Guest Editor’s Note: Several epidemiologic studies have shown an inverse association between healthy dietary patterns and the risk of chronic diseases including cancer. Patients are often interested in exploring different dietary interventions throughout the cancer continuum. However, concrete guidelines are lacking. In this article, Urvi A. Shah, MD, MS, highlights available evidence surrounding diet and cancer and emphasizes the need for more robust data as well as specific dietary recommendations for those with cancer.
Recently, a patient told me this: “My very respectable oncologist’s team told me to keep eating a balanced diet, and I realized that nutrition is ultimately a personal responsibility.” At around the same time, on an unrelated social media thread, an oncologist commented: “We shouldn’t push diet on our patients any more than [suggesting] eating a healthy, well-balanced diet.”
“Despite numerous epidemiologic studies supporting the role for fiber-rich, plant-based diets in cancer risk reduction, there are few ongoing plant-based interventional diet trials.”— URVI A. SHAH, MD, MS
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These diametrically opposed perspectives spurred me to ask these questions: Who knows what a balanced diet is, and who follows it? These questions are among the most frequently asked in oncology. Unfortunately, they are also the least likely to be answered consistently by oncologists. This leaves patients confused, as they search for answers from alternative (and often unreliable) sources. Dietary research and nutrition infrastructure to support patients with cancer are truly unmet needs.
Dietary Guidelines
The 2020–2025 USDA Dietary Guidelines recommend daily intake of fruits (1.5–2 cup-equivalent), vegetables (2–3 cup-equivalent), and fiber (25–35 g).1 However, only 12%, 10%, and up to 5% of Americans follow these recommendations, respectively.2 Similarly, only 12% of cancer survivors adhered to the fruit and vegetable guidance.3
The American Institute for Cancer Research (AICR) and the American Cancer Society (ACS) guidelines also recommend a dietary pattern rich in fruits, vegetables, whole grains, and beans while limiting the consumption of fast foods, processed foods, red and processed meats, sugary drinks, and alcohol.4-6 Furthermore, according to the ACS, at least 18% of all cancers and nearly 16% of cancer deaths in the United States may be prevented by addressing diet, weight, and physical activity.6
Current Evidence
Several studies have shown a positive association between dietary interventions and lower risk of development of a primary cancer. A randomized trial of 463 patients with hereditary Lynch syndrome found a reduced incidence of noncolorectal cancers with daily intake of 30-g resistant starch (incidence rate ratio = 0.52; 95% confidence interval [CI] = 0.32–0.84; P = .0075).7 In our small study of 20 patients with monoclonal gammopathy and smoldering myeloma (body mass index > 25 kg/m2), a high-fiber, plant-based diet led to improvements in weight, quality of life, insulin resistance, microbiome diversity and composition, as well as inflammation. Of note, the trajectory of disease progression was slowed in two patients.8
Few studies have evaluated synergy with chemotherapy. A randomized trial involving patients with stage I–III breast cancer evaluated a home-based exercise and plant-based nutrition intervention. In the subgroup of patients given neoadjuvant chemotherapy, those receiving the intervention were more likely to achieve pathologic complete response (53% vs 28%; P = .037).9 In another study of patients with melanoma receiving immune checkpoint inhibitors, adequate dietary fiber intake was associated with better progression-free survival (P = .047).10 These findings suggest that dietary interventions may deepen treatment response and improve survival.
Guest Editor
Jun J. Mao, MD, MSCE
Dr. Mao is the Laurance S. Rockefeller Chair in Integrative Medicine and Chief of Integrative Medicine Service at Memorial Sloan Kettering Cancer Center, New York.
In the survivorship setting, our observational study of patients with multiple myeloma on lenalidomide maintenance found that those with higher microbiome diversity, increased butyrate producers, and increased stool butyrate concentrations had a higher likelihood of sustained measurable residual disease (MRD) negativity (P = .0035). Plant proteins, seafood proteins, and dietary flavonoids correlated with stool butyrate (P = .009).11 Another trial of stage III colon cancers reported the highest adherence to ACS guidelines was associated with improved disease-free (hazard ratio [HR] = 0.69; 95% CI = 0.45–1.06; P = .03 for trend) and overall survival (HR = 0.58; 95% CI = 0.34–0.99; P = .01 for trend) compared with the lowest adherence to ACS guidelines.12
Of note, in our survey of 421 patients with plasma cell disorders, 34% were aware of the ACS/AICR dietary guidelines; 82% had questions about nutrition, but only 43% had those answered by their oncologist.13 Furthermore, 94% of that group had attempted to follow their oncologists’ recommendations, which shows the impact dietary recommendations can have. Respondents also increased their consumption of healthier foods (eg, fruits, vegetables, whole grains, plant proteins, and seafood) and decreased intake of unhealthier foods (eg, processed meat and junk food) after cancer diagnosis.13
Role of Gut Microbiome
With recent advances in our understanding of the gut microbiome, studies have consistently shown that microbiome diversity correlates with survival in cancer14 and that diet plays a substantial role in shaping the microbiome.15 For example, fermented foods16; high-fiber, plant-based diets8; more than 30 different plants per week17; and high healthy eating index score18,19 have been associated with higher diversity and improved composition. These findings demonstrate that improved diet quality may modulate the microbiome. However, despite numerous epidemiologic studies supporting the role for fiber-rich, plant-based diets in cancer risk reduction, there are few ongoing plant-based interventional diet trials.20
Concluding Thoughts
Key challenges for conducting dietary intervention trials include funding, inadequate behavioral support when scaling up the interventions, drop-in effect in the placebo arm and nonadherence in the intervention arm weakening the signal, and different baseline dietary habits of trial participants. In addition, given the smaller effect sizes and blunting of the signal (vs pharmaceutical interventions), dietary intervention trials require large sample sizes.20
“Providing concrete guidelines on the composition of a balanced diet along with targeted suggestions as well as a dietitian referral may go a long way in effecting change.”— URVI A. SHAH, MD, MS
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Limited phase III dietary intervention trials in cancer have thus far yielded negative results.21-24 These trials highlight the limitations in focusing on food groups instead of dietary patterns, designing studies with long-term survival endpoints, and scaling up such studies. Institutions, agencies, and scientists should prioritize funding studies that address these limitations.
Until more robust data become available, oncologists could do better than saying “diet doesn’t matter” or “just eat a balanced diet” (which is poorly understood by many patients). Providing concrete guidelines on the composition of a balanced diet along with targeted suggestions (eg, > 25 g dietary fiber, two servings of fruit, and three servings of vegetables daily while avoiding sugary drinks) as well as a dietitian referral may go a long way in effecting change. As an added benefit, these healthy dietary patterns are associated not only with improved personal health, but also with a lower environmental footprint.6,25
DISCLOSURE: Dr. Shah has received institutional research funding from Janssen and BMS as well as honoraria for participation in advisory boards from Janssen, Sanofi, and BMS.
REFERENCES
1. USDA: Dietary guidelines for Americans 2020–2025. Available at https://www.dietaryguidelines.gov/sites/default/files/2020-12/Dietary_Guidelines_for_Americans_2020-2025.pdf. Accessed March 20, 2025.
2. Lee SH, Moore LV, Park S, et al: Adults meeting fruit and vegetable intake recommendations: United States, 2019. MMWR Morb Mortal Wkly Rep 71:1-9, 2022.
3. Baughman C, Norman K, Mukamal K: Adherence to American Cancer Society nutrition and physical activity guidelines among cancer survivors. JAMA Oncol 10:789-792, 2024.
4. American Institute for Cancer Research: How to prevent cancer: 10 Recommendations. Available at https://www.aicr.org/cancer-prevention/how-to-prevent-cancer/. Accessed March 20, 2025.
5. American Cancer Society: American Cancer Society guideline for diet and physical activity. Available at https://www.cancer.org/cancer/risk-prevention/diet-physical-activity/acs-guidelines-nutrition-physical-activity-cancer-prevention/guidelines.html. Accessed March 20, 2025.
6. Rock CL, Thomson C, Gansler T, et al: American Cancer Society guideline for diet and physical activity for cancer prevention. CA Cancer J Clin 70:245-271, 2020.
7. Mathers JC, Elliott F, Macrae F, et al: Cancer prevention with resistant starch in Lynch syndrome patients in the CAPP2-randomized placebo controlled trial: Planned 10-year follow-up. Cancer Prev Res (Phila) 15:623-634, 2022.
9. Sanft T, Harrigan M, McGowan C, et al: Randomized trial of exercise and nutrition on chemotherapy completion and pathologic complete response in women with breast cancer: The lifestyle, exercise, and nutrition early after diagnosis study. J Clin Oncol 41:5285-5295, 2023.
10. Spencer CH, McQuade JL, Gopalakrishnan V, et al: Dietary fiber and probiotics influence the gut microbiome and melanoma immunotherapy response. Science 374:1632-1640, 2021.
11. Shah UA, Maclachlan KH, Derkach A, et al Sustained minimal residual disease negativity in multiple myeloma is associated with stool butyrate and healthier plant-based diets. Clin Cancer Res 28:5149-5155, 2022.
12. Van Blarigan EL, Fuchs CS, Niedzwiecki D, et al: Association of survival with adherence to the American Cancer Society Nutrition and Physical Activity Guidelines for Cancer Survivors after colon cancer diagnosis: The CALGB 89803/Alliance trial. JAMA Oncol 4:783-790, 2018.
13. Malik MA, Sweeney NW, Jafri M, et al: Nutrition perceptions, needs and practices among patients with plasma cell disorders. Blood Cancer J 12:70, 2022.
14. Khan N, Lindner S, Gomes ALC, et al: Fecal microbiota diversity disruption and clinical outcomes after auto-HCT: A multicenter observational study. Blood 137:1527-1537, 2021.
15. David LA, Maurice CF, Carmody RN, et al: Diet rapidly and reproducibly alters the human gut microbiome. Nature 505:559-563, 2014.
16. Wastyk HC, Grafiadakis GK, Perelman D, et al: Gut-microbiota–targeted diets modulate human immune status. Cell 184:4137-4153.e14, 2021.
19. Baldeon AD, McDonald D, Gonzalez A, et al: Diet quality and the fecal microbiota in adults in the American Gut Project. J Nutr 153:2004-2015, 2023.
20. Shah UA, Iyengar NM: Plant-based and ketogenic diets as diverging paths to address cancer: A review. JAMA Oncol 8:1201-1208, 2022.
21. Parsons JK, Zahrieh D, Mohler JL, et al: Effect of a behavioral intervention to increase vegetable consumption on cancer progression among men with early-stage prostate cancer: The MEAL randomized clinical trial. JAMA 323:140-148, 2020.
22. Chlebowski RT, Aragaki AK, Anderson GL, et al: Association of low-fat dietary pattern with breast cancer overall survival: A secondary analysis of the Women’s Health Initiative randomized clinical trial. JAMA Oncol 4:e181212, 2018.
23. Pierce JP, Natarajan L, Caan BJ, et al: Influence of a diet very high in vegetables, fruit, and fiber and low in fat on prognosis following treatment for breast cancer: The Women’s Healthy Eating and Living (WHEL) randomized trial. JAMA 298:289-298, 2007.
25. Shah UA, Merlo G: Personal and planetary health: The connection with dietary choices. JAMA 329:1823-1824, 2023.
Dr. Shah is Assistant Attending, Myeloma Service, Memorial Sloan Kettering Cancer Center, New York, and Assistant Professor of Medicine, Weill Cornell Medical College, New York.
