Is fasting the best thing for your brain, or should it be avoided at all costs? Recent years have witnessed a tremendous uptick in people talking about the life-changing value of fasting for weight loss, longevity, and everything in between. But what does the science tell us about the link between fasting and brain health? In this post, we’re exploring the current science to understand what we know, what we’re still learning, and what it means for our diet today.
Background on fasting
Despite the recent preoccupation with fasting as a health hack, it’s notable that humans have been fasting by necessity since the start of the species. More recently (for thousands of years), fasting has been a key part of religious and other rituals. In the last decades, we’ve seen fasting popularized as a way to improve health. Proponents of this type of fasting highlight research suggesting benefits to metabolic health, decreased inflammation, weight loss, and even prolonging lifespan. Yet others have called attention to concerns for the stress placed on the body by fasting and the potential risk to certain groups, including women, the elderly, and people with a history of an eating disorder.
What is fasting?
Fasting is a relatively broad topic encompassing a range of protocols. Technically, fasting just means going without food for a certain period. Some of the more common forms of fasting include intermittent fasting (e.g., alternate-day eating or time-restricted eating like the 16:8 protocol—fasting for 16 hours a day and eating for 8), single or multiday fasting (no food for one or multiple days) and partial fasting (e.g., only drinking juice). Different forms of fasting may have differential effects on the body and varied degrees of research to support them as brain-specific interventions, and, in particular, intermittent fasting has been more heavily studied of late.
Fasting and brain health
When it comes to the brain, all the major pathways purported to be benefited by fasting in the body are relevant to the brain. For example, a decrease in chronic inflammation, regulation of metabolism, weight loss, and activation of lifespan-prolonging cellular cascades all should, in theory, translate to better cognitive health, decreased risk for mental health issues, and clearer thinking. But, while recent clinical research is interrogating these assumptions in detail, the results are far from consistent.
Short-term changes in cognition when fasting
As it relates to attention, one might expect that simple hunger would render fasting people less able to maintain focus. Yet the research here is mixed. In a recent meta-analysis, two studies showed benefits to attention, one reported worsening, and four reported no change. Similarly, processing speed was found to go up in one group of athletes fasting for 12 hours and decreased in a group of university students engaging in 12- to 16-hour fasts. Data from the same meta-analysis concluded that no major changes in working memory were seen. Conversely, psychomotor abilities (think hand-eye coordination) and set-shifting abilities (ability to rapidly change actions based on new data) were generally found to decline in those fasting.
Changes in mood when fasting
While limited, a small subset of clinical data provides some support for the role of fasting in improving mental health. One study of 31 people found lower tension, anger, confusion, and total mood disturbance in the fasting arm, while in a longer study in 1,422 people using 4- to 21-day calorie-restriction (200-250 calorie) fasts, there was a significant reported improvement in emotional well-being after the intervention. In another study using an 8-week intermittent fasting intervention versus control, no changes in mood were seen during the study period, but statistically significant benefits were reported several months later. Finally, in a recent meta-analysis of 1,436 people across 11 randomized controlled trials, it was found that fasters were less likely to have depressive and anxious symptoms than nonfasters. Though these data are overall promising, it’s worth mentioning that fasting has been associated with an increase in symptoms of irritability.
Long-term effects of fasting for dementia
The existing data on fasting for long-term brain health outcomes is sparse and largely mechanistic. One paper looked at 99 people with mild cognitive impairment and grouped them into groups of nonfasters, occasional fasters, or regular fasters and found that those engaging in regular fasting over a three-year window had the best chance at reversing their cognitive decline. But what about those with existing dementia?
Since fasting acts on key pathways in diseases like Alzheimer’s, it’s no surprise that certain researchers feel these modalities hold major promise as therapeutics. As described in a 2023 paper on this topic, some of the key preclinical evidence suggesting a potential value includes benefits to cognitive function and decreased buildup in amyloid plaque in the brains of animals subjected to calorie restriction and fasting. In a 2024 publication, researchers highlight additional benefits of decreased inflammation, metabolic rebalancing, positive effects on the gut microbiome, and the promotion of cell cleanup processes (called autophagy) as other reasons fasting might benefit Alzheimer’s patients. Some important counterpoints include that getting a patient with dementia to fast could be problematic to enforce and that getting adequate nutrient intake can already be a challenge in dementia.
Bottom line: Should you fast for brain health?
Fasting, especially intermittent fasting, is showing promise, especially to fight against metabolic disease and dysfunction. Excess weight, high blood sugar, and other forms of metabolic imbalance may especially benefit from various fasting protocols, and since these conditions also correlate with brain health, it’s not unreasonable to assume that they should benefit the brain. Data seem a bit better for the idea that fasting could benefit mental health in comparison with short-term cognitive outcomes, but there are good reasons to suspect potential benefits to long-term brain health may be seen in future research.
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With this said, the best-studied diets for enhancing short-term brain function, protecting good mood, and promoting long-term brain health remain variants of the Mediterranean diet that focus on sustainable patterns of daily nutrition. Fasting, especially if done without guidance, can create opportunities for insufficient nutrition, which could itself be concerning for brain health. The data to date suggest that, despite being a potentially efficacious dietary strategy for enhancing mental or cognitive health, we simply don’t have a strong enough signal to recommend fasting as a key method of protecting and enhancing brain health over other better-studied options.