Here's a short list of what you can do to get your body to burn fat instead of muscle while you're in your CDL:
1. Eat Enough Protein
Losing fat without losing muscle is all about eating enough protein every day. What's the ideal amount? A good rule of tumb is 1 gram of protein per pound of body weight. It's best to get your protein from whole food sources (think meat), but protein drinks are fine, too, as long as you take into account their calorie content as well.
2. Drink lots of water
In general, you should try to drink between half an ounce and an ounce of water for each pound you weigh, every day. For example, if you weigh 150 pounds, that would be 75 to 150 ounces of water a day.
3. Lift Weights
If you don't currently work out with weights, start. It's the single most important requirement for anyone who wants to lose fat without losing muscle. If you already lift weights, you need to maintain your current weight loads while you're in your calorie deficit level. On a calorie deficit diet, maintaining your current level of strength is what signals your body to maintain muscle. It's not the time to increase weight loads on a calorie deficit diet. That comes later. It's also not a time to lift light weights to 'tone'. Your body would then be like, "Oh, hey - I guess we no longer need this muscle. Let's burn it off!"
This means that your primary weight training goal is to NOT lose strength. This in turn will allow you to NOT lose muscle.
3. Eat well before and after your workout
What you eat before your workout fuels the workout and maximizes your performance. What you eat after is important for recovery. Eating protein and carbs about an hour and a half before your workout is optimal, and eating again (protein and carbs) right after is important.
4. Don't reduce your calories by more than 500 of your Calorie Maintenance Level
I know what you're thinking. "Hey! I could you cut my calories by 1000 and lose 2 lbs. a week!" Don't do it. You will be a hungry, cranky, complaining person who would end up losing muscle and friends, along with the fat. That pretty much defeats the purpose of becoming fit - looking great and feeling happy! The idea is to create a lifestyle of eating that can be maintained over time.
Oh, and let's not be too concerned with what the scale says. If you start working out while you cut the calories, you may actually see an increase in scale weight for the first couple of weeks. The best measurement of your progress is by taking tape measurements. Measure your biceps, neck, hips, waist, upper thigh, lower thigh and calf. Even if the scale weight goes up, I guarantee you that the inches are coming off. You've probably heard "muscle weighs more than fat" more than once. Well... no it doesn't. A pound is a pound - fat, muscle, or feathers! If you have a pound of each one, they will all weigh exactly the same - one pound. It's just that muscle is more dense and takes up less space. Looky here:
See how lean muscle is compared to lumpy, blobby fat? Fat takes up more room on your body. When you burn the fat and build muscle, you shrink because muscle takes up less space. There go your inches! Who cares about the scale? Oh, and gross. I lost 25 POUNDS of that blobby stuff. That's a lot of fluff. How much of that stuff do YOU want to burn off?
5. Maintain a weekly deficit of 3500 calories.
This means possibly eating more calories on training days and less calories on rest days. This is done mainly by manipulating carbs and fat. You want to stay consistently higher with protein, because remember - our goal is to lose fat, NOT muscle. Doing this, you'd be in a larger deficit on certain days and a smaller deficit on the other days, as long as by the end of the week you maintain a 3500 calorie deficit..
6. Don't stay in a calorie deficit to too long.
If you have a lot of weight to lose, it might be a good idea to take a week off after a time and go back up to your calorie maintenance level. This is so that you can recover and go back to normal for a little while. By normal, I don't mean eat like you did when you were storing away the fat! Calorie MAINTENANCE level - the amount of calories your body needs each day (before you subtracted the 500 calories!) When to take this break is up for debate, but it really depends on what keeps you moving forward.
8. Ditch the treadmill.
Cardio needs to be reduced to small bursts during weight training sessions. Forget long sessions of cardio. Weight training is not optional. It's the signal that tells our bodies to maintain muscle and to only burn fat.