For as long as I have been working as a fitness professional, I have been witness to the “cardio vs. strength training” debate. There are those that claim if you want to lose weight, you must do cardio, or aerobic exercise, because of the fat and calorie burning (one hour of running can burn nearly 800 calories for a 150 pound person). After all, how many overweight marathon runners have you seen? On the other side of the debate, there are those that shun cardio, and say that because one pound of muscle tissue burns more calories than one pound of fat tissue, the more muscular you are, the more calories you will burn, so focus on strength training.
Really though, aerobic exercise and strength training are both needed to be healthy and lose weight. Aerobic exercise not only burns a lot of calories (and therefore excess fat), but it improves your endurance and respiratory capacity allowing you to exercise longer and build resilience to more intense activity. It also has many positive health benefits such as improving heart function, reducing cholesterol, decreasing risk of cancer and diabetes, increasing serotonin levels and reducing depression, improving insulin function, and much more! And according to a recent study at Duke University Medical School published in the American Journal of Physiology- Endocrinology and Metabolism, aerobic exercise is more effective at reducing visceral fat (the deep belly fat) compared to strength training.
Strength training is also important ,though, as it helps maintain calcium and other bone-building minerals (though so does weight-bearing aerobic exercise), and helps to fight aging. Muscle breakdown naturally happens as you get older, so fight aging by lifting some weights!! And it is true, the more muscle you have, the more calories you burn just standing still.
In an ideal world, we would all have time to do aerobic exercise, strength train, practice yoga, stretch, etc… every day, but most of us don’t have time for it all. So if you really need to lose weight, and you only have time for just one activity, cardio is still the way to go the majority of the time. It is the most effective at boosting metabolism, burning calories, and reducing fat.
However, this doesn’t mean you should just do cardio, because you don’t want to miss out on the benefits of strength training. So if you need to lose weight and you’re short on time, try focusing on one activity per day; cardio four days a week, strength training twice a week, and one day of rest. Finish each workout with 10 minutes of stretching or yoga. You can get each workout completed in under an hour , get the most effective fat-burning workout program, and reap the benefits of both types of exercise, all while enjoying variety!
 Am. J. Physiol. Endocrinol. Metab. 2011, doi:10.1152/ajpendo.00291.2011