Longer nightly fasting improves breast cancer prognosis
June 20, 2016
Jacob Schor, ND, FABNO
It may be that something as simple as changing the time you eat dinner and breakfast may change risk of cancer recurrence. That’s what a study published March 31, 2016 in JAMA Oncology suggests.
Actually there are two studies that we need to ponder. Both written by Catherine Marinac and colleagues at the University of California in San Diego, the first paper was published in April 2015.
Both papers look at the effect duration of nightly fasting, (those are fancy words for how long you go without eating between dinner and breakfast) on breast cancer.
The 2015 study analyzed data from 2212 women gathered through the US National Health and Nutrition Examination Survey (NHANES). Longer fasting was associated with lower average blood sugar as calculated via A1c levels. Elevated blood sugar is a risk factor for breast cancer recurrence. This was interesting. The next paper gets fascinating. 
In the 2016 study, data from 2413 women who took part in the Women's Healthy Eating and Lifestyle (WHEL) study were analyzed seeking correlation for poor breast cancer outcomes and fasting duration. Marinac et al reports that fasting for less than 13 hours per night was associated with an increase in breast cancer recurrence compared to fasting more than 13 hours per night. Data from women with shorter fasting periods trended toward increased breast cancer mortality but did not reach statistical significance. Longer nightly fasting was again associated with lower hemoglobin A1c results.
The WHEL women fasted for a mean duration of 12.5 hours per night. Fasting less than 13 hours per night was associated with a 36% increase in the risk of breast cancer recurrence compared with fasting 13 or more hours per night. Nightly fasting for less than 13 hours was associated with a non-significant trend toward higher risk of breast cancer mortality, 21%, and a non significant 22% increase in all-cause mortality
Each 2-hour increase in the nightly fasting duration was associated with significantly lower hemoglobin A1c levels and a longer duration of nighttime sleep
The authors write, “Prolonging the length of the nightly fasting interval may be a simple, non-pharmacologic strategy for reducing the risk of breast cancer recurrence. Improvements in sugar regulation and sleep may be mechanisms linking nightly fasting with breast cancer prognosis.”
We always seek simple lifestyle changes that will improve health. In patients with a history of breast cancer this is often measured as reducing the risk of recurrence. This study suggests an elegantly simple prolongation of the period of time in which women abstain from food at night, the fasting period between dinner and breakfast, may have significant benefit. In this cohort of women for whom the mean fasting period was 12.5 hours, those who fasted less than 13 hours per night had a 36% higher risk of breast cancer recurrence.
These two papers appear to be the first human studies that have sought a direct association between nightly fasting and breast cancer outcome. In animals, caloric restriction is an effective way to reduce cancer risk.  Interestingly in animals, intermittent caloric restriction prevents breast cancer development as well or even better than chronic caloric restriction.  Only one study has examined whether meal timing has an effect on tumor progression in mice. Those mice whose feeding times were restricted had smaller tumors than mice fed ad libitum.  Curiously feeding mice when it was light was also associated with less tumor growth. As mice are nocturnal, one might wonder if eating dinner late at night, or being woken to eat dinner might have a similar beneficial effect in humans.
In both these groups of women who were part of either the NHANES or WHEL study cohorts, longer nightly fasting was associated with a lower hemoglobin A1c levels. Giovanucci et al also analyzing data from NHANES reported a similar finding in 2010.  It seems clear that longer fasting is associated with lower blood sugar a measure that may limit growth of breast cancer cells. Erickson et al reported in 2011 in a different analysis of data from the WHEL cohort that women with a A1c > 7.0%, were more than twice as likely to die during the study than women with an A1c less than 6.5%. 
In an August 2015 analysis of NHANES data, Marinac et al reported that among 2019 women, longer night time fasting was associated with significantly lower c-reactive protein levels, but only in women who ate less than 30% of their daily calories after 5 PM. 
In this current paper, longer nightly fasting was not associated with BMI. Longer fasting was associated with long sleep duration. Late night eating disrupts circadian rhythms. Eva Schernhammer’s multiple studies looking at night-shift workers have produced convincing evidence that circadian misalignment is linked with increased cancer risk, including increased risk of breast cancer. 
While these newest findings are the result of retrospective analysis of data gathered two decades ago, the results are intriguing. There are those who will suggest waiting for more definitive data gathered from a prospective randomized trial before bringing this practice into clinical use. This writer is not among that group as at this point there is no evidence that longer night-time fasting is associated with any increase in risk. At the worst it may prove ineffective. As this study suggests a nearly 40% shift in cancer recurrence rates, longer night time fasts may have considerable value.
The obvious question that we do not and will not know the answer to is whether the association revealed by this data is causal or not. It could be that women who produce higher amounts of insulin choose to forgo long night time fasts because they become hypoglycemic easier. It may turn out that this eating pattern serves more as a biomarker than an intervention.
To our already simple prescriptions for daily exercise, a healthy Mediterranean diet, and adequate sleep, we should now tell our breast cancer patients to “Eat an early dinner and a late breakfast.” It sounds almost too simple.
The current 2016 paper:
Marinac CR, Nelson SH, Breen CI, Hartman SJ, Natarajan L, Pierce JP, Flatt SW, Sears DD, Patterson RE. Prolonged Nightly Fasting and Breast Cancer Prognosis. JAMA Oncol. 2016 Mar 31.
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6. Erickson K, Patterson RE, Flatt SW, Natarajan L, Parker BA, Heath DD, Laughlin GA, et al. Clinically defined type 2 diabetes mellitus and prognosis in early-stage breast cancer. J Clin Oncol. 2011 Jan 1;29(1):54-60.
7. Marinac CR, Sears DD, Natarajan L, Gallo LC, Breen CI, Patterson RE. Frequency and Circadian Timing of Eating May Influence Biomarkers of Inflammation and Insulin Resistance Associated with Breast Cancer Risk. PLoS One. 2015 Aug 25;10(8):e0136240.
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