Your food on the best and worst days is calculated based on your symptom score. For the analysis to work, you must track food and symptoms for at least 6 days.
The list of foods on you best and worst days will display foods you tracked at your best / worst 3 days (best days = symptom score low / worst days = symptom score high).
Note here that any food you ate before the symptoms occurred will also be displayed. This means that the foods listed serve as an indication of triggering foods, but have to be checked individually.