A study conducted by scientists from Uppsala University, Sweden investigated the impact of a high-fat/high-sugar diet, also known as a junk food diet, on sleep. The researchers found that after consuming the unhealthy diet, the quality of deep sleep in participants worsened compared to when they followed a healthier diet.

Although the duration of sleep and overall sleep structure were not significantly different between the two diets, the unhealthy diet was associated with reduced deep sleep quality and changes in some important sleep patterns.

A group of 15 healthy men took part in a study where they were given two different diets to follow. They were randomly assigned to either a high-fat/high-sugar diet or a low-fat/low-sugar diet for one week each.

After each diet, the researchers recorded the participants’ sleep patterns in a laboratory setting using a method called polysomnography, a sleep monitoring technique.

They looked at the duration of sleep, as well as the different stages and patterns of sleep, including things like oscillatory patterns and slow waves.

The study found that the duration of sleep was not significantly different between the two diets, as measured by both actigraphy — a method of monitoring sleep using a wearable device — and in-lab polysomnography.

When comparing two different diets, the researchers found that the structure of sleep remained similar after one week on each diet.

“Essentially, the unhealthy diet resulted in shallower deep sleep. Of note, similar changes in sleep occur with aging and in conditions such as insomnia. It can be hypothesised, from a sleep perspective, that greater importance should potentially be attached to diet in such conditions,” explains researcher.