'feel' is a quality lacking from existing food trackers like MyFitnessPal. While I'm not aware of having any food allergies, I track how I feel when I train in the 'notes' box on MyFitnessPal so I can assess the impact of diet/sleep/training volume on performance. This works for me and makes sense in the context of food allergies.

Trying to spot an allergy also won't require the level of detail of MyFitnessPal/similar so I like the stripped down interface.