Just How Bad Is Junk Food for Your Sleep? New Study Reveals the Truth

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Junk Food Before Bed

Is that late night pizza causing morning grogginess? It’s possible, according to a recent study from Uppsula University in Sweden. The study results suggest that a high-fat, high-sugar (HFHS) diet can reduce sleep quality. While a HFHS, typical Western diet didn’t necessarily reduce sleep duration in the study, it was found to affect delta sleep waves, which promote tissue repair, memory consolidation, and mood. 

In the study, 15 young adult male participants followed either a HFHS diet composed of things like processed granola and pizza or a low-fat, low-sugar (LFLS) diet full of unsweetened yogurt, salmon, and vegetables. After one week, the participants spent a night in a lab and underwent electroencephalography (EEG) monitoring. A few weeks later, the men switched diets and repeated the lab monitoring.

Men in both groups consumed the same amount of calories throughout each diet and ate at the same intervals. However, the diets differed significantly in macronutrients and nutritional quality.  In 11 out of the 14 men (for whom full results were collected), the HFHS group showed a higher proportion of beta to delta waves indicating less restorative sleep. 

Beta vs. Delta Waves

When we are awake, high-frequency brain waves called beta waves dominate. However, when we sleep, brain activity slows and lower frequency waves take over. This slow-wave sleep, which usually occurs in the first half of the night and has the highest proportion of delta waves, is the most restorative and deepest stage.

We already know that sleep quality and duration can affect food choices (ever crave sugar after a late night?), but this study is rather unique in that it looked at the role food quality plays in restorative sleep. While this study is a start, it’s still unclear what fewer delta waves mean for longterm health.

Mary Sabat MS, RDN, LD, a Registered Dietician and Ace Certified Trainer agrees that there is a connection between what we eat and how we sleep. Sabat says, “There is a growing body of research that suggests a link between diet and sleep quality. While the relationship between diet and sleep is complex and multifactorial, several factors in a diet can influence sleep patterns and overall sleep quality.” As suggested by the study, Sabat says, “Consuming excessive amounts of sugar and unhealthy fats, such as saturated and trans fats, may disrupt sleep patterns. These types of diets have been linked to increased sleep fragmentation, decreased sleep efficiency, and decreased slow-wave sleep, including delta sleep.”

Junk Food = Junk Sleep

It’s notable that in the study, participants reported similar feelings of appetite and sleep satiety, meaning they weren’t hungrier on one diet and felt like they slept about the same either way. However, the increased ratio of beta to delta waves on the HFHS diet may mean there are lingering health effects that won’t be noticed immediately. 

Shawn M. Talbott, who holds a PhD in Nutritional Biochemistry and regularly conducts sleep studies, praised this latest sleep study. He says, “The new study is a good one because it looked at not only sleep duration, but also sleep quality – and showed that junk food (low diet quality) leads to junk sleep (low sleep quality).” Through his own research, Talbott has seen that transitioning to a whole foods-focused Mediterranean style diet improved mood during the day and improved sleep quality at night, specifically when it comes to the amount of wake ups.

Choose Minimally Processed Foods

The study makes it clear that certain foods (pizza, sugary yogurt) can have negative effects on sleep quality. But what exactly should we be eating? Georgina Wysiecki MSW MBA, a Registered Social Worker and Infant/Child Sleep Consultant, recommends a diet rich in protein to keep blood sugar stable throughout the day and night. Wysiecki says, “Turkey, chicken, nuts, bananas, oats, kidney beans, eggs and dairy are great foods for supporting sleep neurotransmitters like serotonin and melatonin, as they contain tryptophan and B complex vitamins.”  

While the study had its limitations (for example, the participants were all male) and more research is needed, it shed light on the theory that a diet high in fat and sugar may affect the most restorative types of sleep. If you’re looking to improve your own slow-wave sleep, choosing minimally processed foods instead of pizza and chocolate may help you get better quality Zs.

  • Brandão, LEM, Popa, A, Cedernaes, E, Cedernaes, C, Lampola, L, Cedernaes, J. Exposure to a more unhealthy diet impacts sleep microstructure during normal sleep and recovery sleep: A randomized trial. Obesity (Silver Spring). 2024; 1- 12. doi:10.1002/oby.23787

  • Sabat, Mary. Author interview. June 2024.

  • Talbott, Shawn M. Author interview. June 2024.

  • Scoditti E, Tumolo MR, Garbarino S. Mediterranean Diet on Sleep: A Health Alliance. Nutrients. 2022 Jul 21;14(14):2998. doi: 10.3390/nu14142998. PMID: 35889954; PMCID: PMC9318336.

  • Wysiecki, Georgina. Author interview. June 2024.

Megan Harrington

Megan Harrington

Megan Harrington is a writer living in Upstate New York. She graduated from Wesleyan University and has been freelancing for magazines and websites for the past 15 years. When she's not writing, Megan enjoys being active with her family.

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