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Study under review: A whole-grain diet reduces peripheral insulin resistance and improves glucose kinetics in obese adults: A randomized-controlled trial.
Insulin resistance is recognized as one of the fundamental underlying causes of type 2 diabetes. A meta-analysis of six large observational studies comprising nearly three million person-years of follow-up found that eating more whole grains was associated with a significantly lower risk of developing type 2 diabetes. This same meta-analysis also reported on 21 randomized control trials and found that eating more whole grains modestly reduced fasting glucose and insulin levels. These findings raise the question: do whole grains affect insulin resistance? This question is worth asking considering that only 5% of U.S. adults meet the recommended intake level of the U.S. dietary guidelines for whole grain consumption, despite 56% of adults meeting total grain intake recommendations. More info on U.S. grain consumption is shown in Figure 1.
While there have been clear associations between whole grain intake and glucose metabolism and insulin sensitivity in observational/epidemiological trials, there has been little evidence to suggest that whole grains themselves actually improve insulin sensitivity. One small study (n=11) provided initial evidence that consuming whole grains for six weeks lowered fasting insulin and increased peripheral insulin sensitivity in people with established hyperinsulinemia. However, another study in otherwise healthy overweight and obese adults reported that eating whole grains for six weeks had no effect on insulin sensitivity.
Both studies used the gold-standard hyperinsulinemic-euglycemic clamp to measure insulin sensitivity, but the former provided all food to the participants while the latter simply had participants add whole grains into their habitual diet. The latter study also involved an otherwise healthy cohort compared to the use of individuals with hyperinsulinemia in the first study.
In order to build upon the limited data investigating the link between whole grain consumption and insulin sensitivity, the present study examined the effect of whole grains, compared to refined grains, on body composition, insulin signaling, and glucose metabolism in obese adults with normoglycemia and normal insulin signaling at baseline.
Previously, consumption of whole grains has been associated with higher levels of insulin sensitivity and better glucose control than consumption of non-whole grain foods. While these associations are robust and interesting, there is still insufficient experimental data to infer a causal role. The present study was a randomized control trial examining the effects of whole grain consumption on insulin sensitivity in obese adults.
Other Articles in Issue #42 (April 2018)
Interview: Danny Lennon, MSc
We chat with the founder of Sigma Nutrition and combat sports nutritionist Danny Lennon about his background, the unique nutritional challenges faced by combat sports athletes, and two things he thinks everyone can do to improve their lives.
Alpha-lipoic acid for carpal tunnel syndrome
Previous human studies examining ALA have either given it along with other supplements or only administered it post-surgery. This trial looks at ALA's effects on its own, both before and after surgery.
Throwdown, round 3: plant vs. animal protein for bone health
We've previously covered plant vs. animal protein's effects on the metabolic syndrome and diabetes, and both rounds have ended in a draw for main outcomes. Will either come out on top this round?
Protein gains: not just for the men
Women are underrepresented in many areas of research. This study focuses specifically on female physique athletes to see how high vs. low protein intake affects fat-free mass.
From French Paradox to plaque regression
Observational data suggests that moderate wine consumption could be heart healthy. This follow-up to a study we covered in a previous NERD puts this hypothesis to the test.
A fishy relationship between omega-3 fatty acids and heart health
We review a recent major meta-analysis which examined only large and long clinical trials to find out whether omega-3’s really affect CVD risk.
Interview: Michael Crosier, PhD
In this interview, we chat with Dr. Crosier about the ins and outs of learning and teaching nutrition and dietetics, his research on vitamin K, and more.