Dietary habits play an essential role in managing health, especially for cancer patients. Many studies suggest that following a healthy diet can reduce the risk of chronic diseases, including cancer. Despite these findings, there are limited guidelines on how cancer patients should adjust their diets. This article, by Urvi A. Shah, MD, MS, reviews existing dietary evidence in cancer care and emphasizes the need for more specific recommendations.
Contrasting Views on Diet and Cancer
A conversation with a cancer patient reveals a common confusion around the role of diet in cancer care. One patient shared how their oncologist simply advised eating a balanced diet, leaving them unsure of what that really meant. At the same time, another oncologist stated that diet should not be pushed on patients beyond the general advice of maintaining a healthy diet.
These conflicting opinions raise important questions: What does a “balanced diet” mean, and who is truly following it? Unfortunately, oncologists often struggle to provide consistent answers. This lack of clarity can lead patients to seek advice from unreliable sources. It highlights a crucial gap in cancer care — the need for dietary research and infrastructure to support patients.
Current Dietary Guidelines
The USDA’s 2020–2025 Dietary Guidelines suggest daily consumption of 1.5 to 2 cups of fruits, 2 to 3 cups of vegetables, and 25 to 35 grams of fiber. However, studies show that only a small percentage of Americans meet these recommendations, with just 12% of people consuming enough fruits and 10% consuming sufficient vegetables. Additionally, only 12% of cancer survivors follow the recommended intake of fruits and vegetables.
The American Institute for Cancer Research (AICR) and the American Cancer Society (ACS) recommend a diet rich in fruits, vegetables, whole grains, and beans, while limiting processed foods, sugary drinks, and red meats. According to the ACS, addressing diet, weight, and physical activity could prevent 18% of cancers and 16% of cancer-related deaths in the United States.
The Evidence Behind Dietary Interventions
Several studies show that dietary changes can lower the risk of developing cancer. For example, a trial with patients with hereditary Lynch syndrome found that a daily intake of 30 grams of resistant starch reduced the incidence of noncolorectal cancers. In another small study of 20 patients with monoclonal gammopathy, a high-fiber, plant-based diet improved weight, insulin resistance, and inflammation. In two patients, the diet also slowed disease progression.
Some studies suggest that dietary changes can enhance chemotherapy outcomes. In a trial with breast cancer patients, those who followed a plant-based diet and exercised were more likely to achieve a pathologic complete response compared to those who did not. Another study found that patients with melanoma who had a higher intake of dietary fiber experienced better progression-free survival.
For cancer survivors, diet also plays a key role. An observational study of patients with multiple myeloma on lenalidomide maintenance showed that those with higher microbiome diversity had a higher likelihood of achieving sustained measurable residual disease negativity. Adherence to ACS guidelines was linked to better disease-free and overall survival in colon cancer patients.
The Role of Gut Microbiome in Cancer
Recent research shows that the gut microbiome, the collection of bacteria and other microorganisms in the digestive system, plays a crucial role in cancer survival. Diet has a significant impact on the microbiome, with high-fiber, plant-based diets linked to better microbiome diversity. Studies suggest that a healthy microbiome can improve cancer outcomes, yet few clinical trials focus on the role of diet in shaping the microbiome in cancer patients.
Challenges in Conducting Dietary Intervention Trials
Conducting dietary intervention trials in cancer care is challenging. Issues such as limited funding, behavioral support, and participants’ varied dietary habits complicate research efforts. Most dietary intervention trials in cancer care have produced mixed results, often showing smaller effects than pharmaceutical treatments. This highlights the need for large-scale studies focused on long-term survival outcomes and dietary patterns rather than individual food groups.
Moving Forward: Practical Dietary Recommendations for Cancer Patients
Despite the challenges in dietary research, oncologists should not dismiss the importance of diet. Saying “diet doesn’t matter” or “just eat a balanced diet” is not helpful, as many patients do not understand what this means. Oncologists can improve cancer care by offering clear, actionable dietary guidelines. For example, patients could be encouraged to consume more than 25 grams of dietary fiber, two servings of fruit, and three servings of vegetables daily. Referrals to dietitians can also make a significant difference in patient outcomes.
As an added benefit, these dietary changes can improve personal health and contribute to a lower environmental footprint. Until more robust data are available, it is crucial for oncologists to take steps to provide clear dietary advice to cancer patients.
Conclusion
The current research on diet and cancer is promising, but more robust data is needed to create specific, actionable dietary guidelines. Institutions and scientists must prioritize funding research that addresses the limitations of current studies. In the meantime, oncologists can play a vital role by providing concrete dietary recommendations to their patients.
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