Were you told this by a GP OB/GYN or by an ENDOCRINOLOGIST......information on this subject has changed so much over even the past 2-3yrs and many doctors who are not endos or diabetologists still go by the old school of management which basically bans all sugar. The GI approach which is the result of many years of actual scientific research not just previous theory that the simpler the carbohydrate the worse it is for you will teach you how to eat to smooth the curve of "glucose" uptake into the bloodstream which reduces the stress load on the pancreas. For example a banana actually has quite a high GI and is absorbed quite rapidly into the bloodstream creating those high sugars you talk about showing up on the monitor. Another example ...a boiled potato has a higher GI than most forms of chocolate and dark chocolate is actually low GI and an acceptable food for a daibetic where previously this wasn't thought to be so. There are o lot of threads on here that talk about it...I don't know how to post links but there was a good one in the general pregnancy discussion thread not so long ago. To correct your facts just a tad... fat delays digestion and actually lowers the GI of a meal (still is bad for you though...hehe) and Gestational Diabetes does not lead to "proper" diabetes in later life...it may lead to Type 2 Diabetes. It would be a very very rare occurence for it to lead to Type 1 being as type 1 is an auto immune disease much much rarer and serious than Type2.
Btw are your Aunt and Grandad Type 1 or Type 2?