Originally Answered: Upon switching to a gluten-free diet, how long does it take for the intestines to heal? (for a 25 yr old male)?
Average time for an adult diagnosed celiac is 6-12 months, but it can take up to 2 years.
Getting gluten contamination means around 1-2 weeks of healing for a healthy celiac. It may mean a bit longer to heal from a not-yet-healed celiac, because it's kind of a double whammy. You need to heal the damage, but the damage also limits the nutrients that you need to use in order to heal. So the fewer nutrients you have, the slower the healing. It doesn't typically knock you back to 0, although some folks get much worse damage, so perhaps they might have that issue.
It's important to note here that getting 'knocked back' can have more side effects than expected, because of that lack of nutrients. If you catch an illness during this time period, for example, you'll have less resources to fight it off. This can result in a higher likelihood of complications, like sinus infections after a flu, or pneumonia after a bout of bronchitis. If you are injured, it will affect your ability to heal as quickly as normal, or as well. That sort of thing.
Also, it's good to know that severity of gut symptoms doesn't always equal severity of damage. Sometimes it does, but some people can get almost no symptoms and lots of intestinal damage, and some get severe symptoms but very little intestinal damage. It's a weird, mixed-up disease.
Oh, and one last thing. The healing I'm talking about it actually NOT the time it takes to resemble healthy, non-gluten intolerant individuals (well, for a celiac). That's what it takes to get the VILLI to heal. Or at least, for the physical structure to heal.
The villi also make enzymes we use, like lactase and a sucrase. So celiacs can be lactose intolerant, or have problems digesting lots of sugars. These may take longer to come back. Also, celiacs tend to have low levels of good gut bacteria. These can take years and years to come back properly, and some don't seem to do it at all without help (celiacs have a hard time recovering gut flora after antibiotics, too). I've never met any doctors who worry about helping celiacs with this, although I'm sure there have to be some of them somewhere or the studies wouldn't have been done in the first place. But looking at ways to improve your gut flora would probably be useful, too.