your hypothesis seems to be that a lack of carbohydrates (read: sugar) caused an individual to develop diabetes, but "diabetes" generalizes down to:
- the body (pancreas) does not produced insulin at all (type I)
- the body's cells are resistant to the produced insulin (type II)
we should be able to basically rule out type II because there should have largely been no insulin produced by this individual (glucagon would take priority due to low blood sugar), so insulin resistance seems super unlikely. and type I has a mix of factors but they are largely all autoimmune, where various pancreatic cells are destroyed by the body itself, causes generally unknown.
"losing the ability to process sugar" seems really sketchy, because those are all critical cellular processes that don't just go away. i realize you're probably not biologically trained but that statement doesn't make a whole lot of sense.
so which form of diabetes did this individual get diagnosed with?