Eight days on water, and 9 of 15 men felt better than usual by the end, up from 3 on day one. All of them had done it before and expected it to help

Ask most people how the eighth day without food would feel and they will guess miserable. Researchers in Poland put a plainer question to a group of men living through it: "How do you feel today?" Each day the men picked one of three answers, worse than usual, same as usual or better than usual. The paper, published in Nutrients on 31 October, followed them through an eight-day water-only fast while they stayed at home and kept up their work, family and social lives.

On the first day, 20% said better than usual and 40% said worse. On the last, 60% said better and 13% said worse. With 15 men in the analysis, that works out by our count at 3 men against 9, and 6 against 2. The road between was bumpy. Day two was the low point, with 47% feeling worse, and on day seven a third still did. In the researchers' model, the odds of a man landing in a higher category rose 24.5% with each passing day (odds ratio 1.245, 95% CI 1.055 to 1.467).

Who these men were matters more than any of those numbers. To take part, a volunteer had to have already fasted for at least seven days on mineral water alone. They were 37 to 77 years old, 59.8 on average, mostly with higher education, and went in with what the authors call a positive attitude, expecting better health and lower weight. Three of the original 18 volunteers chose not to continue, including both women, and their data were dropped. So the result describes experienced fasters who wanted to be there and stuck it out. By our division, one volunteer in six is missing from that picture.

There was also no comparison group. Nobody was randomised, nobody ate normally alongside them, and nobody could be blinded to going without food. The authors themselves name expectation and placebo effects as a limitation. Well-being is exactly the sort of answer that can drift upward as a hard thing nears its end, and a man counting down to the last day of something he chose may feel better for that reason alone. This design cannot separate that feeling from anything the fast did to the body.

A fuller mood questionnaire, filled in daily, gives a narrower result than the headline number suggests. Tense arousal, the checklist's measure of tension and anxiety, fell from an average of 20.0 to 17.3 between the first and last days (p = 0.011). Hedonic tone, which captures how pleasant a mood is, did not change. Nor did energetic arousal. So the men did not report becoming happier or more energetic on these scales; they reported less tension. Time also explained only 3.8% of the variation in tension scores across the fast, while differences between the men accounted for much more.

Blood tests were taken at rest and three minutes after a maximal cycling test, before and after the fast. Post-exercise cortisol rose from an average of 333 to 530 ng/mL across the fast (p = 0.004). Serotonin after exercise was far higher than serotonin at rest once the fast was over, 632 against 251 ng/mL (p = 0.028). Alpha-endorphin was highest in the same after-fast, after-exercise measurement. Oxytocin showed no significant change. Resting cortisol went from 296 to 469 ng/mL, which looks large, but the paper does not list it as a significant difference after its correction for several comparisons, a reminder of how noisy 15 people can be.

It would be tempting to tie those hormones to the mood story: endorphins up, tension down. The data don't allow it. Changes in resting cortisol, serotonin, oxytocin and alpha-endorphin showed no significant link with changes in well-being or any mood score. The authors say a small sample may be part of the reason, and they offer their account of how body and mind adapt only as a hypothesis for later studies. A blood sample also can't show what is happening inside the brain, and the paper itself notes that more than 90% of the body's serotonin is made in the gut.

What this adds is modest but useful: a day-by-day record showing that, in a small group of practised and medically screened men, an eight-day fast did not bring a steady slide in how they felt. It doesn't show that fasting lifts mood, and it says nothing about women, first-timers, or anyone with a medical reason not to stop eating. These men had a medical examination three days before they started and stayed in phone contact with a physician and a psychologist during the fast and for two weeks afterwards. A proper test would need a control group, a far larger sample and people who haven't already decided that fasting works for them.