It is often believed that depriving the body of food could have a negative impact on intellectual capacity PHOTO Unsplash
As effective as fasting can be for weight loss, it is often believed that depriving the body of food could have a negative impact on intellectual ability.
But is impaired cognitive performance an inevitable consequence of fasting?
According to a recently published extensive analysis, not necessarily.
Based on an evaluation of 63 scientific articles, representing 71 independent studies and including a total of 3,484 participants, the research found that there were no significant differences in cognitive performance between people who were fasting and those who had regular meals.
It’s a solid counterpoint to the idea that moderate, short-term dietary restrictions deplete healthy people’s mental resources—an idea found everywhere from snack advertising (“you’re not you when you’re hungry”) to the mantra that breakfast is the most important meal of the day. The researchers behind the analysis — psychologist Christoph Bamberg of the University of Paris Lodron in Austria and cognitive neuroscientist David Moreau of the University of Auckland in New Zealand — don’t want people who could benefit from fasting to be put off by fears that it will affect their mental clarity.
“For most healthy adults, the findings are reassuring,” Moreau explained in a comment to The Conversation.
“You can try intermittent fasting or other forms of fasting without worrying about losing your mental acuity.”
To analyze all this data, the researchers used a Bayesian statistical approach—a method that estimates probabilities, rather than providing black-and-white, yes-or-no answers.
In this case, they investigated whether or not fasting affects cognitive performance. The method is particularly useful when many different statistical sources have to be compared.
Cognitive abilities assessed in the studies included the memorydecision making, speed of reaction and accuracy of answers. Taken together, these tests showed that short-term fasting (with a median duration of 12 hours) did not significantly alter the results.
But there were also nuances. The researchers observed modest declines in cognitive performance during fasting periods longer than 12 hours, and “noticeable declines” in children and adolescents (although they represented only a small portion of the participants).
This suggests that young, developing brains may be more vulnerable to long periods without food, and that for children and adolescents, three regular meals a day are very important.
Interestingly, the effects were mostly seen in cognitive tasks related to food. It is possible that certain very specific brain circuits begin to function differently during fasting, but further studies will be needed to confirm this.
“Performance deficits often appeared only in tasks involving food stimuli, such as viewing pictures of food or processing words related to foodMoreau said.
“In contrast, performance on neutral content tasks remained largely unaffected.”
“Hunger might selectively divert cognitive resources or cause distraction only in food-related contexts, but overall cognitive functioning remains largely stable.”
The researchers also found that people who fasted tended to score worse on cognitive tests taken later in the day — possibly an indication that the lack of food amplifies the natural lapses in concentration associated with circadian rhythms.
In addition to helping some people manage their weight, fasting has been associated in studies with other health benefits, including improved cardiovascular health and reduced inflammation.
Scientists believe that fasting produces important changes in the way the body works, including how it changes its energy source—from glycogen stores to the use of body fat, mostly in the form of compounds called ketone bodies.
With all this in mind, Moreau concludes that “fasting should be seen as a personal tool rather than a universally valid recommendation”.
There is no one-size-fits-all solution, and fasting is best practiced in consultation with a physician.
“The main finding is reassuring: cognitive performance remains stable during short-term fasting, suggesting that most healthy adults need not fear that a temporary fast will affect their mental clarity or ability to perform daily activities,” Moreau said.
The research was published in the journal Psychological Bulletin, it says sciencealert.com.
