You sleep poorly, so you crave sugar. You eat sugar, so you sleep poorly. It's not just an impression: both directions of this loop have been measured in sleep laboratories with electrodes, and in a cohort of 77,000 women followed over three years. The cycle is real, and it closes in two nights.
This guide follows the research in both directions: what daytime sugar does to your night, what a short night does to tomorrow's appetite, the useful nuance about evening meals, and which end of the cycle to break. It extends our article on sugar cravings and our guide to reducing sugar.
Sugar fragments your night. In a sleep unit at Columbia, 26 adults: the proportion of sugar during the day is associated with more micro-awakenings, and fiber with more deep slow-wave sleep. Over three years, in 77,860 women, the highest glycemic index increases the risk of new insomnia by 16% ; added sugars increase it, fruits and vegetables reduce it. A short night makes you crave sugar. Two nights of four hours: appetite for sugary foods increased by 33 to 45%.
The nuance. A meal with a high glycemic index consumed four hours before bedtime shortens sleep onset from 17.5 to 9 minutes. The problem isn't the carbohydrates at dinner, it's excess sugar throughout the day and snacking in the final hour. Breaking the cycle : through sleep first, because it responds in two nights.
What daily sugar does to your night
Twenty-six normal-weight adults, aged 30 to 45 years and usually sleeping seven to nine hours per night, participated in a hospitalization crossover study. During the first four days, they consumed a controlled diet; on the fifth day, eating was unrestricted. Sleep duration did not differ, but sleep after the unrestricted day contained less deep slow-wave sleep and longer sleep onset. Higher fiber intake predicted less stage 1 sleep and more deep slow-wave sleep. The percentage of energy from saturated fat predicted less deep slow-wave sleep. A higher percentage of energy from sugar and other carbohydrates (neither sugar nor fiber) was associated with micro-awakenings. Low fiber intake and high saturated fat and sugar intake is associated with lighter, less restorative sleep with more awakenings.
St-Onge MP, Roberts A, Shechter A, Choudhury AR. J Clin Sleep Med 2016;12(1):19-24. DOI: 10.5664/jcsm.5384
This is the study that put numbers to an intuition. Sleep is measured by polysomnography, not by questionnaire, and daily diet is weighed. The result is twofold: a day when you eat freely, thus more sugary and fatty than a controlled diet, is followed by a night with less deep sleep and longer sleep onset; and in detail, it is the proportion of sugar that predicts micro-awakenings, and the proportion of fiber that predicts deep sleep. Twenty-six people, one day, but measurements that no questionnaire can replace.
What three years of sugar does to insomnia
In the observational study of the Women's Health Initiative, relationships between glycemic index, glycemic load, added sugars, starch, fiber and specific carbohydrate-containing foods, and insomnia were studied in 77,860 postmenopausal women at baseline and 53,069 after three years of follow-up. In cross-sectional and longitudinal analyses, a higher dietary glycemic index was associated with increasing probability of prevalent insomnia, fifth quintile versus first, odds ratio 1.11, and incident insomnia, odds ratio 1.16, in fully adjusted models. Higher intakes of added sugars, starch and refined cereals were each associated with higher probability of incident insomnia. Conversely, higher intakes of whole fruits and vegetables were significantly associated with lower probability of incident insomnia. Results suggest that high glycemic index diets could be a risk factor for insomnia in postmenopausal women.
Gangwisch JE, Hale L, St-Onge MP, et al. Am J Clin Nutr 2020;111(2):429-439. DOI: 10.1093/ajcn/nqz275
A cohort shows an association, not a cause: women who eat the most sugar may differ from others by traits other than sugar, even after adjustment. But three things give weight to this one: its size, its follow-up over time, which makes it possible to see who develops new insomnia, and the consistency of its results, added sugars and refined cereals in one direction, whole fruits and vegetables in the other. The authors explicitly propose testing the replacement of high-index carbohydrates with complete, fiber-rich carbohydrates as insomnia prevention.
What short nights do to sugar cravings
Twelve healthy men, averaging 22 years old, experienced two days of sleep restriction and two days of sleep extension under controlled conditions of caloric intake and physical activity. Sleep restriction was associated with an 18 percent reduction in leptin, an appetite-suppressing hormone, a 28 percent increase in ghrelin, an appetite-stimulating factor, and an increase in hunger of 24 percent and appetite of 23 percent, particularly for calorie-dense and carbohydrate-rich foods, with an increase of 33 to 45 percent.
Spiegel K, Tasali E, Penev P, Van Cauter E. Ann Intern Med 2004;141(11):846-850. DOI: 10.7326/0003-4819-141-11-200412070-00008
There the circle closes. Sugar fragments sleep; fragmented sleep raises ghrelin and lowers leptin; and appetite shifts toward dense and sugary foods, by 33 to 45 percent, in two nights. The day after a poor night's sleep, the pastry is not a character weakness, it's a hormone. And the pastry prepares the following night. Our article on sugar cravings details this aspect.
The nuance: the evening meal is not the enemy
Twelve healthy men aged 18 to 35 received standardized, isocaloric meals, 90 percent of energy in carbohydrates, based on rice with a low glycemic index, 50, or high, 109, four hours before their usual bedtime. Another time, the high-index meal was given one hour before bedtime. A significant reduction in sleep onset latency was observed with the high-index meal, 9.0 minutes, compared to the low-index meal, 17.5 minutes, consumed four hours before bedtime. The high-index meal given four hours before significantly shortened sleep onset compared to the same meal given one hour before, 9.0 versus 14.6 minutes. No effect on other sleep variables was observed. Carbohydrate intake increases plasma tryptophan concentration, a precursor to serotonin and sleep inducer.
Afaghi A, O'Connor H, Chow CM. Am J Clin Nutr 2007;85(2):426-430. DOI: 10.1093/ajcn/85.2.426
It would be easy to conclude from the first two studies that carbohydrates should be banned in the evening. The Sydney trial says the opposite: a high-index carbohydrate meal, taken four hours before bedtime, makes you fall asleep twice as fast, without degrading the rest of the night, probably because it gets tryptophan into the brain. The same meal one hour before works less well. The lesson is therefore not "no carbohydrates in the evening," it's: carbohydrates at dinner, no sugar in the last hour, and no excess sugar over the entire day. What fragments the night in the Columbia study is the sugar portion of the entire day, not the dinner rice.
What goes with good sleep
The Columbia and Chicago teams reviewed, in 2022, the twenty human studies published since 1975 linking diet composition to objectively measured sleep, by polysomnography or actigraphy, six observational and fourteen interventional. Their conclusion boils down to three points. The quantity of carbohydrates and fats is associated sometimes with better, sometimes with worse sleep, and doesn't settle the question. The type settles it: complex, fiber-rich carbohydrates, unsaturated fats, go with better sleep. And protein -richer diets too. Overall, a diet rich in fiber, fruits, vegetables and anti-inflammatory nutrients, low in saturated fats, Mediterranean-style, is associated with better sleep quality. The authors call for longer trials, in real-world conditions and on whole foods rather than isolated nutrients.
| What was measured | Effect on sleep | Nature of evidence |
|---|---|---|
| Sugar intake during the day | More micro-awakenings | Sleep study unit, 26 adults |
| Fiber | More deep slow-wave sleep, less light sleep | Sleep study unit, 26 adults |
| High glycemic index over three years | New insomnia risk + 16 % | Cohort, 77,860 women |
| Whole fruits and vegetables | Reduced insomnia risk | Cohort, 77,860 women |
| High GI meal four hours before bed | Fall asleep in 9 minutes instead of 17.5 | Crossover trial, 12 men |
| Two nights of four hours | Sugar cravings + 33 to 45 % | Crossover trial, 12 men |
Break the cycle
Pure glycine powder, with a slightly sweet taste, to be dissolved in a glass of water before bed. The amino acid that has studies on sleep quality at 3 g, detailed in our guide, and which replaces the sugar of the last hour with a sweet taste without carbohydrates. A measure of 5 g, or slightly less.
View GlycineSleep is built first through schedules and diet; glycine comes after. Our magnesium bisglycinate covers the stress aspect.
Frequently Asked Questions
Does sugar prevent good sleep?
It fragments sleep, and this is measured in the laboratory. At Columbia University, 26 normal-weight adults, usually sleeping seven to nine hours, spent five nights in a sleep unit with polysomnography. For four days they ate a controlled diet, on the fifth day they ate freely. After the free day, sleep showed less deep slow-wave sleep and longer sleep onset. And in the details of what they had eaten, the proportion of energy from sugar was associated with more nocturnal micro-awakenings, while fiber predicted more deep slow-wave sleep and less light sleep. The authors summarize: few fibers and plenty of saturated fats and sugar result in lighter sleep, less restorative, with more awakenings.
Does sugar promote insomnia?
Over the long term, a very large cohort suggests it does. In the Women's Health Initiative, 77,860 postmenopausal women were followed, and 53,069 were reviewed three years later. Those whose diet had the highest glycemic index had 11% increased risk of insomnia at baseline, and 16% more likely to develop insomnia over three years, after adjustment. Added sugars, starch, and refined grains each increased risk; whole fruits, vegetables, fiber, and whole grains reduced it. This is an observational study, which shows an association rather than causation, but its size and long-term follow-up make it the reference on this question.
Does lack of sleep make you crave sugar?
Yes, and that's the other half of the cycle. In a crossover study from the University of Chicago, twelve young healthy men slept two nights of four hours then two nights of ten hours, with controlled diet. After short nights, leptin had decreased by 18%, ghrelin increased by 28%, hunger by 24% and appetite by 23%, with a 33 to 45% increase in appetite for calorie-dense and carbohydrate-rich foods. Sugar fragments sleep, fragmented sleep makes you want sugar: it's a cycle, and it closes in two nights.
Should carbohydrates be eliminated in the evening to sleep?
No, and that's the nuance that studies provide. At the University of Sydney, twelve healthy men ate a rice-based meal, either at low glycemic index or high glycemic index, four hours before bed, and another time the high-index meal one hour before. The high glycemic index meal taken four hours before shortened sleep onset to 9 minutes versus 17.5 with the low index, without changing the rest of sleep; taken one hour before, it was less effective, 14.6 minutes. A carbohydrate-based meal in early evening thus helps you fall asleep, probably via tryptophan; what's problematic is excess sugar over the day and sweet snacking just before bed.
What diet promotes good sleep?
A review of twenty studies with objectively measured sleep, published by teams from Columbia and Chicago, provides the answer. The amount of carbohydrates and fats is associated sometimes with better, sometimes with worse sleep, but their type makes the difference: complex carbohydrates rich in fiber and unsaturated fats go with better sleep. Diets higher in protein too. Overall, a diet rich in fiber, fruits, vegetables and anti-inflammatory nutrients, low in saturated fats, of Mediterranean type, is associated with better sleep quality. The authors call for longer trials and under real-world conditions.
How do you break the cycle?
On both fronts at once, but sleep is the quickest lever: two nights are enough to increase appetite for sugar, and two nights are enough to decrease it. Protect seven hours of sleep, shift carbohydrates toward early evening and choose those rich in fiber, eliminate sweet snacking in the last hour, and gradually reduce sugar intake over the day. If falling asleep remains the problem, glycine has studies at 3 g before bed, detailed in our dedicated guide.
What to remember about sugar and sleep?
That daily sugar fragments nighttime sleep, with more micro-awakenings and less deep sleep, and that a high glycemic index diet increases the risk of insomnia by 16% in 77,000 women. That short sleep increases appetite for sugar by 33 to 45% in two nights. That a carbohydrate-based meal in early evening helps you fall asleep, and that the problem is excess and late snacking. That fiber, fruits and vegetables, and proteins go with better sleep. And that the cycle is broken first through sleep.
Sources
The studies cited below were identified via PubMed.
- St-Onge MP, Roberts A, Shechter A, Choudhury AR. Fiber and saturated fat are associated with micro-awakenings and deep slow-wave sleep. Journal of Clinical Sleep Medicine, 2016;12(1):19-24. DOI
- Gangwisch JE, Hale L, St-Onge MP, et al. High glycemic index and glycemic load diets as risk factors for insomnia: analyses from the Women's Health Initiative. American Journal of Clinical Nutrition, 2020;111(2):429-439. DOI
- Spiegel K, Tasali E, Penev P, Van Cauter E. Sleep restriction in young healthy men is associated with decreased leptin, increased ghrelin, and increased hunger and appetite. Annals of Internal Medicine, 2004;141(11):846-850. DOI
- Afaghi A, O'Connor H, Chow CM. High glycemic index carbohydrate meals shorten sleep onset time. American Journal of Clinical Nutrition, 2007;85(2):426-430. DOI
- Wilson K, St-Onge MP, Tasali E. Diet composition and objectively measured sleep quality: a narrative review. Journal of the Academy of Nutrition and Dietetics, 2022;122(6):1182-1195. DOI
