The healthiest foods can be a range, fruits and vegetables. The best for you is fruits with low-sugar and with vegetables low carbs.
I have steel cut oats and blueberries for breakfast. Yogurt and fruit for lunch. For dinner, I think genmai is best, and usually have it with grilled chicken breast and a salsa which incorporates many vegetables. Diabetics usually eat very healthy, so just pick up a cook book written for diabetics.
Just check on the net what those folks eat who has the longest lifespan. Like Crete in Greece, Sardinia in Italy, Okinawa in Japan, Seventy day adventinsts in Cali...probably they figured out something about healthy diet
A think a good source of healthy food should be carbohydrates (spaguetty, rice, potatoes, bread, fruits, etc.) and proteins.
Vegetables and Fruits are most healthiest foods. Avoid junk food and start to eat more and more vegetables and fruits.