If you are on a mission to lose weight, any type of physical activity is desirable. Losing weight is a mixture of several elements, including physical activity, proper nutrition and discipline. Weight loss is usually achieved by consuming fewer calories than you spend. To successfully burn fat you need to create around 500 calorie deficit per day. You can create this deficit with lowering your food intake or increasing physical activity. So the answer is that you can lose weight doing only cardio workouts if it creates a daily calorie deficit.
However, human body is an adaptable organism. Doing the same type, frequency and duration of cardio workouts for many weeks or months will force your body to adapt. If you don’t see any improvements for at least three weeks you have most likely reached a plateau with your current diet and exercise regimen. This means that you are now probably consuming about the same amount of calories that you spend. To get past the plateau you need to either further reduce your calorie intake or increase the duration and frequency of your cardio workouts or both.
Here comes the discipline factor. If you are happy with the weight you lost you can just continue to do what you have been doing. You have already improved your health because of an increased physical activity and proper nutrition. However, if you want to lose even more weight you need to start pushing the limits. This is where the negative part of cardio workouts comes. Doing only long cardio workouts will make your body to adapt by losing fat, but you will also lose muscle mass in the process.
Let’s say that you have increased the duration of your cardios from 30 minutes to 90 minutes. Your body will respond by losing the unnecessary weight and the heaviest tissue in the body is muscle tissue. Muscles play an important role for your metabolic rate and having fewer muscles means your body now requires fewer calories per day to support its basic functions. This means that to keep your new weight you need to even further reduce your calorie intake and do hours and hours of cardios per week just to stay at the current level. This can really test your discipline!
The solution for this problem is to build muscle mass by lifting weights or adding the anaerobic element in your cardio workouts. Anaerobic exercises build muscles and have an added benefit of increased metabolic rate hours after you have finished your workout routine. With this approach, you can spend less time in a gym and don’t have to decrease constantly your calorie intake to burn fat. Increasing muscle mass speeds up the metabolism, and your body will actually require more calories just to maintain the new body composition.