Diet and Brain Health, Sleep and Brain Health

A “junk food diet” impacts deep-sleep quality

Anyone who tells you they don’t like the taste of ANY junk food is either lying or suffering from a reduced ability to taste. After all, high-fat and high-sugar foods are designed to appeal to our taste buds, tasking willpower with the near-impossible charge of restraint.

Beyond the effects that a “junk food diet” can have on everything from your waistline and cognitive skills to your gut health and fertility, scientists have recently found that consuming these uber unhealthy foods regularly can worsen the quality of deep sleep.

Read on to find out what the study found—and what it means for even healthy individuals.

What the study found

A team of researchers from Uppsala University conducted a randomized trial to study the impact of a high-fat/high-sugar diet, known as a “junk food diet,” on sleep.

The participants included 15 healthy men who were randomly assigned to either the junk food diet or a low-fat/low-sugar diet for one week. At the end of the week, the researchers assessed the men’s sleep duration, stages, and patterns with a sleep monitoring technique called polysomnography.

Although the researchers found that neither the duration nor structure of sleep was different between the two groups of participants, that was not true for the quality of sleep.

The men who consumed the junk food diet for the week had lower levels of the following sleep characteristics during deep sleep:

• Delta power – a measure of slow brain waves

• The ratio of delta to beta waves

• The amplitude of slow waves

Unfortunately, consuming a junk food diet may launch a vicious cycle, as weight gain increases the risk of sleep disorders (e.g., sleep apnea), and poor sleep negatively impacts hormonal and metabolic parameters and increases the risk of weight gain and metabolic disease.

Limitations of the study

Although it does seem likely that an unhealthy diet could affect our sleep, it’s worth noting that the study used a very small sample size (15 participants) and that only healthy young men were included.

Without including women, children, older adults, or men who were not considered “healthy” in the study, and with the study only covering one week, more research needs to be done to validate the findings and to apply the results to the general population.

For now, Registered Dietitian Kristin Carli, who was not involved in the study, points out that the results aren’t exactly shocking.

“Sugar has been shown to impact sleep quality in prior research, as well as a high-fat diet. However, I will note many researchers pose whether the diet is impacting the sleep quality or the other way around. Regardless, as a registered dietitian, there are many other health benefits, besides sleep quality, to consider choosing a low-fat/low-sugar diet, including weight loss, hearth health, chronic disease prevention, etc.”

The results of the study were published in the May 28, 2023 edition of the journal Obesity.


Wendy Burt-Thomas writes about the brain, mental health and parenting.

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