Gluten, dairy, soy, and nightshades (potatoes, eggplants, peppers, tomatoes) create toxicity or inflammation in the system, says Lipman, and when you remove them, generally you feel better. (Don't think you have a gluten sensitivity? Lipman says most people aren't aware they are because "their symptoms often aren't even related to the GI tract.")
Dairy and soy are relatively straightforward to cut, but as for gluten, you'll need to read labels carefully: Besides the usual culprits – wheat, rye, oats, spelt, couscous, bulgur, and semolina – gluten frequently appears as "modified food starch," "hydrolyzed vegetable protein," or "texturized vegetable protein." What's wrong with tomatoes, potatoes, peppers and eggplants? Some people have sensitivities to nightshades without realizing it – all have inflammation-inducing alkaloids.