Alzheimer's disease (AD) is the most common form of neurodegenerative disorders leading to dementia. Currently, there has been no effective drugs targeting this disease. Functional food is considered as a potentially non-pharmacologic treatment. In this project, the investigators aim to investigate the effectiveness of a mixed functional food with main compositions of ginsenoside, green tea polyphenols and marine collagen peptide on cognition for individuals with subjective cognitive decline (SCD). Taking the randomized, double-blind, placebo-controlled method, participants in the functional food group will take mixed functional foods for three months and those in the placebo group will take placebo. After that, the investigators will investigate the changes of cognitive function. Furthermore, based on the neuroimaging technique, the regulatory mechanism of functional food in intervening SCD will be revealed from the perspective of altered brain functional activity. In conclusion, these results are beneficial for understanding the therapeutic effect of mixed functional foods as a non-drug treatment for early AD and further elucidating the potential brain mechanism, which are of great values in solving scientific and clinical practice issues.