A pizza and chocolate diet led to changes in brain activity during sleep
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Eating a diet high in fat and sugar can impair sleep quality by messing with the brain’s electrical activity during deep sleep.
When we go to sleep, our brain’s electrical activity slows down. The higher frequency brain waves that dominate while we are awake, called beta waves, are gradually replaced by lower frequency brain waves called delta waves.
The deepest, most restorative stage of sleep — called slow-wave sleep — has the highest proportion of delta waves. It usually occurs in the first half of the night and allows the body to repair itself and consolidate memories.
Jonathan Cedernaes at Uppsala University in Sweden and colleagues tested the effects of a Western high-fat, high-sugar diet on slow sleep in 15 men with an average age of 23 years.
The men were randomly assigned to follow either a high-fat, high-sugar diet or a low-fat, low-sugar diet for one week. They then slept overnight in a lab wearing an electroencephalography (EEG) cap to record their brains’ electrical activity. After a few weeks’ break, they switched to the other diet and repeated the lab sleep study.
The participants received all their meals and had to eat them at set times. The high-fat, high-sugar diet included foods such as sweetened granola, pizza, and chocolate, while the…
low-fat, low-sugar diet included foods such as unsweetened granola, salmon, and vegetables. The two diets were calorie-matched.
Each man typically slept the same amount of time on the two diets and found their sleep quality to be the same.
However, the EEG recordings showed that the high-fat, high-sugar diet interfered with slow sleep by reducing the proportion of delta waves and increasing beta waves, suggesting it was less restful. This happened in 11 of the 14 men whose full results were collected.
The effect may be that sugar and fat activate brain pathways that increase how awake people feel, but more work is needed to unravel the mechanisms, Cedernaes says. He also hopes to repeat the study to find out if the change also occurs in women.
We don’t know the long-term effects of interfering with slow-wave sleep in this way, but we do know that poor nutrition usually leads to poorer health, which can be partly explained by their effect on sleep quality, he says.
The amount of slow-wave sleep we naturally get decreases with age, so eating a healthy diet, especially in old age, may be important to protect against further loss of sleep quality, says Cedernaes.
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