Written by Joyce Smith, BS. A whole grain diet, compared with a refined grain diet, significantly reduced body weight, energy intake, fat-free mass, plasma leptin, inflammatory marker CPR, and proinflammatory cytokines IL6 and IL1ß but had no effect on insulin sensitivity or gut microbiota.

whole grainsEpidemiological studies have shown that whole grain consumption has been repeatedly associated with a decreased risk of lifestyle diseases such as type 2 diabetes and cardiovascular diseases 1. Studies also suggest that whole grain diets can positively influence glucose metabolism 2, adiposity 3, blood lipids 4, and markers of inflammation 5.

Accumulating evidence from rodent studies suggest that gut microbiota can influence the effect of diet on metabolic health while human dietary intervention studies show inconclusive results regarding the effect of whole grain diets on gut microbiota and metabolism 6-8. This may be due to large individual differences in the composition of our gut microbiota 7,8

The objective of this randomized, controlled cross-over trial 9 is to investigate whether a whole grain diet alters the gut microbiome and insulin sensitivity, as well as biomarkers of metabolic health and gut functionality. Sixty adults met the inclusion criteria and participated in two 8-week dietary intervention periods consisting of a whole grain diet (75 g daily) and a refined grain diet (50 g daily) in random order, separated by a 6-week washout period.

Assessment of metabolic markers, anthropometry and blood pressure was done at 4 visits.

Postprandial tests, assessment of gut permeability, fecal shotgun sequencing, measurement of intestinal transit time and urinary metabolic profiling were also done. Analysis revealed the following:

  • Energy intake from refined food intake was 14% higher than from whole grain intake (p< 0.001). Compared with refined grain, the whole grain diet did not improve insulin sensitivity or induce changes in the fecal microbiome. Breath hydrogen levels, plasma short-chain fatty acids, intestinal integrity and intestinal transit time were also not affected.
  • However, the whole grain diet did significantly reduce body weight (p<0.001) and fat-free mass (p<0.010), both of which correlated with the reduced energy intake of the whole grain diet. (p<0.001) and (p=0.0052) respectively. Body weight and energy reduction were also significantly associated with plasma leptin reduction (Pearson r=0.47, (p<0.001) and (Pearson r=0.40, p=0.0057) respectively.
  • Inflammatory marker CRP (p=0.003) and proinflammatory cytokines IL6 (p=0.009) and IL1ß (p=0.008) were all significantly reduced.
  • Four urinary biomarkers were positively correlated with whole grain diet intake (p<0.001)

The limited effects of whole grains on the gut microbiota in clinical trials may be due to the fact that whole grains defined as a food group may have included a variety of cereals such as wheat, rye and oats. These grains may exert very different effects on the individual gut microbes; therefore, future studies should focus on examining the effect of specific grains.

In summary, a whole grain diet, when compared with a refined grain diet, reduced energy intake and body weight and the low-grade systemic inflammation markers CRP and IL-6, without significantly altering whole body insulin sensitivity, gut microbiome or gut functionality in terms of intestinal integrity and transit time. Thus, the health benefits of this specific diet rich in whole grains appeared to be independent of changes in the gut microbiome composition within an 8-week diet study. A whole grain diet may be beneficial in weight management strategies and for those individuals at risk of developing inflammation-related diseases.

Source: Roager, Henrik Munch, Josef K. Vogt, Mette Kristensen, Lea Benedicte S. Hansen, Sabine Ibrügger, Rasmus B. Mærkedahl, Martin Iain Bahl et al. “Whole grain-rich diet reduces body weight and systemic low-grade inflammation without inducing major changes of the gut microbiome: a randomized cross-over trial.” Gut (2017): gutjnl-2017.

© Article author(s) (or their employer(s) Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, http://creativecommons.org/ licenses/ by- nc/ 4. 0/

Click here to read the full text study.

Posted November 9, 2017.

Joyce Smith, BS, is a degreed laboratory technologist. She received her bachelor of arts with a major in Chemistry and a minor in Biology from  the University of Saskatchewan and her internship through the University of Saskatchewan College of Medicine and the Royal University Hospital in Saskatoon, Saskatchewan. She currently resides in Bloomingdale, IL.

References:

  1. Furusawa Y, Obata Y, Fukuda S, et al. Commensal microbe-derived butyrate induces the differentiation of colonic regulatory T cells. Nature. 2013;504(7480):446-450.
  2. Hartvigsen M, Laerke H, Overgaard A, Holst JJ, Knudsen KB, Hermansen K. Postprandial effects of test meals including concentrated arabinoxylan and whole grain rye in subjects with the metabolic syndrome: a randomised study. European journal of clinical nutrition. 2014;68(5):567-574.
  3. Pol K, Christensen R, Bartels EM, Raben A, Tetens I, Kristensen M. Whole grain and body weight changes in apparently healthy adults: a systematic review and meta-analysis of randomized controlled studies. The American journal of clinical nutrition. 2013;98(4):872-884.
  4. Magnusdottir OK, Landberg R, Gunnarsdottir I, et al. Whole grain rye intake, reflected by a biomarker, is associated with favorable blood lipid outcomes in subjects with the metabolic syndrome–a randomized study. PloS one. 2014;9(10):e110827.
  5. Montonen J, Boeing H, Fritsche A, et al. Consumption of red meat and whole-grain bread in relation to biomarkers of obesity, inflammation, glucose metabolism and oxidative stress. Eur J Nutr. 2013;52(1):337-345.
  6. Ampatzoglou A, Atwal KK, Maidens CM, et al. Increased whole grain consumption does not affect blood biochemistry, body composition, or gut microbiology in healthy, low-habitual whole grain consumers. The Journal of nutrition. 2015;145(2):215-221.
  7. Walker AW, Ince J, Duncan SH, et al. Dominant and diet-responsive groups of bacteria within the human colonic microbiota. The ISME journal. 2011;5(2):220-230.
  8. Vanegas SM, Meydani M, Barnett JB, et al. Substituting whole grains for refined grains in a 6-wk randomized trial has a modest effect on gut microbiota and immune and inflammatory markers of healthy adults. The American Journal of Clinical Nutrition. 2017;105(3):635-650.
  9. Roager HM, Vogt JK, Kristensen M, et al. Whole grain-rich diet reduces body weight and systemic low-grade inflammation without inducing major changes of the gut microbiome: a randomised cross-over trial. Gut. 2017:gutjnl-2017-314786.