Whole Grain Intake and Glycaemic Control in Healthy Subjects: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Abstract

Backgrounds: There is growing evidence from both observational and intervention studies that Whole Grain (WG) cereals exert beneficial effects on human health, especially on the metabolic profile. The aim of this study was to perform a meta-analysis of randomised controlled trials (RCT) to assess the acute and medium/long-term effect of WG foods on glycaemic control and insulin sensitivity in healthy individuals. Methods: A search for all the published RCT on the effect of WG food intake on glycaemic and insulin response was performed up to December 2016. Effect size consisted of mean difference (MD) and 95% CI between the outcomes of intervention and the control groups using the generic inverse-variance random effects model. Results: The meta-analysis of the 14 studies testing the acute effects of WG foods showed significant reductions of the post-prandial values of the glucose iAUC (0–120 min) by −29.71 mmol min/L (95% CI: −43.57, −15.85 mmol min/L), the insulin iAUC (0–120 min) by −2.01 nmol min/L (95% CI: −2.88, −1.14 nmol min/L), and the maximal glucose and insulin response. In 16 medium- and long-term RCTs, effects of WG foods on fasting glucose and insulin and homeostatic model assessment-insulin resistance values were not significant. Conclusions: The consumption of WG foods is able to improve acutely the postprandial glucose and insulin homeostasis compared to similar refined foods in healthy subjects. Further research is needed to better understand the long-term effects and the biological mechanisms.

Wholegrain Intake and Risk of Type 2 Diabetes: Evidence from Epidemiological and Intervention Studies

“…Despite the fact that several RCTs have explored the impact of wholegrain on insulin sensitivity [ 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 ], a meta-analysis of the available RCTs on this topic has never been performed. The only exception is the meta-analysis of Marventano et al [ 60 ], which only includes studies in which insulin sensitivity was evaluated by the measurement of fasting insulin concentrations and/or the homeostatic model assessment-insulin resistance (HOMA-IR) index. The results of the meta-analysis showed no evidence of an effect on HOMA-IR in medium-term interventions comparing wholegrain consumption with a refined cereal diet (MD = −0.18, 95% CI: −0.48, 0.13).…”

“…As for the evidence from the RCTs [ 61 , 65 ] ( Table 4 ), meta-analyses [ 60 ] carried out in healthy subjects have shown no effects of wholegrain consumption on fasting glucose and insulin concentrations.…”

“…In relation to the blood glucose regulation in the postprandial period, evidence from meal studies, employing in most cases wholegrain oat, barley, or rye, indicates that both postprandial glucose and insulin responses are lowered in healthy people when these cereals are consumed as wholegrains rather than in their refined form. However, the results of the acute studies, included in this meta-analysis, cannot be extended to all wholegrain cereals, and in particular, to wholegrain wheat that is more widely utilized worldwide [ 60 ]. In this paper, a meta-analysis was also performed on medium term RCTs that compared wholegrain rich diets with diets based on refined grains ( Table 4 ).…”

Effects of Polyphenol-Rich Foods on Human Health

“…Thus, several molecular mechanisms have been suggested, however, one of the most investigated biological activities of polyphenols is their antioxidant activity. This Special Issue "Effects of Polyphenol-Rich Foods on Human Health" comprises 64 peer-reviewed papers, including 43 original research papers , one case-report [51] and 20 literature reviews [52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71]. They report on the most recent evidence regarding the dietary intake of polyphenols and polyphenol-rich foods, as well as their effect toward the prevention and treatment of non-communicable diseases.…”

“…In particular, published articles demonstrated that a moderate intake of coffee is inversely associated with the risk of hypertension [23], and cancer, including liver [21], endometrial [58] and postmenopausal breast cancer [28]. Marventano et al reported that a high dietary intake of whole-grain foods is able to improve postprandial glucose and insulin homeostasis in healthy individuals [61]. Moreover, the results of a comprehensive meta-analysis on randomized clinical trials showed that intake of flavanol-containing products is associated with body composition and blood lipids level [56].…”