A diet high in fat and sugar can reduce sleep quality by disrupting electrical activity in the brain during deep sleep.
When we fall asleep, the electrical activity in our brain slows down. The high frequency brain waves that dominate while we are awake, called beta waves, are gradually replaced by low frequency waves called delta waves.
The deepest and 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 high-fat, high-sugar Western diet on slow-wave sleep in 15 men with an average age of 23.
The men were randomly assigned to follow a high-fat, low-sugar diet or a low-fat, low-sugar diet for one week. They then slept one night in a lab wearing an electroencephalography (EEG) cap to record their brain’s electrical activity. After a break of several weeks, they switched to the other diet and repeated the sleep study in the laboratory.
Participants received all their meals and had to eat them at set times. The high-fat, high-sugar diet included foods like sweet granola, pizza, and chocolate, while the…
the low-fat, low-sugar diet contained foods like unsweetened muesli, salmon, and vegetables. The two diets were matched for calories.
Each man generally slept the same amount of time on both regimens and rated their sleep quality to be the same.
However, EEG recordings showed that the high-fat, high-sugar diet disrupted slow-wave sleep by reducing the proportion of delta waves and increasing beta waves, suggesting he was less restful. This happened in 11 of the 14 men for whom full results were collected.
The effect may be because sugar and fat activate brain pathways that increase people’s sense of wakefulness, but more work is needed to untangle 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 impact of disrupting slow-wave sleep in this way, but we do know that poor diet generally leads to poorer health, which may be partly explained by their effect on the quality of sleep. sleep, he said.
The amount of slow-wave sleep we get naturally decreases with age, so a healthy diet may be especially important in old age to protect against further losses in sleep quality, Cedernaes says.