Can diet help with advanced breast cancer? All indications are positive, researchers say

Women with breast cancer who exclusively ate a whole-foods, plant-based diet lost weight, improved cholesterol levels and other key metabolic factors, had less fatigue, and perceived that they felt sharper mentally and generally more well.

The outcomes are from a small study by researchers at the University of Rochester Medical Center and Wilmot Cancer Institute. Study participants were individuals with stage 4 breast cancer, who will be on lifelong treatment.

These patients are typically excluded from dietary studies, but with their survivorship numbers growing, it presented an opportunity to make an impact both short- and long-term, said research leader Thomas M. Campbell, MD, an assistant professor of Family Medicine at URMC and an expert on using plant-based diets to improve health.

What did the clinical trial require?

The study included 30 patients who were on stable treatment and could tolerate food.

Researchers randomly divided participants into two groups: One received standard care, and the intervention group ate meals provided by the research team for eight weeks. The diet consisted solely of fruits, vegetables, whole grains (including whole grain pasta), legumes (beans), potatoes, and nuts and seeds. Participants agreed to avoid animal-based foods (meat, eggs, and dairy), and all oils and added solid fats. They also took a daily multivitamin.

Weekly assessments occurred, and the study reported 95% compliance.

"It's exciting to see that these major dietary changes were feasible, well-tolerated, and acceptable to the clinical trial participants," Campbell said.

No calorie restriction was involved. Individuals were encouraged to eat as often as they wanted of food that was "on plan."

How a clean, plant-based diet makes a difference

The women started with an average BMI of 29.7, which is borderline obese. The patients in the whole-foods plant-based group lost 1 to 2 pounds per week for eight weeks, without mandated exercise.

This is significant because individuals with breast cancer often gain weight during treatment, which is risky. Why? Too much body weight increases insulin levels and hormones (estrogen and testosterone) in the blood, which can fuel cancer.

Another encouraging study result: researchers saw a reduction in blood samples of IGF-1, a growth factor that has been associated with many common cancers, as well as less inflammation.

"Although we cannot say anything yet about whether the diet can stop cancer progression from this small study, we saw preliminary results that suggest favorable changes within the body, which is very positive," Campbell said.

To better understand the implications for cancer growth, the team is collaborating with Isaac Harris, Ph.D., at Wilmot, in a bench-to-clinic investigation.

Scientists know that cancer cells rely on amino acids to survive, and the patients who followed the plant-based diet had changes in their blood levels of amino acids. Harris is studying the effect of amino acid composition on cancer cell survival, and the effect of the amino acids on various cancer drugs.

The journal Breast Cancer Research and Treatment published the primary study, which is believed to be the first of its kind. The breast cancer trial had enough significant results that two additional papers were also published from the dietary intervention: a second study in the same journal, and a third study in Frontiers in Nutrition, all in March 2024.

How to start making healthy changes

Patients should first consult with their oncologists or health care providers before making major dietary changes, Campbell said. This is especially important for people who take blood thinners or insulin medications.

Examples of food provided in the breast cancer clinical trial included peanut soba noodles, steel cut oatmeal, banana flax muffins, sweet potato enchiladas, and Mediterranean white bean soup.

To get started with plant-based recipes and meal ideas that are simple and affordable, Campbell recommends these websites: plantyou.com, shaneandsimple.com, and monkeyandmekitchenadventures.com.

Several factors influence a person's motivation to eat healthier, Campbell added, including family support, taste preferences, and cooking ability.

Whether a person makes dramatic changes overnight, or simply decides to swap out an occasional meal in favor of a plant-based recipe can be a good choice: "You only need five to ten plant-based recipes that are easy, tasty, and convenient enough that you will make them regularly to have a substantial overhaul in your diet," he said.

Higher food costs are often cited as a reason to shirk a plant-based diet, but in 2023 co-author Erin Campbell, MD, published a separate study showing that the diets leading to the biggest health improvements—including Dietary Approaches to Stop Hypertension, or the DASH diet, which is also plant-based—were the same or cheaper in terms of food costs compared to standard American diets with ultra-processed foods and restaurant take-out.