Losing weight is tough enough, but keeping it off -- now that can be really tough. Statistics show that 90-95 percent of overweight people who lose weight will regain it all (and in some cases, even more) within five years.

So, what's a person to do to stay slim? Work out harder, say researchers from Brown University. This may seem like a no-brainer at first, but what their study found was that duration during exercise does not matter as much as intensity when it comes to maintaining weight loss over time.

The good news is that you won't have to spend as long in the gym; the data shows that around 25 minutes per day is perfect. The bad news is that you won't be spending long, leisurely walks while reading a book on the treadmill anymore, because you're going to have to kick your workout into high gear.