Hi Melissa. You don't say whether it was a relatively "clean" dark chocolate, or whether it might contain soy lecithin or added color or flavor. Food allergy is a common cause of mouth ulcers (canker sores). It could be the cacao itself, or some added ingredient. Other common causes of canker sores include stress, autoimmunity or hormonal fluctuations. I would certainly consider an insulin spike to be an hormonal fluctuation. In a shameless cross-referential plug to one of my own questions, I'll suggest that it could be the dreaded "Nocebo Effect" ( http://paleohacks.com/questions/1354/beware-the-nocebo-effect ). However, the most common cause of mouth ulcers is idiopathic (unknown).

Eating Paleo for a while will eventually cause some degree of insulin resistance as your body gets better adapted at using fat for fuel instead of using lots of glucose. Unfortunately, that means when you do eat a bunch of carbs at once, you can get a spike of both insulin and blood glucose. Those, in turn, can play havoc with many different systems in the body, including the immune system -- which might explain your canker (having had them myself, my understanding is that their underlying cause is usually viral). Gut issues are another common response.

If you'd like to follow-up, you might get a blood glucose meter, and check your level before eating, and then again an hour later.

BTW, if you're prone to cankers, the thing that finally cured them for me was to eliminate toothpastes that contain sodium lauryl sulfate, which is a foaming agent. It doesn't work for everyone, but it was 100% effective for me.

I was discussing this with a friend only yesterday - yes, like alcohol or drugs, as time goes by you need more and more of it to get that hit. I was definitely on the more rather than the less side and I now, having been on the paleo diet for a while, even the tiniest bit of sugar sends me back down into depression and moods and I too, get sores in my mouth.

So it seems that just a small amount of sugar will now produce very noticeable symptoms, whereas before those symptoms may have been just part of every day life - if you rasie the notch on healthy living, when the bad bits come back to haunt you, they feel 100% worse than they ever were before when your overall level of health was not so good.

I read that the mouth and tongue, sinuses, skin and reproductive organs (in women) are used as waste disposal units when the system gets overloaded with crud (that's why at the time of menopause, women can have terrible symptoms, as their body tried to find another way of eliminating toxins from their system as the uterus no longer can perform that function). So I suspect it is your mouth that is the route the sugar is taking to leave your body in this instance - and check your period next month, it could be worse than normal.

Canker sores are common in people who are gluten intolerant. Are you? Sometimes chocolate has barley malt added to it in tiny amounts.

I can't eat sugar anymore as it makes me exhausted.

I found this thread by typing "I eat sugar, I get mouth ulcers" in a google search. I'm glad to find I'm not alone in this. I happen to eat very low carb (specifically, low simple sugar) due to candida issues and have done so for 3 years, which has improved my health dramatically. I do indulge in a little frozen yogurt once a month, which seems to send my immune system on a ride and I may develop a mouth ulcer or two. Even lighter sweet treats produce the same effect. Annoying. Sweet potatoes with some cinnamon seem like the only 'sweet' thing I can really handle without a reaction.

Without further examination nobody can tell you that. Try different brands, try different sugars. Also, you didn't say how much is the bar in grams. You might have been living too much on lowcarb and now high carb will rise your blood sugar for prolonged time, this is typical because pancreas produces insulin based on 1 week trends or something. Extra blood sugar means LOW immunity which might cause your canker sores. I don't think you are overly sensitive to insulin. Allergy might be an option but its easy to rule out by switching brand.

This is experienced by all popular lowcarbers that I know of. Check this out: http://goo.gl/epJYO

hi i am also having problem of mouth ulcer only whenever i eat any sweet thing ,else if i don't take any sweet my mouth is normal .this symptomeshas appeared since i was 17 and become severe at 21 now i am male and at 27 and problem is getting severe. anybody please suggest me ............