What you eat is only one part of the weight-loss equation. Diet alone may help you drop pounds, but you'll have trouble keeping them off if you don't exercise. And that's not to mention the added benefits you'll miss out on, from improved mood, to better sleep, to disease prevention. "The exercise has to be there," says Jim White, a registered dietitian and personal trainer certified by the American College of Sports Medicine.
Most experts recommend at least 30 minutes of moderate-intensity exercise, such as brisk walking, most or all days of the week. Typically, 30 minutes a day offers disease-prevention benefits, while 60 minutes helps with weight maintenance. Working out for 90 minutes a day helps on both fronts—and melts additional pounds. Regular exercise also cuts the risk of heart disease and diabetes, improves blood pressure and cholesterol levels, promotes better sleep, and builds healthy bones, muscles, and joints.
Some diets offer specific exercise routines—Jenny Craig members get programs tailored to their individual fitness level, for example—while other diets do no more than recommend it. If that's the case, remember that exercise need not be drudgery. Take a Zumba dance class, go hiking, jump rope, or bounce on a trampoline. Try kayaking, pilates, or swimming; vigorous household chores and yard work count, too. For the best conditioning, switch up your routine every 12 weeks, including frequency, intensity, and type. And avoid an all-or-nothing mentality: It's better to take a 30-minute walk five times a week than to run half a marathon on just one day.
Though exercise is essential to a healthy lifestyle, check with your doctor before starting a new regimen. That's particularly important if you have heart disease, asthma, diabetes, or arthritis; if you smoke; if you're overweight or obese; or if you haven't worked out in more than three months. "Start with just 10 minutes a day," White says. "Slowly increase your intensity by adding more time."
Another reason to tread carefully: Some diets may interfere with your ability to exercise, or even make it unsafe. The Atkins diet, for example, recommends taking it easy for a few weeks to adjust to a low-carb regimen. Carbs are the fuel that powers the body, so when you limit your intake, expending energy can become arduous. If your diet dips you below 1,200 daily calories, dial down your routine until you've adjusted to the new level, then gradually ratchet up intensity and duration. Otherwise, says White: "You'll be tired, weak, and dizzy because you won't have the energy to get positive results."