Proponents of intermittent fasting say the practice can support everything from weight loss and metabolism to blood pressure and healthy blood-sugar levels.
“I am a huge advocate of intermittent fasting,” Julia Zumpano, a registered dietician with the Cleveland Clinic Center for Human Nutrition, tells Nexstar. “I think there are a lot of great benefits.”
The idea behind intermittent fasting — or time-restricted eating — is simple: Eat only between a specific window of time each day (or on certain days of the week), thereby reducing calorie intake and insulin spikes, and hopefully improving health.
Zumpano, however, warns that intermittent fasting isn’t for everyone, and especially those with underlying health conditions or chronic diseases, as well as people who are pregnant or undergoing cancer treatment. But even for the ideal candidates, common mistakes can easily hinder weight-loss goals and overall health.
For starters, studies in recent years have shown more benefits for those who began their intermittent fasting earlier in the evening — i.e., eating earlier in the day and cutting off food in the evening, rather than skipping breakfast and eating until closer to bedtime. A 2024 study from the Barcelona Institute for Global Health suggested that earlier eating windows (though not necessarily intentional intermittent-fasting practices) were associated with better outcomes in terms of weight loss. And a review of time-restricted diets on metabolic outcomes, conducted by researchers in Taiwan and published in 2026, showed improvements in metabolic health, with the findings indicating “early time-restricted eating” being “superior to late time-restricted eating.”
The researchers behind both studies hypothesized that earlier eating windows were associated with these outcomes because they more closely followed the human body’s circadian rhythms, or our natural sleep-wake cycles. Zumpano agrees.
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“When we’re sleeping, we utilizing the least amount of energy all day,” Zumpano said. “If you’re packing in all this food and then going to sleep, what is your body going to do? It’s going to store it. It’s going to cause your insulin levels to rise.”
“You’re stimulating this process in the wrong time of day,” she added.
For this reason, Zumpano recommends that her clients don’t cut breakfast from their eating windows, and try to begin fasting at least three hours before bed to let their blood-sugar levels normalize. The length of an eating window can also vary based on dietary needs or lifestyle, but they most commonly last for eight or 10 hours per day (e.g., eating only between 11 a.m. and 7 p.m., or 9 a.m. and 7 p.m.)
“I think a dietitian would be a great place to find out [what’s right for you],” Zumpano said. “I tell people, just start with a 12-hour window … That’s extremely safe, in almost all cases.”
What she doesn’t often recommend is eating only one huge meal in the middle of the day, and avoiding food altogether until the following day. This fasting method, sometimes called the “OMAD” diet (“one meal a day”) isn’t sustainable, and it isn’t generally believed to provide any additional health benefits, according to Zumpano.
“I think a lot of times you see overeating in that window. Or the opposite: You’re not able to meet your nutrient needs,” she said. “It can lead to disordered eating, and it can be limiting, from a lifestyle perspective.”
Making a mistake here or there isn’t the end of the world, either. In fact, Zumpano said she often recommends “one to two non-fasting days” for clients, to keep the diet sustainable.
There’s always concern, of course, when it comes to the safety of a diet, and especially those that feel more restrictive than others. Such is the case with time-restricted eating, which was the subject of a study linking shorter eating windows (specifically 8-hour windows) to an increase in the risk of death from cardiovascular disease.
Zumpano told Nexstar she believes this study, presented at an American Heart Association conference in 2024, was flawed. And a doctor with the Mayo Clinic, Francisco Lopez-Jimenez, pointed out that the study wasn’t published in any peer-reviewed journal.
Lopez-Jimenez instead pointed to evidence that linked one type of intermittent fasting — skipping breakfast — with increased cardiovascular disease.
“Early morning is the time when people have the most heart attacks,” Lopez-Jimenez wrote in a Q&A published by the Mayo Clinic. “Part of the reason for that is the high-adrenaline state that occurs early in the morning. If you match that with no food, no calories at all, that might be the reason why studies show that people practicing intermittent fasting are not necessarily healthier or safer.”
Another small study from the New England Journal of Medicine suggested that intermittent fasting, which can be a useful method for reducing calorie intake, was just about as effective for weight loss as simply counting calories.
Zumpano didn’t disagree, but responded by saying intermittent fasting is still “absolutely” a “tool in the toolkit” for people looking to lose weight or improve their health. But those who are curious should reach out to a professional to discuss any possible medical complications, and remain realistic about their goals.
“Some people think it’s going to be a cure-all for weight,” she said. “You could see moderate reductions in weight. … It all comes down to the person.”
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