During Ramadan fasting, when eating is limited to nighttime hours, levels of the sleep hormone melatonin decrease at night, and the daily pattern of the stress hormone cortisol shifts—rising in the evening and falling in the morning—which may affect sleep and metabolic processes.

During Ramadan fasting, cortisol levels at night tend to be higher than usual, while morning cortisol levels are lower, which may indicate a disruption in the body’s natural daily hormone cycle and could be related to changes in metabolism and sleep patterns.

During Ramadan fasting, melatonin levels tend to be lower at night, even when the body's daily rhythm is maintained. This may be due to eating at night and could be linked to worse sleep and changes in blood sugar control.

People who fast every morning over a long period show a less pronounced daily rhythm in cortisol levels and are more likely to have insulin resistance and metabolic issues.

Studies on time-restricted eating outside of Ramadan show mixed results on cortisol levels: some report decreases, some show no change, and others report increases, with no clear relationship to when eating occurs during the day.

In obese adults, a 24-hour fast is linked to changes in the daily pattern of cortisol release, including a higher peak level and an earlier timing of that peak, while total cortisol production over the day remains unchanged.