Many individuals often wonder, does regularly skipping breakfast make it harder to concentrate? According to a recent review published in the Psychological Bulletin, the answer may be more reassuring than you think. Researchers have gathered substantial evidence suggesting that short-term fasting does not significantly impact mental clarity. Dr. David Moreau, an associate professor at the School of Psychology at the University of Auckland, New Zealand, and coauthor of the study, explains, “The notion that fasting interferes with mental performance likely arises from the feelings associated with hunger—tiredness, distraction, and irritability. It’s easy to assume that these sensations correlate with diminished cognitive function. Although early studies supported this idea, a comprehensive analysis reveals that these effects largely diminish.”
This revelation could be a game-changer for those interested in intermittent fasting but fearful of experiencing brain fog. However, it's crucial to note that not all fasting is equal. There exists a distinct difference in brain function during short-term fasting compared to long-term fasting. Researchers conducted an analysis of 71 studies involving nearly 3,500 participants who either engaged in fasting or had recently consumed food. They assessed variables such as memory recall, decision-making, response times, and accuracy.
Most of the fasting periods in these studies were short-term, averaging around 12 hours. After thoroughly analyzing the data, researchers concluded that there were no significant differences in cognitive performance between individuals who practiced short-term fasting and those who had recently eaten. Dr. Moreau emphasizes, “The brain possesses built-in mechanisms to maintain functionality and energy even in the absence of food—a reassuring message for anyone practicing intermittent fasting.”
However, the findings differed for individuals who engaged in longer fasting periods exceeding 12 hours. In this group, researchers observed slight declines in cognitive performance. Dr. Sonya Angelone, a consulting nutritionist and former spokesperson for the Academy of Nutrition and Dietetics, notes, “Fasting durations exceeding 24 hours may negatively impact cognitive performance.” Nevertheless, as the study indicates, short-term intermittent fasting appears to be mentally safe for the majority of individuals.
Although the study shows no significant cognitive decline in experienced short-term fasters, newcomers may experience some initial challenges. Albert Matheny, a registered dietitian and co-founder of SoHo Strength Lab, explains that it takes time for your body to adapt to fasting. “For individuals unaccustomed to fasting, the absence of food can be mentally distracting, especially if they are used to eating on a consistent schedule,” he states. Additionally, individuals with metabolic conditions such as diabetes may experience varied cognitive impacts due to intermittent fasting, according to Dr. Moreau.
While fasting does influence your brain, it does not necessarily compromise cognitive abilities, which encompass thinking, learning, remembering, and making judgments. Under normal circumstances, the brain primarily relies on glucose stored as glycogen. However, when fasting occurs, this source of energy diminishes. Dr. Moreau emphasizes the remarkable adaptability of the brain, stating, “As glycogen levels decrease during fasting, the body begins converting fat into ketone bodies, which serve as an efficient alternative fuel for the brain.”
He adds, “Brain metabolism takes precedence over other bodily functions, meaning that during fasting, the brain receives energy before muscles do.” This adaptability allows for stable cognitive function even during short-term fasting. The brain's ability to maintain a consistent energy supply, even in periods of food scarcity, is vital. As Dr. Moreau notes, “From an evolutionary perspective, it makes sense: Our ancestors needed to remain alert and think clearly while foraging for food, rather than becoming sluggish due to hunger. This capacity for cognitive stability likely endures today.”