Most foods and drinks in moderation are safe to consume, and soft drinks are no exception with sperm. Similarly, caffeine from coffee, tea, and soft drinks are safe with moderate or typical use.  We start to see problems when patients are drinking two pots of coffee a day, or soft drinks all day long.  These types of choices are also indications that the rest of the diet is otherwise unhealthy.  There is a myth from grade school that some of the chemicals in yellow or green soft drinks is a problem, but that has not borne out to be true in well-conducted medical studies.  Coffee in the morning, and a tea or soft drink in the afternoon are fine.  Just remember that late evening caffeine can interfere with good sleep.  The three most important tenets of a healthy body are diet, exercise, and sleep.  If these tenets are kept top of mind during the day-to-day choices a man makes, he will generally live healthier and live longer, in addition to having healthier sperm.