Its fully possible. Evolutionarily speaking our bodies were developed to seek the high-energy-dense foods (namely sugary and fatty foods) because those were the best things for us at that time, what with the spontaneous bouts of starvation etc etc.
That's one reason overweight/obesity is so rampant nowadays - we still have that biological need of our neolithic ancestors to go for the sugary, fatty foods, but we no longer have the environment suited to that need. We have sugary, fatty foods everywhere, no need for fasting while tracking wild animals and foraging! Everyone KNOWS to eat healthy - so why don't just go be healthy? Because biologically its difficult (I am a huge believer in personal responsibility, I may believe this but I don't believe it is the only conrolling factor and it is definitely not biologically impossible to be healthy.)
So your body could just telling you what it thinks you need. I know there are chemicals (leptin, ghrelin, etc) that control appetite and satiety. I don't know if there are tests for this, but if you can find out, see if you could get tested for leptin - thats the one that corresponds with the amount of fat on your body and controls the hunger signal. Its supposed to tell you brain to stop eating and to lower your appetite when you've eaten enough and when you have enough body fat (you're not going to stop eating altogether, but just not as much as if you were extremely thin.) It also works the other way, it tells your body/brain when you need to eat.
(Interestingly on a related tangent - there have been tests done on women with amenorrhea (they don't menstruate) while at a normal weight. After being given experimental injections of leptin, they began cycling immediately. I have amenorrhea though at 5'3" and 125 lbs, I have plenty of body fat to be menstruating - but genetically speaking I am underweight (my whole family is, essentially, overweight/obese, so I have to be on the pill in order to have a cycle).
Now that you've lost about 40 lbs, your body might be going into hyper-mode with the leptin thing - we're losing weight! quick eat something! why aren't you eating something? eat a damn doughnut for chris'sake!!! doughnut doughnut doughnut!! aaahhhh!
Why a SPECIFIC item? Perhaps that could be an emotional thing - personally, oreos were a childhood favorite of mine. I don't binge on them, but I could hazard a guess at why you do and why your therapist would suggest emotional eating - maybe you do have some emotional connection to them. Your binging may have the basis in biology, but its utilizing emotion to guide what you eat. Its a two-pronged problem.
This is why when people do extreme dieting (like me when I first started binging in February - 500-900 calories a day + running 3 miles) suddenly succumb to binging. Our bodies are panicking and sending signals at the lack of food that thousands of years ago (in fact, 100 years ago) we could ignore it, heck, we might not have even noticed it; today, surrounded by food and with the knowledge of what the health costs are of being overweight/unhealthy, it creates an environment that all our bodies want to do is stock up for the coming famine - that will never come.
You have such extraordinary will power - way to go to saying no! Its a challenge, but I would suggest kicking it up a notch and going and buying a doughnut, or a small package of oreos (or those 100 calories packs, not quite the same, but it might do the trick). Take them home and make a presentation with them - make it a special event - it would work especially if you maybe think of a reason for it. Maybe that week you gave a homeless guy some money, or you accomplished your exercise goals, or, hell, you didn't kill your boss because he was pissing you off or something, I don't know. Then slowly savor and enjoy the doughnut - don't wolf it down (that's my problem, I eat things WAY too fast, lol). Maybe succumbing once a week to these cravings may quiet them down - factor it into your diet plans (if you have any). Even if you add it on top of what you normally eat, one doughnut isn't going to ruin your life or your weight loss goal. It will help! A few years ago I lost 20 lbs (140 to 120) and I did it by not eating junk food during the week but going out and enjoying "ice cream fridays" with my friends. But, earlier this year when I flipped out, or something, and restricted myself, I have since gained 10 lbs due to the binging!
The irony!
You may be spot on with the chemical/biological thing - but don't entirely discount the emotional thing, either. There may be something there. I myself am realizing that I binge when I get stressed - and after a few months I can tell what days are going to be binge days from the moment I wake up (I just feel stressed. I get stressed easily, lol) - and now that I can tell that I'm learning to cope better with my stress and subsequently my binging. How tired are you? I know that if I don't get a good nights sleep I binge. On those days I make it a point to take a nap, and it really helps.
Ok, that was a lot, sorry! Hope it was a little helpful, though

Love yourself always,
MRose22