Higher overall acidity of the diet, regardless of the individual foods making up that diet, increases the risk of type 2 diabetes, according to a new study from France.

The study, which was published in Diabetologia, the journal of the European Association for the Study of Diabetes (EASD), was the first large prospective study to demonstrate these findings. A total of 66,485 women from the French Centre of the European Prospective Investigation into Cancer and Nutrition (E3N), a well-known ongoing epidemiological study, 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, which are both standard techniques for assessing dietary acid consumption from nutrient intake.

The researchers, led by Dr Guy Fagherazzi and Dr Francoise Clavel-Chapelon from the Centre for Research in Epidemiology and Population Health, INSERM, Paris, said that 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.

Most importantly, from a blood-sugar control perspective, increasing acidosis can reduce the ability of insulin to bind at appropriate recepetors in the body, and reduce insulin sensitivity. With this in mind, the researchers wanted to analyse whether increased acidosis caused by dietary acid loads increased the risk of type 2 diabetes.

Results

During follow-up, 1,372 new cases of incident type 2 diabetes occurred. In the overall population, those in the top 25 per cent (quartile) for PRAL had a 56 per cent increased risk of developing type 2 diabetes, compared with the bottom quartile. Women of normal weight (BMI of 25 and under) had the highest increase risk (96 per cent for top quartile versus bottom) while overweight women (BMI 25 and over) had only a 28 per cent 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,” said the authors. “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,” they wrote.

Acidity  may play a specific role in diabetes development

The authors said that their study showed 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 and vegetables, coffee and sweetened beverages. This suggested that dietary acids may play a “specific role in the development of type 2 diabetes, irrespective of the foods or drinks that provide the acidic or alkaline components”.

“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 the authors. “Our results need to be validated in other population, and may lead to the promotion of diets with a low acid load for the prevention of diabetes,” they said.

The authors said more research is needed to identify the underlying mechanisms.

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