It takes anywhere from seconds to years. It depends on the issue, the person, their diet, and their lifestyle. Lierre Kieth, for instance, felt better the instant she started eating meat again--the tuna was like prana in a can. (Sadly, her back pain from the damage caused by long-term B-12 deficiency will never go away.) There have been a lot of 30-day challenges out there: 30-day paleo, 30-day Whole 9 , even 30-day gluten-free from Dr. Guyanet. (He actually had a terrific blog before he started going on about food reward.) I think these challenges last long enough to get allergens out of your system and let you see if re-exposure bothers you, yet they're short enough to seem manageable. Thirty days is more than long enough to begin clearing up GI problems caused by food. My GERD disappeared within a few days of starting a low-carb diet, and two days on a fat fast cleared up my gastritis. Some issues can take much longer. Almost a year ago, two of my teeth were knocked out of ...
Do-it-yourself health. Low-carb, mostly evolutionary.