In recent years, we’ve gotten used to playing with the clock—shrinking our eating window to eight hours, skipping breakfast, or stretching the night with a small snack. But a new U.S. study flips the script, showing that extremes may actually do more harm than good.
Those who fast too long or, conversely, spread their meals over too many hours may increase their risk of disease—and, in extreme cases, even early death. So where’s the balance? It turns out to be far simpler than we thought: 11 to 12 hours of eating per day—no more, no less. That’s it? Yes, exactly—no extreme fasting and no complicated routines. Surprised? So were we.
The study, published in the journal Aging Cell, analyzed data from about 33,000 adults over age 20—men and women from across the United States—and examined how the length of the daily eating window affects the risk of death from any cause, including cardiovascular disease and cancer. The data was collected as part of the National Health and Nutrition Examination Survey (NHANES) between 2003 and 2018, with participants followed for eight years, through 2019.
What the researchers actually found
Sometimes the numbers tell the story best. The analysis revealed a surprising picture: optimal health wasn’t associated with long fasting or extended eating windows, but rather with a moderate, middle-ground approach.
“The study found a link between the length of the eating window and mortality risk, with the lowest risk observed among those who ate over a period of 11 to 12 hours per day,” says Limor Tal Poni, chief dietitian at Maccabi Healthcare Services. “Those who ate during a shorter window—less than eight hours—had a 34% higher risk of death from all causes compared to the control group. A very long eating window, over 15 hours, also showed increased risk, though the statistical significance was lower.”
Another key finding: researchers broke the data down by subgroups. Among men and older white adults, eating windows of less than eight hours were linked to a sharp rise in cardiovascular mortality—between 50 and 70 percent. Among women, shorter eating windows were also associated with higher mortality risk, though the results were not statistically significant. In men, however, the significance remained.
The takeaway is clear: extremes are harmful, and the balance lies in the middle. “According to this study, an 11–12-hour eating window is the most advisable in terms of reducing mortality risk,” says Tal Poni. “The relationship follows a U-shape—go too far in either direction, and the risks go up. It’s that middle range that appears to be ideal.”
Is intermittent fasting really right for everyone?
Still, Tal Poni stresses that this study is not the only one in the field. “It’s important to remember there are also other studies supporting intermittent fasting, which many people follow today. A common model is 16:8—an eight-hour eating window followed by 16 hours of fasting. Other models include 5:2, where calorie intake is restricted on two days a week and normal on the rest, or even alternate-day fasting. We know that shorter eating windows—less than eight hours—have shown metabolic benefits in some studies, including lower fasting glucose, insulin levels, and insulin resistance. Some have also found improvements in blood lipids, blood pressure, body weight and fat, cardiovascular health, and even anti-inflammatory effects.”
Still, she cautions against drawing overly simplistic conclusions. “You have to be careful. There are many studies on intermittent fasting, and it can get confusing. That’s why it's better to walk away from this with a few clear recommendations.”
Personalization is key
“Intermittent fasting isn’t suitable for everyone,” she says. “While it may have advantages, it's important to personalize. For some people, eating over 11–12 hours a day may actually be more appropriate. There are groups for whom intermittent fasting is not recommended: pregnant women, people with diabetes who use insulin or certain medications, teenagers, and those with a history of eating disorders. In such cases, professional guidance is essential.”
Not just when you eat, but what and how
Once you’ve reorganized your eating schedule, don’t forget that what you eat matters just as much. “You need to pay attention to what enters your body during that window,” she advises. “It’s best to follow a Mediterranean-style diet—rich in fruits, vegetables, whole grains, quality proteins, and healthy fats. That’s just as important as the timing.”
“Watch what goes into your body: fruits, vegetables, fish, and healthy fats, and try to minimize ultra-processed foods. It’s also important to consider sleep cycles, work hours, and physical activity—these all impact health. Ultimately, you have to listen to your body, avoid rigid thinking, and consult with professionals. A clinical dietitian can help tailor your eating schedule to your health status, goals, and lifestyle.”
Tal Poni also notes that the findings from this study align with broader scientific understanding of the circadian rhythm—the body’s internal clock that runs on a 24-hour cycle. “There’s a central clock in the brain that responds to light and darkness, but also peripheral clocks in other organs that are influenced by food timing, sleep habits, activity, and more,” she explains. “The circadian rhythm regulates everything—sleep, hormones, metabolism, even body temperature. When we eat in sync with this clock, we let the body function optimally. Eating against it—like late at night—can come at a health cost.”
Even with the new study’s results, Poni urges caution. “This is an observational study. It shows a correlation, not causation. We can’t say for sure whether the eating window itself reduces risk, or whether healthier people just tend to eat in this way.”
She also points out gaps in the data. “The study didn’t include enough detail about when during the day participants actually ate—for instance, what time their last meal was. That’s an important detail that could change the whole picture. And there are many external factors that can complicate the conclusions, like sleep quality, dietary changes, or shift work—all known to affect health.”
Bottom line: moderation, not extremes
In closing, Tal Poni emphasizes the practical takeaway: “It’s worth maintaining a consistent daily eating window of 11 to 12 hours. For example, starting breakfast around 7 or 8 a.m. and finishing dinner by 7 or 8 p.m. That fits with the circadian rhythm of most people. A very short window of less than eight hours isn’t right for everyone. Anyone considering that approach should speak with a professional. Personalization is the key—matching your eating habits to your lifestyle, preferences, health status, and even your bloodwork.”