Let's say someone says that they want to know if going vegan or vegetarian would reduce their symptoms if they suffered from some specific disease or allergy.
If there is evidence that this is so, or even evidence that it has no effect then clearly we can point to research that shows this.
Is it appropriate to point out non-vegetarian diets that may benefit them? How far should we go here?
It seems deceitful to tell them they could go vegan and reduce their symptoms a little if it's known that some other non-vegetarian diet might reduce their suffering even more. On the other hand non-vegetarian diets are kind of off-topic here rather by definition.