Will I lose weight while traveling through Europe? I am on a budget and will be staying in hostels?

I will be backpacking through Germany, Austria, Italy, and Switzerland? Any suggestions?

It can depend on where you're going... After all remember this joke: "What's a Belgian's favorite vegetable?.......... Sausage....

Also, pork is a BIG staple in more "eastern" European countries, like Austria, Germany or the Czech republic.

ya it really depends on where you are and what you are doing

It depends on what you are eating. Fast food exists in europe as well. Try local eateries, and or markets. Just buy fresh produce and baked goods. My cousin backpacked across the U.S. when he was fifteen. All he ate for about three months was wonder-bread, and milk. He lost about 70 pounds, but had an amazing adventure. Good luck and safe travels.

Most people I know gain weight when traveling (including myself,) even when on a tight budget.

Ice-creams are incredible and not too expensive, chocolate is something to dream about for years to come.
But also the cheap foods in the supermarkets is often heavy with calories, more than you would care to think about.

Try to eat healthy, veggies and fruits, and try to get all the foods you need. And do not worry about loosing or gaining a little. And drink water, in most countries tap water is healthy, in Vienna it is even nice to drink.

And one of the best things about traveling is tasting the local foods, so eating out or at least trying the local ready made meals in the supermarkets are part of the experience.