Some years ago a doctor told me citrus fruits contain milk sugar, which experience tells me is the case. I have never seen any reference to it in the literature. A girlfriend who is LI claims that chicken contains lactose and causes the exact same symptoms for her as a nice big glass of milk. I think she's whacked. This information is missing from the literature because there is no foundation to it.
Milk sugar is found in milk and nowhere else in nature.
The sugar in citrus fruits is fructose. You bet she is. Lactose comes from milk. But people with LI often have problems with other foods and confuse the symptoms. All that happens is that the lactose, the sugar in milk, is broken down to its parts.