If you were eating more than a bite, you might expect the sugar/high low to give you some odd symptoms. But if you're literally eating a "bite", unless it's a large bite of pure sugar, it might be a food sensitivity or even just plain placebo/psychosomatic pain - you expect sugar to screw with you, so you're more aware of otherwise innocuous stuff.

I know insulin is taking a beating these days, but it does play a role in regulating water retention, so if you suddenly swap to a high carb diet you may end up with a dehydration headache (water being sucked up to make glycogen -> moderate dehydration). That's my totally unscientific explanation for my own carb headaches, which go away when I drink some water. But I usually only get those when I eat a pretty big bolus of carb, not from "a bite".

This happened to me when I was vlc. It was like being allergic to sugar!

Once I increased my carbs to around 30-60 gm/day, the problem disappeared.

A rapid drop in blood sugar levels (hypoglycemia) has been correlated with headaches (National Headache Foundation) and can be triggered by the consumption of high glycemic foods.

Blood sugar spikes, insulin is released, and then blood sugar crashes.

This may be exacerbated by the skeletal muscle insulin resistance that may occur when fasting/in ketosis.

Interesting. I was in ketosis when I had 2 pitted Medjool dates with almonds and goat cheese for dessert the other night and within 20 minutes I had a splitting migraine!

Before going Paleo, just one donut would give me a headache all day long...granted, a donut is packed with sugar. 8)

Now, one cup of "conventional" hot chocolate will give me the same headache...I am sure it's a sugar headache as well and my body is letting me know how much it hates it (even if my taste buds enjoy it).

Your one bite sounds extreme, though, especially in the case of fruit. Are you sure there's not some preservative/additive in these bites, perhaps in the applesauce or the chocolate?

it may be psychosomatic or something but i experienced a slight headache also while eating 2 servings of kobari beef from panda which has about about 10g of sugar each. I think I am on ketosis as I seem to be behaving better on my 90-95(slight relapse into atkins) percent palio diet. And most carb cravings have receded. I thought the kobari beef might be paleo-able, but I ate it before examining the nutrition carefully. I knew immediately it had more sugar than I desired but I hoped that it was negligible, I felt a minor headache almost immediately and like the good hyperchondriac I am I immediately consulted google, and thus I am hither. So there may be some substance to this immediate headache, that betrays the ketiotic.(i made up that word, ha ha)

weird i also am in ketosis and had several strawberries and had small headache above my right eye and i very rarely get headaches so was concerned so looked it up. I was thinking maybe there was some chemicals on the strawberries that i was getting the headache from. goes away and I can go without them i guess or just expect it to happen. glad to see its not just me. comfort in numbers i guess. am very intersted in getting to be a fat burner and not a sugar burner. would be happier if i felt better getting there but took a while to get here so will take a while to get through i suppose. anybody else read Ron Rosedale info about fat burning vs. sugar burning? I thought it was very informative and was wondering if someone has gone through it & what to expect.