For this tightly controlled study, researchers had 26 healthy adults (half male and half female) spend five straight nights in a sleep lab where their sleep could be accurately monitored and recorded. For the first four days the study subjects were fed a controlled, “healthy” diet, while on the 5th day they were allowed to self-select their own food. Relative to the control diet, the diet the study subjects self-selected on the fifth day was higher in saturated fat and sugar and lower in fiber, thus less healthy.
When the researchers compared the sleep recordings of the subjects on the days they ate the healthy controlled diet vs. the day they ate on their own, there were notable differences. Study subjects were able to fall asleep faster and spent more time in deep sleep after the higher fiber and lower saturated fat healthy diet. On the fifth day when they ate as desired, the researchers also noted a link between greater sugar intake and more arousals from sleep. The lead researcher commented that it was indeed surprising to see how even a single day of eating less healthy foods could affect sleep.