Beginning Friday evening and ending the following Saturday night, this year’s Yom Kippur falls on the earliest possible day according to the Hebrew calendar. The Day of Atonement is the holiest day of the year for the Jewish people, and it bears certain observances, including ceremonial fasting, prayers, and acts of repentance. Though couched in faith, the practice of fasting may indeed have deep scientific roots that highlight its value in lengthening life and boosting well-being.

The practice of eating moderate to large quantities of food for several days, then depriving the body for one or two, has come to be known as intermittent fasting. Specific interval ranges are still debated among researchers, but the vast majority of food experts often confer fasting’s success, especially among lab rats and other test animals. Recent studies suggest intermittent fasting reduces overall calorie load and uses modest stress to strengthen cellular defenses.

One 2003 study found that mice exposed to a period of fasting developed healthier levels of insulin and glucose than the mice kept on a consistent calorie restriction. Headed by Mark Mattson, who sits as head of the National Institute on Aging's neuroscience laboratory and has long skipped breakfast and lunch on weekdays, the study found intermittent fasting resulted in greater sensitivity to insulin, thereby reducing the fasting mice’s overall risk of diabetes.

“It makes me more productive,” the 56-year-old researcher told Scientific American of his own intermittent fasting habits. Perhaps the most popular fasting program is the 5:2 diet, which involves severe calorie restrictions for two non-consecutive days a week and normal eating for the remaining five days.

While Mattson’s research sits alongside other studies that have found fasting decreases stroke risk, staves off Alzheimer’s disease, and prolongs life, other accounts of fasting paint it as something of a body destroyer, particularly for women.

The female health blog Paleo for Women addresses some of the concerns of Mattson’s and others’ studies, highlighting a potential gender bias that prefers masculinization among mice through fasting.

“Many women find that with intermittent fasting comes sleeplessness, anxiety, and irregular periods, among a myriad of other symptoms hormone dysregulations,” wrote blog author Stefani Ruper, who goes on to analyze a separate study involving mice, also conducted by Mattson, that shows female mice become more masculine.

“They stop ovulating and menstruating,” Ruper wrote. “They become hyper-alert, have better memories, and are more energetic during the periods in which they are supposed to be sleep.”

Her ultimate conclusion is that intermittent fasting simply carries too many unknowns to reliably pursue as a diet. Mattson, meanwhile, remains convinced that the evidence points toward its success. Our ancestors seldom knew when the next meal would come, Scientific American notes, leading them to eat in prolonged meal-like sessions and essentially starve in the ensuing days. It’s Mattson’s belief this behavior has lasting effects today.

“If he is right,” Scientific American argues, “intermittent fasting may be both a smart and smartening way to live,” not to mention a viable diet program in the days surrounding the holy Day of Atonement.