A friend of mine who used to eat sugar, now cannot. She says anything with sugar or high glycemic index makes her break out in cold sweats and feel really bad. This is nothing about low carb, I was just wondering why sugar all of a sudden does this to her? She's a very fit person, no health problems seem to be present.

A person can develop a sensitivity to any food, drug or other substance at any point in their lives.
Still...I'd highly suggest that she pay a visit to her doc to find out if there is some biological cause (hypoglycemia, diabetes, etc...) for her symptoms. Until then...the usual advice my doctor gives me fits here: "If eating that bothers you, don't eat it.".

I think sugar would make me break out in a cold sweat now, too, after a few months away from it. Funny how you get used to feeling that way and you think it's normal, till it's gone for a while.

I ate tomatos for years and then one day I realized they were causing the cold sores I'd never had before. Don't eat tomatos, no cold sores. Don't know what made that happen, that year, but I do remember my great aunt was the same--only I only knew her after the allergy/sensitivity kicked in.

It could be that your friend is in the beginning stages of Type II diabetes or some other form of insulin resistance... I can remember when all I would eat was sugar and starches, now I get very tired and feel sickly after eating too many carbs in one sitting... It's not something that I want to relive very often, but it does happen on days when I just can't resist... Part of the reason for my feeling awful is the development of gestational diabetes during this pregnancy (a precursor to Type II) and part of it is that my body just isn't used to processing that much sugar all at once anymore, so it kind of goes into shock...

I definitely commend your friend for taking note as to what does and does not make her feel good... Most people that I've encountered tend to follow their stomach and ignore signs that some food just isn't good for you...

Thanks for the replies. They refuse to see a doctor, but staying away from sugar. It just baffeled me and I am the type of person that has to know why. Diabetes runs on both sides of her family, so that made me wonder if that is a sign. I have diabetes but don't get ill from sugar.

It sounds like your friend is suffering from a spike (and/or depression) in blood sugar after eating sugar or other high glycemic foods. She could either be feeling the effects of hyperglycemia whereby ingesting carbohydrates causes her blood sugar to spike up, or hypoglycemia, where her blood sugar falls after insulin rushes into her system to combat the sugar. Like Tink said, she could be developing or have developed Type II Diabetes.

When I have high glycemia foods, my blood sugar rises, then can fall suddenly leaving me feeling light headed, cranky, shaky, or not with it at all. When my blood sugar gets really low, I break out in a cold sweat. After that, I can pass out.

The symptoms are different for everyone, but I hope your friend is inclined to see a doctor and have a glucose tolerance test.