Can I eat at restaurants at all on this budget?

Only if they are 'shokken' (ticket machine) style shops where you pay at a kiosk. Avoid any place where you are handed a menu or have to pay at a register.

Is 2,000 yen enough for healthy food?

Yes, if you shop at supermarkets. You can buy bananas, fresh produce, and pre-packaged salads to supplement your carbohydrate-heavy gyudon dinners.

How to Eat for 2,000 Yen a Day in Japan

You can easily eat for 2,000 yen a day by leveraging convenience store breakfasts, supermarket lunch discounts, and filling 'gyudon' (beef bowl) chains for dinner. Avoid sit-down restaurants with table service, as these will quickly double your daily food budget.

Hit the convenience stores (konbini) for breakfast. Go to 7-Eleven, Lawson, or FamilyMart. Buy a triangular rice ball (onigiri) for 150 yen and a carton of milk or coffee for 150 yen. Total: 300 yen.
Shop for marked-down lunch items. Visit a supermarket (like Life, Aeon, or Seiyu) between 11:30 AM and 1:00 PM. Look for 'bento' boxes with yellow discount stickers, which take 100-200 yen off the price. You can find a solid lunch for 500-600 yen.
Use 'Gyudon' chains for a hot dinner. Go to Matsuya, Yoshinoya, or Sukiya. A regular-sized beef bowl (gyudon) with miso soup and pickled ginger typically costs 500-600 yen. It is fast, hot, and filling.
Manage your beverage costs. Do not buy drinks from vending machines (160 yen per bottle). Carry a reusable water bottle and fill it at your accommodation, or buy 2-liter bottles at the supermarket for 100 yen and refill a smaller bottle.

Can I eat at restaurants at all on this budget?: Only if they are 'shokken' (ticket machine) style shops where you pay at a kiosk. Avoid any place where you are handed a menu or have to pay at a register.
Is 2,000 yen enough for healthy food?: Yes, if you shop at supermarkets. You can buy bananas, fresh produce, and pre-packaged salads to supplement your carbohydrate-heavy gyudon dinners.