Family of four plays at the beach with coastline in background

Intermittent fasting: Does it work?

July 23, 2019 | UCI Health
woman eating burger after intermittent fasting

A night owl, Paolo Sassone-Corsi likes to retire to bed well after midnight. In the morning he typically rises at 7 a.m. and goes about various tasks before taking a break to play soccer around noon. Finally, about 1 p.m., he consumes his first meal of the day. The long stretch between meals creates a 14-hour (or more) fast.

To Sassone-Corsi, it’s all about giving the machinery in the cells throughout his body time to rest, recover and switch on cellular pathways that help slow the aging process. He does it because his research suggests that humans aren’t meant to eat whatever, whenever.

“When to eat is as important as what to eat,” says Sassone-Corsi, PhD, the Donald Bren Professor and director of the UCI School of Medicine’s Center for Epigenetics and Metabolism. “We have metabolic pathways in our bodies that peak and trough. Hit them at the wrong time, and we’re not ready to process those calories.”

Regulated by biological clocks

Sassone-Corsi recently published a paper in the journal Cell Reports that provides more evidence to his lifelong work showing that the body’s organs and tissues are controlled by circadian rhythms — biology-based clocks — that influence metabolism and control a range of bodily functions.

Because energy is metabolized within cells under precise circadian controls, when we eat — and fast — affects the functioning of many organs and tissues.

“There are clocks in every single tissue, every organ, every cell of the body. We are really a network of clocks that are all connected to each other,” he says.

 “A large number and variety of metabolic processes are driven by circadian rhythm, and we have discovered that all these organs and clocks are communicating to each other.”

Eating time matters

Mice subjected to a 24-hour fast exhibited reduced oxygen intake and energy expenditure in the study. Those processes resumed when they were fed. This shows that circadian rhythms affect clocks in the liver and skeletal muscle, impacting metabolism, which can help slow age-related disease processes and improve health.

Genetically identical mice were fed at different times of day and compared. The mice fed at midnight became fat, while the mice fed the same diet at midday remained lean.

“What we’ve done is to validate the concept of reprogramming,” Sassone-Corsi says.

“The clock system is able to be flexible, to cope with different types of nutritional challenges. When you have that cheeseburger at midday, that’s OK because those cycles are ready to process that extra food. But if you hit the clock at the wrong time, you impose — on many tissues — an extra effort. They have to cope with this imposition of lots of calories getting to the liver.”

Exercise time matters, too

Fasting, he says, rebalances the body’s clocks.

“The cool thing with fasting is we activate a bunch of new cellular pathways that are not normally activated. Those are the ones that become extra beneficial for the whole organism.”

Sassone-Corsi’s latest research paper suggests morning may be the optimal time to exercise. He is a leader in “metabolomics,” an emerging field that measures metabolites in blood, providing clues to how genes interact with environmental influences such as exercise, meals and sleep.

Metabolomics is a science whose time has come, he says. “I think we are ready for this type of strategy. We are perfectly positioned to be among the first worldwide leaders in this discipline.”

Learn more about Sassone-Corsi’s research at

Related stories

Post a Comment

Your email address will not be displayed.