Eating junk food is linked to lower quality of deep sleep: study

Deep sleep, the third stage of sleep, repairs and restores necessary functions such as memory, muscle growth, and immunity. Researchers at Uppsala University in Sweden looked at how junk food affects sleep. The healthy participants ate a healthier and less healthy diet in a random order.

The study, recently published in the journal Obesity, shows that after eating junk food, participants' quality of deep sleep deteriorated, compared to those who followed a healthier diet. "Both poor diet and lack of sleep increase the risk of several public health conditions," said Jonathan Cedernaes, an associate professor at Uppsala University.

A total of 15 healthy young men of normal weight participated in two study sessions. Participants were first tested on things like their sleep habits, which had to be normal and within the recommended range of seven to nine hours a night.

Participants were randomly given a healthier diet and a less healthy diet. The two diets contained the same number of calories, adjusted to the daily requirements of each individual. Among other things, the unhealthy diet contained higher sugar and saturated fat content and more processed foods. Each diet was consumed for one week, while participants' sleeping, activity, and eating schedules were controlled on an individual basis.

"What we saw was that the participants slept the same amount of time when they were on the two diets. This was the case both while on the diets and after switching to an identical diet," Cedernaes said. The researchers looked at slow wave activity, a measure that may reflect how restful deep sleep is. "Interestingly, we saw that deep sleep exhibited less slow wave activity when participants had eaten junk food, compared to eating healthier foods," Cedernaes said. This effect lasted until the second night, once the participants switched to an identical diet. Essentially, the unhealthy diet resulted in less deep sleep, the scientist said.

Similar changes in sleep occur with aging and in conditions such as insomnia, the researchers said. It can be hypothesized, from a sleep perspective, that potentially greater importance should be placed on diet in such conditions, they added.