Hunger During Intermittent Fasting

What the Best Evidence Actually Shows

This page focuses specifically on hunger during intermittent fasting; for the wider landscape of fasting patterns it sits within, see what is fasting. Trials of intermittent fasting as a treatment for a specific diagnosed disease are a separate area and are not summarized here.

The Key Meta-Analysis: No Clear Difference From Daily Calorie Cutting

The best current evidence finds no clear difference in hunger between intermittent fasting and simply cutting calories every day. A systematic review and meta-analysis pooling 17 randomized trials and 1,111 participants found no clear evidence that intermittent fasting affected hunger (WMD -3.03, 95% CI -8.13 to 2.08; 13 trials), fullness, desire to eat, or how much people felt they could eat any differently from daily calorie restriction; every trial was judged to have some concerns or a high risk of bias (Elsworth et al., 2023) [1]. This is the largest pooled analysis cited here on the question this page is built around, and the honest answer is "no clear difference," not "intermittent fasting reduces hunger."

Why Individual Trials Disagree

Individual trials disagree with each other in ways that do not resolve into a clean pattern. Two differently designed alternate-day-fasting trials found opposite results: an 8-week trial with fast days at 25% of energy needs, food provided, in 59 adults with obesity, found no increase in subjective hunger despite rising ghrelin, with fullness and the satiety hormone PYY increasing instead (Hoddy et al., 2016) [2], while a 22-day trial using zero-calorie fast days in 16 non-obese adults found hunger rose on the first fasting day and stayed elevated throughout, despite no significant change in fasting glucose or ghrelin (Heilbronn et al., 2005) [3]. This page states both rather than picking the more reassuring one; see alternate-day fasting for the fuller trial discussion, since both studies are shared with that page. A separate trial comparing intermittent and continuous energy restriction, with similar total weight loss in both groups, found neither approach produced a significant change in subjective appetite ratings, with no significant differences between the groups on any outcome, even though ghrelin rose in the intermittent-restriction group only; hormone shifts and felt hunger did not move together in that trial (Coutinho et al., 2018) [7]. A controlled crossover trial that cut meal frequency to once a day without reducing total calories found a significant increase in hunger compared with three meals a day, in healthy, normal-weight adults (Stote et al., 2007) [13]. A systematic review of 8 studies and 456 participants focused specifically on ADF and appetite rated the overall evidence low or very low certainty and reached no firm conclusions (Kucuk and Berg, 2022) [14], underscoring how unsettled the Hoddy-versus-Heilbronn disagreement above remains.

What Happens to Appetite Hormones (Ghrelin, Leptin, PYY)

Fasting regimens generally lower ghrelin and leptin (pooled ghrelin WMD -0.57 ng/ml; leptin WMD -2.65 ng/ml), based on a meta-analysis of 16 studies pooling intermittent fasting, time-restricted eating, alternate-day fasting, and fasting-mimicking diets together, in pooled trials that included healthy adults and adults with overweight or obesity; the same analysis found no significant effect on resistin and only a marginal, not-quite-significant rise in adiponectin (Tavakoli et al., 2025) [8]. That pooled result does not isolate intermittent fasting specifically, and no citation reviewed for this page demonstrates that a lower ghrelin level reliably translates into less felt hunger: in one trial, ghrelin rose without a corresponding hunger increase (Hoddy et al., 2016) [2]. A 48-hour period of severe energy deficit in 21 young adults, created by eating less than 10% of energy needs while exercise raised energy expenditure, lowered ghrelin while people rated their appetite higher and later ate about 811 more kilocalories over 36 hours (O'Connor et al., 2016) [9]; the heavy exercise makes this a different situation from ordinary intermittent fasting. Two very small, short trials of early time-restricted eating reported some favorable appetite measures: one found decreased ghrelin and hunger described as "more even-keeled" over the day, in 11 adults over 4 days per schedule (Ravussin et al., 2019) [6], and another found that in 8 men with prediabetes over 5 weeks, with calories matched, early time-restricted eating lowered evening desire to eat and raised fullness, though the change in hunger itself was not statistically significant (Sutton et al., 2018) [5]. Against those two small trials, a meta-analysis of four randomized trials in adults with overweight or obesity found time-restricted eating increased hunger compared with the same calories eaten without a time window (Silva et al., 2025: MD 2.05, 95% CI 1.46 to 2.64) [11].

Does Hunger Get Easier Over Time?

The trials that tracked hunger over time disagree. In one, hunger on fast days fell by week 2 of modified alternate-day fasting and stayed low (Klempel et al., 2010) [12]; in another, hunger rose on the first fasting day and stayed elevated for 22 days of zero-calorie alternate-day fasting (Heilbronn et al., 2005) [3]. Both were small, single-group trials, and the question of whether hunger eases over time on intermittent fasting is unresolved.

Common Practical Tips (Not Proven Fixes)

Protein and Fullness

In an exploratory analysis of one 12-month alternate-day-fasting trial (34 participants), those who lost 5% or more of body weight reported more fullness and less hunger, and increased protein from 15% to 20% of calories (Kroeger et al., 2018) [4]. This is a correlation within one small group; it does not show that eating more protein reduces hunger. Including protein in meals is ordinary general practice, not a tested hunger fix.

Water and Non-Caloric Fluids

Drinking water or other non-caloric fluids during the fasting window is widely recommended practice. No citation reviewed for this page tests fluid intake's effect on hunger during intermittent fasting directly; this is general practice, not a sourced finding.

Staying Busy and Distraction During the Fasting Window

Staying busy or distracted during the hardest part of the fasting window is commonly suggested practice. No citation reviewed for this page tests behavioral distraction specifically; treat this as general practice rather than a sourced finding.

Starting Gradually

Some people start with a shorter fasting window and lengthen it gradually. This is general practice; no study cited here tests whether a gradual start changes hunger. It does not contradict Heilbronn's finding that hunger did not ease within a 22-day trial on an unchanged schedule (Heilbronn et al., 2005) [3]; the two are about different things, how a schedule is approached versus whether hunger fades with time on an unchanged schedule. See alternate-day fasting for the adherence and dropout evidence on sustaining a fasting schedule.

When Hunger Is a Warning Sign, Not Just Discomfort

Hunger that is severe, persistent, or accompanied by lightheadedness, confusion, or a racing heartbeat, as a matter of general clinical knowledge rather than a citation on this page, is a reason to stop fasting and check with a clinician, not something to push through. People managing diabetes with insulin or other glucose-lowering drugs should treat hunger alongside shakiness, sweating, or confusion as a reason to check blood glucose and involve a clinician before continuing; no citation reviewed for this page tests hunger specifically in people on glucose-lowering medication. See what breaks a fast for what does and does not count as ending a fast, relevant if you are considering a small intake to manage hunger.

Authors and Funding of the Cited Studies

• Elsworth et al., 2023 [1]: Disclosure: "The authors declare no conflict of interest." Funding: UK Medical Research Council grant MR/N0137941/1, with support from the National Institute for Health and Care Research Bristol Biomedical Research Centre.
• Kroeger et al., 2018 [4]: Disclosure: "Krista Varady is the author of the book 'The Every Other Day Diet' published by the Hachette Book Group. The other authors have no competing interests to disclose."
• Sutton et al., 2018 [5]: Disclosure: "The authors declare no competing interests."
• Ravussin et al., 2019 [6]: Disclosure: "ER reports past consulting activities with Energesis Pharmaceuticals and Amway and personal fees from serving on the Nutrilite Scientific Advisory Board, outside the submitted work." Funding: an Early Career Research Grant from The Obesity Society, plus National Institutes of Health center grants. The disclosure continues: "This research was funded by The Obesity Society, which operates the journal Obesity. Since ER is the Editor-in-Chief of Obesity, he recused himself from being involved in any way in the review process for this manuscript." ER is Eric Ravussin, the first author.
• Tavakoli et al., 2025 [8]: Disclosure: "no competing interests"; no funding received for this study.
• Klempel et al., 2010 [12]: Krista A. Varady is senior (last) author. Disclosure: "The authors declare that they have no competing interests." Funding: University of Illinois at Chicago, departmental funding.
• Disclosures are listed where the full text of the paper was available to us; a study not listed here is not a statement that its authors have no ties.

Safety and Cautions

This is general information, not medical advice. A history of an eating disorder is a reason to get clinician guidance before using any hunger-management strategy tied to a restrictive eating pattern, rather than self-managing. Pregnancy and being under 18 are reasons to avoid intermittent fasting and its associated hunger-management practices without clinician guidance. None of the practical tips above are a treatment for an underlying medical cause of hunger, such as uncontrolled diabetes; they are general practices for people already cleared to fast, not medical advice. Talk to a clinician before starting or changing an intermittent-fasting practice if you are pregnant, under 18, have a history of an eating disorder, or manage diabetes or blood pressure with medication.