Proper nutrition and adequate exercise can be considerably effective not only in helping to relieve symptoms and enhance quality of life in patients who have been diagnosed with breast cancer, but also to possibly prevent the development and progression of breast and other cancers. Neil Iyengar, MD, a medical oncologist at Memorial Sloan Kettering Cancer Center, has performed extensive research regarding the link between metabolic health and the development and recurrence of breast cancer, a topic which he overviewed at the Society for Integrative Oncology's 16th International Conference in October. In this interview with i3 Health, Dr. Iyengar discusses the benefits that a healthy diet and physical activity can provide during breast cancer treatment and the research advances that could further personalize nutritional and exercise strategies in patients with this disease.
What questions regarding nutrition and exercise do you commonly encounter from patients with breast cancer, and how do you counsel them?
Neil Iyengar, MD: Nearly all of my patients ask about what they could be or should be doing with their diet and physical activity after a breast cancer diagnosis. The questions largely center around whether there are any types of diets or exercise programs that could prevent or relieve symptoms from cancer treatment, improve treatment response, or reduce the risk of metastasis and relapse. These are all very important questions. My responses generally fall into two categories, with the first one focusing on diet and exercise in terms of relieving symptoms that might be related to cancer treatment, as well as improving quality of life.
There isn't a great deal of evidence regarding the regulation of nutrition for addressing side effects. We do know that weight gain is fairly common during breast cancer treatment. This is contrary to the old stereotype that patients going through chemotherapy should try to eat as much as they can to build up their strength. We now know that this isn't the case, and that gaining more than 5% to 10% of the pre-diagnosis weight might actually put a patient at an increased risk of breast cancer recurrence. While we don't yet have evidence to suggest that a particular type of food can be helpful during breast cancer treatment, we should try to pick diets that a person can easily adhere to in order to help prevent weight gain during and after treatment. We also know that by staying active and achieving the exercise guideline goals put out by the American Society of Clinical Oncology (ASCO), patients can improve side effects like fatigue, joint pain, or really any other type of pain that might be caused by breast cancer treatment. Quality of life can also be significantly improved by maintaining at least a moderate amount of physical activity both during and after therapy.
The second category centers around the question of whether or not patients can reduce their chances of breast cancer recurrence through the modification of diet or exercise. There's even less evidence concerning this category, but it's something we're actively working on, with several clinical trials testing whether or not exercise and diet might actually decrease the risk of recurrence. Again, what we do know is that weight gain can increase that risk. The best way to prevent weight gain is through a healthy diet, and exercise can help to support that by increasing the number of calories burned. I tell my patients that while we don't yet have any gold standard data to suggest that a particular type of diet or exercise program can reduce the risk of recurrence, staying physically active and maintaining a healthy diet can certainly help manage side effects.
Based on observational data obtained from large cohorts of patients, we also know that eating a diet that is rich in fiber—30 to 50 grams per day—is associated with not only a reduced risk of cancer, but also a decreased risk of cancer recurrence. One of the most effective means of increasing fiber intake is by eating a plant-centered diet. We also know that a lot of meat products, such as red meat or processed meats like hotdogs and grilled meats, can increase the risk of cancer recurrence because of intrinsic properties like fat content or specific carcinogens. That's yet another reason why I counsel patients to maximize their consumption of fruits and vegetables, minimize their intake of processed foods, and incorporate physical activity not only to help with the side effects of treatment, but perhaps to help prevent recurrence as well.
What other research advances are on the horizon regarding metabolic and adiposity-related drivers of breast cancer risk and progression?
Dr. Iyengar: From a preventative standpoint, we have learned and are continuing to learn a great deal in terms of really understanding an individual's risk of developing breast cancer. From a metabolic standpoint, we have known for a while that obesity and diabetes can increase the risk of developing hormone receptor-positive breast cancer. Aside from classic obesity, normal weight obesity can also increase risk. In a recent study with the Women's Health Initiative, we found that a body fat percentage of over 33% is associated with approximately double the risk of developing breast cancer among women who are at a normal body weight. These women's doctors may have told them that they are healthy and have nothing to worry about.
What we're learning from research is that better risk assessment tools are needed. For example, measuring an individual's body composition might be a more effective method than simply weighing them. We and others are also investigating the creation of a blood test to measure inflammatory and metabolic biomarkers that could predict breast cancer risk. Through the use of better risk prediction tools, we could then determine which specific diets or exercise plans are most likely to benefit individual patients.
About Dr. Iyengar
Neil Iyengar, MD, is a medical oncologist in the Breast Medicine Service at Memorial Sloan Kettering Cancer Center in New York. He also leads the Tri-Institutional Obesity, Cancer, and Metabolic Diseases Working Group. Dr. Iyengar has led numerous clinical trials investigating the association between cancer and metabolic health, including the roles of nutrition and exercise in the treatment of patients with breast cancer. His research focuses on the development and implementation of dietary strategies, exercise plans, and other lifestyle interventions to improve outcomes in patients with breast cancer.
For More Information
Iyengar NM, Arthur R, Manson JE, et al (2019). Association of body fat and risk of breast cancer in postmenopausal women with normal body mass index: a secondary analysis of a randomized clinical trial and observational study. JAMA Oncol, 5(2):155-163. DOI:10.001/jamaoncol.2018.5327
Runowicz CD, Leach CR, Henry NL, et al (2016). American Cancer Society/American Society of Clinical Oncology breast cancer survivorship care guideline. J Clin Oncol, 34(6): 611-635. DOI:10.1200/JCO.2015.64.3809
Transcript edited for clarity. Any views expressed above are the speaker's own and do not necessarily reflect those of i3 Health.