There's some good news if you're about to start the gluten-free diet: plenty of people half or more in my experience start to feel better within just a few days.
However, that doesn't mean you'll be back to feeling absolutely normal within a week's time. It will take a lot more time than that to recover completely, especially if you had severe celiac disease symptoms prior to being diagnosed.
Many people report their digestive symptoms start to improve within a few days of dropping gluten from their diets. Fatigue and any brain fog you've experienced seem to begin getting better in the first week or two, as well, although improvement there can be gradual.
Other symptoms, such as the itchy rash dermatitis herpetiformis, may take much longer to clear up.
You may feel constantly hungry during the first several weeks you're gluten-free, and you may want to eat all the time. This is completely normal it's your body's way of trying to make up for not being able to absorb food. Your ravenous appetite should calm down eventually.
You may also find that you feel significantly better for a few days after starting the diet, but then experience a strong recurrence of your symptoms. If this happens to you, check your diet for hidden gluten it's quite possible you've accidentally ingested some. It's common for your reactions to gluten even to a tiny bit of gluten to be very bad once you've gone gluten-free. You'll need to guard against gluten cross-contamination at all times, but don't worry that soon will become second nature for you.
In addition, to feel better sooner, you may need to address any celiac-caused malnutrition. Lots of celiacs find they have vitamin and mineral deficiencies at diagnosis that can interfere with their well-being. Talk to your doctor about what supplements you should consider, and make sure to use only gluten-free vitamins.
Although you should start to feel a little better quickly, it takes most people who were very sick prior to diagnosis a long time months, usually to feel completely "normal" again. Don't get discouraged if you don't bounce back immediately; if you continue to see gradual improvement, you're going in the right direction. However, if you don't feel as if you're making enough progress, talk to your doctor about your ongoing symptoms.
Celiac Disease Center at Columbia University. Frequently Asked Questions. Accessed Jan. 7, 2012.