Vegetarian Diet Offers Physical, Mental Benefits for Women With Metastatic Breast Cancer

Many women wonder if they should change their diets after being diagnosed with breast cancer. A small study found that women with metastatic breast cancer who switched to a plant-based diet free from added oils and fats for eight weeks lost more weight and felt healthier than women who didn’t change their diets. The findings were reported in two separate papers: one paper on factors measured by doctors; the other on patient-reported outcomes. 

Compared to women who ate their usual diet, women who ate a diet of unprocessed fruits, vegetables, whole grains, beans, nuts, and seeds (also called a whole-food, plant-based diet) for eight weeks:

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  lost about 9 pounds

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  experienced greater drops in total cholesterol and LDL (the so-called bad cholesterol) 

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  reported greater improvements in their emotional well-being and quality of life 

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  said they had less diarrhea and fatigue, fewer skin problems, and fewer symptoms, like shortness of breath, that interfered with their physical activity

Although the study was small — it only included 32 women — the results suggest that women with metastatic breast cancer who eat a whole-food, plant-based diet may feel physically and mentally healthier than women who eat a traditional American diet.

It’s estimated that about 169,000 women will be living with metastatic breast cancer by 2025 — up nearly 30,000 over a seven-year period. However, women with metastatic disease are usually excluded from studies on how diet affects breast cancer outcomes and quality of life. The researchers of this study wanted to know if diet changes could offer benefits for these women.

The researchers randomly assigned the women to one of two diets for eight weeks: 21 women were in the whole-food, plant-based group and 11 were in the regular diet group.

Women in the plant-based diet group received three prepared meals and one side dish per day consisting of fruits, vegetables, whole grains, nuts, and seeds. They were encouraged to eat as often and as much as they wanted to feel full. They were allowed to add their own food in addition to or in place of the prepared meals, as long as the food followed the diet requirements. 

The women in the plant-based diet group also went to a weekly education session on how diet can help ease side effects and improve general health. They also took a multivitamin and received a phone call each week from one of the researchers that allowed the women to ask any questions they had.

The women in the usual diet group received a phone call from one of the researchers at week two and week six to discuss side effects and any treatment changes.

Among women who ate the plant-based diet for eight weeks:

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  average weight dropped from 177.5 pounds to 165.7 pounds (about 1.5 pounds per week)

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  average BMI went from 29.7 to 27.8

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  average total cholesterol decreased 17.7% and average LDL cholesterol decreased 21.4%

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  physical and emotional well-being scores increased

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  perceived cognitive function (how the women felt they were thinking, remembering, reasoning, and concentrating) improved

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  treatment side effects, such as diarrhea, fatigue, skin problems, and shortness of breath improved

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  overall quality of life improved

The women in the plant-based diet group said they liked the food they were given and thought that the study had improved their health.

“This is one of the first dietary randomized controlled trials to improve disease-specific quality of life and treatment-related symptoms in participants receiving treatment for metastatic disease,” the researchers concluded. “Our whole-food, plant-based dietary intervention is both feasible and acceptable; it resulted in large changes in nutrient intake and clinically significant improvements in weight and related cardiometabolic risk factors, quality of life, and symptoms.”

While these results are encouraging, the study only lasted eight weeks, so it raises several questions:

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  Will the women be able to continue to follow the whole-food, plant-based diet without receiving prepared meals each day?

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  Will the benefits last if the women add some animal products or processed food back into their diet?

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  Does the diet affect cancer growth or the women’s mortality?

The study was also very small and all but one of the women were white, so it’s unclear how widely the results can be applied.

Campbell, T.M., et al. A whole-food, plant-based randomized controlled trial in metastatic breast cancer: weight, cardiometabolic, and hormonal outcomes. Breast Cancer Res Treat 205, 257–266 (2024).

Campbell, E.K., et al. A whole-food, plant-based randomized controlled trial in metastatic breast cancer: feasibility, nutrient, and patient-reported outcomes. Breast Cancer Res Treat 206, 273–283 (2024).