How your sleep cycle impacts your weight and your workouts

Wednesday, July 19, 2017. Author Sarah Barron

Are you a morning lark or a night owl?

Are you a morning lark or a night owl? We’ll help you understand your body clock and its effects on weight loss and your performance in the gym.


What is your circadian rhythm?

Have you ever wondered why some people seem to be inherently better at coping with early morning starts, while others need to set multiple alarms at 5-minute intervals in the hope that one of them will give them the motivation to crawl out from under the covers? Although there are other influencing factors, what determines whether someone is intrinsically an ‘early bird’ or ‘night owl’ is down to genetics and an individual’s circadian cycle.    

The word Circadian comes from the Latin phrase Circa meaning “about” and diēm meaning “each day”. Therefore, a circadian rhythm is defined as any biological process that occurs over a 24-hour period endogenously (or in other words is self-sustained and occurs irrespective of any external influences). Bodily processes which occur in a circadian ‘clockwork’ fashion include sleep cycles, hormone fluctuations, core body temperature and even immune and digestive function.


How does genetics determine your circadian rhythm?

One of the main genes associated with body clock regulation is the Circadian Locomotor Output Cycles Kaput or CLOCK gene. Individuals who carry one or two copies of the C allele for this gene, are more likely to prefer the evenings, experience daytime fatigue, have delayed sleep onset, and are therefore more likely to experience sleep deprivation than those who carry a T allele 1.

Both the C allele and sleep deprivation are linked to weight loss resistance, dysregulation of the hormones controlling appetite, and have a higher risk of obesity 2. Therefore, those carrying the C allele may need to be more mindful of setting up a good night time sleeping routine to ensure they catch those all-important zzzz’s.


How does my environment affect my circadian rhythm?

Although your circadian rhythms is endogenous and partially determined by genetics, they can also be entrained or ‘locked onto’ natural external cues such as sunlight, temperature and physical activity (or in the modern world, artificial lighting, handheld devices, and alarm clocks!). In ancestral ‘hunter gatherer’ times, this allowed us to optimize our environment’s resources and keep in synch with seasonal changes in climate change.

However, modern day living is having an increasingly negative impact on our circadian synchronicity, health and well-being. For example, shift workers have a higher risk of developing metabolic, cardiovascular and mental health disorders and even cancer 3,4. This is due in part, to dysregulation of our natural body clock and those circadian cycles controlling blood pressure, heart rate, energy metabolism and hormones such as melatonin and cortisol which are involved with sleep, stress, and inflammation.


How can I use my circadian rhythm to my advantage?

But don’t worry, your circadian rhythm can be rescued or realigned to its natural cycle by including routine activities into your daily schedule and getting enough exposure to natural light during daytime hours. For example, in female night-shift workers and mice who carry a mutation in the CLOCK gene, having structured meal and exercise periods at the same time every day has shown to be helpful in preventing metabolic dysregulation 5,6.

Although the majority of studies show peak performance in strength, anaerobic output, and joint flexibility generally occurs in the late afternoon 7, your own individual peak time may differ depending on your personal circadian programming.

Rather than a specified time of day, ‘time after awakening’ may be a better indicator for optimal performance. For example, one study that divided 121 age-matched athletes into 3 groups: morning larks, intermediates, and night owls, revealed that peak performance was highest at 5.36, 6.30 and 11.11 hours after awakening respectively 8. This study also revealed that performance output can vary by up 26% within the course of the day!

If you have more flexibility in your work-to-leisure ratio, it's likely that optimizing the timings of your workouts according to your genetic traits will lead to better results. For the majority of us that have fixed working hours, having a workout routine at roughly the same time each day will still have a positive effect on mood regulation, sleep quality and metabolism. So plan a schedule that works for you, and follow it as best you can. If mornings and evenings are too hectic for you, maybe try a regularly scheduled “Runch”.


Ready to find out whether you're a morning lark or a night owl? CLOCK is one of the 43 genes that we analyse and provide reports on. Shop our range of products by visiting our online shop.


  1. Katzenberg D, Young T, Finn L, Lin L, King DP, Takahashi JS, Mignot E. A CLOCK polymorphism associated with human diurnal preference. Sleep. 1998;21(6):569–76.
  2. Garaulet M, Esteban Tardido A, Lee Y-C, Smith CE, Parnell LD, Ordovás JM. SIRT1 and CLOCK 3111T> C combined genotype is associated with evening preference and weight loss resistance in a behavioral therapy treatment for obesity. International journal of obesity (2005). 2012;36(11):1436–41.
  3. Knutsson A. Mortality of Shift Workers. Scandinavian journal of work, environment & health. 2017;43(2):97–98.
  4. James SM, Honn KA, Gaddameedhi S, Van Dongen HPA. Shift Work: Disrupted Circadian Rhythms and Sleep—Implications for Health and Well-being. Current Sleep Medicine Reports. 2017;3(2):104–112.
  5. Barclay JL, Husse J, Bode B, Naujokat N, Meyer-Kovac J, Schmid SM, Lehnert H, Oster H. Circadian Desynchrony Promotes Metabolic Disruption in a Mouse Model of Shiftwork Mistlberger RE, editor. PLoS ONE. 2012;7(5):e37150.
  6. Pan A, Schernhammer ES, Sun Q, Hu FB, Hu F. Rotating Night Shift Work and Risk of Type 2 Diabetes: Two Prospective Cohort Studies in Women Groop L, editor. PLoS Medicine. 2011;8(12):e1001141.
  7. Shibata S, Tahara Y. Circadian rhythm and exercise Molecular mechanism underlying the functions of circa- dian and system clocks. J Phys Fitness Sports Med. 2014;3(1):65–72.
  8. Facer-Childs E, Brandstaetter R. The Impact of Circadian Phenotype and Time since Awakening on Diurnal Performance in Athletes. 2015. 518-522 p.

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