The study suggests people whose diets are rich in fiber, in particular cereal fiber, may be at lower risk of type 2 diabetes.
The study - published in the journal Diabetologia - is in two parts. The first part uses EPIC-InterAct study data from eight European countries, and the second part adds data from other studies from around the world.
One of the authors, Dagfinn Aune, a PhD student affiliated with the Norwegian University of Science and Technology and Imperial College London in the UK, says:
"Taken together, our results indicate that individuals with diets rich in fiber, in particular cereal fiber, may be at lower risk of type 2 diabetes."
The EPIC-InterAct study - which is coordinated by the MRC Epidemiology Unit at Cambridge University in the UK - is the largest investigation of new-onset type 2 diabetes in the world.
The EPIC-InterAct data set includes 12,403 verified incident cases of type 2 diabetes, and, for comparison, 16,835 individuals representative of the 350,000 participants in the European Prospective Investigation into Cancer and Nutrition (EPIC) study.
The authors of the new Diabetologia study note that much research on the link between dietary fiber and risk for type 2 diabetes tends to be dominated by data from the US, yet the amount and types of dietary fiber can vary substantially across countries.
Body weight may explain link between higher fiber intake and lower risk for diabetes
For their analysis of the EPIC-InterAct data, the researchers evaluated links between total fiber - as well as fiber from cereal, fruits and vegetables - and new-onset of type 2 diabetes.
They divided the participants into four equally sized groups, ranked according to fiber intake (from lowest to highest), and assessed their risk of developing type 2 diabetes over an average of 11 years of follow-up.
After adjusting for the effect of lifestyle and other dietary factors, the researchers found that the group with the highest fiber intake (over 26 g per day), had an 18% lower risk of developing type 2 diabetes than the group with the lowest fiber intake (under 19 g per day).
However, they suggest that the association may be partly explained by body weight, for when they adjusted the results for body mass index (BMI), they found higher total fiber intake was no longer linked to lower risk for type 2 diabetes.
One way to interpret this is to say that a diet rich in fiber helps people maintain a healthy weight, and this in turn is what reduces their chances of developing type 2 diabetes.
The authors also looked at differences in types of dietary fiber. They found cereal fiber had the strongest effect: compared with those whose diet contained the lowest levels, people consuming the highest levels of cereal and vegetable fiber had a 19% and 16% lower risk respectively of developing type 2 diabetes.
These links also disappeared when the authors adjusted the results for BMI.
In contrast, fiber from fruit sources was not linked with reduced risk for type 2 diabetes.
Pooled data from other studies confirmed importance of cereal fiber
In the second part of the study, the researchers added data from 18 other studies from around the world to the EPIC-InterAct data and re-analyzed the whole pool as if it came from one study (this is called a meta-analysis).
The 18 additional studies included eight from the US, four from Europe, three from Australia and three from Asia. The new pool included over 41,000 new-onset cases of type 2 diabetes.
The meta-analysis found that the risk of type 2 diabetes fell by 9% for every 10 g per day more of total dietary fiber, and by 25% for every 10 g per day more of cereal fiber.
The meta-analysis did not find a significant link between increasing either fruit or vegetable fiber and reduced risk for type 2 diabetes.
Aune says they cannot explain the results from this data, but speculate that perhaps eating more fiber makes you feel full for longer, prolongs the release of hormones, slows down the absorption of nutrients and alters gut fermentation.
"All these mechanisms could lead to a lower BMI and reduced risk of developing type 2 diabetes," says Aune, who adds:
"As well as helping keep weight down, dietary fiber may also affect diabetes risk by other mechanisms - for instance improving control of blood sugar and decreasing insulin peaks after meals, and increasing the body's sensitivity to insulin."
Prof. Nick Wareham, director of the MRC Epidemiology Unit at Cambridge, and senior author of the study concludes:
"This work adds to the growing evidence of the health benefits of diets rich in fiber, in particular cereal fiber. Public health measures globally to increase fiber consumption are therefore likely to play an important part in halting the epidemics of obesity and of type 2 diabetes."
Estimates suggest over 360 million people worldwide are affected by diabetes, and this figure is set to rise to over 550 million by 2030, with serious consequences for the health and economies of all nations, regardless of wealth.
Meanwhile, MNT recently reported a study that suggests women who closely follow a Mediterranean diet may reduce their risk of endometrial cancer by more than 50%. A Mediterranean diet is rich in whole grains, legumes, fruit, vegetables, nuts and olive oil.