September 24, 2025, 2:17 pm | Read time: 5 minutes
What is the ideal eating window per day? And how does it affect mortality? U.S. researchers explored these questions in a large-scale study. The answer is quite surprising.
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For years, the positive attributes of intermittent fasting have been reported and supported by various studies. The takeaway: If you want to maintain your weight or do something good for your health and life expectancy, you should avoid eating for 12 to 16 hours a day (FITBOOK reported). Now, researchers in a recent U.S. study have precisely determined the ideal eating window to positively impact longevity–so you can stay healthy and fit even in old age.1 Surprisingly, people who ate within an 11 to 12-hour window per day had the highest life expectancy. According to the researchers, those who take shorter or longer eating breaks could harm their health and life expectancy.
How was the study conducted?
The study used a prospective cohort design. The researchers utilized data from the NHANES (The National Health and Nutrition Examination Survey). This includes patient data and lab samples collected between 2003 and 2018. These data were also linked to mortality rates up to December 2019. The following individuals were excluded from the study:
- under 20 years old
- missing or incomplete dietary information
- extremely high energy intake from food (overnutrition)
- pregnant women
- missing demographic or health data
- abnormal body mass index (BMI) values
After excluding these groups, the study included 33,052 participants.
The participants had to report their food intake based on two 24-hour recalls. The eating window was defined as the period between the first and last intake of a calorie-containing food within a day. To account for daily fluctuations, the researchers averaged the two reports from the participants. Mortality rates and deaths were obtained from the U.S. National Death Index.
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What was considered in the data analysis
To better control for confounding factors and make the analysis more precise, so-called covariates were also considered. These can influence and distort the data analysis. The following variables were considered:
- demographic data
- socioeconomic factors
- lifestyle habits such as smoking, alcohol consumption, physical activity, and sleep
- diet quality (measured by the U.S. Healthy Eating Index)
- health status, including chronic diseases
- body mass index (BMI) and weight-related perceptions
How researchers determined an ideal eating window
In the study, 33,052 adults were observed over about eight years. During this period, there were 4,158 deaths, including 1,277 from cardiovascular diseases and 989 from cancer. A U-shaped relationship was found between daily eating time and overall mortality.
The lowest mortality risk was among those who ate within an 11 to 12-hour window per day. Surprisingly, those who ate over a period of 8 hours or less per day or fasted for 16 hours or more had a 34 percent higher mortality risk than the reference group. As the U-shaped relationship shows, an eating window of 15 hours or more was also associated with a 25 percent higher mortality rate. However, it should be noted that this relationship was statistically significant only among white participants.
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The researchers examined the individual subgroups more closely and found further connections between eating windows and health.
- Shorter eating windows of 8 hours or less led to an increase in cardiovascular mortality by about 50 to 70 percent, especially among older adults (over 65), men, and white participants.
- In younger adults (under 65), no significant mortality risk was observed for shorter windows.
- Women had an increased but statistically insignificant mortality risk with shorter windows, while significance remained for men.
- For cancer mortality, the connection with short windows weakened somewhat, with this trend observed only in women.
- The cardiovascular mortality rate mirrored these results, with the lowest risk at an 11 to 12-hour window and a significantly higher risk with shorter windows, but without a strong overall connection with longer windows.
Conclusion and limitations of the study regarding longevity
As is often the case in life, the middle ground seems to be best for our health and life expectancy when it comes to the ideal eating window. Fasting too long or too short increases the risk of mortality from cardiovascular diseases or cancer. According to the study, it is best to eat within an 11 to 12-hour window per day and then fast for 12 to 13 hours. Particularly strong connections were observed among adults over 65, men, and white individuals.
The study is supported by the large number of participants, the long observation period, and the consideration of influencing factors such as chronic diseases, lifestyle habits (e.g., smoking), and socioeconomic status. However, a weakness is that participants had to rely on their own memory for eating times. Additionally, only two recalls were considered, which can distort the analysis. Notably, data on the exact timing is missing. For example, it cannot be determined how mortality rates change when eating between 7 a.m. and 7 p.m. compared to 10 a.m. and 10 p.m.