From my experience, I believe that the body is happy so long as you eat enough calories to sustain your weight at your ideal weight. Except for a brief period of time where I tried to eat below 2000 calories per day, I've been satisfied with my meals eating 2000 to 2500 calories a day throughout most of my weight loss. At my goal weight, that is about what I need to eat to maintain. Beyond that, my body has been happy to live off of yesterday's lunch (breakfast, snacks and dinner, too) to make up for the extra calories burned by carrying the extra weight and from my increased activity (mostly walking). As long as you are getting enough protein and eating enough calories, I don't see any reason why you cannot lose fat and gain muscle.

For about the past 2 months I've added weight lifting to my regimen. My eating has been up there (2400 to 2500 calories per day). I eat lots of protein. My weight has crept down a few pounds over the past two months and my upper body has put on some muscle mass. No question about it. So I don't really care what the 'experts' say. I'm losing fat and gaining muscle. Maybe not at the same moment during the day, but over time I am. And unlike the 'Biggest Loser' story where their metabolism was shot by their weight loss, I've been losing weight for 2.5 years and as far as I can tell my metabolism is right on par with what it should be for my gender, age, and size. I think that eating enough calories each day, along with exercise and appropriate levels of protein is what has kept my metabolism strong. There is no way to know for sure. I did what I did and it is what it is. Low carb, moderate protein, and exercise appear to be the right way to lose weight and get healthy. At least it has turned out that way for me and my great experiment.