Proper diet = lower BF.
"Combined anerobic and aerobic training can reduce the gain in muscle girth" [1] and maximum strength [1, 2, 3].
1. Craig, B.W., J. Lucas, R. Pohlman and H. Stelling. The effects of running, weightlifting and a combination of both on growth hormone release. J. Appl. Sport Sci. Res. 5(4): 198-203. 1991
2. Hadmann, R. The available glycogen in man and the connection between rate of oxygen intake and carbohydrate usage. Acta Physiol. Scand. 40:305-330. 1957
3. Hickson, R.C. Interference of strength development by simultaneously training for strength and endurance. Eur. J. Appl. Physiol. 215:255-263. 1980
The most lasting fat loss 'gains' are the ones that occur by means of negative calorie balance over time. Also, this will have the least negative impact in a catabolic sense.
Oops, I forgot to mention that these references are through Essentials of Strength Training and Conditioning (NSCA), Thomas R. Baechle, Roger W. Earle (Editors), 2nd Ed.