When you're on the go or out on the town, we all know how tough it can be to eat healthy.

But you might not realize is that so many foods have sneaky calories that can ruin your diet.

It's a day at the ballpark and it's gonna be hard to find fresh, healthy food ... so do you go for the soft pretzel or the good old fashioned hot dog?

These are the kinds of choices most of us need to make every day; problem is, the decisions can be tricky. Too many foods are either marketed as being healthy or they have hidden nutrition pitfalls.

So hot dog or the pretzel? We asked Registered Dietitian Colleen Gerg just how many calories are in a giant pretzel. And it turns out nearly 500 calories. The jumbo hot dog including the bun and a packet of mustard is only about 280 calories.

This time of year it's easy to grab a smoothie and think you're getting a healthy treat. A lot of them are made with fruit and some of them even have extra protein; but if you look carefully at the nutrition information, you'll see that sometimes smoothies can add up to a whole lot of calories and sugar.

Smoothie King's Medium Orange Ka-Bam smoothie: more than 700 calories and 166 grams of sugar.

Gerg says some store bought smoothies contain syrups and lots of added sugar. That makes it a sweet treat, but it also piles on the calories. A better option she says: all of this fruit along with a serving of low-fat vanilla ice cream: less 250 calories and 20 grams of sugar.

And Chinese take out? You need to watch out here too. Which do you think is the better choice; PF Chang's orange peel chicken with rice or a spring roll, ginger chicken and broccoli and brown rice?

Well that order of orange peel chicken and rice is nearly 1500 calories. But you can have the spring roll, half an order of chicken and broccoli and half a cup of brown rice for 670 calories.

Colleen Gerg's best advice in these tricky situations: while sometimes it's tough to avoid processed foods, whenever possible stick those that at least look natural.