A diet is a plan or strategy for eating certain foods. Anything added to your regular diet to improve your health is called a dietary supplement. Some examples are:

• Vitamins.
• Minerals.
• Amino acids.
• Natural hormones.
• Enzymes and live microbials (often referred to as "probiotics").
• Herbs and other botanicals.

There is no scientific evidence that a person's diet can cure cancer. But you may get medical nutrition therapy from a registered dietitian as part of your regular health care. Your body's needs can be met by eating a balanced diet.

Some supplements might help decrease cancer risk. But there's no clear evidence for this claim. Many such claims made by the makers of some supplements. But they are not scientifically proven. And some supplements might interfere with the safety or effectiveness of some cancer treatments. Be sure to let your health care provider know about any supplements you take before starting treatment. This includes multivitamins.

Some diets and supplements may have side effects, especially if you take high doses. These include weakness, diarrhea, or kidney problems. Following diets that your provider or dietitian has not approved may be unsafe. But this may be more true during cancer treatment. Talk with your provider or registered dietitian before making any changes to your regular diet.

Below is a list of some dietary supplements. Always talk with your provider before taking any of these:

• Vitamins. These are needed in small amounts for the body to grow and stay strong. They include vitamin A, vitamin D, vitamin C, and vitamin E.
• Minerals. These are elemental nutrients. They are needed to stay healthy. They include calcium, magnesium, and zinc.
• Antioxidants. These protect the body's cells from damage caused by free radicals. Free radicals are byproducts of the body's normal chemical processes.
• Enzymes. These are proteins made by the body. They start and speed up chemical processes, such as digestion.
• Amino acids. These are the building blocks of the body's proteins. Proteins are needed for growth and development. Some amino acids are made by the body. Others come from your diet. Examples are tryptophan and glutamine.
• Plant extracts. These are sometimes used to help nourish the body. Followers of the principles of Chinese medicine may use them. Traditional Chinese medicine works to restore a balance of energy, body, and spirit for good health. When cancer causes imbalances, people who use Chinese medicine may try herbs, minerals, and plant extracts as treatment.
• Hormones. These are chemicals made in glands in the body. They affect how organs and tissues work.
• Herbs. These are sometimes called botanicals. They are plants used in food preparation or for medicinal purposes, such as ginseng and St. John's wort.
• Homeopathic products. These are very small doses of natural substances, often herbs, diluted with water or alcohol. Homeopathic medicine is based on the belief that what causes symptoms in a healthy person can cure the same symptoms in someone who is not healthy. These products are used to start healing, not to stop symptoms.

You can find dietary supplements at grocery stores, health food stores, and drug stores. They come in many forms, such as:

• Tablets.
• Capsules.
• Liquids.
• Power bars.
• Cookies.
• Powders.
• Elixirs.

Not all dietary supplements available over the counter are proven to be safe.

Each supplement is different. Most are not scientifically tested. So the side effects are unknown. Many cancer experts advise that you not use vitamins or other dietary supplements. Be sure to tell your provider if you were already taking dietary supplements before the cancer was diagnosed. Some supplements may interfere with your treatment.

Some supplements can make your skin more sensitive. This can be a problem for people getting radiation treatment. Other supplements may increase the risk of bleeding. That can cause problems after surgery. People in chemotherapy (chemo) may have more side effects depending on what supplements they take. Some supplements can make chemo work less well.

Herbal supplements are products made from plants. They are a type of dietary supplement containing 1 or more herbs. Herbal supplements may contain entire plants or plant parts. They are used in managing some health problems. Many prescription and over-the-counter medicines are also made from plants. These products contain only purified ingredients. And unlike herbal supplements, they are closely regulated by the FDA.

Herbal supplements come in all forms. They may be dried, chopped, powdered, or put in a capsule or liquid. They can be used in various ways, including:

• Swallowed as pills.
• Brewed as tea.
• Put on the skin as gels.
• Added to bath water.

The practice of using herbal supplements dates back thousands of years. But they are not for everyone. In fact, some herbal products may cause problems for people getting cancer treatment. Because they are not regulated by the FDA or other agencies, the use of herbal supplements is controversial. Don't take any herbal supplements without first talking with your provider.

The FDA considers herbal supplements to be foods, not medicines. So these products don't get the same testing, manufacturing, and labeling standards and regulations as medicines.

Don't self-prescribe. Talk with your provider before taking herbal supplements.