Researchers at Uppsala University investigated how junk food affects sleep in a new study. In random order, healthy participants consumed an unhealthy as well as a healthier diet. The quality of the participants’ deep sleep deteriorated after the unhealthier diet, compared to those who had followed the healthier diet. The findings have been published in the journal Obesity.
Several epidemiological studies have found that what we eat is related to changes in our sleep. However, few studies have looked into how diet affects sleep. One method is to have the same participant consume different diets in a random order.
“Both poor diet and inadequate sleep increase the risk of a variety of public health conditions.” We thought it would be interesting to investigate whether some of the health effects of different diets could involve changes in our sleep because what we eat is so important for our health. So-called intervention studies have been lacking in this context, studies designed to isolate the mechanistic effect of different diets on sleep,” says Jonathan Cedernaes, Physician and Associate Professor in Medical Cell Biology at Uppsala University.
Previous epidemiological studies have found that diets high in sugar, for example, are associated with poorer sleep. However, as Cedernaes explains, sleep is a synthesis of various physiological states:
“For example, what we eat can influence deep sleep. However, no previous study had investigated what happens when we consume an unhealthy diet and then compared it to the quality of sleep when the same person follows a healthy diet. What’s exciting in this context is how dynamic sleep is. Our sleep is divided into stages that serve different purposes, such as deep sleep, which regulates hormonal release.”
“Furthermore, different types of electrical activity in the brain distinguish each sleep stage. This regulates aspects such as restorative sleep and varies across brain regions. However, factors such as insomnia and aging can have a negative impact on the depth or integrity of the sleep stages. Previously, it has not been investigated whether similar changes in our sleep stages can occur after exposure to different diets.”
We discovered that when the two diets were consumed, the participants slept for the same amount of time. This was true both while they were on the diets and after they switched to a different, identical diet. Furthermore, participants in both diets spent the same amount of time in each sleep stage.
Jonathan Cedernaes
Each study session involved several days of monitoring in a sleep laboratory. Therefore, only 15 individuals were included in the study. A total of 15 healthy normal-weight young men participated in two sessions. Participants were first screened for aspects such as their sleep habits, which had to be normal and within the recommended range (an average of seven to nine hours of sleep per night).
In random order, the participants were given both a healthier diet and an unhealthier diet. The two diets contained the same number of calories, adjusted to each individual’s daily requirements. Among other things, the unhealthier diet contained a higher content of sugar and saturated fat and more processed food items. The meals of each diet had to be consumed at individually adjusted times, which were matched across the two dietary conditions. Each diet was consumed for a week, while the participants’ sleep, activity, and meal schedules were monitored at an individual level.
The participants were examined in a sleep laboratory after each diet. They were first allowed to sleep normally for the night while their brain activity was monitored. After that, the participants were kept awake in the sleep laboratory before being allowed to sleep. In this case, too, their sleep was recorded.
“We discovered that when the two diets were consumed, the participants slept for the same amount of time. This was true both while they were on the diets and after they switched to a different, identical diet. Furthermore, participants in both diets spent the same amount of time in each sleep stage. But we were particularly interested in investigating the properties of their deep sleep.”
“In particular, we looked at slow-wave activity, which can reflect how restorative deep sleep is. Intriguingly, we discovered that when participants ate junk food, they had less slow-wave activity than when they ate healthier food. This effect lasted into the second night after we switched the participants to the same diet. Essentially, the poor diet caused shallower deep sleep. It is worth noting that similar changes in sleep occur with age and in conditions such as insomnia. From a sleep standpoint, it can be hypothesized that greater importance should potentially be attached to diet in such conditions,” Cedernaes explains.
The researchers do not currently know how long-lasting the sleep effects of the unhealthier diet may be. The study did not investigate whether shallower deep sleep may alter functions that are regulated by deep sleep, for example.
“It would also be interesting to conduct functional tests, such as memory function, to see if it can be affected. Sleep regulates this to a large extent. It would also be interesting to learn how long the observed effects might last. We currently do not know which ingredients in the unhealthy diet exacerbated the depth of deep sleep.”
“As in our case, unhealthy diets frequently contain higher proportions of saturated fat and sugar, as well as lower proportions of dietary fibre. It would be interesting to see if there is a specific molecular factor that is more important. Our dietary intervention was also relatively brief, and the sugar and fat content could have been higher. It is possible that an even unhealthier diet would have had more pronounced effects on sleep,” notes Cedernaes.
