Does a diet low in gluten increase the risk of type 2 diabetes?

Researchers involved in a new, long-term study think it might, but some dietitians argue the link could actually be due to a low intake of fiber.

In the observational study commencing in 1984, researchers estimated the daily gluten intake for almost 200,000 participants through food questionnaires completed every two to four years.

The findings were presented today at the American Heart Association's Epidemiology and Prevention / Lifestyle and Cardiometabolic Health 2017 Scientific Sessions.

Read more: Is non-celiac gluten sensitivity a real thing? »

What researchers discovered

In their study, researchers found that those who ate the most gluten had a lower risk for developing type 2 diabetes in the 30 years of follow-up study.

Participants in the highest 20 percent of gluten consumption had a 13 percent lower risk of developing type 2 diabetes compared with those with the lowest daily gluten consumption (fewer than 4 grams).

“We wanted to determine if gluten consumption will affect health in people with no apparent medical reasons to avoid gluten,” Geng Zong, PhD, a research fellow in the Department of Nutrition at Harvard University’s T.H. Chan School of Public Health, said in a press release.

“Gluten-free foods often have less dietary fiber and other micronutrients, making them less nutritious, and they also tend to cost more. People without celiac disease may reconsider limiting their gluten intake for chronic disease prevention, especially for diabetes.”

Janelle Smith, MS, dietitian for the Celiac Disease Foundation, says those who are forced to be gluten-free due to celiac disease shouldn’t be concerned by the study.

“Those with celiac disease might worry that they are at an increased risk of type 2 diabetes based on these results. As of now, research does not show that celiac disease is associated with an increased risk of type 2 diabetes, but it is associated with type 1 diabetes,” she told Healthline.

“It is quite possible that it is not reduced gluten, but overall reduced fiber intake that would result in this correlation.”

Read more: A gluten-free diet may not do you any good »

The fiber connection

Smith is not alone in suggesting a possible link between type 2 diabetes and a low-gluten diet could in fact be due to restricted fiber intake.

Susan Weiner, a registered dietitian and nutritionist, holds a similar view on the research.

“My initial thought is that people who restricted gluten [also] restricted fiber from whole grains as well in their quest to limit their gluten intake,” Weiner told Healthline.

“Additionally, if they ate cake, crackers, and cookies which were gluten free without looking at carbohydrates or calories, that could have caused an increase in weight associated with an increased risk of type 2 diabetes. The cause is not conclusive, but this seems likely.”

Of those who participated in the study, individuals who ate less gluten also tended to eat less cereal fiber, which is considered a protective factor against the development of type 2 diabetes.

Weiner says it is important those who follow a gluten-free diet ensure they are not eating too much processed food.

“When folks go ‘gluten free’ for reasons other than a legitimate reason such as celiac disease or gluten sensitivity, they often purchase processed gluten-free foods such as cookies, crackers, and chips. These foods have low nutritional value, pack on calories, and are low in fiber,” she told Healthline.

“The health consequences of following a gluten-free diet composed primarily of processed foods can lead to weight gain and detrimental long-term consequences associated with low fiber intake,” she said.

Read more: Pediatricians concerned about increase in gluten-free diets for children »

Low-gluten diet popularity

Gluten is a type of protein found in wheat and rye that gives bread and baked goods elasticity and a chewy texture.

Only a small percentage of the population cannot eat gluten. About 1 percent must abstain due to celiac disease.

Despite a lack of evidence that reducing consumption of gluten provides long-term health benefits, gluten-free diets have been gaining popularity.

Experts say this isn’t necessarily a good thing.

“The rise of popularity of the gluten-free diet is a double-edged sword for people with a medical necessity for it,” Alice Bast, chief executive officer of the patient advocacy group Beyond Celiac, told Healthline.

“The gluten-free fad has driven the increase in the availability of packaged food options and to some extent raised awareness of celiac disease and gluten sensitivity,” she added. “However, we’ve also seen the gluten-free fad overshadow the fact that it’s the only current treatment for celiac disease … For those of us for whom the gluten-free diet is not an option, it has resulted in our not being taken seriously in situations in which we don’t have 100 percent control over our food and beverages.”

Smith says the findings of the research may prompt those who abstain from gluten for reasons other than celiac disease and sensitivities to think carefully about doing so.

“I hope that the public will begin to realize that ‘gluten-free’ does not equate with ‘healthy,’ and that a healthy gluten-free diet takes planning and consideration,” she said.