The study is a randomised controlled trial of a dietary intervention consisting of olive oil for cooking , an olive oil based spread , and a daily supplement drink enriched with Vitamin D ( @ microgram daily ) and marine omega-@ fatty acids ( @g daily ) for @weeks preconception versus a control diet of sunflower seed oil for cooking , a sunflower oil based spread , and a daily supplement drink without added Vitamin D or marine omega-@ fatty acids .