Dietary changes made to lose weight can improve sleepiness, even if the person is still heavy, a new study finds.

Previous studies have linked obesity with persistent sleepiness, lack of energy during the day, and poor sleep quality. Weight loss can combat this, but until now, scientists knew little about the link between excessive weight poor dietary habits, and sleep/wake abnormalities.

In this study, researchers used mice to study the effect of diet-induced changes on sleep. Half the mice were randomly chosen to receive regular chow (RC) while the other mice were fed a high-fat diet (HFD) for eight weeks.

At the end of that period, some of the mice were switched to the alternative diet for one week, causing newly fed HFD mice to gain weight and newly-fed RC mice to lose weight, while the rest of the mice continued to consume their current diet.

After the ninth week, mice maintained on HFD weighed 30 percent more, slept more than one hour longer per day, and suffered from increased sleep disturbance compared to the mice on the regular diet. The "diet switch" groups, however, had similar body weight at week nine, but completely different sleep/wake profiles when compared to each other.

Overweight people don’t necessarily need to lose all their extra pounds; just changing their diet to do so may be enough to help them sleep better and be more awake during the day, the researchers say of their study, which appears in the journal Sleep.