How Sleep Deficiency Can Affect Fat Loss

Everyone is always searching for the magic pill to help lose more body fat and make the whole process easier, however, most don’t realise one of the best things we can do to assist fat loss efforts is something we’re already doing – sleeping! We, humans, have a terrible tendency to sabotage the duration of sleep we get and we pay a price for it.

Not only has sleep been shown to improve cognitive function, cardiovascular health, and reduce anxiety and depressive disorders, but it has also been shown to help regulate appetite, food cravings and portion sizes (1), and help improve fat loss and fat-free mass retention – all of which can have significant implications for attempting to lose body fat (2).

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Impaired Appetite Regulation

Sleep loss is associated with decreased leptin and increased ghrelin levels, which can lead to an increase in appetite (3). Leptin is a hormone released by fat cells that signal to the brain that the body has enough stored energy and does not need to consume more food, thereby reducing appetite (4). When leptin levels decrease, appetite is elevated. On the contrary, the hormone ghrelin signals to the brain that energy is required and increases appetite (5). In one study in sleep-deprived men, leptin decreased by 18% and ghrelin increased by 28%, resulting in a total increase in appetite by 23% when compared to the control group with normal sleep levels (6). Thus, when sleep is below the recommended average of 7-9 hours per night (7), it appears that appetite misfires and, consequently, food intake is greater (1).

Insufficient sleep affects hormone regulation and tends to increase appetite significantly.

Increased Cravings and Portion Servings

​Having less than optimal sleep has been shown to increase cravings for highly palatable foods; both savoury and sugary, high-fat foods (1). A study showed individuals who reported a short sleep duration (<7 hrs) reported higher cravings for high-calorie foods (8). Also, when sleep was shortened between the groups, the group with less sleep resulted in more cravings and an increased urge to eat palatable foods that are higher in calories. Whilst some people can withstand cravings and ignore them, it can make dieting a lot harder and, consequently, result in greater total caloric consumption. ​ It’s not just the cravings that make dieting harder though; those who slept for a 33% shorter duration than their usual sleep time also consumed larger portions of food (9); likely due to a reduced awareness of portion sizes (10,11). Larger portion sizes means – again - more calories could be consumed over a day, weeks, months, etc., and, consequently, have negative implications for fat loss.

Insufficient sleep has been shown to result in greater cravings for savoury and sugary, high-fat foods, as well increased portion sizes.

Burn Less Fat, Lose More Lean Mass

People who do not get adequate sleep each night tend to lose less body fat and lose more fat-free mass (i.e., glycogen and muscle). A study showed that despite losing the same amount of weight, those who slept less than 5.5 hours per night lost up to 55% less fat and lost up to 60% more fat-free mass (2). They also had increased appetite and a tendency to use fewer fatty acids (i.e. adipose tissue) as a fuel source and more glucose and glycogen for fuel (12). Consequently, fat loss efforts can be sabotaged by a lack of sleep due to shifting your body towards burning fat-free mass as opposed to fat mass (13). And if you’re already thinking you’ll just catch up on sleep on the weekend, don’t bother! Banking sleep on the weekend to try and make up for sleep lost during the week has also been shown to be ineffective at reversing the effects of insufficient sleep (2).

Insufficient sleep can impair fat loss by increasing the amount of fat-free mass (i.e. glycogen and muscle) utilised for fuel as opposed to free-fatty acids (i.e. body fat).


Science has shown that sleep can have a huge impact on fat loss attempts and should be something everyone should try to address when trying to both lose and maintain their body weight/fat, Even moderate amounts of insufficient sleep can have a detrimental impact on appetite regulation and portion control; all of which can result in excessive caloric consumption. Even if excessive caloric consumption is avoided, it can still significantly impair the amount of weight loss from fat mass and have negative consequences for muscle retention. Simply trying to increase your sleep duration to 7-9 hours per night and improve your sleep quality can go a long way in trying to improve your body composition efforts.


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  9. Lai P.P., Say Y.H. Associated factors of sleep quality and behavior among students of two tertiary institutions in northern Malaysia. Med. J. Malays. 2013;68:195–203.
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  11. Smith ME, McEvoy LK, Gevins A. The impact of moderate sleep loss on neurophysiologic signals during working-memory task performance. Sleep. 25:56–66, 2002.
  12. Steenhuis I, Poelman M. Portion size: Latest developments and interventions. Curr. Obes. Rep.;6:10–17, 2017.
  13. Nedeltcheva AV, Kilkus JM, Imperial J, Schoeller DA and Penev PD. Insufficient sleep undermines dietary efforts to reduce adiposity, Ann Intern Med., 153(7):435-41, 2010.

About the author

Amanda Moroney


With over 15 years of experience in the fitness industry and a burning passion for all things health and fitness, Amanda has a BSc in Exercise Science, a BSc in Health Sciences, and an MSc in Biomechanical Analysis. She is also an international IFBB Bikini competitor and a mother.

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