes.
Typically, acidic foods consist of animal products, the scientists point out. On the other hand, fruits and vegetables help to neutralise acidity - even fruits such as lemons that are widely perceived as acidic.
Chronic acidosis - a condition caused by increased acidity in the blood and body tissues - reduces insulin sensitivity, the ability of the hormone insulin to regulate blood sugar.
The women were taking part in a major European study looking at cancer and nutrition.
Over a period of 14 years, 1,372 new cases of type 2 diabetes were recorded. Women whose potential renal acid load (Pral) scores were in the top 25% had a 56% greater risk of developing diabetes than those in the bottom 25%.
Pral refers to the potential impact of certain foods on kidney and urine acid levels. Meats can have a Pral value as high as 9.5, cheeses 8 and fish 7.9.
In contrast, fruits and vegetables have negative Pral values.
The scientists also measured another marker of acidity in the body called net endogenous acid production (Neap)
Study leader Dr Francoise Clavel-Chapelon, from the Inserm research institute in Paris, and colleagues wrote in the journal Diabetologia: "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.
"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 concluded: "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. 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. Further research is required on the underlying mechanisms."