Human nutrition investigates nutrients requirements, their function, their contents in different foods, and their relationship with health.So,it may be discussed at length.
Agree that any statement should be supported by data.But data always speak the truth if not assessed unbiasedly..Our tradition,belief and culture going on for ages can't be ignored as these are based on experiences.
Rice as staple food without the wholewheat is not healhty. It lacks vitamins B. In case of fish it can be claimed if they contain EPA and DHA and essential amino acids. If wholewheat with fish is eaten it can be that people are more energetic...but as to what??? A varied diet is the best.
Provided the fish is not contaminated by mercury, fish is the best brain food. However larger fish including tuna and shark are more likely to have higher concentrations of mercury than smaller fish because larger fish eat smaller fish..
It is old saying that a person learns from hard work , struggles , rejections. And I think our achievements also make us energetic. If rice and fish would have any impact on energy level we would have lot of Einsteins and lot of Nobel prizes and many more gold medals in Olympic. It can be considered as stereotype. People who do yoga mostly avoid such diet and are very energetic.