While alcohol/drugs and sugar trigger some of the same neurotransmitters and same part of the brain in many people, there are a number of variables at play. There is variability in response to different chemicals (sugar vs heroin) and behaviors (sexual gratification vs gambling) across the population, so while the same general principles of biochemistry and neurology do apply, not every individual responds to the same stimuli with the same intensity, likely b/c of genetic variation, social conditioning, and one's history of personal behavior (e.g., whether one ever formed a habit of relying on food or booze to fill emotional needs).
Personally, I am unsure if cravings exist on a continuum, or if there is actually a particular brain process that is unique. What I think of as cravings feels quite distinct from simply 'wanting to eat/do' something that has the potential to be harmful or 'addictive'. For example, I will sometimes mindlessly overeat or eat more sugar than I meant to out of 1) lack of attention; 2) boredom; 3) succumbing to impulse when someone offers me dessert; 4) b/c there's a large amount in the house, etc. But that does not feel at ALL the same to me as when I crave alcohol...food has never triggered that kind of feeling in me except as a small child before my brain fully developed. If I 'catch' myself over-reating sugar, it's relatively easy to stop myself from eating it even if part of me kind of wants to eat it. And if I really prioritize not eating it, I am not constantly bothered by thoughts of it or urges to eat it.
Whereas, what I think of as 'cravings' for booze seem very intrusive...constantly pushing into my head when I've already decided not to drink. They are distracting and accompanied by a sort of internal voice that wants to rationalize why drinking would be ok, despite my resolution not to. They create (or used to) a palpable sense of anxiety/anger/grief at the prospect of denial.
That's really different from my experience with any of the other things that are classified as addictive, with the exception of sex. I can remember a similar fixation on sex with my SO during the early, charged up days of a romantic relationship...constant distraction, real anxiety/grief/anger if we had to be apart and couldn't have sex frequently, etc.
In addition, cravings for booze came with a feeling of my 'logical risk-averse' brain literally going offline...like I had trouble actually remembering all the reasons I'd told myself not to drink. For a while I started carrying a list with me, so I could pull it out during a craving, but then it would be like a switch had flipped in my brain and, even looking at the list, I had trouble mustering up any emotional reasons to abide by it. I had similar feelings about sex early in a relationship...my emotional brain didn't care if it was 'risky' (missing class, in public, skipping work, etc.) b/c the desire seemed to just shut down the part of my brain that would weigh consequences. (This is one big reason that people make bad decisions about birth control even though they absolutely plan to use birth control). True story; when my husband and I were first having sex after we met in college, his brain got so scrambled that he actually totally forgot he was even enrolled in one particular class and didn't go for about 3 weeks! Like one of those stress nightmares come to life. The crazy thing was, he was in his late 20s, an exemplary grad student at the time, with a long history of being super responsible and working in dangerous, high stress conditions under pressure to perform. But it was like he had some form of insanity during the early weeks we were together. He only remembered his class b/c the professor passed him in the hall one day and asked where the fuck he'd been for the past month.
There is in fact neurological evidence that cravings of that intensity actually DO 'turn off your logical brain'. I was just recently reading about how superactivation of the nucleus accumbens acts like a circuit-breaker that turns down/off function of the pre-frontal cortex (which is the part of the brain that weighs risk and self-regulates behaviors).
So that would explain all the stupid shit we are at risk of doing when in the grips of a neurotransmitter binge in our nucleus accumbens. Whether it's sex or drugs or gambling or sugar or internet or shopping or what have you that really lights up the nucleus accumbens...I think that's more of an individual thing.
