This might shock you, but as an evidence based natural bodybuilding coach I have forgotten more information about this topic than you will EVER learn
Here is a solid review on the subject showing that up to 1% BW loss per week is perfectly fine for muscle preservation while dieting for natural bodybuilders dieting to contest ready condition. The author happens to be someone I keep in regular contact with btw:
JISSN | Full text | Evidence-based recommendations for natural bodybuilding contest preparation: nutrition and supplementation
Now 2 things:
- the OP is NOT getting ready for a contest and doesn't aim to get completely peeled, therefore he can be more severe in his approach than the review recommends.
- the OP is also planning to use clen, an anti-catabolic hormone that will help preserve mass compared to natural bodybuilders highlighted in the review.
With that said, if you actually knew what the fuck you were talking about you would know that 1800cals by itself means absolutely nothing since every individual has different meta-bolic rates & levels of TDEE.
For the OP, 1800cals would equal a 40% caloric deficit. Its high but not even CLOSE to how extreme your making it out to be since it should only lead to around 1.3% BW loss per week.
That means the OP is only SLIGHLTY above what is recommended by the evidence AND isn't planning on getting ready for a contest AND he is using clen AND he is not close to being classified as an "advanced bodybuilder".
There is NO evidence for muscle loss after 2-3 weeks of severe dieting for trained individuals. For more information go read Lyle McDonald's RFL book.
You also forget that LBM is comprised of water, glycogen AND muscle.
The first two go down when dieting and there is jackshit you can do about it without drugs. The final one will be preserved if you diet properly - maintain high protein intake, focus on tension (rather than damage/stress) in the weight room, minimize cardio, etc.
There is NO evidence for your bullshit remark about "slowing down your metabolism" by dieting too hard either.
Meta-bolic slowdown occurs because your dieting REGARDLESS of how slowly you go through the process. This entire process is known as adaptive thermogenesis and you can learn more about it here:
Adaptive thermogenesis in humans
The rest of the meta-bolic slowdown occurs primarily due to too much cardio and happens mostly to women. It has NOTHING to do with the size of the caloric deficit induced through diet.
Anecdotally, I've had clients diet down on very low calories and lose NO more muscle compared to others who have taken the slower approach and had the same start & end points with regards to bf%.
Now they might all happen to be superhuman OR, maybe, just maybe, I know what the fuck I'm doing when it comes to nutrition.
To conclude:
- I AM coming from a position of knowledge.
- YOU need to do more research on the subject
- Provided the OP maintains a high protein intake (1.25g/lb) and focuses on tension in the weight room (weight on the bar, not reps), muscle loss simply isn't a worry at his bf%.