(CBS) — Trail mix and reduced-fat foods are good for you, right? Not always.

CBS 2′s Mary Kay Kleist reveals some surprisingly unhealthy snacks and offers some better choices.

Granola bars may have a reputation for being healthy, but registered dietitian Jennifer Ventrelle of Rush University Prevention Center says they often have extra sugar and extra sodium.

“This is a glorified candy bar,” she says.

To keep it healthy, look for more than 5 grams of protein,  less than 10 grams of sugar and no more than 150 calories.

How about muffins? Whether bran or blueberry, a typical muffin has 27 grams of carbs. More than half is sugar.

“Muffins are dessert,” Ventrelle says.

Canned fruits come with high-fructose corn syrup, and cans are lined with a chemical preservative linked to health problems.  Fresh fruit is best. Dried fruits may be convenient, but they’re loaded with sugar, so don’t eat more than 2 tablespoons a day.

Some microwave popcorns have more than 4 grams of unhealthy trans fats.

“A lot of times they’ll put coating inside of the bags,” Ventrelle says. “They need something to make the popcorn not stick to the bag.”

Another snack with a lot of salt or sugar: flavored rice cakes.

“A better choice would be a whole grain cracker,” Ventrelle says.

If you’re buying reduced-fat peanut butter, you’re missing out on some healthy monounsaturated fats –but getting more of something else.

“There’s double the sugar in reduced fat peanut butter, versus full-fat peanut butter,” Ventrelle says.

Honey roasted peanuts may not be such a great snack choice.

“You’re taking something that is naturally very good, high in fiber, (with) healthy fat, and coating it with sugar and salt,” Ventrelle says.

The same is true for pre-packaged trail mixes. “I encourage people to make their own mini-bags of trail mix,” the dietitian says.

Two other snacks on the watch list: smoothies, unless they’re loaded with fiber and protein, and yogurt with fruit on the bottom. Plain yogurt is best.

Whatever snack you choose, it’s important to space them out so you won’t have cravings and overeat. If you’re trying to lose or maintain weight, snacks over 200 calories are probably not a good idea.