05.27.2015
by Jeff Minerd
Contributing Writer, MedPage Today
A fiber-rich diet reduced risk of developing type 2 diabetes by 18%, according to a large European cohort study published in Diabetologia.
Cereal fiber emerged as the strongest protector against diabetes, compared with vegetable fiber and fruit fiber, reported senior investigator Nick Wareham, PhD, MSc, MBBS, an epidemiologist at the University of Cambridge, and colleagues.
Furthermore, fiber seemed to work its protective power at least partially by lowering body-mass index (BMI), the researchers reported.
Previous studies also reported associations between fiber intake and reduced type 2 diabetes risk. However, most of those studies were conducted in the U.S., where sources and amounts of dietary fiber are substantially different from European countries, the investigators said.
The researchers analyzed data from the EPIC-InterAct Study, a cohort of more than 340,000 individuals from 10 European countries designed to investigate the relationships between diet, lifestyle, environment, and various chronic diseases.
During approximately 11 years of follow up, the investigators identified 12,403 new cases of type 2 diabetes. Their analysis also included a random subcohort of 16,835 representative individuals for comparison.
The researchers divided study participants into quartiles based on fiber intake, from lowest (less than 19g/day) to highest (more than 26g/day). They then used Cox proportional hazard models to calculate hazard ratios, adjusting for lifestyle and other factors.
Compared with individuals with the lowest total fiber intake, those with the highest were 18% less likely to develop type 2 diabetes (HR 0.82; 95% CI 0.69-0.97).
When examining this effect by source of fiber intake, the investigators found it was highest for cereal fiber (HR 0.81; 95% CI 0.70-0.93), slightly lower for vegetable fiber (HR 0.84; 95% CI 0.74-0.96), and absent for fruit fiber (HR 0.98; 95% CI 0.89-1.08).
However, when the investigators adjusted their analysis for BMI, the results became attenuated and no longer statistically significant. Total fiber intake, for example, was associated with a mere 9%, nonsignificant reduction in risk (HR 0.91%; 95% CI 0.81-1.03).
This finding “suggests that the beneficial effects of fibre may be partly mediated by a lower BMI, and this is consistent with other studies,” the researchers wrote. In other words, study participants who ate more fiber were less likely to be overweight, thereby mitigating risk for type 2 diabetes, they explained.
“However, as the observed effects of fibre intake on adiposity and weight change are relatively modest, BMI may act as both a confounder and a mediator in the relationship between fibre intake and diabetes,” they added.
In addition to their primary analysis, the investigators also undertook a meta-analysis, pooling the results of 18 similar studies with the EPIC-InterAct data. These 18 studies included 8 from the U.S., four from Europe, and three each from Australia and Asia. The meta-analysis included 41,000 incident cases of type 2 diabetes.
Results were similar to the primary analysis. For each 10g/day increase in total fiber intake, risk of diabetes fell by 9% (HR 0.91; 95% CI 0.87-0.96). For each 10g/day increase in cereal fiber intake, the risk fell by 25% (HR 0.75; 95% CI 0.65-0.86). Vegetable and fruit fiber were associated with small, nonsignificant risk reductions.
“Taken together, our results indicate that individuals with diets rich in fibre, in particular cereal fibre, may be at lower risk for type 2 diabetes,” Dagfinn Aune, lead study investigator and PhD student at the Norwegian University of Science and Technology, said in a press release.
“We are not certain why this might be, but potential mechanisms could include feeling physically full for longer, prolonged release of hormonal signals, slowed down nutrient absorption, or altered fermentation in the large intestine. All these mechanisms could lead to a lower BMI and reduce risk of developing type 2 diabetes,” Aune said.
“As well as helping keep weight down, dietary fibre may also affect diabetes risk by other mechanisms,” Aune said. “For instance, improving control of blood sugar and decreasing insulin peaks after meals, and increasing the body’s sensitivity to insulin.”
“This work adds to the growing evidence of the health benefits of diets rich in fibre, in particular cereal fibre. Public health measures globally to increase fibre consumption are therefore likely to play an important part in halting epidemics of obesity and of type 2 diabetes,” senior investigator Wareham said in a press release.
In the United States, individuals at high risk for diabetes should be encouraged to achieve the U.S. Department of Agriculture‘s recommendation for dietary fiber: 14g/1,000 kcal, according to a position statement from the American Diabetes Association.
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This research was supported by the European Union Framework Programme for Research and Innovation.
The study authors disclosed no relevant relationships with industry.
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