A randomised controlled trial to assess the impact of a polyphenol-enriched diet on intestinal permeability in the elderly: The MaPLE study

Intestinal permeability increases in elderly populations and can result in increased systemic inflammation and contribute to low grade chronic inflammation. The barrier function of the gut can be affected by the gut microbiota and by dietary components. Dietary intervention strategies have the potential to improve intestinal barrier function either directly by affecting intestinal tissue functions or indirectly by beneficially altering the structure/function of the gut microbiota. In the context of a diet-microbiota-intestinal permeability (IP) axis, food bioactives such as polyphenols are a good candidate because there is emerging evidence that they can (i) affect the expression of intestinal tight junction proteins and (ii) beneficially alter gut microbiota profiles by increasing the populations of commensal bacteria. Within this framework the MaPLE project* (Microbiome mAnipulation through Polyphenols for managing gut Leakiness in the Elderly) has been developed to test the hypothesis that an increased intake of polyphenol-rich foods can reduce IP and lower inflammogenic bacterial factors in the bloodstream, promoting a protective metabolic phenotype in the elderly. The first specific tasks addressed have been the development of a polyphenol-rich dietary pattern to use for the intervention study and the evaluation of intestinal permeability in the target population. A polyphenol rich dietary pattern has been developed for the randomised, controlled cross-over dietary intervention study (polyphenol-rich (PR)-diet versus control (C)-diet) carried out on subjects (>60 y) living in a well-controlled setting (i.e. nursing home and associated independent houses at OIC Foundation, Padua Italy). To define the PR-diet, baseline polyphenol intake was firstly calculated through the analysis of recipes used to prepare the daily menu served at OIC Foundation (using www.phenol-explorer.eu). Mean baseline polyphenol intake in the target population was estimated to be about 750 mg/day. Three daily portions of polyphenol-rich food products were added to the PR-diet in order to double the amount regularly introduced by the older volunteers. PR-foods included: berries and derived products, blood oranges and derived products, pomegranate juice, Renetta apple and purée, green tea and dark chocolate products. The control treatment (C-diet) was defined in order to be comparable in terms of energy intake and nutrient composition except for the polyphenol-rich products. IP evaluation in the volunteers was performed by quantifying serum zonulin levels using an ELISA kit).Where possible, IP was also evaluated using a multi-sugar test which involves quantifying sugars in 6 h urine collections following the intake of 5 g of lactulose and 1 g of mannitol. High IP is conveyed for urine lactulose (L)/mannitol (M) ratio > 0.03, evaluated through mass spectrometry analysis.