Fighting fat

Jacqueline Stenson MSNBC contributor

Which exercises help you lose the most weight? If fat truly burns off, then why can it reappear? And does sitting in the sauna help you shed pounds? Smart Fitness answers your queries. Have a fitness question? To send us an e-mail, click here. We’ll post select answers in future columns.

Q: I'm confused about all the weight-loss advice lately. For instance, I have read several times that exercising within the "fat-burning zone" is not the most effective way to lose weight. But that makes no sense to me. If it's true, then which exercises are best? Also, if fat burns off, why can it reappear (when people regain the weight they lost)?

A: Let me first address your question about why fat can reappear. When you "burn" fat, you're not completely wiping out fat cells — they're just shrinking. And they can bulge at the seams again if you consume more calories than you expend through physical activity.

"The fat cells are always there, and they're always hungry," says Barbara Ainsworth, a professor of exercise and nutritional sciences at San Diego State University.

So which type of physical activity is best to help you shrink those fat cells and lose weight? That depends.

Targeting the "fat-burning zone" — a level of exercise intensity that's low to moderate — has been widely touted as the ideal way to lose weight. And various types of exercise equipment have digital readouts that tell you when you're working out at this level.

At first glance, the idea of a fat-burning zone seems sound. It's true that our bodies burn a greater percentage of body fat during low- to moderate-intensity exercise (around 60 percent) than during high-intensity activities (roughly 35 percent). As we increase exertion, the body relies less on fat as fuel and more on carbohydrates, explains Ainsworth. Carbohydrates are stored in muscle and can be quickly released when our bodies need them for vigorous activity.

INTERACTIVE Quiz: Test your exercise knowledge

So does that mean that 20 minutes of walking will help you lose weight (in the form of fat) much better than 20 minutes of running? No. (Little wonder you're confused).

Why? Because what ultimately matters in weight loss is how you balance your calories. To lose weight, you need to expend more calories than you take in. To lose a pound of body fat, for instance, you need to create a deficit of 3,500 calories. And minute for minute, high-intensity exercise will help you lose weight fastest because it burns the most calories.

It's also important to note — and this math indeed gets a little confusing — that even though you burn a smaller percentage of fat at high intensities, you can still actually burn more total fat calories at this activity level because you're burning more calories overall, and a good number of them are coming from fat.

Now, what's the best exercise for you? That depends on a lot more than just how many calories a particular exercise burns. Running may burn the most calories but if you hate it and aren't likely to do it on a regular basis, it's not the best exercise to help you lose weight even though it's keeping your neighbor slim and trim.

"It's better to work out at an intensity that you're comfortable with and will be consistent with," says Gerald Endress, fitness manager at the Duke University Diet and Fitness Center in Durham, N.C.

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