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Study: Can long periods of fasting protect against breast cancer recurrence?

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This study is about:

How nighttime fasting affects breast cancer recurrence and mortality. 

Why is this study important?

If longer fasting at night is linked to a better breast cancer prognosis, as the study 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.”

Study findings: 

  1. Women who reported fasting fewer than 13 hours per night had an increased risk of breast cancer recurrence compared to women who reported fasting for more than 13 hours per night.

What does this mean for me?

Everyone has a period of nighttime fasting—from their last meal or late night snack until breakfast.  This study looked at the length of that interval, and suggests that late night eating, which shortens the length of the nighttime fast, is associated with breast cancer recurrence. But this study does not definitively conclude that nighttime eating results in breast cancer recurrence; only that there is an association. A large, controlled trial with patients who are randomly assigned to either the nighttime fasting group or a control group is needed to provide more definitive information and confirm this association. Additionally, no current research indicates that late night eating is associated with worse health outcomes. Based on the results of this study, lengthy nighttime fasting is not needed to prevent cancer recurrence.

Research on weight gain and late night eating has produced mixed results—researchers still do not know whether late night eating makes it easier to gain weight. However, dieticians recommend avoiding late night eating because they say it is easy to overdo eating at nighttime (eating out of boredom or stress instead of hunger, for example, and portions are not as well controlled). Ultimately, the results of this research should not stop women from eating a light snack at night when hungry.

Posted 5/31/16

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Marinac MR, Nelson SH, Breen CI, et al. “Prolonged Nightly Fasting and Breast Cancer Prognosis.” JAMA Oncology, Published online first on March 31, 2016.   


FORCE receives funding from industry sponsors, including companies that manufacture cancer drugs, tests and devices. All XRAYS articles are written independently of any sponsor and are reviewed by members of our Scientific Advisory Board prior to publication to assure scientific integrity.

This article is relevant for:

Breast cancer survivors

This article is also relevant for:

men with breast cancer

people with triple negative breast cancer

people with ER/PR + cancer

people with Her2-positive cancer

people with a genetic mutation linked to cancer risk

people with breast cancer

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Study background:

Previous work in mice that were fed a high-fat diet showed that long periods (16 hours) of fasting protected the mice from inflammation and weight gain, two factors that are associated with a poor cancer outcome. However, nothing is currently known about how long periods of fasting affect human breast cancer recurrence and mortality. Catherine Marinac and her colleagues from the University of California, San Diego and other institutions published a report in the journal JAMA Oncology looking at whether the length of time a person goes without eating at night could predict recurrence and mortality for women with (stages I-III) breast cancer.

Researchers of this study wanted to know:

Does fasting at night help prevent breast cancer recurrence and mortality?

Population(s) looked at in the study:

This research used data from 2,413 women who participated in the Women’s Healthy Eating and Living (WHEL) study. These women had breast cancer (stages I-III), did not have diabetes, and were between the ages of 27-70 years old. Their dietary assessment consisted of multiple phone calls in a three-week period when they were asked what they ate and when they ate. The women were questioned in the year they enrolled in the study (baseline), the next year, and then again two years later. All 2,413 women completed the baseline assessment, about 91% completed the assessment the next year, and about 80% completed the assessment the last year. 

Study findings:  

  1. Women who reported fasting for fewer than 13 hours per night had a 36% increased breast cancer recurrence risk compared to women who reported fasting for more than 13 hours per night. This increase is modest.
  2. No association was found between fasting time at night and mortality due to breast cancer.


This study used data taken from the Women’s Healthy Eating and Living (WHEL) study; researchers did not produce the questions asked from the dietary assessment, or control for other things they might have wanted to ask. Additionally, the women were asked to self-report their diets and times that they ate. Self-reporting is a definite study limitation, because, memory is not infallible—women may forget the exact time they ate—and is subject to many biases. The study also followed women for a four-year period, so whether this effect lasts over longer periods is unknown.  Finally, it is unclear whether shorter nighttime fast periods are responsible for the increase in recurrence or if other lifestyle factors that accompany shorter nighttime fasting, such as alcohol consumption, amount of sleep a person gets each night, or other lifestyle choices that leads to the increase in recurrence risk play a role.


While this study suggests that long periods of fasting at night are associated with protection against breast cancer recurrence, more work needs to be done to confirm this finding. A large clinical trial would also allow researchers to control for other factors, such as when the women sleep. Many previous studies have found an association in people who sleep at times that disrupt their natural circadian rhythm and an increased risk for breast cancer. Based on this study, women do not necessarily need to avoid eating a light snack at night if they are hungry.

Posted 5/31/16

Share your thoughts on this XRAYS article by taking this brief survey.  

Expert Guidelines
Expert Guidelines

Nutrition for people diagnosed with cancer

The National Comprehensive Cancer Network (NCCN) recommends the following for cancer survivors: 

  • Think about your food choices and amount of fruits, vegetables and unrefined grains you eat compared with red and processed meats, alcohol, and foods or drinks with added fat or sugar. 
  • Think about your eating habits, including portion size, snacking, how often you eat out and use of added fats or sugars.
  • All survivors should be encouraged to:
    • Make informed choices about food to ensure variety and adequate nutrient intake.
    • Limit refined sugars.
    • Eat a diet that is at least 50% plant-based, consisting mostly of vegetables, fruit and whole grains.
    • Track calorie intake; monitoring of calories is an effective way to manage weight.
    • Minimize alcohol intake to no more than one drink per day for a woman and two drinks per day for a man.
  • For patients desiring further dietary guidelines, the USDA approximate food plate volumes are:
    • Vegetables and fruits should comprise half the volume of food on the plate
    • Vegetables: 30% of plate; Fruits 20% of plate
    • Whole grains: 30% of plate
    • Protein: 20% of plate
  • Recommended sources of nutrients:
    • Fat: plant sources such as olive or canola oil, avocados, seeds and nuts, and fatty fish.
    • Carbohydrates: fruits, vegetables, whole grains and legumes.
    • Protein: poultry, fish, legumes, low-fat dairy foods, and nuts.

The Academy of Nutrition and Dietetics, the United States Office of Disease Prevention and Health Promotion  and the American Institute for Cancer Research also publish expert guidelines on nutrition and health. 

Updated: 12/12/2021

Questions To Ask Your Doctor
Questions To Ask Your Doctor

  • How do my eating habits affect my risk for breast cancer recurrence?
  • What foods, if any, are known to reduce risk of breast cancer recurrence?
  • How else can I reduce my risk for breast cancer recurrence?

Open Clinical Trials
Open Clinical Trials

The following are studies focused on nutrition for people diagnosed with breast cancer. 

Visit our Featured Research Page and Research Search and Enroll Tool to find additional studies enrolling people with, or at high risk for cancer.

Updated: 05/29/2023

Peer Support
Peer Support

The following organizations offer peer support services for people with, or at high risk for breast cancer:

Updated: 05/07/2024

Find Experts
Find Experts

The following resources can help you locate a nutritionist near you or via telehealth

Finding nutritionists

  • You can find a registered dietician in your area through, the website for the Academy of Nutrition and Dietetics. Search for nutritionists by specialty, including "cancer," "weight management" and "heart health."

Related experts

  • The Livestrong at the YMCA program includes a free 12-week membership and fitness training with certified exercise experts. You can search by zip code for a program near you.  

Other ways to find experts

  • Register for the FORCE Message Boards and post on the Find a Specialist board to connect with other people who share your situation. 
  • The National Cancer Institute (NCI)-Designated Comprehensive Cancer Centers have specialists to manage the symptoms and side effects of cancer prevention or treatment. 
  • FORCE partners with Savor Health® to provide free, personalized, evidence-based nutrition support 24/7 and “on-demand" through their text-based Intelligent Nutrition Assistant (Ina®). You can subscribe here


Updated: 11/20/2023

Who covered this study?

The Telegraph

Simple night-time trick could stop breast cancer returning This article rates 4.0 out of 5 stars

Medical News Today

Nightly fasting may help reduce breast cancer risk This article rates 4.0 out of 5 stars

The Washington Post

Why breast cancer survivors should avoid late-night eating This article rates 3.5 out of 5 stars

How we rated the media

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