Yogurt enriched with a natural extract rich in PAF inhibitors and polyphenols. Study design and rationale of a randomized, double blinded, placebo-controlled, parallel intervention study Maria Detopoulou, Tzortzis Nomikos, Elizabeth Fragopoulou, Mary Yannakoulia, Adamantini Kyriakou, Demosthenes Panagiotakos, Smaragdi Antonopoulou