For some people diet can play a role in their acne. For me it does and I'm still experimenting. Stress definitely causes me 3-4 cysts, I've noticed it a few times.

For example, I've kept this strict diet for 7 months now: I haven't had sugar, dairy, chips, fast-food, oceanic fish, high glycemic index food, corn, eggs, bananas, grapes, nuts, almonds, soda, sweets, pasta, pizza potatoes etc. None, zero. The worst breakout I had was about 3 weeks ago, it wasn't much, about 7-8 cysts that went away in maximum 15 days. I'm pretty sure it was from drinking over 1L/day of orange juice (Pfanner, no added sugar).

It did help as my face was pretty clear, but my dermatologist told me I have to keep it for the rest of my life. I'm now starting to eat everything again and see how my body reacts. I went from having severe acne to having clear or almost clear face. But then again, the diet might not have been what did the trick, for some people is not working. It might have been the antibiotics and creams I used for a few months when I changed my diet, or I'm simply out growing acne. Or it might just come back any day now. My dermatologist told me that you have to be fully committed, otherwise it won't work, you have to cut out completely these foods, basically eat like a diabetic. It is worth to give it a shot for a few months, but I'm not willing to keep it for the rest of my life.