Millennials and Gen Zers driving changes in dining habits.

Menu items considered snack foods continue to gain greater appeal and encroach on traditional meal periods. Snack foods eaten at main meals will grow approximately 5 percent over the next 5 years or to 86.4 billion eatings in 2018, according to data from the NPD Group.

The strongest growth of snack foods eaten at meals will be in the better-for-you categories, like refrigerated yogurt, bars, and fresh fruit, which consumers perceive as more healthful and convenient and are more prone to eating between and at meals, according to NPD's study The Future of Eating: Who's Eating What in 2018. Ready-to-eat sweetened snack foods and desserts, which consumers are less likely to eat at main meals, will be flat in the next five years.

Millennials, ages 24-37, Generation X, ages 38-48, and Generation Z, ages 0-23, will drive much of the growth in better-for-you snack food consumption between and at meals. Their positive attitudes about snacking, desire to eat more healthfully, and need for convenience are among the reasons for the growth in this category, according to NPD.

"The growth in better-for-you snack foods in between and at meals is a good example of how consumers are redefining the foods they eat, and how the traditional lines between snack foods and main meal foods are blurring," says Darren Seifer, NPD food and beverage industry analyst. "Consumers clearly associate certain times of day with main meals and between meal occasions but what they are eating at those occasions is changing."