Approximately one-third of all cancer deaths can be attributed to poor diet and inactivity, according to the ACS. The good news is that you don't have to be a total gym rat to reap the rewards of reduced cancer risk. A June 2012 study published in the journal Cancer found that even mild physical activity before or after menopause can reduce breast cancer risk. Women who exercised 10 to 19 hours per week experienced the greatest benefit with an approximate 30 percent risk reduction. Intensity level didn't matter—a brisk walk is just as worthwhile as a spinning class that leaves you drenched in sweat. Just be sure to keep your diet in check: Weight gain can eliminate the beneficial effects of exercise on breast cancer risk.