Ballor et al. 1996 conducted a classic and interesting study on body composition changes induced by aerobic and strength training. This study gets cited a lot, but apparently for the wrong reasons. One of these reasons can be gleaned from this sentence in the abstract:

“During the exercise training period, the aerobic training group … had a significant … reduction in body weight … as compared with the [strength] training group …”

That is, one of the key conclusions of this study was that aerobic training was more effective than strength training as far as weight loss is concerned. The authors refer to the strength training group as the “weight training group”.

Prior to starting the exercise programs, the 18 participants had lost a significant amount of weight through dieting, for a period of 11 weeks. The authors do not provide details on the diet, other than that it was based on “healthy” food choices. What this means exactly I am not sure, but my guess is that it was probably not particularly high or low in carbs/fat, included a reasonable amount of protein, and led to a caloric deficit.

The participants were older adults 56 to 70, who were also obese mean body fat of 45 percent, but otherwise healthy. They managed to lose an average of 9 kg about 20 lbs during that 11-week period.

Following the weight loss period, the participants were randomly assigned to either a 12-week aerobic training five women or weight training five women exercise program. They exercised 3 days per week. These were whole-body workouts, with emphasis on compound multiple-muscle exercises. The figure below shows what actually happened with the participants.

How to lose fat and gain muscle at the same time?

As you can see, the strength training group WT gained about 1.5 kg of lean mass, lost 1.2 kg of fat, and thus gained some weight. The aerobic training group AT lost about 0.6 kg of lean mass and 1.8 kg of fat, and thus lost some weight.