Table 1 displays baseline characteristics of participants. The mean BMI of participants was 29.6 kg/m2 with 71% of participants in either the overweight or obese BMI range. The majority of participants had hormone receptor positive BC. Metastatic disease to the bone was the most common site of metastasis, present in 84% of participants. The most common treatment regimens were a cyclin-dependent kinase 4/6 inhibitor combined with an aromatase inhibitor.
Feasibility
Thirty of 32 randomized participants completed their study participation. One participant was lost to follow-up immediately following randomization to the control arm. One intervention participant was withdrawn by investigators in March 2020 shortly after baseline, due to the COVID-19 pandemic shutdown (Figure 1). All 30 remaining participants completed assessments at 8 weeks. All (100%) intervention participants attended at least 6 of the 8 weekly visits, our prespecified criterion for study visit adherence.
Intervention participants were highly adherent to the diet. Eighteen of 19 (94.7%) intervention participants with complete dietary assessments met the study’s prespecified adherence criterion that they derive ≥ 80% of their kilocalories from on-plan foods. In fact, 94.3% of total calories consumed by the intervention participants with complete dietary assessments were from on-plan foods (foods without added oils, solid fats, or animal-based ingredients). Changes in dietary intake between baseline and final 3-day food records are shown in Table 2.
Within the intervention group, dietary intake changed significantly. Intervention participants consumed 25.9% fewer calories (p<0.001). Fat as a percentage of total kilocalories and dietary cholesterol intake were significantly reduced by 43.0% (p<0.001) and 96.5% (p<0.001), respectively. Protein as a percentage of total kilocalories was modestly reduced (-13.7%, p<0.017). Carbohydrates as a percentage of total kilocalories increased 36.8% (p<0.001). The proportion of total protein provided by plant sources increased 105.4% (p<0.001) and dietary fiber increased 84.6% (p<0.001).
The composition of the control group’s diet was largely unchanged despite knowing that we were studying a WFPB diet. Within the control group, participants reduced their total calories (-10.0%, p<0.034) and reduced their dietary fiber intake (-16.5%, p<0.021). There were no statistically significant changes to the percent of total calories from any of the macronutrients, dietary cholesterol, or the proportion of protein provided by plant sources.
The groups differed significantly in their mean nutrient changes from baseline to week 8 in all nutrients displayed in Table 2 except for change in percent of calories from protein.
Of note, there was a significant between-group effect (p<0.01); intervention group participants lost a mean of 6.6% of their body weight, whereas control group participants lost a mean of 0.7% of their body weight. When adjusted for baseline weight, intervention participants lost 9.0 pounds more than control participants (p<0.001). Changes in BMI, cardiometabolic outcomes, and hormonal markers are described in a separate publication (companion paper reference).
Adverse Events
Adverse events during the trial were infrequent and mild. Grade 2 hypotension occurred in three intervention participants. In each case, symptoms were mild and resolved after referral to their routine medical providers for medication adjustments. One control participant reported lightheadedness following a blood draw. Other adverse events included aphthous ulcer, transient, mild hyponatremia, and mild, transient neutropenia, all deemed medication-related. One participant in each arm had her primary cancer treatment dose reduced by her oncologist due to adverse events typical of that medication.
Patient-Reported Outcomes
Table 3 shows the effect of the intervention arms on various patient-reported outcomes. The total FACT-B total score (+8.0, p<0.001), as well as physical (+1.5, p=0.016) and emotional well-being (+1.8, p=0.012), and BC-specific symptoms (+3.2, p=0.002) subscale scores improved significantly within the intervention group; surpassing the clinically important difference (CID) for each of these measures[30-32]. The change in emotional well-being score from baseline to 8 weeks was significantly different between the groups (+2.3, CID=0.9;[30] p=0.016, ES=0.54). The between-group difference in the FACT-B score approached significance (+5.1, CID=6.0;[31, 32] p=0.067, ES=0.29).
Perceived cognitive function, as measured by the FACT-Cog questionnaire, showed clinically significant improvements within the intervention group as well as between the groups. (Table 3). Between groups, there were statistically and clinically significant improvements on the overall FACT-Cog score (+16.1, CID=9.6;[33, 34] p=0.04, ES=0.46) as well as on the comments from others subscale (+1.6, CID=0.4;[34] p=0.006, ES=0.79) and the impact of perceived cognitive impairments on QOL subscale (+4.1, CID=0.9;[34] p=0.049, ES=0.52) in the intervention group compared to the control. Perceived cognitive impairment improved in the intervention group (p=0.007) and the between-group difference in change from the baseline to 8 weeks approached significance (+8.4, CID=5.5;[33] p=0.076, ES=0.37). Improvement in the perceived cognitive ability subscale approached significance within the intervention group (p=0.056).
On the symptom inventory, there were statistically significant between group differences favoring the intervention group in improvements in problems remembering things (p=0.024, ES = −0.67), problems concentrating (p=0.039, ES = −0.5), and problems multitasking (p=0.029, ES = −0.73). Reported problems paying attention trended towards improvement in the intervention group compared to the control group in which the score worsened (p=0.056, ES = −0.54). Diarrhea (p=0.044) and skin problems (p=0.007) improved in the intervention group compared to the control. Shortness of breath (p=0.039) and interference of symptoms with physical activity (p=0.057), walking (p=0.020), and QOL (p=0.053) improved within the intervention group. Fatigue trended towards improvement within the intervention group (p=0.054).
Mirroring results of the FACT-Cog questionnaire, there was a significant improvement in perceived cognitive functioning in the intervention group (p=0.004) as assessed by the EORTC QLQ-C30. This difference approached significance between the groups (p=0.061, ES=0.47). Social functioning (p=0.023) and fatigue (p=0.013) improved significantly in the intervention group, but not between groups. There was a trend towards improved insomnia in the intervention group (p=0.072).
Fatigue, as measured by the BFI, improved in the intervention group. There were significant within-group improvements in fatigue severity (p=0.047) and fatigue at its worst (p=0.011) and a trend towards improvement in global fatigue (p=0.058) for the WFPB group.
Acceptability
Intervention participants had positive perceptions of the intervention and provided food. When asked “Do you feel that your health has benefited from the study intervention?”, 19 of 20 intervention participants answered “Yes” (95.0%, 1 did not give an answer). As shown in Table 4, participants strongly recommended the intervention, reported minimal hunger, and positively reviewed both the amount and taste of provided meals.