Just because people don't have an M.D. doesn't make them automatically wrong. The patients that complain about gluten have access to information you do not have. Namely, they are able to experiment with their own diet. When they eat gluten, they feel bad. When they stop, they feel better. Who cares if it's placebo effect? If they feel better not eating gluten, tell them to stop eating gluten and support them in their decision instead of writing them off as part of a dietary fad.

And I certainly hope you have at least done some research on fructose metabolism before writing that woman off as a kook. Even if it is all in her head, you can make her at least happier, if not healthier by suggesting that she also avoid foods with sucrose or monomeric fructose, and substitute them with alternatives such as xylitol, glycerol, maltose, or ordinary glucose corn syrup.

If the patient is ignorant, that is a condition the doctor should be expected to cure. If the patient is stupid, they should find a less arrogant personal physician.