“You better cut the pizza in four pieces because I’m not hungry enough to eat six.”
— Yogi Berra
Almost everyone these days has heard about intermittent fasting and fasting in general—the practice of abstaining from consumption for a designated period of time. It is a practice often associated with the exercise of religion, but its origins remain shrouded in the mists of time. For early humans and their forebears, as hunter-gatherers, periods of abstinence between meals were likely the norm rather than an intentional practice.
Fast-forward to today, when in many industrialized countries the problem is not the absence of food but its ever-present availability in one form or another 24/7/365. And accompanying the ever-present opportunity to indulge is the ever-present sales pitch to go ahead and do so; we’ve all been told that “you’re not you when you’re hangry.” We’ve been told that breakfast is ‘the most important meal of the day’ if we want to be our mentally sharpest. We’ve been told that intermittent fasting causes ‘brain fog,’ leaving us ill-tempered and less productive.
Last week’s column discussed research findings that contradicted the conventional wisdom about coffee drinking and atrial fibrillation. Is the conventional wisdom about fasting and cognition just another example of a commonly held view that is fundamentally flawed?
The basis for such specious recommendations lies in the commonplace perception, still widespread in health and wellness circles, that the human body can be viewed simply as a machine that we must ‘fuel,’ and the meals that we consume are nothing more than ‘fuelings.’ It is as if we are a car that requires only gasoline to keep our engines humming, and dining experiences are nothing more than ‘pit stops’ devoid of emotion, feelings, and meaning. All we need is a steady supply of energy to be consistently sharp, efficient, and alert. It is a perfect corollary for a culture constantly on the go.
But what if it’s wrong?
Can we reach back and tap our ancestral roots; can we engage in practices like time-restricted eating (TRE) and intermittent fasting (IF) without dulling our intellectual machete?
This week’s Study Spotlight looks at one of the most comprehensive meta-analyses to date that examines this question.
- This study was a meta-analysis of 63 study reports comparing cognitive performance between fasted and satiated healthy adults.
- The study examined 3,484 participants with a mean fasting time of 12 hours and involved 222 different measures of cognition.
- There was no meaningful difference in cognitive task performance between fasting and satiated participants.
- An exception was younger participants, who did exhibit a modest reduction in cognitive performance with longer fasting intervals.
- The overall take-home message suggests “that cognitive performance remains remarkably stable during short-term fasting, supporting the feasibility of fasting practices.”
The Caveat:
Quite often in this column, we have addressed the role of time as a variable in the food-health equation, a discipline referred to as chrononutrition. This area of study interweaves with various aspects of consumption and digestion, one of which is the time between meals. That time between meals is quite literally a fast. We recognize that every morning when we awake and consume the first meal of the day, which quite literally breaks our fast that occurred when we were sleeping (however long that might’ve been); in other words, we have breakfast.
As the study noted, the idea that prolonged fasting could deplete glycogen stores and impair energy delivery to the brain, leading to cognitive impairment, is a long-standing argument within the medical community against its practice. This persists in some circles, even though it is well known that when glycogen stores are low, energy can be generated by mobilizing fat reserves. This is the mechanism behind ketogenic diets.
Beyond serving as the basis for ketogenic weight loss, fasting also activates a cellular recycling process called autophagy that appears to improve cellular function and longevity. Fasting also seems to be beneficial in treating metabolic disorders, such as diabetes, by improving insulin sensitivity. In light of these findings, the idea that we must constantly and consistently ‘fuel’ our brains by eating “may be neither necessary nor optimal for overall health.”
Nonetheless, a pervasive fear of decreased mental performance continues to cause many to eschew engagement. However, based on the results of the current study, those folks can R-E-L-A-X. As this this meta-analysis observed, “ there was no meaningful difference in cognitive performance between fasted and satiated healthy adults. People performed just as well on cognitive tests measuring attention, memory, and executive function, whether they had eaten recently or not.”
However, there was one important caveat. That is the finding that children and adolescents did worse on tests when they skipped meals. A possible explanation is that developing brains may be much more sensitive to fluctuations in energy supply, particularly glucose availability. Another interesting finding was that longer fasts were associated with smaller performance gaps between fasting and satiated states. The one exception to that is related to food-related cues. Participants who were fasting were more susceptible to distraction when the cues involved food. Hunger, per se, does not reduce our cognitive ability, but it does make us more easily distracted when food and food-related cues are present.
The Takeaway: Individuals can engage in intermittent fasting or other fasting protocols without fear of cognitive dullness. It is, however, essential to remember that it may be best to avoid the practice in children and teens, whose brains are still developing and who appear to need regular meals to perform at their best. The same caution extends to specific groups, such as those with medical conditions or special dietary needs, for whom fasting may not be advisable without professional guidance.
For the average person, fasting can be another tool in our personal toolbox. As the authors note, “These findings challenge the common belief that fasting inherently compromises cognition.” Another conventional pillar of dietary wisdom crumbles into dust.
Additional references:
Cooper, L. F. (1917). How to cut food costs. Good Health Publishing Company.
Longo, V. D., Di Tano, M., Mattson, M. P., & Guidi, N. (2021). Intermittent and periodic fasting, longevity and disease. Nature Aging, 1(1), 47–59.
