According to Kelly McGonigal in The Willpower Instinct, (p 40) 4-6 breaths per minute, or 10-15 seconds per breath for 1-2 minutes will increase your heart rate variability, which is a great predictor of whether alcoholics will relapse. EDIT: For anyone interested she cites the work of Suzanne Segerstrom, a psychologist at University of Kentucky. Apparently they have identified something like the opposite of the fight-or-flight response called the pause-and-plan response..
Yes, breathing is powerful thing. When im laying alone in bed with huge balls demanding for relapse that energy i imidiately focus on breathing, most slow breathing you can imaging and all fantzies sexusal thouths fade away, thats why meditation is very good in no fapp/no porn journey.