Colleges trying to encourage a well-balanced diet have a message for students sizing up that all-you-can-eat smorgasbord in the dining hall: What you don’t know can help you.

More than a dozen Massachusetts colleges have recently embarked on a stealth health campaign - covert operations to address the chronic problem of overindulging students throwing nutrition to the wind.

Portions have shrunk at Wellesley College, Tufts University, and the University of Massachusetts at Amherst. Plate sizes have been reduced at Merrimack College, where newly trained servers are sneaking fresh vegetables onto plates alongside meat entrees.

Northeastern University is experimenting with tapas-style dining to encourage students to sample small plates of various cuisines. Babson College is dishing up 5-ounce servings of ice cream rather than 10. And at UMass, burgers now come as 2-ounce “sliders.’’ Even chocolate chip cookies there are made with whole wheat - a sly substitution that escaped the notice of many a taste bud.