Complaints of excessive daytime sleepiness would have most doctors reaching for their referral pad to send the patient to the nearest sleep lab. However Australian research suggests another, more readily-modifiable, lifestyle factor might be to blame.
According to a large-scale epidemiological study, researchers from Flinders University determined a high intake of saturated fats and carbohydrates increases the risk of excessive daytime sleepiness.
And it’s not simply because a diet of hot chips and thickshakes will cause weight gain, and obesity is a well-known risk factor for sleepiness. No. In this study, they compared fats, carbohydrates and protein calorie for calorie – so it wasn’t how much you ate, or how energy-dense your food was – it was, in fact, the type of food you ate. The study found that increasing the proportion of energy intake to be from saturated fat was positively associated with excessive daytime sleepiness, with carbohydrates having a similar but less pronounced effect.
Conversely, increasing the proportion of energy intake coming from protein was inversely associated with excessive daytime sleepiness.
“After adjusting for potential confounders, substituting 5% energy intake from protein with an equal amount of saturated fat and carbohydrate increased the odds of [excessive daytime sleepiness],” the study authors wrote in the journal, Nutrients.
And the reverse also held true.
“The odds of [excessive daytime sleepiness] were lower when saturated fat was substituted with unsaturated fat, protein or carbohydrate.”
To conduct the study, researchers used data from the community-based, longitudinal North West Adelaide Health Study. Almost 2000 adults aged 24 years and older were assessed for daytime sleepiness (using the Epworth Sleepiness Scale) and their daily dietary intake was assessed using a food frequency questionnaire.
In terms of why this link between macronutrients and sleepiness should occur, two possible mechanisms were proposed by the study authors.
Firstly, it could be due to the direct effect of these different foods on hormonal and neuroendocrine signalling, in particular insulin and cholecystokinin levels. Previous studies have shown increased levels of these hormones are associated with reduced alertness.
The other theory relates to the effect of fat and carbohydrate intake on different stages and quality of sleep. Basically, while people whose diets have a higher proportion of fats and carbohydrates might go to sleep more readily tend to have a poorer sleep quality, so they will be fatigued because their night-time sleep is “less efficient”.
Excessive daytime sleepiness is a common complaint in the Australian population, with an estimated 15% of adults currently affected.
“It is associated with health and societal consequences, including increased risk of work-related errors and injuries and cardiovascular diseases and mortality,” the researchers said.
As a result, this study has important implications. It has demonstrated that dietary interventions, particularly substituting one food type for another, could be an effective therapeutic option for treating or at least alleviating excessive daytime sleepiness.
“Clinical and public health interventions aimed at lowering [excessive daytime sleepiness] and associated consequences should consider dietary approaches as important strategies at the individual and population levels.
“People who have sleep-related disorders (such as OSA patients) and disturbed circadian rhythm (such as shift-workers) may benefit from dietary interventions to alleviate [excessive daytime sleepiness],” they concluded.
Nutrients 2019, 11, 2374; doi:10.3390/nu11102374