Researchers have already identified obesity as a risk factor for cancer, so some doctors recommend reducing caloric intake to help prevent tumors. However, a new study now finds that prevention may be less about how many calories you consume and more about when you eat your meals.

Recent research has emphasized the link between the presence of obesity and an increased risk of developing certain types of cancer. The increase in the risk of breast cancer is particularly high in women who are overweight and have been through menopause. For this reason, doctors may advise some women to adopt various weight loss strategies to prevent the development of tumors. Now, a new study suggests that rather than changing what they eat to prevent tumor growth, a person may benefit from simply timing their meals differently.

"Improving the metabolic health of postmenopausal women with obesity may mitigate their risk for breast cancer," explains the study's lead researcher Manasi Das, PhD, from the University of California in San Diego.

Das and colleagues, who conducted their study in mouse models, have found that time-restricted eating could arrest tumor growth. Moreover, they have uncovered some mechanisms that may explain the link between obesity and cancer. The researchers presented their findings on Saturday at ENDO 2019, the annual meeting of the Endocrine Society, which is taking place in New Orleans, LA.

Time restriction vs calorie restriction

Time-restricted eating requires a person to have all of their daily meals within a specific window of time each day. This approach, the researchers suggest, could have a more positive effect on metabolic health than simple calorie restriction. "Time-restricted eating may be more successful than calorie restriction in controlling the negative effects of obesity, due to the hunger and irritability that makes it more difficult to stick with long-term calorie restriction," notes Das.

In the current study, the team conducted their research using female mice with no ovaries to simulate postmenopausal conditions. The researchers split their study into three stages. In the first stage, the researchers induced obesity by feeding the mice a 60% high-fat diet for 10 weeks. Then, they gave some of the mice unrestricted 24-hour access to food, while the rest had their access to food restricted to the 8-hour window during which they were the most active (in the case of mice, this occurs at night).

All of the mice also received injections with breast cancer cells for 3 weeks after the start of the experiment. The researchers then periodically monitored the growth of cancer tumors in each rodent.

The researchers compared the results for the obese mice with findings in a control group of rodents who had received a low-fat diet instead.

A cheap and effective prevention strategy?

In the second phase of the study, the researchers genetically engineered a group of mice to develop spontaneous breast cancer. Then, they fed some of these mice an unrestricted diet, while the others received a time-restricted diet. Both groups' diets were high in fat. As before, the researchers monitored tumor growth in each rodent.

Finally, in the study's third phase, the researchers focused on the potential role of insulin resistance—which can be an effect of obesity—in tumor growth. To do this, the team increased insulin levels in mice on a low-fat diet by implanting an insulin pump. They gave a group of control mice saline solution instead. The researchers then gave diazoxide, a substance that reduces insulin levels in the body, to mice on a high-fat diet. In this case, the researchers compared the mice with a control group that did not receive diazoxide.

The study results revealed that obese mice on time-restricted diets experienced much less tumor growth than mice who ate unrestrictedly. The results for obese mice on time-restricted diets were, in fact, comparable with those of the lean mice who had unrestricted access to food but received low-fat feed.

The researchers also found that rodents that had higher insulin levels due to the insulin pump implant had faster tumor growth than control rodents. Conversely, the mice that received diazoxide to lower their insulin levels had slower tumor growth than the control mice.

According to Das, "The results suggest the antitumor 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 lead researcher believes that the current findings may, in the future, lead the way to better prevention strategies for people at risk of cancer: "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."