April 22, 2017
Low- or Gluten-free Diets Linked to Type 2 Diabetes
Gluten is a protein that is commonly found in wheat, rye and barley, which gives bread and other baked goods elasticity and a chewy texture. It is avoided in a small percentage of the population that cannot tolerate gluten due to Celiac disease or gluten sensitivity. Gluten-free foods often contain less dietary fiber and other micronutrients, such as, vitamins and minerals, thus making them less nutritious and they also tend to cost more. However, recent popularity of gluten-free diets has been trending even among people without any health problems.
A ‘Gluten-free’ diet has been interchangeably used to represent a ‘healthy diet.’ On the contrary, researchers have shown concern that it may actually lead to the development of type 2 diabetes (T2D) over a period of few decades. Although there is no scientific evidence that low-gluten will contribute to diabetes, the scientists are concerned about the long-term health benefits with the reduction in gluten consumption. An analysis of a large study of U.S. health professionals observed the effects of food on health in nearly 200,000 subjects. The study suggested that gluten intake might not exert significant adverse effects on the incidence of T2D or excess weight gain. Thus, limiting gluten from the diet is unlikely to facilitate T2D prevention and may lead to reduced consumption of cereal fiber or whole grains that help reduce diabetes risk. The purpose of the study was to determine if gluten consumption would affect health in people with no apparent medical reasons to avoid gluten.
A long-term observational study looked at the data from three big previously held studies that started 40 years ago with the Nurses’ Health Study (NHS) and continued with Nurses’ Health Study II (NHS II) and the Health Professionals Follow Up Study (HPFS) to observe the effect of nutrition on long-term health. The studies, NHS (n=69,276), NHSII (n=88,610), and the HPFS (n=41,908), estimated the gluten intake using a validated food-frequency questionnaire collected every 2 to 4 years and the T2D incident was defined as physician-diagnosed and confirmed diabetes with supplementary information. The major dietary sources were pastas, cereals, pizza, muffins, pretzels, and bread. The average daily gluten intake was 5.8 grams per day for NHS, 6.8 grams per day for NHSII, and 7.1 grams per day for HPFS.
The researchers found that most subjects consumed less than 12 grams gluten per day and surprisingly, within this range, the subjects who ate the most gluten had lower risk of T2D during 30 years of follow-up. However, subjects who ate less gluten consumed less cereal fiber that is a protective factor from progression of T2D. Moreover, participants in the highest 20% of gluten consumption had a 13% lower risk of developing T2D versus subjects with the lowest daily gluten consumption less than or equal to 4 grams per day. The mean gluten intake (± 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 greater than 0.6).
During the prolonged 4.24 million years of follow-up from 1984-1990 to 2010-2013, 15,947 T2D cases were confirmed. An inverse association between gluten intake and T2D risk was observed in all three cohorts after multivariate adjustment and hazard ratio (HR) comparing extreme quintiles was 0.80 (0.76, 0.84; P less than 0.001). Further adjusting for cereal fiber resulted in slight attenuation in the association (HR [95%CI]= 0.87[0.81, 0.93]), but not other carbohydrate components. There was no significant association with weight gain in participants without major chronic diseases and aged less than 65 years with changes in gluten intake 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-gram increase in gluten intake.
In conclusion, the study suggested that gluten intake might not exert significant adverse effects on the incidence of T2D or excess weight gain. In the conference media release, the author acknowledged that the study does not conclude the effects of gluten in the prevention of T2D, but limiting gluten from the diet may lead to reduced consumption of cereal fiber or whole grains that help reduce diabetes risk. The study suggested that if avoiding gluten is not clinically deemed necessary, then avoiding foods that have other benefits could be harmful unless replaced with healthy, naturally gluten-free grains, such as quinoa or buckwheat. Overall, although gluten-free diets have grown in popularity, evidence is lacking regarding gluten intake and long-term health, thus it is crucial to have a comprehensive understanding of diet and nutrition prior to making dramatic changes in the diet.