Customers don't know what they want. There's plenty of good psychology research that shows that people are not able to accurately predict how they would behave in the future. So asking them 'Would you buy my product if it had these three features?' or 'How would you react if we changed our product this way?' is a waste of time. They don't know.
If I'm playing in the morning I'll get some carbs early: porridge with chopped banana. If I'm playing in the afternoon I'll start with less carbs and have some eggs and fruit for breakfast then a light lunch about 90 minutes before I play so I don't feel sluggish or full.