"I'm really happy, because it's been unofficial since Tokyo and now I'm formally named. I feel like I can start now heading to my big goal," Noguchi said.
The 21-year-old Nakamura won her debut race at Sunday's Nagoya marathon in 2:25.51. But Sydney Olympic champion Naoko Takanashi finished 27th, ending her dreams of competing in Beijing.
Nakamura said she feels a "heavy responsibility" but is "ready to work harder."
"Four years ago, I was never able to imagine that I can take part in the Olympics," she said.
Tosa said she planned to "refresh" for the August Games.
"Hopefully, I can line up in the starting position without any injuries," she said.
The men's squad will be led by Tsuyoshi Ogata, who took fifth at the world championships in Osaka last year.
The other two men are Atsushi Sato, third at the Fukuoka marathon, and Satoshi Osaki, third at the Lake Biwa marathon.