What Happens When You Sleep Less Than 6 Hours

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You didn’t sleep well last night and now you’re feeling grumpy. You check yourself in the mirror; your face looks tired and pale. You have a lot of work and can’t seem to give your 100% focus or be as productive as other days. You know that sleep affects how you look, feel and perform but this is not all:  lack of sleep disturbs your metabolism and hormones. Here are 5 facts about how sleep insufficiency affects your body:

#1- You Eat More

Lack of sleep increases your appetite: it disturbs your appetites hormones. In a study, those who slept less than 5 hours had 15% more ghrelin, the hormone that stimulates hunger, than those who slept for 8 hours. They also had 15% less leptin, the hormone that tells the brain you’re full. Disturbances in leptin and ghrelin levels were shown to increase appetite and food cravings throughout the day. So less sleep means more food cravings and therefore more snacking.


#2- You Gain Weight 

Lack or sleep makes you gain weight. Disturbances in appetite hormones make you feel hungry all day and therefore increase the chances of snacking or eating more. The same previously mentioned study found that those who slept less than 5 hours had higher body fat compared to those who slept for 8 hours. So if you’re not sleeping enough over a long period of time, you will start consuming extra calories unintentionally and end up gaining those unwanted kilos.


#3- Your Weight Loss Progress Slows Down 

Sleeping habits were shown to predict the magnitude of weight loss. In this study, overweight adults followed a calorie controlled diet to lose weight for 3 months. Their sleeping quality and duration were recorded. Results showed a significant positive relationship between sleep duration and body fat loss. Also, better sleep quality was associated with greater fat mass loss. So sleeping less will make you lose less fat and therefore slow down your progress to reach your weight loss goals.


#4- More Belly Fat 

Lack of sleep increases your chances to have a belly. How? Sleeping regulates cortisol, your stress hormone. When you don’t sleep enough your body releases more cortisol. A study found an increase of 50% in cortisol after 1 week of insufficient sleep of 5 hours. Cortisol’s main job is to regulate your glucose metabolism, blood pressure and immune response. But it also plays a role in moving fat from your periphery storage depots to centeral ones- your tummy!  So less sleep means more cortisol and therefore more belly fat.

#5- Your Carb Metabolism Is Disturbed 

Lack of sleep messes up your carb metabolism: short sleep duration is associated with reduced insulin sensitivity. In a study, healthy men who slept for less than 5 hours had 11% reduced insulin sensitivity after 1 week.  Insulin is the hormone that regulates your blood sugar levels when you eat carbs. When your insulin become sensitive or you become insulin resistant, your cells don’t respond to the normal action of insulin leading to high blood sugar levels. So your body’s ability to process and store carbs for use in the muscle is reduced.

Take Home Message

A good night sleep is important to keep your appetite hormones and weight and carbs metabolism in check.  The national sleep foundation recommends 7 to 9 hours of sleep so try getting into the habits of sleeping at least 7.5 hours per night!



Chaput, J-P., and Angelo Tremblay. “Sleeping habits predict the magnitude of fat loss in adults exposed to moderate caloric restriction.” Obesity facts 5.4 (2012): 561-566.


Nedeltcheva, Arlet V., et al. “Insufficient sleep undermines dietary efforts to reduce adiposity.” Annals of internal medicine 153.7 (2010): 435-441.


Hairston, Kristen G., et al. Sleep duration and five-year abdominal fat accumulation in a minority cohort: the IRAS family study. Sleep. 2010; 33.3: 289.

Taheri, Shahrad, et al. “Short sleep duration is associated with reduced leptin, elevated ghrelin, and increased body mass index.” PLoS medicine 1.3 (2004): 62.

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