Fact: We don't know much scientifically about how nutritional or herbal supplements may interact with chemotherapy. Some could be harmful. There is some suggestion that certain vitamins, including folate, when taken in excess, may counteract the effects of some chemotherapy drugs. The best strategy is to consume a diet that's as healthful as possible, including lots of vegetables and fruit. If your loss of appetite is keeping you from eating well for more than a few days, you might consider taking a multivitamin to help you get the vitamins and minerals you need. Check the label and look for a multivitamin that doesn't give you more than 100 percent of the Daily Value (DV) of all the vitamins and minerals.