If you improve your diet, you may grow muscle but not lose fat until you reach a calorie deficit. You can do either cardio or weights, but if you are not properly fueling, you will waste your time in the gym. Eating enough food is essential for building muscle and losing fat. Cardio alone will never make you leaner or stronger. Only doing cardio while eating a lot of calories will cause you to gain body fat. Weight training is needed to build muscle. Muscle burns more calories than fat at rest. The more muscle you have, the faster you will lose weight. People who only do cardio tend to lose weight, but they usually end up being weaker and less able to fight off illness because their muscles have atrophied from not using them. The best thing you can do for your health and fitness goals is to mix up your workout routine by adding some strength training into it. This will help you burn more calories both during exercise and at rest. Also, eating plenty of fruits and vegetables helps out your heart as well as your stomach. They're full of antioxidants that protect against cancer and other diseases. Finally, get outside! The more active you are, the better. Exercise is recommended for everyone, no matter what your age or health status.