How much do you need to exercise to stay fit and lose weight? That’s a good question. Actually, it’s two good questions, because staying fit and losing weight are two different things.Keeping fit is a fabulous goal in it of itself. But that alone may not get rid of those extra pounds. If you really want to get tighter and lighter you’ve got to stay above the line.What does that mean? It means always pushing yourself, trying hard and being present and aware of what you’re doing and why you’re doing it. (It’s not just good advice for working out, it’s true for jobs and friendships—just about anything!)COLUMN: How to Get to 10,000 Steps, EasilyIf you want to not only stay fit, but lose weight or at least maintain your weight, then you’ve got to stay above the line when you exercise. You can’t just show up and think that simply because you’re there change will happen. You are your own control agent. You can make this happen.Here’s how.The most recent government guidelines, from the Centers for Disease Control (CDC), the 2008 Physical Activity Guidelines for Adults, recommend that adults need at least 150 minutes each week of moderate-intensity aerobic activity—that’s 30 minutes a day for five of seven days.What qualifies as moderately intense? Think brisk walking, bicycling, dancing. If 150 minutes is too much for you each week, then up the intensity decrease the time. Opt for vigorous activities like running and spinning.It’s not a simple equation of more is better. In a recent study, a group of Danish researchers assigned healthy men to one of three different groups—one engaged in moderate-intensity exercise for 30 minutes daily, another did vigorous-intensity for 60 minutes and the third remained sedentary. Interestingly, both exercise groups lost similar amounts of body fat, but they found that the moderate-intensity group actually had a greater than expected loss.QUIZ: Are You Active Enough?The men were not supposed to alter their diets during the study; however, food diaries revealed that the vigorous-intensity group increased their food intake and were more sedentary during the rest of the day. The moderate-intensity group was more active the rest of the day, perhaps more energized after their workout and motivated to make other healthy choices. (The sedentary group, well, they saw no weight loss, to nobody’s surprise.)The study is far from perfect: first of all, they studied men, not women, so it’s not generalizable. Second of all, the vigorous-intensity group was adding more muscle, which weighs more than fat. And finally, the study was short-term.Still, I like the study because it shows that it’s not just about how hard we work out and how often…it’s also about the food we eat. Lots of research has looked at exercise and weight loss, and again and again, it comes back to diet. What you eat, when you eat it, how much you eat. Food is fuel for your body. And your body needs the right fuel.The other thing I like about the study is that it dares us to stay above the line.GALLERY: Seven High-Intensity Exercises So, go ahead and get above the line! Get active, push yourself. Go for at least 30 minutes daily—60 if you can, at least two times a week. You’ll be more fit, you’ll alter your waistline and you’ll feel better!