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Many research studies have looked into the effects of particular diets from different cultures. For example, studies have found that a Mediterranean diet, which is concentrated on nuts and good oils, contributes to better weight and overall health. Other studies have denounced fast foods and added sugars for contributing to the obesity epidemic. In a new study, researchers looked at the types of foods in terms of their categories and how these kinds of food can lead to different cognitive functions.  The researchers, headed by Alexandros Vgontzas, MD, professor of psychiatry at the Penn State College of Medicine in Hershey, PA, wanted to see how fat consumption, carbohydrates and protein affected objective daytime sleepiness and alertness.

The researchers recruited 31 healthy and non-obese adults within the age range of 18 to 65-years-old. These volunteers participated in a five-day study, in which they were required to stay at a laboratory for four nights. They were given access to meals and enough hours of sleep. None of the participants had a sleep disorder, such as sleep apnea. On the last day, the researchers measured the participants' objective daytime sleepiness via the multiple sleep latency test (MSLT). The participants' alertness levels were also monitored.

The team found that an increase in fat consumption led to an increased in objective daytime sleepiness. An increase in carbohydrate intake resulted in higher levels of alertness, while protein consumption did not seem to affect either factor.

"Increased fat consumption has an acute adverse effect on alertness of otherwise healthy, non-obese adults," said Vgontzas."Excessive daytime sleepiness and fatigue are very prevalent in the modern world and on the rise. It appears that a diet high in fat decreases alertness acutely, and this may have an impact on an individual's ability to function and also public safety."

The researchers accounted for age, gender, body mass index, daily calorie intake, and the amount of sleep in this study. The study was published in the journal, Sleep.