What if we told you exercises are not the key to weight loss?

Maybe not an outright lie, after all, exercises have their own uses, but they are not directly responsible for weight loss.

In her lifelong quest to slim down, Mara Schiavocampo, an Emmy Award–winning journalist, swallowed everything from get-thin-quick shakes to diet pills.

Having lost 90 pounds slowly over two years and kept them off for more than a year, she says, "If you want to lose weight, you have to eat fewer calories, full stop. If you're still not losing weight, eat even less. The diet industry has tried to make it sound like you can tweak your lifestyle and—voilà—you're thin. Well, guess what? You can't."

Just 25 percent of people who have lost weight are successful at keeping it off for five years or more, according to one survey and new research is starting to explain why.

The insights dovetail with Schiavocampo's: "It requires sacrifice, and it's gonna hurt."

Exercise alone won't make you slim."It's frustrating but true; If you just exercise and don't change your diet, you may have a modest weight loss of only a few pounds," says John M. Jakicic, the director of the Physical Activity and Weight Management Research Center at the University of Pittsburgh. "That's because most of us unknowingly compensate for the calories we burn by eating more."

If a five-foot-four, 135-pound woman walks four miles in one hour, she burns 317 calories. High-incineration sessions, create a greater calorie deficit and, as a result, contribute more to your overall efforts, but even those hard-core workouts might not have as much impact as you'd think.

Studies show that in some cases, vigorous exercise can leave you so depleted, you actually move far less for the rest of the day than you would normally, says Jakicic,.

"You should absolutely exercise, at least 30 to 40 minutes most days, because it's good for your health and burns calories. But you need to focus your weight-loss efforts on eating less."

You can't lose weight without feeling hungry.If the world were fair, our appetite would shrink when our dress size does but our bodies, which evolved to survive in lean times, were designed to keep weight on, and they developed some wily methods for blocking weight loss.

Take leptin, a hormone whose major function is to maintain our usual body weight by signaling when our energy stores, also known as fat, are too low. It's produced by fat cells, so as you slim down, levels drop.

"As you lose weight, you're hungrier than before, you have to eat more to feel full, and your brain responds to food differently, so you have an increased drive to eat and decreased levels of restraint," says Michael Rosenbaum, a researcher in body-weight regulation.

While leptin-based drugs may one day help circumvent the problem, for now we're left to try to trick the body into feeling full.

The best methods: Eat protein with every meal, and snack on high-volume, low-calorie foods. Barbara Rolls, a professor calls these "low-\u000Benergy-density" foods.

"Our studies show that you can eat up to a pound a day more food and still lose weight if you choose things that are low in energy density and water-rich," she says.

The most appealing foods on that list: broth-based soups, vegetables, beans, fish, and most fruit.

You're a poor judge of how much you eat.When it comes to diet, self-deception is rampant. For instance, researchers from the University of South Carolina recently reviewed the accuracy of the self-reported calorie intakes in National Health and Nutrition Examination Survey research conducted from 1971 to 2010 and came to an alarming conclusion.

Nearly 70 percent of the 34,000-plus female participants reported eating so little that their consumption was "not physiologically plausible."

As in they couldn't survive on so little food. "The reasons people underreport aren't completely understood; there's some evidence they don't want to admit how much they're eating, but many genuinely don't realize how many calories they're taking in," says Andrew Brown, a scientist at the University of Alabama's Nutrition Obesity Research Center.

Once you lose it, you're not home free.Sixty percent of people who lose weight regain it, not because they're weak or unmotivated, but because maintenance is harder than losing.

"Those who weigh 120 pounds without dieting don't have to work that hard to stay there," says Rosenbaum. "But people who used to weigh 160 pounds and now weigh 120 burn fewer calories on average about 350 a day less so they have to eat less and exercise more."

The National Weight Control Registry (NWCR), a database of people who've kept off 30-plus pounds for at least one year backs this up.