Need a quick snack and don't want to bust your diet? New 100-calorie snack packs promise to do the trick.

They're certainly popular. There are more than 150 different kinds of the snack packs on the market, and they had sales of more than $200 million last year.

But before you buy in to the new craze, nutritionists want to warn you about just what you're eating.

Bryce Jackman is a health-conscious dad. But says he wasn't always. "These days it's quite easy just to go the easy route with fast foods," he admitted.

That easy route led to extra pounds. Now the family is looking to make a life change and get healthier. But because they're still always on the go, the 100-calorie snack packs looked like a great solution.

Traci Thompson, who is with the American Dietetic Association, said you need to think before you crunch. "I would consider these to be foods that have calories with very little nutrients, so empty calories," she told us.

The snack packs are often smaller, thin versions of the originals, and those don't always satisfy the snack craving.

"Whenever I eat the snack packs, I always want to have more," student Kaitlynn Jackman admitted.

In fact, in a recent study, 140 kids gathered to watch TV and snack. They could choose a small bag of chips, or a larger one.

Turns out, the kids who chose the smaller bags ended up eating more chips. Even children who have been educated about health and weight ate more chips when out of the smaller snack bags.

"Only about a quarter of those in the study opened the larger bags. About 59% opened the smaller snack packs and ended up consuming more because they opened more packages," Thompson explained.

The food companies say these products are designed for those who want traditional snacks-- just smaller portions. But then you can only eat one pack.

Thompson said using those guidelines, the snack packs work. "Perhaps families working toward cutting back on their portion sizes where parents still have control over one going into the lunch bag."

But for the rest of us? Fresh fruits and veggies, a handful of nuts or a low-fat granola bar, may make more sense.

Dad Bryce Jackman found another reason to go natural. "Dollar for dollar, it's much cheaper doing the natural route and it's better for you."

One more thing to realize-- those low cal packs are mostly packaging. You end up paying about twice as much for the same amount of product. One solution is to buy the bigger bag, then use a food scale to measure appropriate portions.