Impact of a whole-food plant-based diet on breast cancer

Aim

Breast cancer is associated with weight gain and occurs in 50% to 96% of women receiving chemotherapy for metastatic disease.

Among these women, rates of obesity are comparable to or even higher than rates of obesity in the general population, which can lead to higher symptom burden and reduced quality of life.

As there is predicted to be 169,000 women living with metastatic breast cancer by 2025, it is important to assess how dietary intervention can address these risk factors.

This study explores the feasibility and preliminary effects of a whole-food, plant-based (WFPB) dietary intervention in women with metastatic breast cancer. 

Method

Women with metastatic breast cancer were recruited between February 2018 to March 2022 from oncology clinics in Rochester, NY, USA. Eligibility criteria included women with stage 4 breast cancer who were expected to live at least 6 months and who were on a stable treatment regime for the past 6 weeks.

After exclusions, 32 participants were randomised into two groups (1) WFBP diet intervention (n = 21) or usual diet control (n = 11).

The WFPB diet group received 3 prepared meals and one side dish per day for 8 weeks.

Support included weekly assessment visits and a weekly phone call with the study physicians.

Assessment included education, coaching, and evaluation of adverse events or other medical changes.

The WFPB diet consisted of fruits, vegetables, whole grains, legumes, nuts and seeds. The diet excluded animal products and added oils/solid fats.

Participants were encouraged to eat as much and as often as they wanted to be comfortably full. They were encouraged to add their own food in addition to, or in place of, the provided food, as long as it was ‘on-plan.’

The control group continued their usual diets for 8 weeks and received phone calls from a study physician at weeks 2 and 6 to assess for adverse events and treatment changes.

A daily multivitamin was provided to all participants. 

Key findings

Thirty of 32 (94%) of participants completed the 8 week study.

Among intervention participants mean weight decreased by 6.6%, from 177.5 lbs (80.5kg) to 165.7 lbs (75.1kg). BMI decreased from 29.7 to 27.8 kg/m2. Intervention participants lost 9lbs (4kg) more than control subjects (p ≤ 0.01, effect size − 0.21) and lost 1.7 kg/m2 more from their BMI (p ≤ 0.01, effect size − 0.26).

This amount of weight loss is greater and faster compared to previous cancer dietary interventions, however, it is consistent with other interventions using WFPB diets, even when no prepared food is provided.

Participants achieved weight loss without portion or calorie restriction or mandated exercise. Weekly coaching included recommendations to eat greater volumes of food and eat more frequently, while choosing foods that were ‘on plan.’

When the final three-day food diary was compared to baseline, the intervention participants' dietary intake increased by 16% in terms of weight, but they consumed 26% fewer calories, indicating that the study diet had a significantly lower calorie density than their baseline diets.

Other statistically significant cardiometabolic and hormonal risk factor changes within the WFPB diet intervention group included; sex hormone binding globulin increased (p ≤ 0.01) (likely related to weight loss), insulin resistance, as calculated by HOMA-IR, decreased from 4.4 to 2.7 (p = 0.01), insulin like growth factor 1 (IGF-1) significantly decreased by 10% (p = 0.01), and urea nitrogen was significantly lower at 8 weeks (p ≤ 0.01).

The cancer markers, CA 27.29, CA 15-3, and CEA, which were all within the normal range at baseline, did not show any statistically significant changes at 8 weeks.

Conclusion

This study demonstrates that a WFPB dietary intervention is well tolerated and promotes significant weight loss and improves several cardiometabolic and hormonal risk factors among women with metastatic breast cancer.

The authors call for trials of longer duration to understand the sustainability of these findings as well as their effects on cancer progression and mortality. 

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