Over the last forty years or so, the number of people with diabetes has jumped from around 100 million to more than 500 million, with matching rises in associated health problems like obesity and cardiovascular disease risk.

It's a significant health problem that is getting worse, which is why researchers are investigating the underlying issues behind the trend.

One of those issues is likely to be diet, according to a new study into type 2 diabetes – which accounts for 95 percent of overall cases.

Researchers analyzed data from 184 countries collected between 1990 and 2018, pulling in statistics from public health databases, previous studies, and population demographic records. A poor diet could account for up to 14.1 million type 2 diabetes cases identified in 2018, the team found, which is around 70 percent of new diagnoses globally.

Of the 11 different dietary factors considered, three were shown to be most significant: insufficient whole grains, too much refined rice and wheat, and too much processed meat. Other factors, such as not eating enough nuts or non-starchy vegetables, seemed to have less of an impact.

"Our study suggests poor carbohydrate quality is a leading driver of diet-attributable type 2 diabetes globally, and with important variation by nation and over time," says Dariush Mozaffarian, a cardiologist and professor of nutrition at Tufts University in Massachusetts.

Poor diet was more clearly linked to diabetes cases in men compared to women, the researchers found, and seems to be having more of an impact in younger people compared to older people, and urban areas rather than rural areas.

Central and Eastern Europe and Central Asia were the regions with most type 2 diabetes cases linked to diet, possibly because of the prevalence of red meat and processed meat in the average diet. Numbers were high in Latin America and the Caribbean too.

"These new findings reveal critical areas for national and global focus to improve nutrition and reduce devastating burdens of diabetes," says Mozaffarian.

All 184 countries included in the research saw a rise in diabetes cases over the study period, indicating this is a global problem with few, if any nations successfully curbing the rising incidence of diabetes across their population.

The researchers suggest that different approaches – from a greater emphasis on healthy dieting from educators to improved nutritional labeling on food – are going to be required in different countries to start making a difference here.

While previous studies have also linked less healthy diets to more cases of diabetes, this is by far the strongest association to date, and for the highest percentage of cases. Without serious intervention, it's a problem that's only going to get worse.

"Left unchecked and with incidence only projected to rise, type 2 diabetes will continue to impact population health, economic productivity, health care system capacity, and drive health inequities worldwide," says nutrition epidemiologist Meghan O'Hearn, from the Food Systems for the Future Institute in Illinois.

"These findings can help inform nutritional priorities for clinicians, policymakers, and private sector actors as they encourage healthier dietary choices that address this global epidemic."

The research has been published in Nature Medicine.