Prolonged Nightly Fasting Cuts Risk for Breast Cancer Return

Roxanne Nelson

April 01, 2016

Not eating in the evening and at night could reduce the risk for recurrence of breast cancer, according to a new study published online March 31 in JAMA Oncology.

In a cohort of 2400 women with early-stage breast cancer, researchers found that fasting less than 13 hours per night was associated with a 36% higher risk for disease recurrence as compared with fasting 13 or more hours per night.

A nonsignificant 22% higher risk for mortality from any cause was also observed among patients who fasted for shorter periods in comparison with those who fasted for 13 hours or more overnight.

"Prolonging the overnight fasting interval may be a simple, nonpharmacological strategy for reducing a person's risk of breast cancer recurrence and even other cancers," said first author Catherine Marinac, a doctoral candidate at Moores Cancer Center, University of California, San Diego (UCSD), in a statement.

Previous research has focused on what to eat for cancer prevention, but when we eat may also matter. Catherine Marinac

"Previous research has focused on what to eat for cancer prevention, but when we eat may also matter, because it appears to affect metabolic health," she said.

The authors also found that fasting fewer hours per night was associated with significantly less sleep and higher levels of glycated hemoglobin (HbA1c).

These findings are relevant to cancer prevention and control efforts, they note, inasmuch as elevated levels of HbA1c and poor sleeping habits have been linked to an increased risk for breast cancer.

"To our knowledge, this is the first paper examining nightly fasting and breast cancer prognosis in humans," said senior author Ruth E. Patterson, PhD, professor, Department of Family Medicine and Public Health, Moores Cancer Center, UCSD.

"Therefore, the data are not mature enough to make clinical or public health recommendations," she told Medscape Medical News.

The upside is that this eating pattern does not appear to pose any risk in generally healthy adults.

"There doesn't seem to be any downside, and it might help some individuals with sleep, metabolic health, weight management, or chronic disease risk," Dr Patterson said. "But that is just an hypothesis, and we can't promise any health outcomes at this stage of the research."

Lowers Recurrence Risk and HbA1c

For their study, Dr Patterson and colleagues used data from the Women's Healthy Eating and Living Study, a multisite, randomized trial that was conducted between March 1, 1995, and May 3, 2007. This trial was designed to test whether a diet rich in vegetables, fruit, and fiber and low in fat reduced the risk for breast cancer recurrence and mortality.

The current analysis included 2413 participants who had early-stage breast cancer and who did not have diabetes mellitus. The patients were aged 27 to 70 years at diagnosis.

The primary outcomes were invasive breast cancer recurrence and new primary breast tumors occurring during a mean of 7.3 years of study follow-up and death from breast cancer or any cause during a mean of 11.4 years of surveillance.

The patients self-reported their sleep duration. Archived blood samples were used to assess concentrations of HbA1c and C-reactive protein (CRP).

The mean duration of nightly fasting was 12.5 hours, and patients engaged in 4.4 eating episodes per day. About one third of the cohort (788 [32.7%]) consumed 25 kcal or more after 8:00 PM.

A short nightly fasting duration (<13 hours per night) was significantly associated with college education, a lower body mass index (BMI), shorter sleep duration, higher self-reported kilocalorie intake, more eating episodes, and eating after 8:00 PM.

The researchers found that fasting less than 13 hours per night was associated with an increase in the risk for breast cancer recurrence compared with fasting 13 or more hours per night (hazard ratio, 1.36).

However, there was no effect on deaths, either from breast cancer or from all causes. Fasting less than 13 hours was not associated with a statistically significant higher risk for breast cancer mortality (hazard ratio, 1.21) or a statistically significant higher risk for all-cause mortality (hazard ratio, 1.22).

Each 2-hour increase in nightly fasting duration was statistically significantly associated with a 0.37 mmol/mol lower HbA1c level (β = –0.37) and more hours of sleep per night (β = 0.20).

Nightly fasting duration was not, however, associated with BMI or CRP concentrations.

Each additional daily eating episode was associated with significantly lower HbA1c and CRP concentrations and lower BMI.

Consuming food after 8:00 PM was associated with significantly higher CRP concentrations and BMI.

Caveats to Be Considered

Although this study is interesting, one expert cautions that there are several factors that one must strongly consider "before drastically changing one's lifestyle from a conclusion that this will lower their risk of recurrence."

Approached by Medscape Medical News for an independent comment, Richard J. Bleicher, MD, FACS, leader of the Breast Clinical Program and associate professor of surgical oncology at the Fox Chase Cancer Center, Philadelphia, Pennsylvania, pointed out that the study was performed via participant recall.

"In other words, the patients had to accurately remember and document what, when, and how their dietary intake proceeded, and the authors themselves noted this big caveat," he said. "Although the study doesn't specify, some past studies have suggested that an individual's assessment of a food portion, if not weighed or measured, can be 40% lower than what they actually ate."

Another caveat is that the study only assessed dietary intake during a 3-week period during the year, and it is unknown whether alcohol intake or smoking habits were assessed. It is also unknown whether the fat content of their diet was uniformly known.

"These are examples of significant factors that have been shown to affect breast cancer recurrence and do not appear to have been factored in," Dr Bleicher said.

Another issue was that the women appear not to have been instructed to fast and that this was something they did on their own. "So while some treatments, stage, and grade were included in the assessment, there are other confounding factors that might play a role," he pointed out.

For whatever reason, the women who were not inclined to eat for a prolonged period may have a lower risk for recurrence, and there may be specific reasons why some patients normally fasted at night for longer periods whereas others did not.

"This could be related to innate hormonal factors or side effects in some women, or effects they experience from their treatment or medications," Dr Bleicher said.

"The point is that the relationships here are interesting, but all we can say is that, while there was a correlation between fasting at night and the risk of recurrence, we can't say that one was specifically due to the other," he said.

"On the other hand, what the study does do is tell us that much more research is needed before making any conclusions about fasting and recurrence," Dr Bleicher added.

The study received support from the National Cancer Institute. Catherine Marinac and a coauthor were supported by the National Cancer Institute.

JAMA Oncol. Published online March 31, 2016. Full text


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