Scientists think that nearly every living organism — including humans, dogs, mice, worms, bacteria, and, possibly, even extremophiles that live in harsh conditions like the deep sea or enormous caves — has some type of internal clock. These internal clocks, or circadian rhythms, are 24-hour cycles that govern the behavior of living things, all of which evolved in the context of Earth's alternating day/night pattern. Researchers are finding more and more evidence that disruptions to this timing can influence diet and sleep and lead to obesity, stress, metabolic disorder and possibly even cancer.

Circadian rhythms that follow a daily cycle are among the most common types of biological clock, as most organisms, including people, are active during the day and sleep at night. But other aspects of life can also oscillate throughout the day, including cognitive ability or even mood. 

“The circadian clock is the body’s internal timing system, which interacts with the timing of light and food to produce our daily rhythms,” says Satchidananda Panda, a professor in Salk’s Regulatory Biology Laboratory. 

Panda studies the genes, molecules, and cells that keep the whole body on the same internal clock. His lab has discovered that nearly 80 percent of genes follow a circadian rhythm, and identified a pair of genes that help keep eating schedules in sync with daily sleep cycles. He often refers to the “discipline of the clock,” the fact that biological activity — such as the production of proteins that help process food — rises during an animal’s waking period and slows during its resting period.

Humans evolved to hunt and forage during the day and sleep at night, meaning that human biology is designed to support eating and activity during the day and cellular repair and cleanup at night, according to Panda. But modern society offers access to food 24/7. These changes in eating patterns affect how the body processes food and functions.

The Salk lab previously demonstrated that confining mice to time-restricted eating during a ten-hour window can protect against obesity and diabetes. These groundbreaking studies have launched a new approach to potentially improving human health: restricting one’s calorie intake to an 8- to 10-hour window could confer a host of health benefits, including weight loss. 

Even though the research in humans is early, the lab is optimistic. “The circadian system is this core pillar of how our body works that affects everything. You are mentally and physically a different person at different times of day,” says Emily Manoogian, Salk postdoctoral fellow in Panda’s lab. (Hear more from Manoogian on diet and timing at the Where Cures Begin podcast). 

Currently, she is helping conduct a three-year study to examine whether restricting food intake to a 10-hour window can improve firefighters’ well-being. Firefighters, like other shift workers, are at higher risk for chronic diseases because of how their schedule disrupts the body’s circadian rhythms. The goal of the study is to see if time-restricted eating can help counter some of the circadian rhythm disruptions and negative health effects that accompany shift work. 

The team has also pursued studies around cancer and circadian rhythm. In January 2018, the lab published a paper in the journal Nature, describing how targeting the circadian clock in cancer cells could work as a therapy. Cancer cells disrupt their cellular clocks so they can get nutrients all the time to support their unchecked growth. The team found that when drugs are used to reactivate the circadian clock in tumors, cancer cells can’t survive. Meanwhile healthy cells are unharmed because they are already accustomed to the “discipline of the clock,” pointing to a new possible target for cancer therapy.

To pursue human studies, the team developed an app that tracks the timing of people’s food intake to further understand the relationship between circadian interventions and health. It has already been tested by thousands of people to conveniently track food intake, sleep and exercise habits.

“In the future, we would like to examine the differences in eating times across the world,” says Manoogian. “People in different areas are getting different exposure to light, so when they eat might be very different than someone else in another part of the globe.”

Based on their time-restricted eating research so far, the team has some general tips:  

· Avoid eating for at least one hour after waking up.

· Do not eat two to three hours before bedtime.

· When traveling, especially by plane, cut your calories by half on those days. 

To learn more about this field of research and listen to an interview with Manoogian, check out the Where Cures Begin podcast on Salk.edu/podcast, iTunes or anywhere your listen to podcasts.