In a new study, researchers from Uppsala University have investigated how junk food affects sleep. Healthy participants consumed a healthier and less healthy diet in a random order. After the unhealthy diet, the quality of the participants’ deep sleep had deteriorated, compared to those who had followed the healthier diet. The results have been published in the journal Obesity .
Several epidemiological studies have shown that what we eat is associated with changes in our sleep. However, few studies have investigated how diet itself directly affects sleep. One way to do this is to have the same participant consume different diets in a random order.
"Both poor diet and lack of sleep increase the risk of several public health conditions. Since what we eat is so important to our health, we thought it would be interesting to investigate whether some of the health effects of different diets could involve changes in our sleep. In this context, so-called intervention studies are lacking so far, studies designed to allow isolating the mechanical effect of different diets on sleep," says Jonathan Cedernaes, physician and associate professor of medical cell biology at the University of Uppsala.
Previous epidemiological studies have shown that diets higher in sugar, for example, are linked to poorer sleep. However, sleep is an interaction of different physiological states, as Cedernaes explains:
"For example, deep sleep can be affected by what we eat. But no study had previously investigated what happens if we eat an unhealthy diet and then compared it to the quality of sleep after that same person eats a healthy diet. What’s exciting about this is that sleep is very dynamic. Our sleep consists of different stages with different functions, like deep sleep that regulates hormone release, for example. Additionally, each stage of sleep is marked by different types of electrical activity. in the brain. This regulates aspects such as how restful sleep is, and differs between different regions of the brain, but the depth or completeness of sleep stages can also be negatively affected by factors such as insomnia and aging. "It has not been investigated whether similar changes in our sleep stages may occur after exposure to different diets."
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 young men of normal weight participated in two sessions. Participants were first tested on things like their sleeping 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, participants received 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 and more processed foods. The meals of each diet had to be consumed at individually adjusted times, which coincided in the two dietary conditions. Each diet was consumed for one week, while participants’ sleep, activity, and eating schedules were monitored on an individual level.
After each diet, the participants were tested in a sleep laboratory. There, they were first allowed to sleep a normal night, while their brain activity was measured to monitor their sleep. Participants were then kept awake in the sleep lab, before being allowed to catch up on sleep. His dream was also recorded in this case.
The unhealthy diet resulted in less deep sleep . Of note, similar changes in sleep occur with aging and in conditions such as insomnia. "It can be assumed, from a sleep perspective, that potentially greater importance should be given to diet in such conditions," explains Cedernaes.
Researchers currently don’t know how long-lasting the sleep effects of the unhealthy diet may be. The study did not investigate whether less deep sleep can alter functions that are regulated by deep sleep, for example.
"It would also be interesting to perform functional tests, for example, to see if memory function may be affected. This is largely regulated by sleep. And it would be equally interesting to understand how long the observed effects may last." Currently, we do not know which unhealthy dietary substances worsen the depth of deep sleep. As in our case, unhealthy diets usually 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 more important role. Our dietary intervention was also quite short, and both the sugar and fat content could have been higher. "It’s possible that an even less healthy diet would have had more pronounced effects on sleep," Cedernaes notes.
Conclusions Short-term consumption of a less healthy diet alters the oscillatory characteristics of sleep that regulate the restorative properties of sleep. Whether such changes may mediate adverse health outcomes associated with consuming an unhealthy diet merits investigation. |
Importance of the study
What is already known?
- Consumption of high-fat, high-sugar (HFHS) diets has been associated with adverse metabolic outcomes and increased risk of metabolic diseases.
- Cross-sectional clinical studies and some intervention trials have suggested that dietary factors may affect our sleep, but it is currently unknown how exposure to an unhealthy diet directly affects sleep parameters, and specifically its macrostructure, in humans.
What does this study add?
- In a randomized study, we found that a one-week exposure to an HFHS diet, compared with a low-fat/low-sugar diet, did not affect sleep duration or macrostructure during regular sleep or during recovery sleep.
- During regular sleep, exposure to the HFHS diet reduced the relative power of delta frequencies and the amplitude of slow waves during deep sleep.
- The oscillatory sleep pattern was also affected in a similar direction during recovery sleep.
How might these results change the direction of research or the focus of clinical practice?
- The observed changes in sleep parameters induced by diet are known to modulate numerous physiological and behavioral outcomes (such as memory consolidation, mood, attention, and glucose metabolism).
- Therefore, our findings warrant further investigation to determine the extent to which the adverse outcomes of exposure to less healthy diets, which are high in sugar and fat, are mediated by the diet’s impact on the neurobiological properties of sleep.
Reference : Luiz Eduardo Mateus Brandão, Alexandru Popa, Erasmus Cedernaes, Christopher Cedernaes, Lauri Lampola, Jonathan Cedernaes. Exposure to a more unhealthy diet impacts sleep microstructure during normal sleep and recovery sleep: A randomized trial. Obesity, 2023; DOI: 10.1002/oby.23787
