Scientists at the University of Hyogo in Japan have found that a breakfast consisting of sweet and fatty foods can negatively affect cognitive function and alertness in the morning. The study was published in the journal Food and Humanity.
Although breakfast is traditionally considered an essential source of energy, when people start their day with pastries and sugary drinks, researchers say this habit can reduce concentration and impair effective mental performance.
The authors studied how the composition of the morning meal affects the nervous system’s activity, which regulates bodily processes. The sympathetic division is responsible for wakefulness and readiness for action, while the parasympathetic division is responsible for relaxation and “rest mode.”
The study involved 13 healthy female students. Each woman ate two breakfasts with the duplicate calorie content (approximately 500 kcal) on separate days. One option was a balanced traditional Japanese meal of rice, fish, eggs, vegetables, and fruit. The second was a typical “fast” breakfast of pancakes and a sweet milk drink, which is high in fat and sugar.
After eating, the researchers measured body temperature and heart rate variability for two hours and administered cognitive tests. Participants also rated their well-being, alertness, and sleepiness.
It turned out that the balanced breakfast increased body temperature and heart rate, signs of sympathetic nervous system activation. This was accompanied by a sense of alertness and improved performance on tasks requiring planning and concentration.
The sweet and fatty breakfast, on the other hand, did not cause a similar physiological response. Instead, participants showed a predominance of parasympathetic activity and reported more sleepiness. “We found that the quality of breakfast directly affects morning physiological arousal and cognitive function,” said study leader Fumiaki Hanzawa.
According to the authors, planning functions, a key element of productivity, were particularly affected. The slight improvement in visual attention after eating sweets was likely due to a short-term dopamine response to sugar. Still, it did not compensate for the overall decline in mental performance.
