They discovered that animal products such as meat, cheese and egg yolks trigger stomach acids linked to the disease.

However, 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 ­neutralize 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.

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.

In addition, alarmingly, women whose potential renal acid load (Pral) scores were in the top 25% had a 56% greater risk of getting 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 13.2, cheeses 26.8 and fish 10.8.

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).

Clavel-Chapelon, whose research is published in the journal Diabetologia, said, “Our study suggests that dietary acids may play a specific role in promoting the development of type 2 diabetes.

“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.”

She added, “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.”

About 132,000 people in the UK are diagnosed with the condition each year.

The total number of confirmed cases currently stands at over three million, but a further 850,000 are thought to have undiagnosed type 2 diabetes, caused by obesity and an unhealthy lifestyle.

The cost of diabetes treatment to the NHS is put at £1million every hour. Experts warn the diabetes epidemic could cripple the health service as patients succumb to complications including heart disease, stroke and amputations.

However, experts agree there is a “real opportunity” to turn the tide if patients make simple lifestyle changes such as getting their glucose, blood pressure and cholesterol under control, eating a healthy diet and exercising regularly.

Sufferers are almost 50% more likely to have a heart attack and are at a 25% greater risk of a stroke than the general population.

However, just 150 minutes a week of moderate activity, such as fast walking or cycling, could prevent almost 295,000 cases of diabetes every year, experts believe.

Dr Richard Elliott, of Diabetes UK, said of the new study in France, “This is a complex area of research.

“Further studies will be needed before we can be confident there really is a link between diets high in foods that increase acids in the body and an increased risk of type 2 ­diabetes.

“What we currently know for sure is that the best way to avoid type 2 diabetes is to maintain a healthy weight by getting plenty of exercise.

“As well as eating a healthy, balanced diet that is rich in fruits and vegetables and low in fat, salt and sugar.”