Gluten-free diets shouldn't be promoted to prevent heart disease among people without celiac disease, gastroenterologists say after a large U.S. study.
The food industry has stimulated popularity in gluten-free diets. Recognizing this public interest, researchers at Harvard Medical School said they wanted to see whether avoiding gluten actually has health benefits for those without the disease.
To that end, Dr. Andrew Chan, an associate professor of medicine at Harvard, and his team used diet and health outcome data collected from 110,000 health professionals over 26 years to link estimates of gluten in the diet to diagnoses of coronary heart disease.
Celiac disease affects one to two per cent of Canadians, or about 300,000 people, Health Canada estimates.
The researchers recognized that celiac disease is associated with an increased risk of coronary heart disease, which is reduced after these individuals go gluten free.
Based on the answers to diet questionnaires, the researchers divided participants into five groups of estimated gluten consumption. Gluten, a mix of two proteins that gives dough its elastic texture, is found in wheat, rye and barley.
"There was actually no absolute difference in risk of heart disease in individuals according to their gluten intake," Chan, a gastroenterologist who treats patients with celiac disease, said in an interview.
"In fact, in those individuals that actually had low intakes of gluten, they also tended to have diets that were also low in whole grains and so subsequently because of that also had a somewhat higher risk of developing heart disease."
In this week's issue of The BMJ, the researchers tried to disentangle the effects of higher intake of whole grains that are associated with lower risk of heart disease from gluten.
Whole grain limit
"For individuals that are looking at a gluten as a potential factor to consider in their diet, there is really no evidence that restricting the amount of gluten you take in actually has benefits for your heart and there is also this possibility that if you are overly restrictive in your intake of gluten that you may also be limiting your intake of whole grain, which actually could cause harm."
Physicians and medical researchers have an understanding of why gluten potentially causes allergy. But since those mechanisms don't occur in people without the disease, the findings aren't surprising, Chan said.
Since the study was observational and participants weren't randomly assigned to follow a specific diet, cause and effect can't be determined.
As well, the researchers didn't test for impact of gluten among people with celiac disease or determine whether trace amounts of gluten were present in some foods.
The findings in no way alter recommendations for people with celiac disease or gluten sensitivity to avoid it, Chan stressed.
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While gluten-free diets are sometimes promoted for weight loss, eliminating gluten can lead to weight gain if an individual substitutes gluten-free items that are high in fat, sugar and calories, said Shelley Case, a registered dietitian in Regina. Case is a member of professional advisory council of the Canadian Celiac Association. She was not involved in the study.
"Going gluten free is not a magic bullet for losing weight and improving your health for individuals who don't have celiac disease," Case said.
Some may lose weight or feel better on a gluten-free diet not from the elimination of gluten, Case said, but because they've replaced calorie-laden items with more nutritious fruits, vegetables and lean protein foods and ended a reliance on processed, prepackaged foods.
Celiac disease is diagnosed with both a blood test and biopsy. In one Canadian study, the average delay between symptoms starting and diagnosis was up to 12 years, Case said.
The new findings aren't likely to end the debate, Case said. "Hollywood celebrities, athletes, personal trainers and others will continue to tout the benefits of the gluten-free diet for those who do not have celiac disease."
The researchers are funded by the American Gastroenterological Association, Massachusetts General Hospital and U.S. National Institutes of Health.