If you try intermittent fasting, a 16-hour overnight window was easier than alternate-day fasting
A small randomized crossover trial found higher diet satisfaction and less first-day mood disruption with a 16-hour overnight fast than with alternate-day fasting, supporting a cautious tolerability test rather than a weight-loss claim.
If intermittent fasting is on your list this week, start with a 16-hour overnight window rather than a 24-hour alternate-day fast, provided fasting fits your health situation. In a small randomized crossover trial, the overnight schedule produced higher diet satisfaction and avoided the temporary mood disruption seen after the first 24-hour fast. The result describes short-term tolerability. It says nothing about weight loss, blood sugar, cholesterol, or long-term adherence. 1
What the trial tested
The trial included 23 healthy females aged 18 to 19. Participants had a normal body mass index, exercised regularly, had regular menstrual cycles, did not smoke, and were free of several chronic and psychiatric conditions. The researchers recruited the sample at McMaster University between January and March 2024. 2
Every participant tried both fasting patterns in randomized, counterbalanced order. One four-day period used three 16-hour fasts from 8:00 p.m. to noon. The other used two 24-hour fasts from noon to noon, with a regular eating day between the fasts. The periods were separated by a four-day washout. Each protocol therefore included 48 hours of fasting, but the hours were distributed differently. 1
The schedule matters because the trial compared two different burdens. The 16-hour protocol placed the fasting period across the night and morning. The alternate-day protocol placed a full day without food between regular eating days. Participants answered the same mood, hunger, diet-satisfaction, and sleep questions at noon each day. 1
What changed during four days
| Outcome | 16-hour time-restricted feeding | 24-hour alternate-day fasting |
|---|---|---|
| Schedule | 8:00 p.m. to noon for three fasting days 1 | Noon to noon for two fasting days, with a regular eating day between them 1 |
| Mood | No significant increase in mood disturbance across fasting days 1 | Mood disturbance rose from fed baseline to the first 24-hour fast; Cohen's dz was 0.84, a large within-person effect. The change had faded by the second 24-hour fast 1 |
| Hunger | Hunger rose on all three fasting days, with Cohen's dz values of 0.62, 1.08, and 0.53 1 | Hunger rose on both 24-hour fasting days, with Cohen's dz values above 0.8 1 |
| Diet satisfaction | Higher than with alternate-day fasting; partial eta-squared was 0.22 1 | Lower than with the 16-hour schedule 1 |
| Sleep quality | No significant change in the self-reported measure 1 | No significant change in the self-reported measure 1 |
| Protocol adherence | 100% self-reported adherence 1 | 98% self-reported adherence; two participants reported milk with tea 1 |
The hunger result deserves a careful reading. Both protocols made participants hungrier, so the 16-hour window was not hunger-free. The difference appeared in the surrounding experience: the first 24-hour fast also produced a temporary mood disturbance, while the 16-hour fast did not produce a statistically significant mood change in this sample. 1
The overall condition-by-time result for mood had a partial eta-squared of 0.15. Diet satisfaction favored the 16-hour schedule with a partial eta-squared of 0.22. The study used repeated self-report measures, so these numbers describe how participants felt during the experiment rather than a clinical change in health. 1
Adverse events were common in both short protocols. Sixteen of 21 participants, or 76%, reported at least one event after the 16-hour protocol. Twenty of 23, or 87%, reported at least one after alternate-day fasting. The difference was not statistically significant, with an exact McNemar p value of 0.687. The study recorded more events numerically during alternate-day fasting, but the sample was too small to establish a reliable difference. 1
What the result can support
This trial supports a practical question about how a fasting pattern feels at the start. The 16-hour schedule kept the fasting period overnight and into the morning, while the 24-hour schedule required a full day without food. The first schedule was associated with greater diet satisfaction and fewer short-term mood changes in these participants. 1
The trial leaves several important questions open. Researchers did not measure body-weight change, fat loss, blood glucose, blood lipids, blood pressure, or long-term adherence. The study lasted four days per protocol, and the sample contained only 18- to 19-year-old healthy women with normal BMI. The findings therefore apply most closely to the early subjective experience of a similar group. 12
The study also has two design details that limit precision. The two protocol periods occurred on different approximate days of the menstrual cycle, and the researchers did not measure hormone differences within the follicular phase. An intervention-order interaction appeared for mood, and the sample was small. These details make the finding useful for choosing a cautious first experiment, while they leave room for later, larger studies to produce a different comparison. 1
People who are pregnant or breastfeeding, have diabetes, take medicines that can cause low blood glucose, have a current or past eating disorder, or have a chronic condition need individualized clinical advice before fasting. The trial excluded pregnancy and breastfeeding, diabetes, severe chronic disease, psychiatric conditions including eating disorders, antidepressant use, and recent prolonged fasting. 1
The same-day decision
For an otherwise healthy adult who has decided that intermittent fasting is medically appropriate, use the study's gentler schedule as a short trial of tolerability:
- Finish dinner around 8:00 p.m. and plan the first meal around noon the next day, creating a 16-hour overnight fast.
- Try the schedule for three days while keeping the food eaten during the eight-hour eating window adequate and balanced. The trial compared fasting schedules, not a special menu.
- Track hunger, mood, sleep, and ability to meet normal work, exercise, and nutrition needs. The study measured those experiences at noon.
- Stop the experiment and seek clinical guidance when fasting causes faintness, persistent weakness, disordered-eating thoughts, difficulty managing medication or glucose, or an inability to meet nutritional needs.
The decision is about choosing a lower-burden starting point, not about claiming a superior fasting diet. A dietitian can use the study to ask about tolerability before discussing longer-term goals, then adjust meal timing around medical conditions, training, medications, and nutritional adequacy. The paper was published in PLOS One on August 26, 2026, and reported no competing interests; funding came from Canadian NSERC grants, whose funders had no role in the study design, analysis, publication decision, or manuscript preparation. 12
References
- 1PLOS One full article
journals.plos.org
- 2PubMed record for the randomized crossover trial
pubmed.ncbi.nlm.nih.gov
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