Burning fat or muscle

So I met with my nutritionist again today and learned so much. Had a two hour sit down to go over everything. Great info max. I found out that my aggressive calorie deficit was to much to start at. Have to leave room to adjust your calorie intake when you hit plateau s. So I had to adjust my calorie intake up 800 cal. Which I was very hesitant to do but once he taught me the math and facts of calorie intakes needed for your personal bmr along with body fat percentages for cutting and bulking he had my attention. he showed me his journal when he was cutting and his calorie intake for 3100 and his bmr was much lower than mine. But his results were great. So guess I have to add 800 more cals. My goals I currently set before I was defenitly gonna lose weight but at the cost of lean muscle tissue loss. So if your trying to lose weight and want to lose as little muscle tissue as possible do not so your weekly weight loss goals any higher than 1% of your total body weight. One pound of fat is equal to 3500 calories. So for example I weigh 260lbs my bmr is 3700 calories if my goal was to lose 1% of my body weight each week, I would lose 2.6 lbs each week I order to meet that goal I need to take 2.6 lbs of fat calories which is 9100 calories. I need to divide that 2.6 lbs goal of 9100 by 7 (day per week) to get my calorie deficit per day. So my number is 1300. So I would take my bmr and subtract my deficit leaving me with 2400 calories per week to lose fat rather than both fat and muscle. Don't forget to add extra calories you lose due to workouts.