PURPOSE: To obtain an assistant food effective for promoting the action of vitamin B12 to repair a damaged nucleic acid and prevent the aging by adding aspergillus produced in Southern Kyushu to steamed unpolished rice, inoculating the obtained malt to effect the fermentation and drying and crushing the fermented product.

CONSTITUTION: Unpolished rice cultured without using agrichemicals is washed with water, steamed for 45min with pressurized steam in a steaming pot by conventional method and allowed to cool. The steamed rice is inoculated with solid malt prepared by using an aspergillus produced in Southern Kyushu (Aspergillus oryzae sp.) and fermented at 40°C for 50hr. The fermentation product is dried and crushed to fine powder to obtain the objective assistant food for promoting the effect of vitamin B12 to repair damaged nucleic acid in the body and prevent the aging of the body. As necessary, the assistant food for promoting the effect of vitamin B12 is incorporated with one or more components selected from serine or phosphoserine (phosphatidyl-serine), tryptophan and vitamin B12 which are liable to become deficient in the body.