From the Harvard Health site:
How to Lose Weight without Losing Muscle
If you’re trying to
lose weight by cutting calories, you’re likely losing muscle, too. But
strength training can counteract this effect. According to a research
review in The Journal of Sports Medicine and Physical Fitness, on
average, 27% of the weight lost by dieting is muscle. Those who combined
dieting with cardio exercise cut muscle loss in half. But when
participants combined dieting and resistance training (strength
training), all of the pounds lost were fat. What’s more, the more muscle
you have and the stronger your muscles are—the more benefits you’ll get
beyond weight loss. You’ll develop a slimmer, firmer figure and have
the energy to be more active. And, you’ll get more from cardio workouts
because you’ll be able to go faster and last longer.