Gluten-Free Diet Doesn't Protect Against Heart Disease
Consuming gluten was not significantly associated with risk of coronary heart disease long-term, according to results from two large prospective cohorts.
After adjustment for known risk factors, those in the highest fifth of estimated gluten intake had a multivariable hazard ratio for coronary heart disease of 0.95 (95% CI 0.88 to 1.02; P=0.29). Additional adjustment for whole grains yielded a multivariate hazard ratio of 1.00 (95% CI 0.92 to 1.09; P=0.77).
For people who don't have a true gluten allergy or sensitivity, avoiding gluten may result in reduced consumption of whole grains, which actually offer cardiovascular benefits, reported Andrew T. Chan, MD, of Massachusetts General Hospital and Harvard Medical School, and colleagues in the The BMJ.
After additional adjustment for intake of refined grains, estimated gluten consumption was linked to a lower risk of coronary heart disease (multivariate hazard ratio 0.85, 0.77 to 0.93; P=0.002).
"In recent years, some food companies and diet books have pushed the idea that gluten is harmful and restricting gluten may yield health benefits. Our data suggest that this is not the case and in fact, may be associated with harm since low intake of gluten is often associated with low intake of whole grains, which is associated with a lower risk of heart disease," Chan told MedPage Today.
"This is yet another factor why a gluten-free diet is not advised unless one has celiac disease or definite symptoms related to gluten intake (wheat allergy or gluten sensitivity)," added fellow author Peter H.R. Green, MD, of the Celiac Disease Center at Columbia University in New York City.
Other potential downsides to a gluten-free diet include its lack of fiber and deficiency in vitamins, noted Green in an email.
Skylar Griggs, MS, RD, of Children's Hospital Boston, who was not involved with the study, interpreted the results to mean that "avoiding gluten and limiting whole grains, which are rich in cardio-protective fiber, may affect cardiovascular disease risk."
"There is no cardio-protective effect of following a gluten-free diet if you do not have celiac disease," she wrote to MedPage Today.
Chan and colleagues studied 64,714 women in the Nurses' Health Study and 45,303 men in the Health Professionals Follow-up Study, both groups without a history of coronary heart disease.
All participants completed a 131 item semiquantitative food frequency questionnaire in 1986 that was updated every 4 years through 2010. Patients were followed until the development of coronary heart disease, death, or the end of follow-up in 2012.
The researchers derived the quantity of gluten consumed based off the protein content of wheat, rye, and barley and then divided cohort participants into fifths of estimated gluten consumption, according to energy-adjusted grams of gluten per day.
Mean daily estimated intake of gluten at baseline was 7.5 g (SD 1.4) among women and 10.0 g (2.0) among men in the highest quintile and 2.6 g (0.6) among women and 3.3 g (0.8) among men in the lowest fifth. By 2010, grams of gluten intake was 7.9 (2.4), 9.2 (2.8), 3.1 (1.2), and 3.7 (1.3), respectively.
Chan and colleagues found that 2,431 women and 4,098 men developed coronary heart disease over the 26 year follow-up period. Fatal MI developed in 2,286 participants (540 women and 1746 men), and non-fatal MI developed in 4,243 participants (1,891 women and 2,352 men), they added.
Compared with participants in the lowest fifth of gluten intake, who had a coronary heart disease incidence rate of 352 per 100,000 person years, those in the highest fifth had a rate of 277 events per 100,000 person years -- with an unadjusted rate difference of 75 (95% CI 51 to 98) fewer cases of coronary heart disease per 100,000 person years.
The researchers concluded that gluten-free diets should not be promoted for coronary heart disease prevention.
"Doctors and nutritionists should counsel their patients that restricting gluten may not be beneficial for one's heart health and should not be considered an alternative to eating a balanced diet high in whole grains," commented Chan.
Griggs agreed, writing: "I would not encourage patients who are following a balanced diet to instead follow a gluten-free diet in an effort to reduce their risk of cardiovascular disease."
Study limitations included possibility of unmeasured or residual negative confounding, as well as an inability to determine whether gluten was present in trace amounts in certain foods.
Chan also noted that the study cannot determine cause and effect since a specific diet was not assigned to participant.
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