Do I really have to lift weights if I want to lose weight?

The answer is absolutely yes and for two reasons:

1) To replace age related loss of muscle: We all start to lose muscle as we get older. It is a natural part of the aging process. Muscle is very metabolically active tissue. In other words, it burns lots of calories. A pound of muscle burns three times as many calories as a pound of fat. To keep your metabolism humming, you need to hit the weights at least a few times a week. 

2) To spare lean body mass during the weight loss process: When you lose weight without resistance training, you lose a combination of both muscle and fat. This is one of our body’s defense mechanisms to letting its fat stores get too low, too fast. If 20 or 30% of your weight loss is muscle, your metabolism drops and you’ll burn less calories each day. This makes it much more likely that you’ll regain your lost weight. When you lift weights during the weight loss process, you’ll maintain your muscle mass and metabolic rate, which makes permanent weight loss much more likely.