The mechanisms of action for rapamycin and metformin are different. While rapamycin directly inhibits mTOR, metformin indirectly inhibits it by inhibiting the respiratory chain.
Metformin is popular as it is used to reduce cancer rates on diabetics, however, there are assumptions that need to be validated such as its effects as a pro-lifespan agent and if it is beneficial for all tissues of the body. There are cohort studies that show differences between patients taking and not taking Metformin, but randomized controlled trials are needed.
Lifestyle changes such as reducing alcohol consumption, not smoking, maintaining a healthy weight, and regular exercise can lead to a 15-20% reduction in the incidence of cancer and a 20-30% reduction in mortality or extension of survival once diagnosed with cancer.