According to the study’s authors only half of the laboratory-based studies found that a dietary intervention may have had a significant effect on sleep.
Current thinking suggests that food interventions are a potential treatment for improving sleep. Evidence has shown that those who sleep less are more likely to consume energy-rich foods (such as fats or refined carbohydrates), consume fewer portions of vegetables and have more irregular meal patterns.
Dietary factors are also believed to influence neurotransmitters, such as serotonin that are involved in the sleep-wake cycle.
The study set out to evaluate dietary interventions targeting sleep behaviour in humans age 18–50 years. Studies covered fifty years of research from January 1965 to August 2015.
The 21 studies included both in vivo and in natura (in a non-laboratory environment). Studies of particular interest included papers targeting sleep behaviour in humans, and recruitment of a nonclinical, adult population within the specified age range.
Of the 17 in vivo studies, eight (47%) suggested improvement in sleep quality. Only four studies that achieved improvements in sleep quality fed subjects with mixed composition meals, where carbohydrates and proteins varied in their composition, makeup and quantity.
The results from these four studies suggested that mixed-composition meals decreased time in slow-wave sleep. However, a solid meal shortened sleep latency relative to a liquid meal and a mixed meal consumed at midday increased postprandial sleep time.
Limited evidence of the carbohydrate effects on sleep meant conclusions were difficult to make.
One study suggested that a high-glycaemic index meal could decrease the onset of sleep when eaten four hours before bed.
However, a very-low-carbohydrate meal could increase time spent in slow-wave sleep and decrease time in rapid eye movement sleep.
Protein-focused studies suggested that this source combined with carbohydrates improved sleep in insomniacs and tryptophan-rich meals consumed before bed increase morning alertness.
In natura studies
In the four studies that took place in natura, macronutrient composition appeared to have no effect. However, some markers of sleep, such as sleep fragmentation and sleep latency did improve.
“Possible explanations for absence of significant findings include the relatively small effect of nutrition for improving sleep, recruitment of healthy sleepers, and the difficulty of controlling dietary treatments in a free-living environment,” the study remarked.
Current thinking has pinpointed nutritional interventions as a way of improving sleep behaviours and quality by acting on the neurotransmitters involved in the sleep-wake cycle.
As well as serotonin, research has identified a number of neurotransmitters associated with the sleep–wake cycle. These include serotonin, gamma-aminobutyric acid, orexin, melanin-concentrating hormone, cholinergic, galanin, noradrenaline and histamine.
Nutritional effects that act on these neurotransmitters may also influence sleep. Carbohydrate, tryptophan, valerian, melatonin and other nutritional interventions have been investigated as possible sleep inducers and represent promising potential interventions.
The reviewers concluded that the role of food intake as a treatment option for sleep was not demonstrated by this review of study literature.
“Nearly half of the in vivo studies reviewed showed improvement on at least one indicator of sleep, while the in natura studies were unable to do so,” the authors said.
“Several limitations, including paucity of studies, small sample sizes, acute manipulation of nutrition, difficulty in controlling diet, and recruitment of healthy sleepers, may partially explain the lack of results.”
Source: The Journal of Alternative and Complementary Medicine
Published online ahead of print, doi:10.1089/acm.2015.0238
“Systematic Review of Dietary Interventions Targeting Sleep Behavior.”
Authors: Adam Knowlden, Christine Hackman, Manoj Sharma