Realistically you're talking about like 12% bodyfat for a male - which is something many of us would dream of. Sorry, but that's absolutely not what's happening with regular overweight people who lose weight, you're talking about micro-optimization for athletes.

The deal is whenever you lose weight you lose muscle and fat. All you can do is shift the ratio. Resistance exercise helps shift that ratio. Proper diet (ie: enough protein) helps shift that ratio.