Each character has a minimum weight, and it's generally best to keep them at that weight (or as close as possible) on the rereleases. On the vintage models, weight doesn't matter and you can safely eat snacks up to 99 oz/g.
Babytchi/Shirobabytchi - 5 oz/g
Marutchi/Tonmarutchi- 10 oz/g
Tamatchi/Tongaritchi - 20 oz/g
Kuchitamatchi/Hashitamatchi - 20 oz/g
Mametchi/Mimitchi - 30oz/g
Ginjirotchi/Pochitchi/Nyatchi - 30 oz/g
Maskutchi/Zuccitchi - 30 oz/g
Kuchipatchi/Hashizoutchi - 20 oz/g
Nyorotchi/Kusatchi - 10 oz/g
Tarakotchi/Takotchi - 20 oz/g
Secret Characters - 30 oz/g