First of all there is no such thing as too much oxygen. There is over breathing which is caused by hyper ventilation but not too much oxygen.
So it makes more sense to battle against the causes of hyperventilation than against the by products of hyperventilation.

Secondly, adopting a certain diet is just like any other diet. It's a regimen. If a person has a metabolic illness like diabetes - then I'd say that they have no alternative but to watch their glucose rates in the food, carbs, etc'. But, if a person had ENS only - the benefit from a certain diet will be minimal if at all to their symptoms. So, in large the extra suffering and self punishment of putting yourself on an "ENS diet" in my opinion and physical and mentla health philosophy - is simply not worth it and far worse - can raise false hope and cause people doing it to focus their time energy and beliefs on the wrong things.