A new review challenges the idea that fasting always compromises cognition.
05 January 2026
By Emma Young
Fasting is one of the most popular eating regimens, with non-disordered engagement with fasting regimes getting plenty of endorsements from health professionals as well as medical researchers.
However, the term 'fasting' covers a lot of ground — from skipping lunch a few days a week to avoiding food for twelve hours or more, per day, for long periods. And, although research has shown that fasting can help in the long term with weight loss, blood sugar control, heart health, and more, given that the brain is such a calorie-guzzling organ, there are still questions about potential short-term impacts on cognitive function.
For this reason, Christopher Bamberg at Paris Lodron University in Salzburg and David Moreau at the University of Auckland set out to conduct a large-scale, rigorous, systematic review and meta-analysis of all the quality research they could find in this field — which, they note, has exploded in recent years. In the end, for their paper in the Psychological Bulletin, the pair synthesised evidence from more than 70 experimental studies, covering a wide range of fasting durations and focusing on broadly healthy participants (rather than studies on specific patient groups).
They concluded that, on average, whatever the fasting regimen, and whatever the type of cognition that was tested, there were only minimal (if any) resulting impairments in cognitive function. However, Bamberg and Moreau also make a number of more nuanced, and potentially important observations.
Firstly, they found that the later in the day that fasted participants were tested, the worse their performance was relative to the satiated ones. This was probably down to circadian, time-of-day factors, rather than the amount of time that had passed without food, because Bamberg and Moreau also concluded that the slight performance advantage of non-fasting participants diminished when fasted participants had fasted for longer. (It's worth noting, though, that only very few of the studies included participants who fasted for more than 24 hours; most featured 12-hour fasts.)
The pair suggests two possible, non-exclusive reasons for this. Firstly, a metabolic one: after about 8 to 12 hours of no food, the body transitions to using ketones, rather than glucose, for energy. This transition "may enable cognitive recovery following initial glucose depletion," they write. Another possibility is that after hours of fasting, the participants had gotten used to feeling hungry, reducing the potential impact of that feeling on cognitive performance.
The researchers also found that age mattered — unlike fasting adults, fasting children did worse on cognitive tests than children who were not fasting. This finding aligns, they write, with earlier research showing that developing brains are more vulnerable to fluctuations in energy availability, "and the consistent cognitive benefits of breakfast consumption in children, especially for working memory, attention and executive function."
Bamberg and Moreau also note that prior fasting experience may matter, too. Initial evidence suggests that people who have just started fasting experience more negative psychological states than people who are used to it, and this could impact cognitive performance — but they also note that this has not been well-studied.
There are other gaps in the literature, too, they write. Only 10 of the studies that they analysed reported blood glucose levels, which are an important marker for understanding the effects of fasting, they write. "Even more strikingly", 35 of the studies failed to mention the time of cognitive testing, "hindering any systematic analysis of circadian influences". Also, there were many studies that would have been eligible for inclusion if only they had included effect sizes — or the detail required to calculate them. And there were few studies on non-Western populations.
Clearly, despite the massive growth in research in this field, more work is needed to answer detailed questions about the cognitive impacts of fasting. But, as the pair write, these findings "challenge the common belief that fasting inherently compromises cognition", while showing that it's important to consider additional factors — most clearly, age, and the length of a fasting interval.
Read the paper in full:
Bamberg, C., & Moreau, D. (2025). Acute effects of fasting on cognitive performance: A systematic review and meta-analysis. Psychological bulletin, 151(9), 1147–1169. https://doi.org/10.1037/bul0000492
SOURCE:
https://www.bps.org.uk/research-digest/does-fasting-make-it-hard-think(accessed 14.01.26)
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