It was not until the mid-twentieth century that some researchers began to consider the role of dietary factors in cancer. Walter Willett, chair of the department of nutrition at the Harvard School of Public Health, outlined four stages in thinking about diet and cancer in a lecture he delivered to the National Cancer Insitute (NCI) in 2012. In the first stage, the 1960s, scientists focused on carcinogens in food, particularly chemicals produced by barbecuing and other high-temperature methods of cooking. In the second stage, the 1980s, dietary fat was considered the most likely villain because it had been linked to heart disease and diabetes. Willett notes, however, that present data do not support the notion that the type or amount of fat in a people's diets is linked to their cancer risk.
The third stage, the 1990s, concerned the role of fruits and vegetables in the diet as cancer preventives. Willett states that fruits and vegetables are nutritious in a number of ways, but their specific benefit as cancer preventives is “probably very small and limited to certain foods and certain cancers.” The most recent area of research is the relationship between obesity and cancer. Although the number of cancers attributable to overweight and obesity is about equal to the number attributable to smoking, according to Willett, “on an individual basis, however, the cancer risk due to smoking remains substantially higher than that due to obesity.” Research in the 2010s began looking at diet across the lifespan, not just the diet of adults in the age brackets in which cancer is most likely to appear, to see if the eating patterns of pregnant women, infants, children, and adolescents can be linked to cancer in later life.
According to the National Cancer Institute (NCI), 1,685,210 new cases of cancer were diagnosed in the United States in 2016 (the most recent year for which data are available), and 595,690 people died from the disease. The number of new cases each year in North America is 454.8 per 100,000 population for both men and women. Cancer accounts for 8.8 million deaths worldwide each year, or 13% of the global total. In 2015, 90.5 million people around the world were diagnosed with cancer, according to the World Health Organization (WHO). More than half of all new cancers occur in developing countries. The greatest 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 lowest levels of education. The greatest single risk factor in general, however, is age; most invasive cancers worldwide are diagnosed in adults over age 65.
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 a person's risk of cancer through changes in eating habits were developed since the 1960s and include the following:
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:
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 factor associated with certain types of cancer. Occupation, environmental factors, and heredity also influence a given individual's risk of developing cancer, and changing the diet does not guarantee that a person will never develop cancer. The National Cancer Institute notes that “studies of human populations have not yet shown definitively that any dietary component causes or protects against cancer…Study participants with and without cancer could differ in other ways besides their diet, and it is possible that some other difference accounts for the difference in 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, especially chemotherapy. 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 total 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, fat tissue, and muscle mass (sarcopenia). 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, or diarrhea; by adding as many high-protein, high-calorie foods to the diet as possible but balancing this with high-fiber foods to prevent constipation; by drinking extra fluids to cope with such problems as dry mouth or changes in the sense of taste. Good choices for those who need extra calories include cheese and crackers, puddings, muffins, nutritional supplements, milk shakes, yogurt, ice cream, and chocolate.
Conversely, some cancer patients gain weight from stress eating because they are anxious and fearful about their diagnosis. The Academy of Nutrition and Dietetics advises these patients to consult their healthcare providers about other ways to manage stress. The Academy notes that most cancer centers in Canada and the United States offer free or low-cost psychotherapy, massage, art therapy, or other ways to manage the emotional stress of living with cancer.
Some complementary and alternative (CAM) dietary therapies are promoted as cancer treatments.
Readers should note, however, that little scientific evidence supports these therapies. Patients should never take it upon themselves to replace any prescribed treatments with CAM therapies without first consulting their physicians.
GONZALEZ REGIMEN. 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:
MACROBIOTIC DIET. The macrobiotic diet is a diet based on the 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; and the person's sex, age, activity level, and 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 (1926–2014). 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. Yet, Kushi himself died of pancreatic cancer.
The function of general recommendations for a healthful diet is to help all people maintain a healthy weight and good nutritional status across the lifespan, which reduces the risk of heart disease and type 2 diabetes as well as cancer. The function of special diets for patients diagnosed with and undergoing treatment for cancer is to maintain a healthy body weight without excess loss or gain due to the side effects of therapy and to maintain the patient's nutritional status as much as possible.
Although the relationship between diet and an individual's risk of cancer is unclear as of 2018, the general benefits of healthful eating patterns are known to include a lowered risk of such chronic diseases of adult life as cardiovascular disorders, type 2 diabetes, and other complications of obesity.
The benefits of following a specialized diet overseen by a physician and a dietitian as part of cancer therapy include an increased chance of long-term survival and greater well-being during treatment itself.
As the number of cancer survivors continues to increase, people in this category should watch their weight and try to keep it at a healthy level for their age, sex, and height. While some may need to gain weight, survivors of breast and ovarian cancer often find that they have gained weight during treatment as a result of drug therapy and that the weight is difficult to lose. The Mayo Clinic advises survivors to speak with their doctor first and then to lose the weight slowly—no more than 2 lb. (.91 kg) per week—through a combination of diet and exercise.
No known risks have been noted to eating a healthful diet to stay at a healthy weight and reduce the risk of cancer, nor in following the nutritional recommendations of the treatment team if being treated for cancer.
The primary risk of following either the Gonzalez regimen or the macrobiotic diet is premature death due to using them as a therapy for cancer instead of mainstream cancer treatment. In regard to the claim that the macrobiotic diet can prevent cancer, some 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 main-stays of the macrobiotic diet.
Recent research has discredited the Gonzalez regimen and largely ignored the macrobiotic diet as treatments for cancer. Neither the ACS nor Cancer Research UK recommend the macrobiotic diet as cancer therapy, and both organizations note that any well-balanced plant-based diet offers the same health benefits as the macrobiotic diet. No active clinical trials of the macrobiotic diet were underway as of 2018, and the single trial of the Gonzalez regimen was terminated in 2013. The trial's sponsoring institutions reported that patients on the Gonzalez regimen survived on average only 4 months with low quality of life compared to patients receiving mainstream chemotherapy, who lived on average for 14 months with satisfactory quality of life. Gonzalez himself died in 2015, and his office was closed. Although the Gonzalez Foundation still maintains a website ( http://www.dr-gonzalez.com/index.htm ), no evidence showed that any patients were being treated with the regimen as of 2018.
Another dietary intervention that is being studied more intensively as of 2018 is the effect of fasting or calorie-restricted diets on cancer patients. The theory underlying this approach is similar to that associated with the ketogenic diet, namely that calorie restriction weakens cancer cells and thereby increases the effectiveness of standard radiation and chemotherapy. Twenty-three clinical trials of fasting and calorie-restricted diets were being tested as adjunctive therapies for cancer patients and potential aids to the longterm survival of cancer patients who have completed standard therapy. Most of these trials are being conducted in the United States, Germany, and the Netherlands.
Relatively little, however, is known as of 2018 about the role of diet in cancer recurrence or the longterm life expectancy of cancer survivors. Researchers possess too little evidence about the survivors of most types of cancer for generalizations to be possible other than the general benefits of a high-quality rather than a typical Western diet.
See also Antioxidants ; Calorie restriction ; Cancer ; Cancer-fighting foods ; Carotenoids ; Dietary supplements ; Ketogenic diets ; Macrobiotic diet ; Malnutrition .
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American Cancer Society, 250 Williams St. NW, Atlanta, GA, 30303, (800) 227-2345, http://www.cancer.org .
International Agency for Research on Cancer (IARC), 150 Cours Albert Thomas, Lyon, France, 69372 CEDEX 08, +33 04 72 73 84 85, http://www.iarc.fr .
National Cancer Institute, BG 9609 MSC 9760, 9609 Medical Center Dr., Bethesda, MD, 20892-9760, (800) 422-6237, https://www.cancer.gov .
National Center for Complementary and Integrative Health (NCCIH), 9000 Rockville Pike, NIH Campus, Bldg. 31, Bethesda, MD, 20892, (888) 644-3615, https://nccih.nih.gov/tools/emailnccih , https://nccih.nih.gov .
U.S. Food and Drug Administration (FDA), 10903 New Hampshire Ave., Silver Spring, MD, 20993, (888) 463-6332, https://www.fda.gov/AboutFDA/ContactFDA/default.htm , https://www.fda.gov .
Rebecca J. Frey, PhD