Intermittent fasting’s real benefit may come after you start eating again

Research continues to uncover new details on how fasting may help extend life.

A new study published in the journal Nature Communications investigated how intermittent fasting can boost longevity in small worms often used in aging research.

Researchers from the University of Texas Southwestern Medical Center in Dallas compared worms that were fed normally to those that underwent a 24-hour fast in early adulthood and were then re-fed for 24 hours, according to a press release.

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The scientists measured a variety of factors, including stored fat, gene activity related to fat metabolism, and lifespan.

The results showed that the life-boosting benefit did not depend on the fasting itself, but on the body’s behavior after eating again.

Study lead Peter Douglas, PhD, associate professor of molecular biology and a member of the Hamon Center for Regenerative Science and Medicine at UT Southwestern, suggested that these discoveries "shift the focus toward a neglected side of the metabolic coin – the re-feeding phase."

"Our data suggest that the health-promoting effects of intermittent fasting are not merely a product of the fast itself, but are dependent on how the metabolic machinery recalibrates during the subsequent transition back to a fed state," he said.

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"Our findings bridge a gap between lipid metabolism and aging research," he added. "By targeting aging, the single greatest risk factor for human disease, we move beyond treating isolated conditions toward a preventive model of medicine that enhances quality of life for all individuals."

Lauri Wright, director of nutrition programs at the University of South Florida's College of Public Health, called this a "high-quality" study that adds an "important nuance to how we think about fasting and longevity."

The benefits of the re-feeding phase after fasting were "especially interesting," Wright, who was not involved in the study, told Fox News Digital.

"The researchers showed that longevity was linked to the body’s ability to turn off fat breakdown after fasting, allowing cells to restore energy balance," she reiterated.

"From a scientific standpoint, that’s a meaningful shift, because it suggests fasting is not just about burning fat, but about metabolic flexibility."

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Fasting may support longevity through triggering metabolic switching, enhancing cellular repair and stress resistance, and improving markers like insulin sensitivity, research shows.

Although this study provides "important insight" on the power of re-feeding, Wright noted that the findings should be approached with caution, as the study was done in worms and cannot always be translated to humans.

"Additionally, it explains how a process might work in a controlled lab condition rather than real-world eating behaviors," she added as a limitation. "Finally, the study is short-term and doesn't give us the long-term translation on lifespan outcomes."

Wright cautioned that fasting is "not a magic solution for longevity, and how you eat overall matters more than when you eat."

"I advise, first and foremost, to focus on diet quality, including a variety of fruits and vegetables, healthy fats and minimally processed foods," she said.

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For those who are considering fasting, it’s better to stick with a moderate plan — like a 12- to 14-hour overnight fast — rather than going to extremes, Wright said. After fasting, she recommends focusing on well-balanced meals.

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Several groups of people should be cautioned against fasting, according to Wright, including those with diabetes who are on insulin or hypoglycemic medications, people who are pregnant or breastfeeding, anyone with a history of eating disorders, and older adults at risk of malnutrition.

Anyone considering intermittent fasting should consult with a doctor before starting.