Going without food for 24 hours can increase the daily fluctuation of cortisol levels, and doing this every day may change how the body's stress response system functions over time.

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.

In obese women, skipping food for 24 hours is linked to higher peaks and an earlier timing of the daily cortisol rhythm, but these changes do not occur in obese men, suggesting that fasting affects cortisol patterns differently by sex.

Exercise might help your body handle stress better, especially when studied in controlled trials, but the effect isn't huge and varies a lot between people.

In obese adults on a calorie-restricted diet, a 24-hour fast is linked to a measurable increase in the daily peak of cortisol and a shift in when that peak occurs, without changing the total amount of cortisol produced over 24 hours.

In obese adults, a 24-hour fast shifts the peak time of the stress hormone cortisol earlier by about 42 to 57 minutes in those who naturally wake up early, but does not change the timing in those who naturally stay up late. This suggests that a person's internal body clock affects how their cortisol rhythm responds to fasting.