The UCSD School of Medicine campus is shown here on May 1, 2019.
The UCSD School of Medicine campus. (Brandon Quester/inewsource)

In a study published Monday, UC San Diego School of Medicine researchers found when — not what — mice ate in a lab reduced the risk of breast cancer and improved insulin levels.

Restricting eating to an eight-hour window, when activity is highest, decreased the risk of development, growth, and metastasis of breast cancer in mouse models, the researchers at UCSD School of Medicine, Moores Cancer Center, and Veterans Affairs San Diego Healthcare System reported.

The findings, published in Monday’s edition of Nature Communications, show time-restricted feeding — a form of intermittent fasting aligned with circadian rhythms — improved metabolic health and tumor circadian rhythms in mice with obesity-driven postmenopausal breast cancer.

“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,” said senior author Nicholas Webster, professor at UCSD School of Medicine and senior research career scientist at VASDSH. “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.”

Breast cancer is the second most common cancer among women in the United States, after skin cancers. One in eight women will develop breast cancer in their lifetime.

Researchers used female mouse models mimicking postmenopausal hormone conditions to investigate whether time-restricted feeding of obese mice affected the development and growth of tumors and reduced breast cancer metastasis to the lungs. Three groups were compared in different mouse models. One group had 24-hour access to food. A second had food access for eight hours at night when mice are most active and a third group had an unrestricted low-fat diet.

Both obesity and menopause can disrupt circadian rhythms, the researchers said, which in turn can lead to the development of insulin resistance, predisposing individuals to chronic diseases like cancer.

The report indicates elevated insulin levels in obese mice are driving the accelerated tumor growth. Artificially elevating insulin levels accelerated tumor growth, whereas reducing insulin levels could mimic the effect of the time-restricted feeding.

The results suggest the antitumor effect of time-restricted feeding is due to improving metabolic health and lowering the levels of insulin, said Manasi Das, postdoctoral fellow in Webster’s lab and first author.

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,” Das said. “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.”

Exploring the ability of time-restricted eating to prevent breast cancer in women, or cancer in general, could affect a wide range of patients, Webster said, suggesting that clinical trials are warranted.

“The increase in risk of breast cancer is particularly high in women who are overweight and have been through menopause. For this reason, doctors may advice women to adopt weight loss strategies to prevent tumor growth,” Das said. “Our data suggests that a person may benefit from simply timing their meals differently to prevent breast cancer rather than changing what they eat.”