There's a folk saying that eating fish makes you smarter.
Tips
usage
说法 is incredibly versatile: (1) a way of expressing something (换一种说法 = rephrase it), (2) someone's version of events (他的说法 = his account), (3) a folk belief or saying (有一种说法 = there's a saying that...).
usage
The pattern X法 creates 'way of X-ing': 做法 (way of doing), 看法 (viewpoint), 想法 (idea/thought), 写法 (way of writing).