The phrase cancer diet can be used to refer to several different approaches to the associations between cancer and nutrition. Some people think of a cancer diet as a preventive approach to cancer or a way to lower one’s risk of cancer by avoiding foods associated with specific types of cancer. Cancer diet may also refer to the special diets or nutritional therapy prescribed for cancer patients to prevent them from developing malnutrition as a side effect of their cancer therapy. Last, cancer diet is sometimes used to refer to complementary and alternative (CAM) approaches to cancer that involve the use of special diets and nutritional supplements. The best-known of these are the macrobiotic diet, a largely vegetarian diet that originated in Japan; and the Gonzalez regimen, an alternative therapy for pancreatic cancer. The Gonzalez regimen includes a special diet, nutritional supplements, pancreatic enzymes in capsule form, and coffee enemas.
The purpose of preventive cancer diets is to lower an individual’s risk of cancer, particularly cancers of the digestive system. The purpose of nutritional therapy for cancer is to minimize loss of appetite, tissue wasting, and other symptoms of the disease or side effects of treatment; to help the patient tolerate cancer treatment; to protect the functioning of his or her immune system; and to maintain or improve the patient’s quality of life. The purpose of the Gonzalez regimen and other CAM dietary therapies for cancer is to treat the disease itself rather than its symptoms or the side effects of mainstream cancer therapies.
As of 2009, the evidence indicates that diet is second only to tobacco as a preventable cause of cancer. The World Health Organization (WHO) and the National Cancer Institute (NCI) both estimate that between 30% and 40% of all cancers in developed countries and 20% of all cancers in the developing countries are related to dietary factors. Diet has been linked not only to cancers of the mouth, esophagus, stomach, intestines, and rectum, but also to cancers of the prostate, breast, kidney, liver, and pancreas.
Cancer accounts for 7.1 million deaths worldwide each year, or 12.5% of the global total. About 20 million people around the world are presently living with cancer; this figure is expected to rise to 30 million by 2020. More than half of all new cancers occur in the developing countries. The greatest single risk factor for cancers related to diet is not race or sex but socioeconomic status (SES); cancer risk factors are highest and survival rates are lowest in groups with the least education.
People concerned to lower their individual risk of cancer by changing their diet should consult their primary care physician, or a reliable source like the American Cancer Society (ACS), the National Cancer Institute (NCI), or the World Health Organization (WHO) to be sure that they have up-to-date information about the relationships between cancer and nutrition. Patients being treated with nutritional therapy as part of cancer treatment should follow the recommendations of their doctors and dietitians. People considering CAM therapies for cancer should find out as much as they can about these approaches and talk to their primary care doctor before using them. They should not use CAM therapies as substitutes for mainstream cancer treatments
Diet as a cancer preventive
Dietary changes as a preventive measure for lowering an individual’s risk of cancer are sometimes called an anticancer diet, although this term does not have a precise definition. Most recommendations for lowering one’s risk of cancer through changing one’s eating patterns include the following:
- Eat less total fat and avoid hydrogenated fats—the type of fats often used to prepare fast foods.
- Choose foods that are high in fiber, such as wheat bran, kidney beans, garbanzo beans, navy beans, whole wheat, whole grains, legumes, whole-grain bread, and prunes.
- Eat large amounts of fresh fruits and vegetables, particularly the cruciferous vegetables (broccoli, cabbage, Brussels sprouts, mustard greens, kale, and cauliflower).
- Switch from red meat to fish; if possible, move from a meat-based to a vegetarian diet.
- Use olive oil rather than oils containing saturated fats when cooking.
- Choose foods that are high in calcium.
- Drink less alcohol.
- Consider using dietary supplements or foods reported to reduce cancer risk. These include vitamin D, selenium, green tea, and garlic.
One mainstream approach to diet that is often recommended as a way to lower cancer risk is the Mediterranean diet. The Mediterranean diet is better described as a nutritional model or pattern of food consumption rather than a diet in the usual sense of the word. There is more than one Mediterranean diet, if the phrase is understood to refer to the traditional foods and eating patterns found in the countries bordering the Mediterranean Sea. In general, however, Mediterranean diets have five major characteristics:
- High levels of fruits and vegetables, breads and other cereals, potatoes, beans, nuts, and seeds.
- Olive oil as the principal or only source of fat in the diet.
- Low to moderate amounts of dairy products, fish, and poultry; little use of red meat.
- Eggs used no more than 4 times weekly.
- Wine consumed in moderate amounts—two glasses per day for men, one glass for women.
These characteristics are in line with most of the recommendations of so-called anticancer diets. It is important to remember, however, that diet is not the only risk factor for certain types of cancer. Occupation, environmental factors, and heredity also influence a given individual’s risk of developing cancer. Thus changing one’s diet to reduce the intake of high-risk foods and eating more foods associated with lowering one’s cancer risk is not a guarantee that one will never develop cancer.
Nutritional therapy for cancer
Nutritional therapy for cancer patients is intended to help them maintain normal energy levels and avoid malnutrition. Appetite, taste, smell, and the ability to eat enough food or absorb the nutrients from food may be affected by the symptoms of the disease itself or by the side effects of treatment. Cancer patients frequently experience such symptoms as loss of appetite, nausea and vomiting, constipation, diarrhea, sore mouth, trouble swallowing, and depression. The most common nutritional problems in cancer patients are failure to eat enough high-protein foods and failure to take in enough overall calories.
The most common cause of malnutrition in cancer patients is anorexia, or loss of appetite, It may appear together with cachexia, a wasting syndrome in which the person loses weight, muscle, and fat tissue. Cachexia is not the same as starvation. A healthy person’s body can adjust to starvation by slowing down its use of nutrients, but the body cannot adjust in this fashion in cancer patients with cachexia.
Nutrition therapy for cancer patients may be very different from standard guidelines for healthful eating. It is tailored to each patient’s individual nutritional needs, response to cancer treatment, and personal food preferences. Patients who cannot take foods by mouth may require enteral nutrition (tube feeding) or parenteral nutrition (nutrients infused directly into the bloodstream through a catheter). Those who can take foods by mouth may need to change their eating habits by having several small meals a day rather than one large one; by taking medications for such problems as nausea, vomiting, constipation, or diarrhea; by drinking extra fluids to cope with such problems as dry mouth or changes in the sense of taste; and by adding as many high-protein, high-calorie foods to the diet as possible. Good choices include cheese and crackers, puddings, muffins, nutritional supplements, milk shakes, yogurt, ice cream, and chocolate.
CAM dietary therapies
The Gonzalez regimen is an alternative dietary therapy for pancreatic cancer developed by Nicholas Gonzalez, a physician in New York City. It is a complex combination of dietary changes, various nutritional supplements, and detoxification procedures.
- Diet. In general, the diet in the Gonzalez regimen requires the patient to consume mostly organic foods, and avoid such synthetic and refined foods as white flour and white sugar. The diet is, however, tailored to each patient. There are ten basic diets with 90 variations, ranging from nearly vegetarian diets to diets high in meat and fat.
- Supplements. These may include vitamins, minerals, trace elements, antioxidants, animal glandular concentrates and other food concentrates. Like the diet, the combination of supplements is also customized for the individual patient.
- Proteolytic enzymes made from pig pancreas. The basic theory underlying the Gonzalez regimen is that toxins from processed foods and environmental sources are responsible for cancers in humans, and that the pancreas is the organ primarily responsible for detoxifying the body. Gonzalez maintains that these pancreatic enzymes, taken in capsule form, enter the bloodstream and help the body eliminate and destroy malignant cells, waste material, and abnormal proteins that are toxic to the body. Overall, a cancer patient on the Gonzalez regimen will take between 150 and 175 capsules per day of nutrient supplements and pancreatic enzymes.
- Coffee enemas, taken twice daily. Gonzalez maintains that these enemas serve to detoxify the body by improving liver function and stimulate the gallbladder to empty, thereby speeding up the elimination of toxins and waste products.
The macrobiotic diet is a diet based on heavy consumption of whole grains, vegetables, soy products, seaweed, beans and bean products, mild flavorings, fruit, fish, nuts, and seeds. All products used should be locally grown whenever possible and processed as little as possible. The specific foods are selected according to the time of year, the climate, the person’s sex, age, and activity level, and their overall health status. The macrobiotic diet developed in Japan from traditional folk medicine. It was given the name ‘‘macrobiotic’’ in the 1950s by George Ohsawa (1893–1966) and brought to the West in the late 1950s.
The macrobiotic diet was first touted as a cure for cancer by one of Ohsawa’s disciples, Michio Kushi (1926– ). Kushi wrote a book about the macrobiotic diet as a cancer preventive and treatment, titled The Cancer Prevention Diet: The Macrobiotic Approach to Preventing and Relieving Cancer and first published in 1993. The website of the Kushi Institute includes personal testimonials from people who maintain that their cancers, ranging from uterine and pancreatic cancers to leukemia and brain tumors, were cured by following the macrobiotic diet.
The Gonzalez regimen is based on the theories of William Donald Kelley (1925–2005), an orthodontist who developed pancreatic cancer in 1962 and claimed to have cured himself by a combination of dietary changes along with pancreatic enzymes, an individualized diet of vitamins, minerals, and other nutrients, and detoxification by means of coffee enemas. Kelley’s theories were rejected by mainstream physicians, and his dental license was revoked in 1976.
The origins of the macrobiotic diet have been outlined in the previous section.
There are no known risks to eating a healthful diet in order to reduce one’s risk of cancer nor in following the nutritional recommendations of one’s treatment team if one is being treated for cancer.
Gonzalez notes that patients on his dietary regimen frequently experience muscle aches and pains, low-grade fevers, skin rashes, and other flu-like symptoms. He attributes these to the body’s reaction to detoxification. Other reported side effects include bloating, gassiness, and indigestion.
The primary risk of following the macrobiotic diet is using it as a therapy for cancer instead of mainstream cancer treatment. Other people who have used it as a preventive diet to lower their risk of cancer have developed mild forms of malnutrition by failing to supplement the diet with vitamin D and vitamin B12, which are not available in sufficient amounts in the foods that are the mainstays of the macrobiotic diet.
Health care team roles
Dietary changes as a cancer preventive for individual patients should be overseen and monitored by a primary care physician and a dietitian. Dietary therapy for cancer patients is usually designed and modified by a treatment team that includes a dietitian as well as doctors and nurses.
Patients with pancreatic cancer who are interested in the Gonzalez regimen should consult their present treatment team before contacting Dr. Gonzalez. Similarly, patients already diagnosed with cancer should consult their treatment team before using a macrobiotic diet as cancer therapy. The ACS ‘‘strongly urges individuals with cancer not to use a dietary program as an exclusive or primary means of treatment.’’
Research & general acceptance
The World Health Organization (WHO) has summarized recent findings about the relationship between lifestyle and dietary factors and cancer as follows:
- Convincing evidence for lowering cancer risk: Regular physical activity.
- Convincing evidence for increasing cancer risk: Overweight and obesity.
- Probable evidence for lowering cancer risk: High consumption of fresh fruits and vegetables.
- Probable evidence for increasing cancer risk: Excessive alcohol consumption; salted and preserved meats; highly cooked rather than rare or raw meats; fermented fish; very hot (temperature) drinks and food; and aflatoxins (toxins produced by fungi sometimes found in peanuts, grains, and tree nuts).
- Possible or insufficient evidence for lowering cancer risk: Plant fiber, soya, fish, omega-3 fatty acids, carotenoids, vitamins B2, B6, folate, B12, C, D, E, calcium, zinc, selenium, and non-nutrient plant constituents.
- Possible or insufficient evidence for increasing cancer risk: Animal fats, heterocyclic amines (chemicals found in well-cooked meat), polycyclic aromatic hydrocarbons, and nitrosamines.
Evidence for CAM dietary therapies for cancer is considerably lower than that for preventive dietary modifications. The NCI’s summary of the Gonzalez regimen states that ‘‘Existing clinical data concerning the effectiveness of the Gonzalez regimen as a treatment for cancer are limited and inconclusive,’’ primarily because of the small size of the subject groups and the lack of a control group. In August 2009 a group of researchers in New York and Boston reported that patients following the Gonzalez regimen survived only a third as long as those receiving conventional chemotherapy and had a lower quality of life. There are no data as of 2009 regarding the effectiveness of the Gonzalez regimen in treating other types of cancer. There is one clinical trial of the Gonzalez regimen underway as of early 2010.
The macrobiotic diet is generally considered ineffective as a treatment for cancer. The ACS states, ‘‘After studying the literature and other available information, the American Cancer Society has found no evidence that macrobiotic diet is useful as a cure for cancer in humans.’’ This position was reinforced by the fact that the wife and daughter of Michio Kushi both died of cancer (as did two physicians who claimed to have cured themselves of cancer by following the macrobiotic diet) and that Kushi himself had a cancerous tumor removed from his intestines in 2004. There are no clinical trials of the macrobiotic diet as cancer therapy as of 2009.
Caregiver concerns include making sure that a cancer patient receiving nutritional therapy at home is following his or her dietary guidelines, and consulting the patient’s doctor if the patient expresses interest in CAM dietary therapies.
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- Aflatoxins—A group of naturally occurring toxins produced by fungi of the genus Aspergillus.
- Cachexia—Unintentional loss of body weight and muscle mass, and weakness that may occur in patients with cancer, AIDS, or other chronic diseases.
- Enteral nutrition—The medical term for tube feeding.
- Gonzalez regimen—An alternative therapy for pancreatic cancer that includes a special diet, nutritional supplements, pancreatic enzymes, and coffee enemas.
- Macrobiotic diet—A diet based primarily on whole grains, vegetables, and beans, and avoiding refined or processed foods. It is sometimes recommended by practitioners of alternative medicine as a preventive for cancer.
- Parenteral nutrition—Providing a person with necessary nutrients through intravenous feeding.