The problem is finding the offending food(s).
Once you've found the sensitivity eliminating the offending food is easy.
Food sensitivities can show up in the strangest ways. Somebody can have a full-body rash for years on end, another has joint aches and pains, a third has recurrent coughs, a fourth has alopecia, and a fifth has ongoing explosive diarrhoea.
If you have strange troubles and the docs simply can't find a cause, try one or the other elimination diet.
If you have Crohn's, irritable bowel syndrome (IBS) and/or ulcerative colitis: do the elimination diets before things progress so far that parts of your guts rot (go necrotic) and have to be removed. Do this before you're cursed with a belly bag, because you don't have a colon anymore.
Honest. Severe sensitivities to foods are the cause of severe gut troubles, nevermind what docs believe (and tell you).
The three most common culprits
- Gluten. That's no gluten-containing products at all. So it's absolutely no wheat, rye, barley, and oats. Oats might be OK once things have calmed down. Spelt is wheat, and yes, it contains gluten. You'll find barley (as malt) in all beers, and you'll find rye in whiskey. Other alcohols are iffy: you don't know what that vodka is made of, nor do you have any idea what the herbal tincture base is. Wine is OK, though. Spaghetti is right out, as are most breads and cookies. Read labels, they put wheat flour into the strangest places.
And note, you can be severely sensitive to wheat without having celiac disease.
- Milk. That's no milk products at all - so it's absolutely no butter, cream, milk, cheeses, yogurts, sourcreams, and so on. Read labels, they put milk powder and/or lactose (= milk sugar) into the strangest things - for instance, prescription meds. If you have to have milk in your morning coffee, go for rice or oat milk, that doesn't come from cows. Lactose-free products aren't all that helpful, either, as about half of those sensitive to milk are sensitive to milk protein, not milk sugar.
- Solanaceous plants. That's no foods at all from the nightshade family: potatoes, tomatoes, chili (cayenne), sweet peppers (paprika), aubergines (eggplant), husk tomato, tomatillo and similar (various species of Physalis). There's a few others, but those are the most common solanaceous foods. Read labels, they put potato starch, cayenne, powdered sweet pepper, and tomatoes into the weirdest things.
There are others, of course, like citrus fruit, and eggs, and artificial colors (especially red), and so on. The three above are, however, unique in that we ingest something or other from these groups almost every day. That means that we don't notice that we get ill from them, and it also means that we are hooked on them, and want to eat them every day: a food sensitivity, if severe, gives the metabolism a good kick, without which we feel rundown. Luckily, that wears off after the first 10 days or so of absolutely and completely no severely sensitising food.
Which should you start with?
If you have joint pains and similar you should start with the solanaceous foods.
If your ancestry is weak on traditional milk drinkers (Germans, Danes, Swedes, Dutch, northern Swiss, Norwegians, Maasai, etc.) you should start with the milk products.
The elimination diets
The skin-prick tests of docs are generally a waste of time, for dietary sensitivities. No, what you should do is this:
For two full weeks, leave out all and any foods from one or the other of the most common food sensitivity groups.
Then, eat your normal diet for one week.
Did you feel better than you've felt for years during the last few days of the special diet? Did you feel lousy when going back on your normal diet? Right, you should stay off that particular food group for at least 6 months, totally and completely, to give your gut a chance to heal, totally and completely.
Then you can try to reintroduce parts of the food group - perhaps you can take tomatoes but not potatoes, perhaps you can do hard cheeses even if milk is out of the question, perhaps you can eat oats where wheat is a complete no-no.
Or was there no change in your general well-being at all? Right, it's on to the next food group then, and do 2 weeks totally without that particular group, then 1 week on a normal diet.
Then the next.
If these were all negative, next up is a test of both gluten and milk in one go: they might cross-react, and if you eat one while your gut is raw from the other you could have trouble with that one, too.
If that didn't help either you'll need to do a food diary, and try to track the offending foods down. That's very tricky. Honest, these three total eliminations are easier than keeping a food diary.
Trouble can show up for up to 10 days after you ingested an offending food, which is why the 14 day test. Also, you need to be consistent. One cookie can give you a 10-day flareup. One bit of milk in your morning coffee can give you 10 days of problems. It's also wise to use a dedicated cutting board for your bread for the gluten-free time; that way, you don't get bread crumbs from other breads. Yes, you really can be that sensitive.