WASHINGTON (dpa-AFX) - A large review suggests that intermittent fasting may not be very helpful for people who are overweight or obese when it comes to losing weight.
Researchers examined 22 earlier studies involving nearly 2,000 adults to see whether short-term intermittent fasting (for up to 12 months) helped people lose more weight compared to a regular diet. They also reviewed a much wider set of research on how fasting affects brain function. In total, they looked at 63 scientific articles covering 71 studies, involving 3,484 people and 222 different tests of thinking ability. These studies were conducted over almost 70 years, from 1958 to 2025.
After analyzing all the data, the researchers found no meaningful difference in mental performance between healthy adults who had eaten and those who hadn't. People performed equally well on tests that measured attention, memory, and decision-making, whether they were fasting or not. However, the study found three important factors that influence how fasting affects the brain.
First, they noticed that adults did not show any drop in mental performance while fasting. But children and teenagers performed worse on tests when they skipped meals. Their developing brains seem to be more sensitive to changes in energy levels. This supports the long-standing advice that children should eat breakfast before school to help with learning.
Second, they found that longer fasting periods were linked to smaller differences in performance between those who had eaten and those who hadn't. This may be because the body starts using ketones for energy, which can provide the brain with a steady fuel supply when glucose levels fall. Also, fasting individuals tended to perform slightly worse when tests were taken later in the day. This suggests fasting may increase the natural energy dips people feel as the day progresses.
Finally, the analysis showed that when tasks involved neutral images or shapes, fasting made little difference. But when food-related images were included, fasting participants were more distracted and performed worse. Hunger may not cause overall mental fog, but it can make people more easily distracted by food.
Overall, the findings suggest that most healthy adults can try intermittent fasting without worrying about major effects on their thinking ability. However, fasting may not be suitable for everyone, especially children and teenagers, who need regular meals for proper brain development. People with health conditions should also seek professional advice before trying fasting.
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