Coeliac disease, an allergy to gluten that causes damage to the intestine, affects only 1% of the population but 11% of Australians follow a gluten-free diet and 30% of people in the US try to reduce their gluten intake. Suzanne Mahady of Monash University points out in The Conversation that ‘recent large studies have not found health benefits for a gluten-free diet, and in fact the opposite may be true’.
Mahady, a gastroenterology and clinical epidemiologist at Monash University in Victoria, Australia, writes: “Recent large studies have not found health benefits for a gluten-free diet, and in fact the opposite may be true. Researchers led by Andrew T Chan at the Massachusetts General Hospital, Brigham and Women’s Hospital and Harvard Medical School followed a group of more than 100,000 people in the US for nearly 30 years and found a gluten-free diet was not associated with a healthier heart. It’s not clear whether this was due to something in the gluten-free foods, or the avoidance of wholegrains, which are considered protective against heart disease.”
Mahady says that one study from researchers at the department of nutritional sciences, faculty of medicine, University of Toronto, Ontario, Canada suggests gluten may be beneficial because it lowers levels of triglycerides in the blood. These are ‘bad’ fats that increase the risk of heart disease.
She says that another large study by researchers at the Harvard TH Chan School of Public Health and the Coeliac Disease Centre, department of medicine, Columbia University College of Physicians and Surgeons, New York, has found an inverse association between gluten intake and type 2 diabetes. People with a lower gluten intake had higher rates of type 2 diabetes. The researchers found this group also had lower fibre intake, and wondered whether low fibre was the culprit. But even after accounting for the lower fibre intake, an association remained, suggesting avoiding gluten is not protective against developing type 2 diabetes.
Wholegrain products are made using the three parts of the grain – the bran (outside, which is rich in fibre), the germ (the seed) and the endosperm (the starchy, carbohydrate-rich centre). Together they form a bundle of fibre, carbohydrate, vitamins and minerals. Packaged gluten-free products such as bread frequently use only the carbohydrate component using refined flours from rice, corn or potato.
These high carbohydrate foods may cause a sharp rise in blood sugar levels and may predispose to diabetes in the long term. Packaged gluten-free products often have added sugars to enhance flavour, and add emulsifiers and thickeners to improve the texture and make it similar to bread.
Mahady writes that gluten-free markets have risen exponentially in the last decade due to consumer demand, even extending to the production of gluten-free food for dogs.
She says: “Whether the market will expand or diminish with time is unknown, but food fashions are not new. Consider the popularity of low-fat diets in the 1980s, when butter was a villain. Now butter is now back in vogue, with sales increasing. Similarly, red wine used to be considered protective for cardiac health, but guidelines for safe alcohol consumption now recommend reduced intake.
“Of course, naturally gluten-free products such as plant-based foods, ancient grains and dairy are all part of a healthy and balanced diet, but there does not seem to be a health benefit for the processed and packaged gluten-free replacements over wheat-based versions.”
Mahady says that non-coeliac gluten sensitivity is different from coeliac disease. In coeliac disease, gluten intake causes damage to the intestine’s lining, which reverses with a gluten-free diet. In non-coeliac gluten sensitivity (also called “gluten intolerance”), symptoms like bloating and wind are common, but no intestinal damage or long-term health effects occur.
She says to better understand this condition, researchers at the department of gastroenterology, Eastern Health Clinical School, Monash University, set out to determine whether it was gluten intake or the perception of gluten intake that may be contributing. They designed a study in which self-identified gluten-sensitive people were fed gluten-free, low gluten and high gluten foods, but didn’t know which they were eating.
All diets were also low in wind-causing sugars, called FODMAPs, which can cause similar symptoms. They found most of the group improved regardless of whether they were on a high gluten, low gluten or gluten-free diet. They concluded there was no evidence for gluten alone being responsible, but the reduction in FODMAPs could explain the symptom improvement.
Mahady writes that another reason people may report improvement when commencing a gluten-free diet is the exclusion of many other foods that are known not to be healthy, such as cakes, biscuits, crackers and beer. These dietary changes may also contribute to overall wellbeing.
She says that for people without coeliac disease, there’s no evidence to support claims a strict gluten-free diet is beneficial for health. It’s even possible the opposite is true, and the avoidance of dietary whole grains resulting in a low fibre intake may be detrimental.
She argues that given gluten-free foods cost around 17% more, perhaps it’s time to reconsider a strict gluten-free diet chosen for health benefits alone, and instead include a diversity of gluten and gluten-free foods, with dietary variety as the key.
Objective: To examine the association of long term intake of gluten with the development of incident coronary heart disease.
Design: Prospective cohort study.
Setting and participants: 64 714 women in the Nurses’ Health Study and 45 303 men in the Health Professionals Follow-up Study without a history of coronary heart disease who completed a 131 item semiquantitative food frequency questionnaire in 1986 that was updated every four years through 2010.
Exposure: Consumption of gluten, estimated from food frequency questionnaires.
Main outcome measure: Development of coronary heart disease (fatal or non-fatal myocardial infarction).
Results: During 26 years of follow-up encompassing 2 273 931 person years, 2431 women and 4098 men developed coronary heart disease. 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, leading to an unadjusted rate difference of 75 (95% confidence interval 51 to 98) fewer cases of coronary heart disease per 100 000 person years. After adjustment for known risk factors, participants in the highest fifth of estimated gluten intake had a multivariable hazard ratio for coronary heart disease of 0.95 (95% confidence interval 0.88 to 1.02; P for trend=0.29). After additional adjustment for intake of whole grains (leaving the remaining variance of gluten corresponding to refined grains), the multivariate hazard ratio was 1.00 (0.92 to 1.09; P for trend=0.77). In contrast, after additional adjustment for intake of refined grains (leaving the variance of gluten intake correlating with whole grain intake), estimated gluten consumption was associated with a lower risk of coronary heart disease (multivariate hazard ratio 0.85, 0.77 to 0.93; P for trend=0.002).
Conclusion: Long term dietary intake of gluten was not associated with risk of coronary heart disease. However, the avoidance of gluten may result in reduced consumption of beneficial whole grains, which may affect cardiovascular risk. The promotion of gluten-free diets among people without celiac disease should not be encouraged.
Benjamin Lebwohl, Yin Cao, Geng Zong, Frank B Hu, Peter H R Green, Alfred I Neugut, Eric B Rimm, Laura Sampson, Lauren W Dougherty, Edward Giovannucci, Walter C Willett, Qi Sun, Andrew T Chan
Objective: Wheat fiber appears to protect from cardiovascular disease despite its lack of consistent effect on serum lipids. We therefore wished to determine whether reported inconsistencies in the effect of wheat bran resulted from differences in particle size or its high gluten content.
Methods: Two studies were conducted. In one-month metabolic diets, 24 hyperlipidemic subjects consumed breads providing an additional 19 g/d dietary fiber as medium or ultra-fine wheat bran and extra protein (10% of energy as wheat gluten). In two-week ad libitum diets, 24 predominantly normolipidemic subjects consumed breakfast cereals providing an additional 19 g/d of dietary fiber as coarse or a mixture of ultra-fine and coarse wheat bran with no change in gluten intake. Both studies followed a randomized crossover design with control periods when subjects ate low-fiber breads and cereals respectively with no added gluten. Fasting blood lipids were measured on day zero and at the end of each phase.
Results: Wheat bran had no effect on total, LDL or HDL cholesterol irrespective of particle size or level of gluten in the diet. However, consumption of increased gluten in the metabolic study was associated with a 13+/-4% reduction in serum triglycerides (p = 0.005) which was not seen in the normal-gluten ad libitum study.
Conclusions: The protective effect of wheat fiber in cardiovascular disease cannot be explained by an effect of wheat bran in reducing serum cholesterol although in hyperlipidemic subjects displacement of carbohydrate by gluten on the high-fiber phases was associated with lower serum triglycerides.
Jenkins DJ, Kendall CW, Vuksan V, Augustin LS, Mehling C, Parker T, Vidgen E, Lee B, Faulkner D, Seyler H, Josse R, Leiter LA, Connelly PW, Fulgoni V 3rd
Background: Gluten-free diets have grown in popularity, but evidence is lacking regarding gluten intake and long-term health.
Methods: In Nurses’ Health Study (NHS, n=69,276), NHSII (n=88,610), and the Health Professionals Follow-Up Study (HPFS, n=41,908), we estimated gluten intake using a validated food-frequency questionnaire collected every 2-4 years. Incident T2D was defined as physician diagnosed diabetes and confirmed with supplementary information.
Results: Gluten intake (mean ± standard deviation) was 5.83±2.23, 6.77±2.50, and 7.06±2.76 grams/day in NHS, NHSII, and HPFS, respectively, and strongly correlated with intakes of carbohydrate sources, especially refined grains, starch, and cereal fiber (Spearman correlation coefficients > 0.6). During 4.24 million years of follow-up, 15,947 T2D cases were confirmed. An inverse association between gluten intake and T2D risk was observed in all three cohorts after multivariate adjustment (table), and hazard ratio (HR, 95% confidence intervals [95%CI]) comparing extreme quintiles was 0.80(0.76, 0.84; P<0.001). The associations were slightly attenuated after further adjusting for cereal fiber (HR[95%CI]= 0.87[0.81, 0.93]), but not other carbohydrate components. Among participants without major chronic diseases and aged <65 years, changes in gluten intake were not significantly associated with weight gain in multivariate adjusted model: 4-year weight change (95%CI, lb) was 0.08(-0.06, 0.22; P=0.25) in NHS, -0.05(-0.18, 0.08; P=0.43) in NHSII, and 0.36(-0.24, 0.96; P=0.24) HPFS for each 5 grams increase in gluten intake.
Conclusions: Our findings suggest that gluten intake may not exert significant adverse effects on the incidence of T2D or excess weight gain. Limiting gluten from diet is thus unlikely to facilitate T2D prevention and may lead to reduced consumption of cereal fiber or whole grains that help reduce diabetes risk.
Geng Zong, Benjamin Lebwohl, Frank Hu, Laura Sampson, Lauren Dougherty, Walter Willett, Andrew Chan, Qi Sun
Background & Aims: Patients with non-celiac gluten sensitivity (NCGS) do not have celiac disease but their symptoms improve when they are placed on gluten-free diets. We investigated the specific effects of gluten after dietary reduction of fermentable, poorly absorbed, short-chain carbohydrates (fermentable, oligo-, di-, monosaccharides, and polyols [FODMAPs]) in subjects believed to have NCGS.
Methods: We performed a double-blind cross-over trial of 37 subjects (aged 24-61 y, 6 men) with NCGS and irritable bowel syndrome (based on Rome III criteria), but not celiac disease. Participants were randomly assigned to groups given a 2-week diet of reduced FODMAPs, and were then placed on high-gluten (16 g gluten/d), low-gluten (2 g gluten/d and 14 g whey protein/d), or control (16 g whey protein/d) diets for 1 week, followed by a washout period of at least 2 weeks. We assessed serum and fecal markers of intestinal inflammation/injury and immune activation, and indices of fatigue. Twenty-two participants then crossed over to groups given gluten (16 g/d), whey (16 g/d), or control (no additional protein) diets for 3 days. Symptoms were evaluated by visual analogue scales.
Results: In all participants, gastrointestinal symptoms consistently and significantly improved during reduced FODMAP intake, but significantly worsened to a similar degree when their diets included gluten or whey protein. Gluten-specific effects were observed in only 8% of participants. There were no diet-specific changes in any biomarker. During the 3-day rechallenge, participants’ symptoms increased by similar levels among groups. Gluten-specific gastrointestinal effects were not reproduced. An order effect was observed.
Conclusions: In a placebo-controlled, cross-over rechallenge study, we found no evidence of specific or dose-dependent effects of gluten in patients with NCGS placed diets low in FODMAPs.
Biesiekierski JR1, Peters SL, Newnham ED, Rosella O, Muir JG, Gibson PR