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Weight loss intervention did not change eating timing or sleep duration in breast cancer survivorsDo breast cancer survivors eat later and sleep longer than other women?

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Key Takeaway
Consider that weight loss programs may need specific components to address eating timing and sleep in breast cancer survivors.

This randomized controlled trial enrolled 159 female breast cancer survivors (stage I-III, median 9.5 months post-diagnosis, mean age 55 years, mean BMI 31.4 kg/m²) to evaluate changes in eating frequency, meal timing, and sleep duration. Participants were assigned to either a 12-month weight loss intervention or usual care, with follow-up at 18 months. At baseline, survivors showed higher prevalence of eating after 8 PM (67% vs. 52% in national survey), short nightly fasting duration (<13 hours: 83% vs. 75%), and long sleep duration (>9 hours/day: 26% vs. 17%) compared to national survey data.

From baseline to 18 months, there were no significant changes in these health behaviors between the intervention and usual care groups (p > 0.05). Effect sizes for all behavior changes were small (Cohen's effect sizes < 0.3), indicating minimal practical difference. The study did not report safety, adverse events, or discontinuation data.

Key limitations include that behaviors were estimated and categorized based on existing associations rather than direct measurement. The study population consisted of breast cancer survivors with specific characteristics (median 9.5 months post-diagnosis, elevated BMI), limiting generalizability. The authors note that future multi-behavior interventions in this population should consider specific messages to target eating timing and sleep behaviors. The weight loss intervention did not demonstrate efficacy in modifying these particular health behaviors.

After a breast cancer diagnosis, daily life gets reshuffled. A study of 159 survivors looked at when they ate and how long they slept, comparing them to national survey data. At the start, two-thirds ate after 8 PM, and over a quarter slept more than nine hours a night—both rates were higher than in the general population.

The women were part of a year-long weight loss study, with half getting the program and half receiving usual care. The researchers checked in 18 months later to see if these daily habits had shifted. They found no real change. Whether a woman was in the weight loss group or not, her eating times and sleep duration stayed about the same. The differences were so small they could have been due to chance.

This tells us that a standard weight loss program might not automatically fix late-night eating or long sleep in survivors. The study didn't measure these behaviors directly but estimated them from other data, which is a limitation. It also focused on a specific group of survivors, so we can't say if the same patterns hold for everyone. The takeaway isn't that these habits are bad, but that they might be common and stubborn features of life after treatment, worthy of a closer look.

What this means for you:
A weight loss program didn't change survivors' late eating or long sleep, suggesting these habits need specific attention.

Study Details

Study typeRct
EvidenceLevel 2
Follow-up12.0 mo
PublishedApr 2026
View Original Abstract ↓
PURPOSE: To examine eating frequency, timing of meals, and sleep duration before and after a weight loss intervention for breast cancer survivors. METHODS: Female breast cancer survivors (n = 159; 55 ± 9 years; 31.4 ± 5.0 kg/m; stage I-III, median [IQR] 9.5 [5.5] months post-diagnosis) participated in a randomized controlled trial of a 12-month weight loss intervention versus usual care. Eating frequency, proportion of daily calories consumed after 5 PM, eating after 8 PM, nightly fasting duration, and sleep duration were estimated and categorized based on existing associations with factors influencing breast cancer prognosis and breast cancer outcomes. These behaviors at baseline were compared to women from an Australian national survey with similar age and BMI range. Mixed-effects linear regression models were used to examine the changes in health behaviors from baseline to 18 months between intervention and usual care groups. RESULTS: Before the trial, eating after 8 PM (67%) was higher, and short nightly fasting duration (< 13 h, 83%) and long sleep duration (> 9 h/day, 26%) were marginally higher, in breast cancer survivors than women in the national survey (52%, 75%, and 17%, respectively). "Less optimal" eating behaviors and sleep duration tended to co-occur. Behaviors remained unchanged over the 18-month follow-up, irrespective of the study group (p > 0.05; Cohen's effect sizes < 0.3). CONCLUSIONS: Later timing of eating and long sleep duration were prevalent in breast cancer survivors and continued following a weight loss intervention. IMPLICATIONS FOR CANCER SURVIVORS: Future multi-behavior interventions in breast cancer survivors should consider specific messages to target eating timing behaviors and sleep.
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