You can lose body-fat without gaining muscle mass by keeping your strength training very light, however I recommend that you at least maintain muscle mass. The reason is simply that:
1) Muscle mass is metabolically precious. This means that the more muscle mass you carry, the more Calories you burn at rest. It makes it easier to get lean and stay lean when you have more muscle because instead of eating 3 meals per day you may be able to eat 4-5 meals while still getting just as lean.
2) The first 1-2 years where you gain muscle mass, the muscle mass doesn’t make your body bigger. Instead, it has a tonality effect. The reason is that muscle mass is much more dense than fat mass and you gain it a slow rate (at most 0.5-1 KG per month if you train hard), therefore there’s no way you will suddenly blow up in size. Becoming visibly bigger because of muscle mass takes YEARS of hard training and dieting.
To show you an example of the tonality effect, take a look at the photo below:
In the 3rd photo I had already been training hard for nearly 3 years, but I did not look big by any means.
I was a light 177 pounds at 6’2″ height and my body was toned.
At this time I was able to deadlift 400 pounds, squat 300 pounds and military press around 135 pounds for reps.
As you can see, the muscle mass I gained only created a more toned physique rather than a bigger one.
Training for 3 years and gaining such a small amount of muscle mass was mostly a result of my inferior training method (focusing too much on lifting heavy rather than doing higher volume), however my point still stands.
The first 1 year of training you’re unlikely to gain such an amount of muscle mass that you appear physically bigger – unless you eat a high Calorie diet and start from an undermuscled base.
Instead, you’ll likely just add some muscle tonality with the first 10-15 KG of muscle mass you gain and then you can always stop at that point and just maintain your lean and toned physique.
Be proud but stay hungry!
Oskar Faarkrog, ISSA Certified TrainerRead my free 50 page guide "The 2 Phases of a Skinny-Fat Transformation"