This goes against common wisdom but it's something I've just recently been observing after like two decades.

Not to give TMI, but I always tended to get constipated pretty easily and it's just been one of those things that I figured i had to live with, along with lost of bloating and just overall stomach discomfort. I did always notice that during times where I'd revert back to heavily processed food is when my skin generally showed a lot less inflammation, but I never looked into it and figured it was a coincidence.

Lately I've been trying to tackle all my digestive issues, and though never diagnosed, it became glaringly obvious that I have some degree of gastroparesis or just very, very slow motility. I started following the diet of a gastroparesis patient, which is usually things like baby food, gatorade, rice cakes, rice cereals.... just a very processed, low fiber diet (low fat and low in hard to digest meats as well) that's as easy to digest as possible. Within hours of this my stomach feels so much better, I become regular, and, this has not cured my acne, but I've noticed I don't get cysts, just smaller spots that come and go within a day, which is a victory. I did not do this for acne, so I didn't really take time to document things appropriately, but it's something I noticed rather quickly as I otherwise get cysts on a weekly basis almost without fail.

This isn't the healthiest approach, and if you don't have these digestive issues I don't recommend it, but it's just food for thought for anyone who might also be suffering from slow digestion along with their acne. There's lots of info if you do a search on gastroparesis, but basically I try to eat zero fiber, or keep it to a bare minimum, but also avoid most fats (you need some, do not eliminate completely), and most meat other than lean ground beef or white fish like cod. My daily foods mainly consist of protein powder, plain rice cereals, cream of rice, gatorade, corn flakes, baby food.... basically foods that will hit my stomach and be absorbed as quickly as possible. I can handle lean ground meats, white rice etc. a few days per week, but not daily, which allows me to eat a bit more normally when I'd like to. I also supplement with magnesium, vitamin d, vitamin k2, potassium, iodine and a quality multi-vitamin, this is important as obviously this is a very low-nutrient way to eat, so you want to make sure all your vitamin/mineral needs are adequately met.