While a link between obesity and diabetes has long been promoted by medical professionals, figures on both conditions across the EU fail to back this up. 

In Europe, 10.3 percent of men and 9.5 percent of women over the age of 25 have diabetes, according to the World Health Organization (WHO). And between 65 to 80 percent of people who develop type 2 diabetes are obese. 

However, of the 28 EU countries, several have high obesity rates but relatively low diabetes rates and vice versa. For example, Ireland has one of the highest rates of obesity in the EU, at 25.3 percent – only the Czech Republic, Lithuania, Hungary, the UK and Malta have higher. Despite this, it has one of the lowest rates of diabetes in the EU, at 3.3 percent, according to the International Diabetes Federation. 

Switzerland has the lowest rate of obesity in the EU, at 19 percent, but has a higher rate of diabetes than Ireland, at 5.6 percent. Portugal, which has an obesity rate of 20.8 percent, has one of the highest rates of diabetes in the EU, at 9.8 percent. 

All the other countries have diabetes rates between 3 and 10 percent.

Why the numbers do not match

According to Antonio Paroli, an Italian doctor who specializes in obesity and diabetes: "There is without a doubt a correlation between obesity and diabetes. I am almost 70, in my career I have seen an increase of diabetes which is without a doubt due to the increase in obese and overweight people."

However, the data for obesity and diabetes in the EU do not reflect this. In Italy, Paroli explained, in addition to the number of people who are diabetic, around 7 percent, there are an unknown number of people who are undiagnosed. 

According to the WHO, half of all people with diabetes are undiagnosed. In the UK, there are 2.85 million people with type 2 diabetes, and an additional 850,000 who are living with it but do not know it. 

In addition, people start showing signs of type 2 diabetes when they are older, while younger people are more likely to be obese in the EU, Paroli explained. While Italy has one of the lowest rates of overall obesity, around 19 percent, it has the highest rate of childhood obesity. 

The number of people with diabetes can also be misleading when trying to determine if there is an increase in the rate of the illness. 

People with diabetes are living longer now than they were a decade ago, according to an article published in the British Medical Journal. As a result, there would naturally be a larger percentage of people with diabetes in the EU now than in the past. 

There are also other causes of type 2 diabetes than just weight, according to the WHO. Other factors that could lead to this include a person's physical inactivity, how much a person weighed when they were born, their age, family history, and socio-economic factors.