Truth: Your body and symptoms should guide you.
There are two groups of people who absolutely must cut gluten. People who have the autoimmune disorder celiac disease need to strictly avoid it, because even small amounts cause their immune system to damage or destroy villi, the tiny, fingerlike outgrowths that line the small intestine. When villi get damaged, they can’t absorb nutrients properly, which can lead to pain and extreme fatigue. If you have celiac (which can be diagnosed with a blood test and biopsy of the small intestine), nixing gluten is the only way to reverse the damage and ensure you get the nutrients you need from food.
What if you test negative for celiac but feel crummy when you eat bagels, pasta and the like? You may have non-celiac gluten sensitivity (NCGS), which can cause rashes, bloating, mental fogginess, and fatigue. There is no universally accepted test for the condition, though, so if you think you have it, the only solution is to completely avoid gluten and monitor how you feel; consult a registered dietitian for help. (Adding to the confusion, it’s also possible to be allergic to wheat, which means you have an immunologic reaction that shows up through conventional allergy testing; you must drop wheat from your diet, but you may still tolerate gluten-containing foods like barley and rye.)