Healthy is a big wishy-washy purely contextual-based term. In my opinion, only diet is healthy or unhealthy, no particular food or restaurant is healthy or not. Healthy is a trendline of "what recommended allowances count as part of a nutritious, varied and balanced diet?".
Meeting AND not exceeding Recommended Daily Allowances (RDA)s on all nutrition types
Avoiding known carcinogenic foods such as processed meats
Fruit and vegetables "5 a day"
Calorie-counting and watching Body Mass Index (BMI)
Self-determining RDAs for items that don't have them, such as antioxidants
Acceptable Daily Intake (ADI) for specific E numbers that have known effects such as E129 Allura Red AC which can cause hyperactivity.
There is some conflicting advice:
'Smaller, more regular meals'
'Breakfast like a king, lunch like a prince, dinner like a pauper'
Maintain alkaline pH in mouth to prevent gingivitis / brushing teeth twice a day and leaving 30 mins before and after