Hi wondering, welcome to healing well forum, glad to have you. The thing that caught me about your post was that you said "abrupt change in diet"...well, as Geebs said this can disrupt your body. You should always speak to your doctor before starting any diet as you want to get their input first and make sure that you blood levels are normal...all that jazz, get a physical done. Most people dont but it is recommended and low blood sugar can lead to all sorts of nasty feelings.
I would consider speaking to your doc...eating smaller portions and spacing them out 3-4 times a day. You can eat actually 4 or 5 times a day if you eat smart. You dont have to starve yourself. Take care