Nighttime Fasting Decreases Breast Cancer Risk

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Women who spend less time eating each day and an increased amount of hours fasting overnight had a decreased risk of breast cancer, according to the results of a study presented at the American Association for Cancer Research (AACR) Annual Meeting, held April 18 to 22 in Philadelphia. This study was also published in Cancer Epidemiology, Biomarkers & Prevention.

Catherine Marinac, a doctoral candidate in public health at the University of California, San Diego, and colleagues found that for every 3-hour increase in fasting during the night, women had a 4% lower glucose measurement 2 hours after a meal (P < .05) and a non-statistically significant 0.4-unit decrease in hemoglobin A1c (HbA1c). Each 3-hour increase in nighttime fasting was also linked with an approximate 20% reduced odds of elevated HbA1c and a non-significant reduced odds of elevated glucose 2 hours after a meal.

Fasting for longer periods of time overnight significantly improved glucose levels, independently of how much the women ate during the day.

This work suggests that by decreasing the hours spent eating in a 24-hour cycle, women may be able to lower their body’s glycemic control, which may impact tumorigenesis.

“We believe that a regular prolonged, 12 to 14 hour nightly fast could potentially target fasting-responsive pathways related to the risk of type 2 diabetes, cardiovascular disease, and many cancers,” Marinac and study author Ruth E. Patterson, PhD, leader of the cancer prevention program in the Moores UCSD Cancer Center, told Cancer Network. “These diseases account for over 50% of deaths among US adults.”

Previous population studies suggested that poor glucose control-such as in individuals with diabetes or metabolic syndrome-is a risk factor for certain types of cancers, including breast cancer, and that diurnal feeding and fasting cycles influence metabolism. A 2007 meta-analysis showed that women with type 2 diabetes have a 23% higher relative risk of developing breast cancer compared with women who are not diabetic. Currently, researchers hypothesize that higher concentrations of circulating glucose can fuel cancer growth and cancer progression since hyperglycemia, a characteristic of diabetes, is linked to increased risk of breast cancer.

According to the authors, this is one of the first studies to show an association between prolonged nightly fasting and breast cancer risk in a nationally representative sample of women.

Studies in mice have suggested that decreasing the hours spent eating each day and increasing the length of time fasted overnight that aligned with sleep/wake cycles can improve glucose metabolism and potentially reduce the risk of chronic diseases such as cancer.

The researchers analyzed the link between length of nighttime fasting with glycemic control biomarkers and breast cancer risk in a sample of women who took part in the 2009–2010 US National Health and Nutrition Examination Survey. The participants had a median age of 47 years.

“An important aspect of this dietary pattern is that it does not require nutrition education, access to healthy foods, or costs involved in many other dietary recommendations. We believe that this change in the nightly fasting interval is a simple and feasible behavioral target that could lead to increased self-efficacy and stimulate people to make additional healthful lifestyles,” said Patterson.

Patterson added that she and her colleagues have submitted a proposal to test their hypothesis in a randomized controlled trial of 326 overweight or obese postmenopausal women whose usual nightly fasting interval is less than 12 hours. “Our pilot data support the feasibility of this intervention in white women and Latinas,” said the authors. They are continuing to investigate this in other study samples, including the Women’s Healthy Eating and Living Study of breast cancer survivors to test whether a prolonged nightly fast can reduce the risk of breast cancer recurrence and mortality.