The body can eliminate free radicals naturally, but it may have difficulty eliminating all of them. Cell damage can result, and this can lead to health problems. However, if too many free radicals build up in the body, it can cause a condition known as oxidative stress. Environmental exposures also cause the body to take in free radicals. The body naturally produces unstable molecules called free radicals during metabolism. These play a key role in balancing and maintaining many systems in the body. Romaine lettuce is a good source of vitamins C and A, which are antioxidants. Share on Pinterest Romaine lettuce is an excellent source of antioxidants.