Many people have sworn by intermittent fasting as a way to lose weight or address other health concerns. Could it have an impact on your risk of developing breast cancer, too? A new study says it just might.

Researchers from the University of San Diego School of Medicine, Moores Cancer Center, and Veterans Affairs San Diego Healthcare System looked into how modifying meal times played a role in the development and growth of breast cancer tumors in mice. The findings were published in the journal Nature Communications.

Using female mouse models to mimic postmenopausal hormone conditions, researchers put obese mice onto a time-restricted feeding schedule and monitored the development and growth of tumors, as well as how often the tumors spread to the lungs. There were three meal schedules used: one group with 24-hour access to food, one with an eight-hour window during their most active hours, and one with an unrestricted low-fat diet. Those that ate within that eight-hour time frame had a lower risk of cancer developing, growing, and spreading.


Dr. Nicholas Webster, professor at UC San Diego School of Medicine and senior career research scientist at VASDSH, was the study’s senior author.

He says, “Previous research has shown that obesity increases the risk of a variety of cancers by negatively affecting how the body reacts to insulin levels and changing circadian rhythms. We were able to increase insulin sensitivity, reduce hyperinsulinemia, restore circadian rhythms and reduce tumor growth by simply modifying when and for how long mice had access to food.”

Obesity and menopause can both disrupt circadian rhythms, which can lead to insulin resistance and an increased risk of chronic diseases like cancer. The researchers say data shows that elevating insulin levels in mice accelerates tumor growth while reducing levels could mirror what happens with time-restricted feeding. This could mean that intermittent fasting and its impact on tumors is due to the improvement in metabolic health and lower insulin levels.


Dr. Manasi Das, postdoctoral fellow in the Webster lab, is the study’s first author. He explains, “Time-restricted eating has a positive effect on metabolic health and does not trigger the hunger and irritability that is associated with long-term fasting or calorie restriction. Through its beneficial metabolic effects, time-restricted eating may also provide an inexpensive, easy to adopt, but effective strategy to prevent and inhibit breast cancer without requiring a change in diet or physical activity.”

The study authors say that the risk of breast cancer is particularly high among post-menopausal women who are overweight, so doctors sometimes recommend weight loss as a means to reduce their chances of developing the disease. Their findings mean that women may not have to change what they eat, just when they eat it.

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The American Cancer Society says that being overweight can also raise your risk of breast cancer due to increased estrogen levels, so avoiding weight gain is helpful. You don’t have to overboard with exercising, though. They say just 75 to 150 minutes of brisk walking each week has been shown to lower risk.


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