What Japanese food is the healthiest?
I'd like to introduce you a very healthy one pot dish; 水炊き（みずたき）"mizu-taki." 水（みず）"mizu" means water and 炊（た）き is a noun form of 炊く "taku" boil/ cook. You can use any part of chicken you prefer.
【Materials】(for 2 person)
Chicken: 3 pieces (cut in bite size and dip into boiling water for a moment to remove its smell)
Nappa (or Napa) cabbage: 3 leaves (cut in bite size)
Cabbage: 3 leaves (cut in bite size)
Carrot: 1/3 (round slices)
Tofu: 1/2 [not indispensable]
Green Onion: 2 pieces (chopped)
Cellophane Noodles (Saifun Bean Threads): 1 (boiled and cut twice)
Water: 1.5 litter (6 cups. Adjust to your pan size.)
Chicken Gara soup (or Chicken bouillon): 1.5 TBS [not indispensable]
Salt: a few sprinkles
Nanami Togarashi (Assorted Chili Pepper) [not indispensable]
1) To make Nappa cabbage sweeter, you should bake it at 150 ℃（300°F）for about 10 minutes.
2) Put chicken into the water with Gara soup and salt (*). Cook for about 30 minutes and turn off the heat and rest it for 30 minutes. [This process makes the meat tender.]
(*) You eat this dish with Ponzu later. So soup and salt shouldn't be strong. If you don't have the substitution for the soup, only salt is enough.
3) Add veggie from tough one like carrot first. Then thick part of Nappa cabbage→soft part of it→Cabbage→Tofu, Cellophane Noodles, Green onion etc.
4) Eat it with Ponzu and Nanami Togarashi.
People rave about how healthy natto (fermented soybeans) is. Soy beans in general are pretty good sources of protein and fermentation adds more micronutrients or healthy bacteria as I understand it.
I wonder if other pickles like umeboshi (pickled plums) are also good. They might have too high a sodium level, but again, going on the pickled principle, shouldn't be too bad.
Japanese also have a lot of health drinks. For example, they have daily vegetable intake drinks that you can pick up in cartons or individual packets at convenience stores. I'm not sure they replace actually eating vegetables, but it's a good supplement on the go for a day or so.