The only way to properly find out is to take a body fat reading,.
Agree
you can do that with body fat callipers at home If you weigh yourself and do a bodyfat reading once a month it will be easy for you to keep track of what's happening...
Calipers are only as good as the person using them. Most people will have a tendency to give lower bf% readings than actual.
Some years ago, I had a clinician do a caliper test just before I did a bodpod. The caliper differed by 5%, which to me, means it's basically useless.
agree with shindemac, losing 10 pounds of fat for zero pounds of muscle is unfortunately impossible (or possible via doping?), everytime I lost 10 pounds or so I lost strenght (and I was eating very healthy and exercising almost everyday).
OK, Just tell me what you think the body composition change will be in the OP's scenario? I say no body composition change.
You can argue if he gains muscle just by gaining weight and then loses that muscle when he loses weight. I won't get into that, except to say that I took bodpod tests when I dieted down from 198 to 180 and my LBM stayed almost exactly the same (1.5 lb. LBM increase actually, but this is simply accepted testing error range). Then I started on (what I thought was) and intense weight training program. I went from 180 to 210 and gained only fat (2 lb LBM increase). I still have the test results. They helped me realize I was all wrong in my training (I got a lot stronger by the way, but I didn't gain any muscle) . I made changes, kept taking tests, and 4 years later, had the results I wanted.
To the OP, if you really want to know the answer, the only way is before/after body composition tests that are accurate (bodpod, hydrostat, Dexa).