Longevity science

Ray & Terry recommend green tea as a healthy beverage containing calming l-theanine and many useful plant nutrients. 

Green tea has been examined for numerous potential health benefits, including glucose management, cognitive support, immune health, weight management, and cellular function.

This resource compilation by the University of Maryland explains the potential benefits and uses of green tea, complete with extensive references.

It is not a definitive  prevention and more research is needed to elucidate the health benefits. However, chocolate (the purer the better) may help keep the colon healthier.

"Chocolate is rich in a particular variety of plant polyphenols which are powerful natural antioxidants. Though many plant foods contain polyphenols, chocolate seems to have particular potent health-promoting and disease fighting effects. These compounds include procyanidins, catechins and epicatec...