Okay, so first I'll wear my academic hat (ignore if you like), then the practical side hat.
When you have a calorie deficit your body burns both excess fat and muscle to fuel itself. The idea behind a higher protein diet like this is that it is supposed to minimize the muscle loss (some research supports this) versus if you cut protein. Your body cannot make protein, it has to be ingested. Your body is fueled for energy by carbohydrates...which is why I would never try low carb diet until I saw this which totally makes sense physiologically...your body can't make protein from carbs, but it can make carbs (stored in your body in the muscle as glycogen) from fat and protein. It's not a very easy process...but that is why something like MRC works. Remember how the first few days on detox and start of the plans you had a lot of muscle fatigue, but then as time went on you had more energy? Your body got better at using fat and protein to convert it to carbs. Neat, huh?
A majority of our calories are burned through what is called resting metabolic rate. This is influenced by your age, gender, height, genetics...none of which we can do anything about. But it is also influenced by your lean body mass (muscle). So everything you can do to preserve it (or build it) will help you burn more calories at rest.
A couple other things research shows. 1. Women's success at weight loss is more influenced by their nutrition than exercise (partly because we lack the testosterone to build big muscles) and 2. When people exercise a lot then have a tendency to overeat...and it's really hard to burn 500 calories in a workout, but darn easy to overeat by that many.
Okay, so academic hat off now...I had always tried to outexercise my mediocre eating habits (they weren't horrible, but bad enough to keep me stuck at 183 after having been up to 220). So when I started this I knew I had to focus on the eating side...and have kept in my mind that until I hit maintenance or get closer to my goal, I am not going to try and build my exercise. I do, however, want to maintain my muscle (I don't want to be skinny fat) and maintain my cardio. I have been doing mainly body weight strength (in my opinion this is sufficient for most people doing weight loss to maintain muscle mass...push ups, squats, lunges, etc.) with some light weights or resistance bands. I do some yoga, some pilates, some walking...and last night after taking a month off I went for a run. I ran 2 miles and it felt so good. I kept telling myself "it feels so much better being 10 lbs lighter, can you imagine the next 25??" Again, I'm not going to build my running now, but when I get to my goal in the spring I am definitely training for a triathlon.
So, in short. Nutrition is first and most important (especially for women) and exercise is 2nd and should be an accessory...like a great necklace. Whatever works for you is best.
I hope I didn't step on toes or anything. I'm still working on what I academically know and what people are experiencing in the real world. Since I started focusing on nutrition...really focusing on it...I finally broke through where I had been stuck for 2 years.
PS-now having said that...I went off plan for the first time in a month...was out to eat and was being so good...then the waiter (one of my former students) brought us cheesecake. Oh yes, I had a couple bites and am going to go undo some of that naughtiness on the elliptical...it was just so nice of him...sigh...can't outwork a bad diet...have to remember that!