The optimal dietary pattern for cancer survivors—anyone who has ever been diagnosed with cancer, whether they are in treatment or maintenance therapy or long-term remission—is the plant-based diet that we should all be eating to lower the risk of developing several types of cancers in the first place as well as diabetes, heart disease and even dementia. (For people in active treatment, different dietary regimens may be indicated on a short-term basis, as we’ll explore in the next article.)
“Plant-based” doesn’t mean vegetarian—let alone vegan—although these can be healthy versions. A plant-based diet can include all types of animal-based as well as plant-based foods. The difference between a plant-based diet and the way many of us eat is that most of the calories come from whole grains, vegetables, fruits, beans and other legumes, nuts, seeds and vegetable oils, such as olive oil. It can include dairy foods, with a bias toward fermented types, such as yogurt and cheese; eggs; fish and seafood; and modest amounts of poultry. It generally includes only small amounts of red meat (if any), little or no processed or cured meats, little or no alcohol and little or no highly processed foods, such as packaged snacks and sweets, which tend to be low in fiber and high in salt and sugar. It is sometimes called the prudent diet.
Perhaps the most famous model is the Mediterranean diet. This term, which dates from the 1960s, refers to the dietary pattern that evolved over centuries in Southern Europe (such as Southern France, Italy and Greece), Northern Africa (including Morocco and Tunisia) and parts of the Middle East (such as Turkey and Israel). Healthy plant-based dietary patterns, have been identified throughout the world, including Asia, Africa and South America. They contrast with the so-called standard American diet (SAD), with its origins in England, Germany and Northern Europe, and generally eschew commercial food production, which tends to be high in meat, dairy and ultra-processed foods that contain few nutrients but plenty of salt and sugar and relatively few healthful fruits and vegetables.
The scientific evidence is strongest for primary prevention of cancer, according to Lorenzo Cohen, PhD, the Richard E. Haynes Distinguished Professor in Clinical Cancer Prevention at MD Anderson Cancer Center in Houston. “Together with the influence of weight and obesity, diet influences the development of prostate, breast, endometrial, colorectal and even lung and esophageal and head and neck cancers,” he says. “A plant-based dietary pattern results in less inflammation, leading to a lower risk of several cancers.”
The evidence for people during and after cancer treatment is less voluminous but points in the same direction, emphasizes Cohen. “Individuals in these epidemiological studies who are eating the prudent, versus the Western or standard American diet—that is, a plant-based, Mediterranean-style diet—tend to live longer and have a lower [rate of] recurrence of their cancers. It’s pretty consistent.” Epidemiological studies follow specific populations over time. They provide important information but can’t prove cause and effect.
“We know a lot from observational studies, but we don’t have a lot of clinical trials,” says Wendy Demark-Wahnefried, PhD, RD, associate director for cancer prevention and control for the O’Neal Comprehensive Cancer Center at the University of Alabama at Birmingham. The strongest evidence relates to weight control, she adds. “At least 13 different cancers are considered obesity-related.” The evidence is quite strong, especially for primary prevention. “For some cancers, such as endometrial cancer, there’s a several hundred-fold increase in risk for women with obesity. For postmenopausal women, obesity increases risk of developing breast cancer by about 10%.” But there is also evidence that obesity plays a role in cancer survivorship. (For tips on weight management for cancer survivors, see “Managing Cancer-Related Weight Gain.”)
Major cancer organizations have endorsed a plant-based diet for cancer survivors. The American Institute for Cancer Research (AICR), in conjunction with the World Cancer Research Foundation (WCRF), publishes respected guidelines for the prevention of cancer in the general population—and for cancer survivors as well. A 2022 report from the American Cancer Society (ACS), "Nutrition and Physical Activity Guideline for Cancer Survivors,” which Demark-Wahnefred contributed to, notes that “There is growing evidence that being physically active, consuming foods that reflect a healthy dietary pattern, and avoiding obesity after completion of cancer treatment improves long-term survival.” The ACS recommendations for cancer survivors include “maintaining a healthy body weight, being physically active, consuming a healthy diet, and avoiding or limiting alcohol.” The recommended dietary pattern is “rich in a variety of plant foods, such as vegetables, whole fruits, whole grains, and beans/legumes, but limited in or not including red and processed meats, sugar-sweetened beverages, highly processed foods, and refined grain products.”
The recommendation to limit alcohol reflects emerging evidence that alcoholic drinks are a risk factor for the development of many cancers. According to AICR, two or more alcoholic beverages a day increases the risk for colorectal cancer, three or more a day increases the risk for stomach and liver cancer and “there is limited but suggestive evidence that alcoholic beverages increase the risk of lung, pancreatic and skin cancer…[and] pre- and postmenopausal breast cancer.” For those undergoing cancer treatment, the report continues, “alcohol consumption can worsen side effects. Mouth sores, inflammation to the inside of the mouth, painful swallowing and diarrhea can all be exacerbated by drinking alcohol.” For those who have completed treatment, AICR recommends that it is best to talk with your health care team about consuming alcohol. “Studies are not clear if alcohol intake causes cancer recurrence, but alcohol consumption increases risk for a secondary cancer and other chronic disease, like liver disease and obesity.”
The ACS guidelines have some cancer-specific recommendations as well:
- For breast cancer survivors, there is evidence for “better survival among women with breast cancer who have a healthy body weight, are physically active, eat foods containing dietary fiber, eat foods containing soy.” However, the evidence that “fat intake or its subtypes are associated with mortality is inconsistent and limited.”
- For colorectal cancer (CRC): “A Western dietary pattern is related to worse survival after CRC.”
- For laryngeal, head and neck or hepatic (liver) cancers, “available evidence supports limiting or avoiding alcohol after diagnosis because alcohol increases treatment side effects and all-cause mortality among survivors of these cancers.”
- For prostate cancer, “Western, as opposed to prudent, diet patterns are associated with higher prostate cancer-specific and overall mortality, and a Mediterranean-style dietary pattern is associated with lower all-cause mortality among prostate cancer survivors.”
- There is insufficient evidence to recommend specific dietary patterns for survivors of ovarian cancer, lung cancer or blood cancers.
Demark-Wahnefried emphasizes the ACS guideline’s emphasis on overall health. “Cancer survivors are at much higher risk for cardiovascular disease,” she says. Primary cancer prevention is important for cancer survivors too. “Once you have a cancer, you’re at greater risk for a second cancer. Today, roughly one out of five cancer diagnoses is a new cancer in a cancer survivor, a second primary cancer. For example, if a man has prostate cancer, he’s at increased risk for colorectal cancer. So it’s important to guide all people toward a healthier diet—but even more important for cancer survivors.”
“Even independent of cancer, the data are overwhelming that heart disease, stroke, diabetes and even Alzheimer’s and dementia are reduced [in people with this dietary pattern],” says Cohen. “These are all inflammatory diseases. What’s the benefit of being cured of cancer and dying five years later from heart disease? Cancer is a teachable moment. This dietary pattern is important for a patient’s overall health. If you’re not already eating this way, it’s time to shift now.”