As someone who struggled with sleeping problems for years, I can tell you that sleep touches everything. And the science tells us that getting enough sleep is one of the select few things with an impact on weight loss worth writing home about.

Why is this?

Let’s play devil’s advocate.

Let’s assume you didn’t sleep well last night.

You Won’t Feel Full

The hormone that makes you feel full is called leptin. Feeling “full” is, more or less, feeling leptin. If your body is in good working order, the more leptin in your blood, the fuller you will feel.

Inadequate sleep causes your body to produce less leptin.^1336,1337 And with less leptin, you’ll feel less full.

Or in other words, more hungry.

You’ll Be Extra Hungry

The opposite of leptin is ghrelin, the “hunger” hormone.¹³³⁸ Ghrelin makes you feel hungry. The more ghrelin in your blood, the hungrier you will feel. Ghrelin is the yin to leptin’s yang. Hungry and full. Full and hungry. Leptin and ghrelin.

Inadequate sleep causes your body to make more ghrelin.¹³³⁹

And more ghrelin means…more hunger.

So inadequate sleep means you’ll have less leptin to make you feel full, and more ghrelin to make you feel hungry. On average, this nasty one-two punch (less leptin, more ghrelin) will cause you to eat more food—and gain more fat.

A 2010 study found that, compared to eight hours of sleep, young men on just four hours of sleep ate an average of 559 more calories per day.¹³⁴⁰

That’s an extra Big Mac.

A 2013 study found that just five days of sleep restriction led to nearly two pounds of weight gain.¹³⁴¹

And it gets worse.

You WILL Crave Junk Food

Not only is Tired You hungrier and less full, but according to a 2013 study in Nature, you’ll have a special craving for “weight-gain promoting high-calorie foods.”¹³⁴² In this study, they found that lack of sleep not only makes people crave more food in general, but specifically makes them crave junk food.

A well-controlled 2016 study may shed light here. It found that sleep-deprived people have more endocannabinoids in their blood.¹³⁴³ If you noticed the first seven letters of “cannabis” lurking in that word, you’re on the right track: endocannabinoids bind to the same brain receptors as the THC of marijuana.¹³⁴⁴

On a chemical level, being sleep deprived may be similar to having the munchies.

You WILL Have Less Willpower

Willpower can be scientifically measured, and a broad range of studies have found that when people don’t sleep enough, they have less willpower the next day.^{1345,1346,1347,1348}

If this is true, can you really blame your tired self for gaining weight? It was practically inevitable. On top of feeling less full and more hungry, Tired You really craves junk food—and has less willpower to resist it.

Can you imagine a more fattening scenario?

This is why a 2008 meta-analysis of the sleep habits of 634,511 people found a “consistent increased risk of obesity amongst short sleepers [less than five hours per night]”¹³⁴⁹ and why a 2014 meta-analysis concluded that “short sleep duration was significantly associated with incidence of obesity.”¹³⁵⁰

It’s why the twin who sleeps less is significantly more likely to be overweight,¹³⁵¹ and why a 2009 study of 537 Canadians found that sleeping under six hours a night was the single greatest risk factor for being overweight.¹³⁵² (Even more than dietary factors.)

Did lack of sleep make America fat? If sleep played a major role in the recent obesity epidemic, then Americans would be sleeping less today than they slept in the recent past.

Sure enough, between the 1960s and 2000—when obesity rates took off like the Apollo 11 space shuttle—average US sleep time dropped from about 8.5 hours to just 7 hours per night.¹³⁵³

That’s nearly 20% less sleep. And polls suggest that since the year 2000, we’ve been sleeping even less.^1354,1355

And since then, we’ve gotten even fatter.¹³⁵⁶

How to Sleep More

The evidence is overwhelming. You need to get enough sleep.

But what’s enough? We’re all different, and there’s no golden number. Experts generally recommend between seven and nine hours of sleep a night.¹³⁵⁷

The important thing is to get enough sleep to feel rested most days. If you don’t feel rested most days, then getting more sleep is probably one of the best things you can possibly do for weight loss.

So how do you get more sleep?

It depends. If you fall asleep easily, the answer is also easy: just go to bed earlier. Get some rough idea of how much sleep you need to feel rested, subtract that from the time you plan to wake up, and add 30 minutes for good measure.

Problem solved.

On the other hand, if your problem is falling asleep or staying asleep, my condolences. Here are some helpful, science-based tips:

Go to bed and wake up at consistent times.Our circadian rhythms adapt to the time we’re typically asleep,¹³⁵⁸ so try to give your body what it’s expecting. Aim to sleep and wake at regular times.

Reduce artificial light at night. Staring at bright screens tricks your body into thinking it’s daytime; circadian rhythms are regulated in the eyes.¹³⁵⁹ Make it a rule not to look at bright screens (cell phones, laptops, TVs, etc.) in the hour before bed. If this is too much, at least download free software called f.lux. At night, this software reduces the blue light your screen emits. Blue light is the spectra of light with the worst impact on our circadian rhythms.¹³⁶⁰

Move around during the day. Physical activity improves sleep quality,¹³⁶¹ among other things. We’re not evolved to sit all day.

Get sunlight. Morning sunlight can help reset your biological clock.¹³⁶² We didn’t evolve indoors. Vitamin D deficiency is caused by lack of sunlight, and it’s a serious health problem.¹³⁶³ Get outside.

Avoid caffeine after noon. Caffeine keeps you awake, and lingers in your system. The half-life of caffeine (how long it takes to clear half the caffeine you ingest) is almost six hours.¹³⁶⁴

Avoid nicotine, big meals, and intense exercise within two hours of bedtime. All of these can interfere with your sleep.¹³⁶⁵

Make a to-do list for the next day. Thinking about upcoming duties can keep you up, and writing them down can help relax your mind.¹³⁶⁶ If your mind is still racing after a bit, get out of bed and do something else.

Use relaxation techniques to fall asleep faster. Deep breathing,¹³⁶⁷ listening to relaxing soundtracks,¹³⁶⁸ and progressive muscle relaxation¹³⁶⁹ can help people fall asleep faster. (That last one means tensing and then relaxing all the muscles in your body, starting at the head or toes and working down or up, respectively.)

Do cognitive behavioral therapy (CBT). CBT effectively treats many mental disorders,¹³⁷⁰ including insomnia.¹³⁷¹ Learn about CBT.

Take-Home

If you sleep better, you’ll feel better. You’ll feel more full, less hungry, and less tempted by junk food.

And you’ll have the willpower to make your dreams come true.

Habit 4: Get enough sleep to feel rested most days.

LEARN MORE

References

1336. Stern et al., “Short Sleep Duration Is Associated with Decreased Serum Leptin, Increased Energy Intake and Decreased Diet Quality in Postmenopausal Women,” Obesity 22, no. 5 (2014): E55-E61.

1337. Robertson et al., “Effects of Three Weeks of Mild Sleep Restriction Implemented in the Home Environment on Multiple Metabolic and Endocrine Markers in Healthy Young Men,” Metabolism 62, no. 2 (2013): 204-211.

1338. Higgins et al., “Ghrelin, the Peripheral Hunger Hormone,” The Annals of Medicine 39, no. 2 (2007): 116-136.

1339. Broussard et al., “Elevated Ghrelin Predicts Food Intake During Experimental Sleep Restriction,” Obesity 24, no. 1 (2016): 132-138.

1340. Brondel et al., “Acute Partial Sleep Deprivation Increases Food Intake in Healthy Young Men,” American Journal of Clinical Nutrition 91, no. 6 (2010): 1550-1559.

1341. Spaeth et al., “Effects of Experimental Sleep Restriction on Weight Gain, Caloric Intake, and Meal Timing in Healthy Adults,” Sleep 36, no. 7 (2013): 981-990.

1342. Greer et al., “The Impact of Sleep Deprivation on Food Desire in the Human Brain,” Nature Communications 4 (2013): 2259.

1343. Hanlon et al., “Sleep Restriction Enhances the Daily Rhythm of Circulating Levels of Endocannabinoid 2-Arachidonoylglycerol,” Sleep 39, no. 3 (2016): 653-664.

1344. Ibid.

1345. Christian, M., and Ellis, A., “Examining the Effect of Sleep Deprivation on Workplace Deviance: A Self-Regulatory Perspective,” Academy of Management Journal 54, no. 5 (2011): 913-934.

1346. Wu et al., “The Effect of Sleep Deprivation on Cerebral Glucose Metabolic Rate in Normal Humans Assessed with Positron Emission Tomography,” Sleep 14, no. 2 (1991): 155-162.

1347. Venkatraman et al., “Sleep Deprivation Elevates Expectation of Gains and Attenuates Response to Losses Following Risky Decisions,” Sleep 30, no. 5 (2007): 603-609.

1348. Meldrum et al., “Sleep Deprivation, Low Self-Control, and Delinquency: A Test of the Strength Model of Self-Control,” Journal of Youth and Adolescence 44, no. 2 (2015): 465-477.

1349. Cappuccio et al., “Meta-Analysis of Short Sleep Duration and Obesity in Children and Adults,” Sleep 31, no. 5 (2008): 619-626.

1350. Wu et al., “Sleep Duration and Obesity Among Adults: A Meta-Analysis of Prospective Studies,” Sleep Medicine 15, no. 12 (2014): 1456-1462.

1351. Watson et al., “A Twin Study of Sleep Duration and Body Mass Index,” Journal of Clinical Sleep Medicine 6, no. 1 (2010): 11-17.

1352. Chaput et al., “Risk Factors for Adult Overweight and Obesity in the Quebec Family Study: Have We Been Barking Up the Wrong Tree?” Obesity 17, no. 10 (2009): 1964-1970.

1353. Buxton et al., “Association with Sleep Adequacy with More Healthful Food Choices and Positive Workplace Experiences Amongst Motor Freight Workers,” American Journal of Public Health 99, Supplement 3 (2009): S636-S643.

1354. “Summary of Findings,” Sleep in America Poll, 2005. National Sleep Foundation. https://sleepfoundation.org/sites/default/files/2005_summary_of_findings.pdf

1355. “Summary of Findings,” Sleep in America Poll, 2009. National Sleep Foundation. https://sleepfoundation.org/sites/default/files/2009%20SLEEP%20IN%20AM

1356. “Obesity Rates and Trends Overview,” Better Policies for a Healthier America. https://stateofobesity.org/obesity-rates-trends-overview/

1357. Hirschkowitz et al., “National Sleep Foundation’s Sleep Time Duration Recommendations: Methodology and Results Summary,” Sleep Health 1, no. 1 (2015): 40-43.

1358. Arendt, J., “Melatonin, Circadian Rhythms, and Sleep,” New England Journal of Medicine 343 (2000): 1114-1116.

1359. Dijk, D., and Archer, S., “Light, Sleep, and Circadian Rhythms: Together Again,” PLOS Biology 7, no. 6 (2009): e1000145.

1360. Burkhart, K., and Phelps, J., “Amber Lenses to Block Blue Light and Improve Sleep: A Randomized Trial,” Chronobiology International 26, no.8 (2009): 1602-1612.

1361. Yang et al., “Exercise Training Improves Sleep Quality in Middle-Aged and Older Adults with Sleep Problems: A Systematic Review,” Journal of Physiotherapy 58, no. 3 (2012): 157-163.

1362. Smith. S., and Trinder, J., “Morning Sunlight Can Advance the Circadian Rhythms of Young Adults,” Sleep and Biological Rhythms 3, no. 1 (2005): 39-41.

1363. Holick, M., “Vitamin D and Sunlight: Strategies for Cancer Prevention and Other Health Benefits,” Clinical Journal of the American Society of Nephrology 3, no. 5 (2008): 1548-1554.

1364. Statland, B., and Demas, T., “Serum Caffeine Half-Lives: Healthy Subjects vs. Patients Having Alcoholic Hepatic Disease,” American Journal of Clinical Pathology 73, no. 3 (1980): 390-393.

1365. Kotagal, S., and Pianosi, P., “Sleep Disorders in Children and Adolescents,” BMJ 332 (2006): 828-832.

1366. Ibid.

1367. Konsta et al., “Stress Management Techniques in Primary Insomnia: A Randomized Controlled Trial,” Sleep Medicine 14, Supplement 1 (2013): e173.

1368. De Niet et al., “Music-Assisted Relaxation to Improve Sleep: A Meta-Analysis,” Journal of Advanced Nursing 65, no. 7 (2009): 1356-1364.

1369. Konsta et al., “Stress Management Techniques in Primary Insomnia: A Randomized Controlled Trial,” Sleep Medicine 14, Supplement 1 (2013): e173.

1370. Butler et al., “The Empirical Status of Cognitive Behavioral Therapy: A Review of Meta-Analyses,” Clinical Psychology Review 26, no. 1 (2006): 17-31.

11371. Trauer et al., “Cognitive Behavioral Therapy for Chronic Insomnia: A Systematic Review and Meta-Analysis,” Annals of Internal Medicine 163, no. 3 (2015): 191-204.