oa Influence of the glycemic load (GL) on subjective and objective measures of sleep quality in insomnia

Evidence in healthy sleepers suggests the glycemic index (GI) can mediate changes in sleep onset latency, given the availability of tryptophan to the brain (i.e. TRP/LNAA ratio) is increased after high GI carbohydrate-only food. However, these meals have limited clinical application given the high glycemic load (GL) and insulin responses. Therefore, we investigated the efficacy of a mixed macronutrient high GI (MHGI) compared to an isoenergetic (∼1915 kJ) low GI (MLGI) meal taken three hours prior to habitual bedtime to improve sleep quality in participants meeting research diagnostic criteria for insomnia. Four men and four women (n=8) were randomized to the MHGI or MLGI meal for two consecutive nights. Blood samples were taken prior to the meal, and 60, 120, 180 min after eating. Subjective (sleep diary) and objective (polysomnography, PSG) sleep was also measured each night. The individual 10cm visual analogue scales indicate that meal palatability was identical for both meals; which were of good taste (average 7.8cm); meal satiety was maintained until bedtime after the MHGI meal (>5cm), whereas after the MLGI meal satiety ratings in men were low (<5cm); and the average meal energetic load (kJ/kg) was greater for women (33.0 ± 4.1) than men (25.4 ± 3.8; p<0.05). Postprandial measures indicate glucose was larger after the MHGI meal but there was no difference in insulin response; the peak percentage rise in plasma TRP/LNAA from baseline after the MHGI meal (17%) was substantially but only marginally different than the MLGI (8%) meal (p = 0.12); postprandial serotonin was unaltered. The participant group self-reported (5pt Likert scale) feeling more rested after the MHGI (2.8) compared to the MLGI meal (2.3; p<0.05); also ratings were higher in women (3.0) than in men (2.6; p<0.05). There were no differences in PSG sleep variables. This study demonstrates symptoms of insomnia are improved, especially in women, after a high GI mixed macronutrient meal. Given the present data, we suggest the possibility for a physiological threshold within the postprandial plasma TRP/LNAA response that must be surpassed in order to promote measurable changes to serotonin and PSG sleep. Further studies should evaluate the potential long-term risks and benefits of habitual mixed macronutrient high GI meals to improve sleep.