Abstract
Objectives
Carbohydrate is the nutrient most commonly said to influence sleep: it is proposed that a high intake increases the uptake of tryptophan by the brain, where it is metabolized into serotonin and melatonin. As this mechanism depends on the relative amount of carbohydrate and protein, studies were reviewed where diets differed in these macro-nutrients.
Methods
The Web of Science and Medline were interrogated using terms related to carbohydrate and sleep. Papers were retained if two diets, differing in the percentage of calories coming from carbohydrate, had been contrasted using either polysomnography or actigraphy. Measures considered with polysomnography included sleep onset time; sleep efficiency; rapid eye-movement (REM) and slow wave sleep (SWS). Measures examined from actigraphy included: sleep efficiency; duration of sleep. Meta‐analysis was conducted using Review Manager 5.2 (Cochrane) using a random-effects model.
Results
With the polysomnography measures six studies met the inclusion criteria. A lesser consumption of carbohydrate was associated with more SWS (SMD = 0.47; CI 0.06 – 0.88; P = 0.02; I2 = 0%) and less REM (SMD = – 0.47, CI –0.87– –0.07, P = 0.02, I2 = 0%). A lower intake of carbohydrate was also associated with a shorter time before falling asleep (P = 0.03; I2 0%). Sleep efficiency is the percentage of time spent asleep, relative to the total time in bed. Using polysomnography there was a trend for better sleep efficiency to be associated with with a lower intake of carbohydrate, although it just missed significance (P = 0.06). However, using actigraphy those eating less carbohydrate were more sleep efficient (SMD = 1.25; CI 0.35 – 2.15; P = 0.007; I2 = 0%).
Conclusions
No study had the high level of carbohydrate needed to raise tryptophan; rather studies had enough protein to reduce the uptake of tryptophan. A novel possibility is that blood glucose levels modulate sleep. Glucose metabolism varies; it is less during SWS and greater with REM. There are many reports associating the nature of sleep with glucose tolerance. As several hormones control glucose levels, some stimulated by the level of glucose, there is a need to consider diet hormonal interactions. As SWS is believed to be restorative and aid plasticity, increasing SWS with lower carbohydrate have may functional implications.
Funding Sources
No external funding.