Junk food consumption impairs deep sleep patterns

Several studies have already shown that what we eat is associated with changes in our deep sleep patterns. However, research examining how diet itself directly affects sleep has been scarce. 

According to a new study led by Uppsala University in Sweden, one way to overcome this limitation is to have the same participant consume different types of diets in a randomized order. 

What the researchers learned

By enrolling a cohort of 15 healthy participants and asking them to alternate between a healthy and unhealthy diet, the experts found that consumption of junk food led to a deterioration in the quality of participants’ deep sleep patterns.

“Both poor diet and poor sleep increase the risk of several public health conditions. As what we eat is so important for our health, we thought it would be interesting to investigate whether some of the health effects of different diets could involve changes to our sleep. In this context, so-called intervention studies – designed to allow the mechanistic effect of different diets on sleep to be isolated – have so far been lacking,” said senior author Jonathan Cedernaes, a professor of Medical Cell Biology at Uppsala.

While previous epidemiological studies have shown that diets with higher sugar content, for instance, are associated to poorer sleep, they failed to take into account the full complexity of sleep as an interplay of different physiological states, each marked by different types of electrical activity in the brain. 

“Our sleep consists of different stages with different functions, such as deep sleep which regulates hormonal release, for example. Furthermore, each sleep stage is hallmarked by different types of electrical activity in the brain. This regulates aspects such as how restorative sleep is, and differs across different brain regions. But the depth or integrity of the sleep stages can also be negatively affected by factors such as insomnia and ageing. Previously, it has not been investigated whether similar changes in our sleep stages can occur after exposure to different diets,” Cedernaes explained.

How the research was conducted 

The study sessions involved several days of monitoring in a sleep laboratory of 15 healthy individuals with normal sleep habits (an average of seven to nine hours of sleep per night). In random order, the participants were given both a healthy and unhealthy diet containing the same number of calories. 

The unhealthy diet consisted of a higher sugar and saturated fat content and more processed food items. Each diet was consumed for a week, while participants’ sleep, activity, and meal schedules were monitored at an individual level. After each diet, participants’ deep sleep patterns were monitored in a sleep laboratory.

The investigations revealed that participants slept the same amount of time when they consumed the two diets and spent the same amount of time in different sleep stages. However, their deep sleep patterns – particularly their slow-wave activity, a measure reflecting how restorative deep sleep is – appeared to be significantly affected by the unhealthy diet.

“Intriguingly, we saw that deep sleep exhibited less slow-wave activity when the participants had eaten junk food, compared with consumption of healthier food. This effect also lasted into a second night, once we had switched the participants to an identical diet. Essentially, the unhealthy diet resulted in shallower deep sleep. Of note, similar changes in sleep occur with ageing and in conditions such as insomnia. It can be hypothesized, from a sleep perspective, that greater importance should potentially be attached to diet in such conditions,” Cedernaes reported.

More research is needed on deep sleep patterns

Further research is needed to clarify how long-lasting the deep sleep pattern effects of unhealthier diets may be, and how various functions that are regulated by deep sleep are altered by diet-induced shallower sleep. 

Moreover, since previous studies have shown that memory is also regulated to a large extent by sleep, functional tests examining how memory processes are affected by reduced sleep quality due to unhealthy diets are necessary. Finally, it is not yet clear which substances in the unhealthy diet – and in what quantities – worsen the quality of deep sleep.

“As in our case, unhealthy diets often contain both higher proportions of saturated fat and sugar and a lower proportion of dietary fiber. It would be interesting to investigate whether there is a particular molecular factor that plays a greater role. Our dietary intervention was also quite short, and both 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,” Cedarneas concluded.

The study is published in the journal Obesity.

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By Andrei Ionescu, Earth.com Staff Writer

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