Coffee does dehydrate. As soon as I notice the early symptoms of a migraine I need to stop drinking coffee/alcohol and avoid sugary things.
Starving your body of something it is used to is a bad idea. I advocate slow transitions to allow your body to adjust. The only exception to that would possibly be addiction treatment as in some cases cold turkey is the only option. But food?
No, diets are bollocks. Eat sensibly. And when there is cake on offer, have it. Just don't go overboard eating crap. It really is that simple.
After all, if the body has to gain energy by slowing down other parts of the body (e.g.: a headache, or allowing a virus to take hold) in order to cope with adjusting from having something to having nothing, it can't possibly be good for you. We faint if we get too low in blood sugar, we go in to shock when we lose to much blood. Both of these responses are designed to allow this amazing machine a.k.a. our body to keep us alive by diverting all energy to our vital organs.
Sensible people treat that machine with respect. That means sensible people do not:
- take weight loss tea/coffee/tablets
- have meal replacement shakes instead of a balanced meal
- starve yourself for a long(er) period of time
- stuff your body full of supplements or drinks (Aloe gelly anyone?) that have no scientifically proven benefits
But of course all of the above is rocket science to some...