For whatever reason this topic often gets far too technical. Realistically we’re talking about building muscle and losing fat over the course of days, weeks or months.
Yes this is possible, but with some caveats. To build muscle your body needs the additional required calories and nutrients. Thermodynamics (calories in, calories out) do matter, but we also have to take into this equation your bodies own calorie reserve (body fat).
As long as you’re getting the nutrients from your diet, the additional calories can be taken from existing body fat. This essentially means the holy grail of gainz, losing body fat while gaining muscle.
Now the bad news... this is typically only realistic for:
The human body is designed to be capable, fairly lean and strong. Most beginners can make rapid gainz in their first few months, as essentially they are way below their genetic limits and the body has no issues returning to it’s genetic norm.
2. People that have a lot of excess body fat
Bodyfat is essentially stored energy. The higher the body fat % the more likely your body is to tap into this reserve when you are in a calorie deficit.
3. Those on performance enhancing drugs
Drugs such as steroids change your anabolic hormone profile in your favour and have been proven to elicit muscle growth in unfavourable conditions. Such as a calorie deficit or without any training at all.
I understand we’re impatient creatures and want everything now. While it’s still possible to lose fat and gain muscle for more advanced trainees, any progress made is usually painfully slow and harder to assess accurately. While I do not advocate the extreme bulks and cut phases used by some bodybuilders. I do believe once you get beyond the beginners phase (at least 1-2 years of consistent training with good results), you’ll often be better served targeting one clear goal at a time.
So instead of eating at maintenance or just below for 8 weeks and hoping for a recomposition effect. You could spend 6 week in a calorie surplus and then 2 weeks in a calorie deficit. Obviously there are a million ways you can structure your bulks/cut phases, but having a clear goal will allow you to set up other areas of your life (training, supplements etc..) to coincide with this goal.