A preliminary study in mice suggests that when a person eats, and not what a person eats, may decrease the risk of breast tumors in obese women.
Researchers at the University of California San Diego investigated whether time-restricted feeding (TRF) — eating all meals and snacks within a specified period of time each day, when the individual is most active — could improve metabolic health and decrease the risk of breast cancer development and growth. In these studies, time-restricted eating had a dramatic effect, delaying the development of tumors and reducing tumor growth in obese mice, who were fed a high-fat diet, to levels seen in lean mice, researchers said.
The anti-tumor effect of TRF appeared to rely, at least in part, on the lowering of insulin levels, which are typically high in obese subjects and are linked to a higher risk of cancer, the study showed.
“Exploring the ability of time-restricted eating to prevent breast cancer could provide an inexpensive but effective strategy to prevent cancer impacting a wide range of patients and represents a groundbreaking advance in breast cancer research,” said Manasi Das, PhD, the study’s lead researcher, in a press release.
“Improving the metabolic health of postmenopausal women with obesity may mitigate their risk for breast cancer,” Das said.
The study’s findings were communicated in a poster titled “Time Restricted Feeding Delays Breast Cancer Initiation and Growth in a Mouse Model of Postmenopausal Obesity” at the Endocrine Society’s meeting ENDO 2019, held in March in New Orleans.
Researchers noted that time-restricted feeding — a type of intermittent fasting — does not necessarily lead to weight loss. TRF does not imply any changes in the amount of calories ingested, only the time period in which they are eaten.
There is increasing evidence, gathered both in mice and in small clinical studies in humans, that TRF benefits the metabolic health of obese individuals, regardless of weight loss.
For instance, a study in prediabetic obese men showed that TRF is able to lower insulin resistance (a precursor of diabetes), blood pressure, and oxidative stress, even if men did not lose weight.
According to several studies, obesity and poor metabolic health, known as metabolic syndrome, elevate the risk of cancer, particularly breast cancer, among postmenopausal women. Metabolic syndrome is characterized by high blood pressure, high blood sugar, excess fat around the waist, and abnormal cholesterol or triglyceride levels. In addition, excess insulin levels in the blood (hyperinsulinemia) is common in obese people, and has also been linked to a higher risk of breast cancer.
Researchers reasoned that using TRF to improve the metabolic health of obese postmenopausal women may reduce their risk for breast cancer. They also questioned whether any potential effect could be related to insulin.
They chose TRF, rather than calorie restriction (reducing calorie intake without incurring malnutrition), because they theorized that time-restricted eating would be easier for patients to stick with, given the hunger and irritability that come with long-term caloric restriction.
Researchers conducted experiments in female obese and non-obese mice, which mimicked the postmenopausal state.
They compared breast cancer development in obese mice who had 24-hour access to high-fat food versus mice on TRF with eight-hour access to the same type of food. The TRF mice were given access to food only at night, which is when they are most active.
According to the study, TRF had a “dramatic effect,” reducing tumor growth to levels comparable to non-obese mice.
In a different cancer mouse model, the dietary regimen also significantly delayed breast tumor onset and growth, reinforcing the prior results.
In the second part of the study, the insulin dependency of tumor growth was studied by increasing insulin levels using an implanted insulin pump, or by slowing insulin release into the bloodstream using the drug diazoxide.
Mice implanted with the insulin pump had faster tumor growth in contrast with mice treated with diazoxide, which had a delay in tumor development.
“The results suggest the anti-tumor effect of time-restricted eating is at least partially due to lowering levels of insulin, suggesting this intervention may be effective in breast cancer prevention and therapy,” the researchers said.
