Nutrition and Cancer: What You'll Need to Know (2023)

By Dr Frank Yap, MD June 17, 2023

Most of us know Steve Jobs, Chadwick Boseman (Black Panther), Robin Gibb (Bee Gees), Donna Summer, Farrah Fawcett, Eartha Kitt, Peter Jennings, Paul Newman, Patrick Swayze, Sydney Pollack, Michael Crichton, Bob Denver, Ted Kennedy, Jerry Orbach, Anne Bancroft, William Rehnquist, and Tony Snow, just to name a few. What do they have in common? They all died from 'cancer'.

Most of them have access to the best possible medical care available in the world. What are we missing here? Is cancer still a mystery to mankind? Is cancer preventable?

Cancer is a complex and multifaceted disease that is still not fully understood by scientists and medical professionals. There have been significant advances in cancer research and treatment in recent years, and many types of cancer can now be effectively managed or cured with a combination of surgery, chemotherapy, radiation therapy, and other treatments. However, there are still many types of cancer that are difficult to treat and can be fatal.

Overall, while we have made significant progress in understanding and treating cancer, it is still a complex and often difficult disease that poses significant challenges for individuals and society as a whole. NIH-National Cancer Institute has a resource page for nutrition for cancer care for patients which are general recommendations and not personalized for cancer indication and treatments.

What is Cancer?

Cancer is the name given to a collection of related diseases. In all types of cancer, some of the body’s cells begin to divide without stopping and spread into surrounding tissues (National Cancer Institute).

Cancer is the second leading cause of death in the United States, behind only heart disease. People with cancer also often experience physical effects (from the cancer itself and from treatment), distress, and a lower quality of life.

For most Americans who do not use tobacco, the most important cancer risk factors that can be changed are body weight, diet, and physical activity. At least 18% of all cancers diagnosed in the US are related to excess body weight, physical inactivity, excess alcohol consumption, and/or poor nutrition, and thus could be prevented.

Genetic changes that cause cancer can be inherited from our parents. That said, environmental factors could contribute up to 95% of cancers. They can also arise during a person’s lifetime as a result of errors that occur as cells divide or because of damage to DNA caused by certain environmental exposures. Cancer-causing environmental exposures include substances, such as the chemicals in tobacco smoke, and radiation, such as ultraviolet rays from the sun.

There are many types of cancer treatment. The types of treatment that you receive will depend on the type of cancer you have and how advanced it is. Surgery, radiation, and chemotherapy are the standard types of treatment for cancer. While your cancer specialist is focusing on staging your disease, the type of surgery, radiotherapy or chemotherapy, many people tend to lose focus on their nutrition. There is also a lot of confusion due to the overwhelming mixing of credible scientific information and marketing hypes available on the internet.

There are also many phoney “cancer treatment” with amazing claims but devoid of any scientific data to back them up, typical of health scams. Cancer is a life threatening disease and therefore many consumers fell prey to these phoney cancer treatments.

Can foods and diet influence your risk of getting cancer? What types of foods reduce your risk and types that might increase your risk? What about vitamin and mineral supplements? Can supplements reduce your cancer risk or do they actually increase your cancer risk? Find out the answers below.

Benefits of good nutrition during cancer treatment

When you’re healthy, eating enough food to get the nutrients and calories you need is not usually a problem. Most nutrition guidelines stress eating lots of vegetables, fruits, and whole-grain products; limiting the amount of red meat you eat, especially meats that are processed or high in fat; cutting back on fat, sugar, alcohol, and salt; and staying at a healthy weight. But when you’re being treated for cancer, these things can be hard to do, especially if you have side effects or just don’t feel well.

Good nutrition is especially important if you have cancer because both the illness and its treatments can change the way you eat. They can also affect the way your body tolerates certain foods and uses nutrients.

During cancer treatment you might need to change your diet to help build up your strength and withstand the effects of the cancer and its treatment. This may mean eating things that aren’t normally recommended when you are in good health. For instance, you might need high-fat, high-calorie foods to keep up your weight, or thick, cool foods like ice cream or milk shakes because sores in your mouth and throat are making it hard to eat anything. The type of cancer, your treatment, and any side effects you have must be considered when trying to figure out the best ways to get the nutrition your body needs.

"Nutrition is the provision, to cells and organisms, of the materials 'necessary' (in the form of food) to support life." (Wikipedia)

Therefore, nutrition is not an option or a desire but rather a basic necessity. That makes it all the more important reason to make nutrition as part of your overall strategy to fight the cancer battle. Do not give up. Many people with cancer have been cured or survived longer than those without cancer.

The following are the essential things you should know about nutrition and cancer.

#1. Proteins

We need protein for growth, to repair body tissue, and to keep our immune systems healthy. When your body doesn’t get enough protein, it might break down muscle for the fuel it needs. This makes it take longer to recover from illness and can lower resistance to infection. People with cancer often need more protein than usual. After surgery, chemotherapy, or radiation therapy, extra protein is usually needed to heal tissues and help fight infection.

Good sources of protein include fish, poultry, lean red meat, eggs, low-fat dairy products, nuts and nut butters, dried beans, peas and lentils, and soy foods.

#2. Fats

Fats play an important role in nutrition. Fats and oils are made of fatty acids and serve as a rich source of energy for the body. The body breaks down fats and uses them to store energy, insulate body tissues, and transport some types of vitamins through the blood.

You may have heard that some fats are better for you than others. Choose monounsaturated and polyunsaturated fats more often than saturated fats or trans fats.

Monounsaturated fats are found mainly in vegetable oils like olive, canola, and peanut oils. Polyunsaturated fats are found mainly in vegetable oils like safflower, sunflower, corn, and flaxseed. They are also the main fats found in seafood.

Saturated fats are mainly found in animal sources like meat and poultry, whole or reduced-fat milk, cheese, and butter. Some vegetable oils like coconut, palm kernel oil, and palm oil are saturated. Trans-fatty acids are formed when vegetable oils are processed into margarine or shortening. Sources of trans fats include snack foods and baked goods made with partially hydrogenated vegetable oil or vegetable shortening. Trans fats also are found naturally in some animal products, like dairy products. Trans fats can raise bad cholesterol and lower good cholesterol; try to eliminate them from your diet.

#3. Carbohydrates

Carbohydrates are the body’s major source of energy. Carbohydrates give the body the fuel it needs for physical activity and proper organ function. The best sources of carbohydrates – fruits, vegetables, and whole grains – also supply needed vitamins and minerals, fiber and phytonutrients to the body’s cells. (Phytonutrients are chemicals in plant-based foods that we don’t need to live, but that might promote health.)

Whole grains or foods made from them contain all the essential parts and naturally occurring nutrients of the entire grain seed. Whole grains are found in cereals, breads, flours, and crackers. Some whole grains, such as quinoa, brown rice, or barley, can be used as side dishes or part of an entree.

Fiber is the part of plant foods that the body cannot digest. There are 2 types of fiber. Insoluble fiber helps to move food waste out of the body quickly, and soluble fiber binds with water in the stool to help keep stool soft.

Other sources of carbohydrates include bread, potatoes, rice, spaghetti, pasta, cereals, corn, peas, and beans. Sweets (desserts, candy, and drinks with sugar) can supply carbohydrates, but provide very little in the way of vitamins, minerals, or phytonutrients.

#4. Water

Water and liquids or fluids are vital to health. All body cells need water to function. If you do not take in enough fluids or if you lose fluids through vomiting or diarrhea, you can become dehydrated (your body doesn’t have as much fluid as it should). If this happens, the fluids and minerals that help keep your body working can become dangerously out of balance. You do get some water from the foods you eat, but a person should drink about eight 8-ounce glasses of liquid each day to be sure that all the body cells get the fluid they need. You may need extra fluids if you are vomiting or have diarrhea. Keep in mind that all liquids (soups, milk, even ice cream and gelatin) count toward your fluid goals.

#5. Vitamins and minerals

When it comes to vitamins and minerals it is confusing due to the many choices, claims and promises created by the healthcare supplement industry. While alluring claims and network marketing sell products, the products are not always suitable for cancer patients.

The body needs small amounts of vitamins and minerals to help it function properly. Most are found naturally in foods. Vitamins and minerals help the body use the energy (calories) found in foods.

A person who eats a balanced diet with enough calories and protein usually gets plenty of vitamins and minerals. But it can be hard to eat a balanced diet when you are being treated for cancer, especially if you have treatment side effects that last for a long time. In this case, your doctor or dietitian may suggest a daily multivitamin and mineral supplement.

If you are thinking of taking a vitamin or supplement, be sure to discuss this with your doctor first. Some people with cancer take large amounts of vitamins, minerals, and other dietary supplements to try to boost their immune system or even destroy cancer cells. Vitamins and minerals alone are not sufficient to fight cancer. Remember, nutrition is not about vitamins and minerals but there are other important elements (e.g. protein, water etc.) as well.

Clinical trials on vitamins and minerals are expensive, and have generally borne little fruit. One high-profile example is the Selenium and Vitamin E Cancer Prevention (SELECT) trial of a decade ago, which cost US$114 million and demonstrated no meaningful benefit. Exacerbating the problem is the lack of a strong business model: drug companies have little incentive to invest in trials of a product that is cheap and widely available.

Some of these substances can be harmful, especially when taken in large doses. In fact, large doses of some vitamins and minerals may make chemotherapy and radiation therapy less effective.

If your oncologist says it is OK for you to take a vitamin during treatment, it may be best to choose a supplement with no more than 100% of the Recommended Daily Value (RDV) of vitamins and minerals.

If you want to take in more antioxidants, health experts recommend eating a variety of fruits and vegetables, which are good sources of antioxidants. Taking large doses of antioxidant supplements or vitamin-enhanced foods or liquids is usually not recommended while getting chemo or radiation therapy. Talk with your doctor to find out the best time to take antioxidant supplements.

#6. Can antioxidant supplements help prevent cancer?

In laboratory and animal studies, the presence of increased levels of exogenous antioxidants has been shown to prevent the types of free radical damage that have been associated with cancer development. Therefore, researchers have investigated whether taking dietary antioxidant supplements can help lower the risk of developing or dying from cancer in humans.

Many observational studies, including case–control studies and cohort studies, have been conducted to investigate whether the use of dietary antioxidant supplements is associated with reduced risks of cancer in humans. Overall, these studies have yielded mixed results (Source). Because observational studies cannot adequately control for biases that might influence study outcomes, the results of any individual observational study must be viewed with caution.

Randomized controlled clinical trials, however, lack most of the biases that limit the reliability of observational studies. Therefore, randomized trials are considered to provide the strongest and most reliable evidence of the benefit and/or harm of a health-related intervention. To date, nine randomized controlled trials of dietary antioxidant supplements for cancer prevention have been conducted worldwide. Many of the trials were sponsored by the National Cancer Institute.

Overall, these nine randomized controlled clinical trials did not provide evidence that dietary antioxidant supplements are beneficial in primary cancer prevention. In addition, a systematic review of the available evidence regarding the use of vitamin and mineral supplements for the prevention of chronic diseases, including cancer, conducted for the United States Preventive Services Task Force (USPSTF) likewise found no clear evidence of benefit in preventing cancer (Source), published in 2013.

It is possible that the lack of benefit in clinical studies can be explained by differences in the effects of the tested antioxidants when they are consumed as purified chemicals as opposed to when they are consumed in foods, which contain complex mixtures of antioxidants, vitamins, and minerals (Source). Therefore, acquiring a more complete understanding of the antioxidant content of individual foods, how the various antioxidants and other substances in foods interact with one another, and factors that influence the uptake and distribution of food-derived antioxidants in the body are active areas of ongoing cancer prevention research.

Several randomized controlled trials, some including only small numbers of patients, have investigated whether taking antioxidant supplements during cancer treatment alters the effectiveness or reduces the toxicity of specific therapies (Source). Although these trials had mixed results, some found that people who took antioxidant supplements during cancer therapy had worse outcomes, especially if they were smokers.

In some preclinical studies, antioxidants have been found to promote tumor growth and metastasis in tumor-bearing mice and to increase the ability of circulating tumor cells to metastasize (Source, Source). Until more is known about the effects of antioxidant supplements in cancer patients, these supplements should be used with caution. Cancer patients should inform their doctors about their use of any dietary supplement.

#7. Safety considerations for nutrition and cancer

Many people believe that if they find a pill or supplement in stores, it is safe and it works. Remember, a 'natural' product does not mean its a 'safe product. Some poisons are also natural but they are certainly not safe.

The US Food and Drug Administration (FDA) put out rules in 2007 to help ensure that supplements contain what their labels claim they do, but the supplement’s safety and its effects on the body are not addressed by any FDA rules. The FDA does not make manufacturers of these products print possible side effects on their labels. And the FDA cannot pull a dietary supplement or herbal product from the market unless it can prove that the product is unsafe. Stop taking the product and call your doctor right away if you have side effects, like wheezing, itching, numbness, or tingling in your limbs.

Tell your health care team about any over-the-counter products or supplements you are using or are thinking about using. Take the bottle(s) to your doctor to talk about the dose, and be sure that the ingredients do not interfere with your health or cancer treatments.

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