Tart Cherry Concentrate Does Not Alter the Gut Microbiome, Glycaemic Control or Systemic Inflammation in a Middle-Aged Population

Abstract

Limited evidence suggests that the consumption of polyphenols may improve glycaemic control and insulin sensitivity. The gut microbiome produces phenolic metabolites and increases their bioavailability. A handful of studies have suggested that polyphenol consumption alters gut microbiome composition. There are no data available investigating such effects in polyphenol-rich Montmorency cherry (MC) supplementation. A total of 28 participants (aged 40-60 years) were randomized to receive daily MC or glucose and energy-matched placebo supplementation for 4 wk. Faecal and blood samples were obtained at baseline and at 4 wk. There was no clear effect of supplementation on glucose handling (Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) and Gutt indices), although the Matsuda index decreased significantly in the MC group post-supplementation, reflecting an increase in serum insulin concentration. Contrastingly, placebo, but not MC supplementation induced a 6% increase in the Oral Glucose Insulin Sensitivity (OGIS) estimate of glucose clearance. Serum IL-6 and C reactive protein were unaltered by either supplement. The faecal bacterial microbiome was sequenced; species richness and diversity were unchanged by MC or placebo and no significant correlation existed between changes in Bacteroides and Faecalibacterium abundance and any index of insulin sensitivity. Therefore, 4 weeks of MC supplementation did not alter the gut microbiome, glycaemic control or systemic concentrations of IL-6 and CRP in a middle-aged population.

Keywords: Montmorency; cherry; microbiome; polyphenol.

Figure 1

Systemic Glucose and Insulin Responses to an Oral Glucose Tolerance Test (OGTT) in Placebo and Montmorency Cherry Supplemented Middle-Aged Participants. A total of 28 non-obese middle-aged men and women (40–60 years) consumed a daily dose of Montmorency cherry concentrate (n = 13) or an equivalent volume of glucose and energy-matched placebo (n = 15) for 4 weeks. An oral glucose tolerance test was conducted pre- and post-supplementation. (A) Blood glucose concentrations during OGTT; (B) Blood glucose total area under the curve (tAUC) during OGTT; (C) Serum insulin concentrations during OGTT; (D) Serum insulin tAUC during OGTT. Missing data points are due to failure of venous access at a necessary timepoint. * p < 0.05. In Figure 1B,D, black squares = placebo, black circles = cherry.

Figure 2

Indices of Glucose Tolerance and Insulin Sensitivity in Placebo and Montmorency Cherry Supplemented Middle-Aged Participants. A total of 28 non-obese middle-aged men and women (40–60 years) consumed a daily dose of Montmorency cherry concentrate (n = 13) or an equivalent volume of glucose and energy-matched placebo (n = 15) for 4 weeks. An oral glucose tolerance test was conducted pre- and post-supplementation and surrogate measures of insulin sensitivity were calculated. (A) HOMA-IR = Homeostatic model assessment insulin resistance; (B) the Gutt index of insulin sensitivity; (C) Matsuda index; (D) OGIS = Oral Glucose Insulin Sensitivity Model. * p < 0.05. Missing data points are due to failure of venous access at a necessary timepoint. Black squares = placebo, black circles = cherry.

Figure 3

Metabolic Substrate Utilisation During an Oral Glucose Tolerance Test in Placebo and Montmorency Cherry Supplemented Middle-Aged Participants. A total of 28 non-obese middle-aged men and women (40–60 years) consumed a daily dose of Montmorency cherry concentrate (n = 13) or an equivalent volume of glucose and energy-matched placebo (n = 15). An oral glucose tolerance test was conducted pre- and post-supplementation. Oxygen consumption and carbon dioxide production were measured by pulmonary gas analysis and standard indirect calorimetry equations were applied to calculate respiratory exchange ratio as well as fat and carbohydrate oxidation rates. (A) Respiratory exchange ratio; (B) Carbohydrate oxidation; (C) Fat oxidation.

Figure 4

Systemic Inflammatory Burden in Placebo and Montmorency Cherry Supplemented Middle-Aged Participants. A total of 28 non-obese middle-aged men and women (40–60 years) consumed a daily dose of Montmorency cherry concentrate or an equivalent volume of glucose and energy-matched placebo for 4 weeks. IL-6 and CRP were quantified in plasma pre- and post-supplementation. (A) Serum IL-6 concentration; (B) Serum C-reactive protein concentration. Missing data points are due to values falling >3 SD from the sample mean in participants reporting an acute illness. Black squares = placebo, black circles = cherry.

Figure 5

Gut Microbiome in Placebo and Montmorency Cherry Supplemented Middle-Aged Participants. A total of 28 physically inactive and non-obese middle-aged men and women (40–60 years) consumed a daily dose of Montmorency cherry concentrate (n = 13) or an equivalent volume of glucose and energy-matched placebo (n = 15) for 4 weeks. Faecal samples were collected pre- and post-supplementation, genomic DNA was isolated and the bacterial microbiome was sequenced. (A) Relative abundance of genera of abundance >2% of the faecal microbiome. Paired bars represent participant microbiome before (left bar) and after (right bar) the intervention. (B) Species richness. (C) Species diversity—inverse Simpson Index. (D) Principal component analysis.