I don’t really know much about what dieticians do, so I suppose it would depend on the context.
If they were advising me how introduce new foods to a pick eater - yes
If they were advising me what to look for on food labels to avoid allergens or manage a specific medical condition - yes
If I genuinely did not know what foods to eat to maintain a healthy weight - yes, but who really falls into that camp now?
If I needed support to lose weight - no, sorry, their own weight would have the effect of casting doubt on how usable their advice was