Women’s Health has a great piece on why yoghurt is a great food to eat (this applies to women and men btw).

Your digestive tract houses much of your immune system, a complex constellation of cells and tissues that fight pathogenic organisms that can make you sick. Having more of the beneficial organisms there may help prevent illness: They protect you both by stunting the growth of the nasty ones on the spot and by forcing them out, essentially taking all the free seats in the digestive tract; the bad guys just have to move on, ultimately exiting your system. When the number of good bugs drops — for example, after a course of antibiotics, which kills many of the good guys as well as the bad — you might be more likely to get sick. And as you age, your natural levels of beneficial bacteria decrease. But swallowing ‘em can help get you healthy, plus stop trouble before it starts.