It's no secret: To drop pounds, you should eat less and move more. But what you may not realize is that at different points in your take-it-off efforts, the key is to emphasize diet or exercise. "It's easy to get overwhelmed by all the changes we're supposed to make on the road to weight loss," says Donald Hensrud, MD, medical director of the Healthy Living Program at the Mayo Clinic in Rochester, Minn. There are so many fitness apps and diet-friendly foods, he continues, "that often people take on too much and then give up altogether." Consider this your guide to a smart, sane and more sustainable slimdown.
If you need to: Kick-start weight loss
Focus on: Diet
Good for your body: "To lose weight initially, emphasize reducing calorie intake rather than increasing physical activity," says Louis Aronne, MD, obesity expert at New York–Presbyterian Hospital/Weill Cornell Medical Center. A study from the University of Missouri–Columbia found that participants who attended Weight Watchers meetings for 12 weeks lost an average of 5 percent of their body weight (about 9 pounds); those who just joined a gym shed only about 3 pounds.
Related: 16 Ways to Lose Weight Fast
Why not go on an exercise bender to launch weight loss?, you might wonder. Well, for safe reduction, experts recommend taking off about 1 pound a week. That requires a deficit of 500 calories a day—simply eliminating soda, juice and coffee drinks can do the trick. But you'd have to walk for almost two hours to burn off that many calories.
You'll want a structured eating plan to make sure you consume fewer calories than you burn, whether that's by cutting down on carbs or shrinking portion sizes. "Whatever healthy diet you will adhere to best is the one for you," says Holly Wyatt, MD, medical director of the Anschultz Health and Wellness Center at the University of Colorado. Meanwhile, move more; take lunchtime walks, or do extra laps around the grocery store.
Good for your motivation: Rebooting both your diet and exercise at the same time can lead to failure. "I've seen weight losers who change too many habits at once and get thrown off track," says Susan B. Roberts, PhD, senior scientist at Tufts University's Jean Mayer USDA Human Nutrition Research Center. "It's a bandwidth issue—if you make multiple changes, you can't do them all correctly. And it's often easier to adjust diet than exercise."
If you need to: Reach your goal weight
Focus on: Diet + some exercise
Good for your body: Once you've taken off the first several pounds, combine your dieting with regular exercise, Roberts recommends: "In my experience, it's easier to work out once you've lost some excess pounds, rather than starting when you feel heavy and lack energy." A meta-analysis of studies in the journal Health Technology Assessment found that the combination of diet and moderate exercise for people on long-term programs yields the best results.
Cardio burns calories, but resistance training helps you lose fat, not muscle, explains Felicia Stoler, RD, a nutritionist and exercise physiologist in Red Bank, N.J. People who do only aerobic exercise typically have less muscle mass, and thus a lower resting metabolism, than those who pair it with strength training.
Good for your motivation: It takes an average of two months for a new behavior—like downing vegetables before a main course—to turn into a habit, research shows. So once you're past that initial hump, making better food choices becomes second nature, and it won't be overwhelming to bump up your exercise. "This is a good point to focus on getting more physical activity during the week if you're used to doing so just on weekends," Dr. Aronne says. Schedule in an evening walk on at least two weekdays, or follow a DVD before work a couple of days a week.
Related: Get a Flat Belly in 4 Weeks
If you need to: Maintain weight loss
Focus on: Exercise
Good for your body: People who regularly work out are nearly twice as likely to keep pounds from piling back on as those who don't, says research in the American Journal of Preventive Medicine. "When you exercise, you activate hormones that tend to favor using more fat as fuel," says Pamela Peeke, MD, author of Body for Life for Women and assistant clinical professor of medicine at the University of Maryland School of Medicine. And, of course, continue to eat well: Regular exercise gives you a little leeway, Dr. Wyatt notes, "but it won't cover 3,000-calorie meals."
Good for your motivation: Nobody can remain in diet mode forever—which is why you want to embrace exercise as part of your lifestyle. As Dr. Wyatt says, "Emphasizing the positives, like how much better you feel, helps cancel out a sense of deprivation." Even if you were to stop exercising now, she continues, you'd likely miss it: "Being physically active isn't something you tend to just turn on and off. It becomes a part of who you are and how you feel"—so it's easier to stay lean for life.