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High-Glycemic-Index Carbohydrate Meals May Shorten Sleep Onset

Authors: News Author: Laurie Barclay, MD CME Author: Laurie Barclay, MDFaculty and Disclosures


February 26, 2006 — A high-glycemic-index (GI) carbohydrate-based meal shortened sleep onset latency in healthy sleepers when consumed 4 hours before bedtime, according to the results of a small study reported in the February issue of the American Journal of Clinical Nutrition.

"Dietary carbohydrate intake has been shown to increase the plasma concentration of tryptophan (Trp), a precursor of serotonin and sleep-inducing agent," write Ahmad Afaghi, MD, of the University of Sydney in Australia, and colleagues. "A factor that promotes the entry of Trp into the brain is its plasma concentration relative to that of the other large neutral amino acids (LNAAs: tyrosine, phenylalanine, leucine, isoleucine, valine, and methionine). It is now known that high-GI carbohydrates have the ability to increase the ratio of circulating Trp to LNAAs (Trp:LNAA) via a direct action of insulin, which promotes a selective muscle uptake of LNAAs."

The investigators compared the effect on sleep quality of high- and low-GI carbohydrate–based meals consumed 4 hours or 1 hour before bedtime. Twelve healthy men, aged 18 to 35 years, underwent a familiarization night followed by 3 test nights in random order 1 week apart. On the test nights, they consumed standard, isocaloric (3212 kJ; 8% of energy as protein, 1.6% of energy as fat, and 90.4% of energy as carbohydrate) meals of either Mahatma (low GI = 50) or Jasmine (high GI = 109) rice 4 hours before their usual bedtime. On another occasion, they received the high-GI meal 1 hour before bedtime.

Compared with a low-GI meal consumed 4 hours before bedtime, consumption of a high-GI meal was associated with a reduction in mean sleep onset latency (9.0 ± 6.2 vs 17.5 ± 6.2 minute; P = .009). Compared with the high-GI meal given 1 hour before bedtime, the same meal given 4 hours before bedtime was associated with shorter sleep onset latency (9.0 ± 6.2 vs 14.6 ± 9.9 minute; P = .01). No effects were observed on other sleep variables.

"We showed that a carbohydrate-based high-GI meal resulted in a significant shortening of sleep onset latency in healthy sleepers compared with a low-GI meal and was most effective when consumed 4 h before bedtime," the authors write. "The relevance of these findings to persons with sleep disturbance should be determined in future trials."

Study limitations include small sample size, lack of generalizability to other groups, and inclusion of an elite athlete who did not exercise on study days and had a paradoxical response to dietary manipulation.

"The fact that a simple manipulation of food intake can significantly improve sleep onset lends itself to a possible convenient, inexpensive, and noninvasive therapy for treating difficulty with sleep initiation," the authors conclude. "Future research that explores the potential benefit of manipulating the GI or GL [glycemic load] of meals for persons with sleep disturbance is warranted."

Sydney University and Riviana Food Pty Ltd in Victoria, Australia, supported this study.

Am J Clin Nutr. 2007;85:426-430.

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