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What Are Circadian Rhythms and How Do They Impact Your Health?

By Stephanie E - Jenny Craig

Has this ever happened to you? You wake up abruptly, unsure of what disturbed you, and immediately reach for your phone to check the time. Is it time to wake up? The numbers stare back at you – it’s 7:00 a.m. Frantic, you’re just about to leap out of bed when you realize…it’s Saturday. (Oh, great!)

If you’ve ever wondered why you couldn’t snooze past your weekday wake-up time, there’s a silver lining: your circadian rhythms are probably working just fine. 

You may have heard the phrase “circadian rhythm” before. And with the recent popularity of weight loss strategies like time-restricted feeding and intermittent fasting, circadian rhythms are getting more attention than ever. Research on circadian rhythms even won the 2017 Nobel Prize in Medicine.

But what exactly are circadian rhythms and how could they impact your health and weight? Get the answers to this and other common circadian rhythm questions below. 

What are circadian rhythms?

Circadian rhythms are defined as the behavioral, mental and physical changes your body experiences throughout a daily 24-hour cycle.1 These rhythms are created by your biological clocks, an internal “timekeeping” system that helps regulate your body’s processes.1,2 Your body’s “master clock” is made up of a cluster of nerves in your brain and keeps all your biological clocks and circadian rhythms in sync.1 

The hours of lightness and darkness you experience between sunrise and sunset trigger many of your biological clocks.2 Most people feel awake when the sun is up and become tired as it sets, but when certain rhythms can’t adjust to your environment, your health may feel the effects. 

What is a “sleep-wake cycle” and what does it have to do with my rhythm? 

pink alarm clockYour sleep-wake cycle is typically 8 hours of nighttime sleep and 16 hours of wakefulness during the day.3 Your circadian rhythm helps keep your sleep-wake cycle in check. To get the best possible sleep, the National Sleep Foundation suggests going to bed and waking up around the same time each day, even on days when you might feel tempted to sleep past your alarm.3

Sleep-wake disorders can occur when your circadian rhythms aren’t in sync with your environment. People with sleep-wake disorders often have extreme difficulty falling asleep or staying awake, according to the Journal of the American Medicine Association (JAMA).4 Two of the most common sleep-wake disorders are jet lag disorder and shift-work disorder, which can be caused by an irregular work schedule.4

How could my circadian rhythm affect my health?

You might not notice anything unusual about your circadian rhythm until something feels “off.” Some of the most obvious changes to your rhythm occur when you have jet lag, if you start to work a night shift, or when you turn your clock back for daylight saving time.

Jet lag

woman sleeping on planeExperiencing jet lag is one of the easiest ways to spot a change in your rhythm. Moving through more than one time zone within a short period doesn’t give your body enough time to sync up – that’s when jet lag sets in. Your internal clock uses information from the environment to reset itself, but it’s a slow process. It usually takes your body an entire day to reset itself by one hour. As a result, travelers flying in a west to east direction or overseas often have difficulty adjusting to the changes.5 


Common signs of jet lag include:6

  • Fatigue
  • Difficulty sleeping
  • Decreased mental and physical abilities


Feeling jet lagged can also disrupt your eating habits, making it difficult to tell when you’re hungry or thirsty.7 When you don’t eat at the right times, your blood pressure, heart rate and digestive enzymes may be affected,8 potentially leading to indigestion.6 Fortunately, there are simple ways to avoid and ease jet lag symptoms

Shift-work disorder and diabetes

Not all shift workers develop shift-work disorder (SWD), but 14 to 32 percent of night shift workers and 8 to 26 percent of rotating shift workers were estimated to have experienced symptoms, according to one study.9 Symptoms of SWD include insomnia and extreme tiredness.

The U.S. Bureau of Labor Statistics reported nearly 15 million people in the U.S. work evening shifts, night shifts, or other irregular schedules.10 Night shifts often occur between 11 p.m. and 3 a.m.,11 forcing people to stay awake and work against their circadian rhythm. 

Shift-work disorder isn’t the only complication that workers may face. A large 2018 study of more than 270,000 people found that individuals who worked eight or more irregular or rotating schedules per month were 36 percent more likely to develop Type 2 diabetes, compared to those who never worked nights.12 The study’s research suggested that night shift workers, especially those with inconsistent schedules, were more likely to be at risk for Type 2 diabetes.12 

In a separate study conducted by the Endocrine Society of Thailand and Mahidol University, night shift workers with Type 2 diabetes reported higher blood sugar levels, “shorter sleep duration, higher daily intake of calories and higher body mass index” than daytime workers or those who were unemployed.13

What Is Circadian Rhythm_Healthy_Food.jpgWorking night shifts may be unavoidable, but according to Johns Hopkins Medicine, taking these steps may help reduce your risk of developing Type 2 diabetes:14

  • Focus on making healthy food choices 
  • If you are overweight, consider losing 5-10 percent of your body weight 
  • Make time for regular exercise 

Seasonal changes

The winter solstice and the end of daylight saving time can also signal changes in your circadian rhythm. Having fewer hours of daylight or turning your clock back an hour might not seem drastically different, but they can disrupt your rhythm. During these times of the year, you may feel tired, experience headaches, or feel irritable. Here are a few ways you can help keep your rhythm on track:15

  • Stick to a consistent sleep schedule
  • Avoid digital devices before bed
  • Try to get outside for some sunlight or open your blinds to let in some morning light

I’m trying to lose weight – can my circadian rhythm help?

It’s important to maintain a regular eating schedule to keep your rhythm running smoothly. In fact, eating with your circadian rhythm may help support your weight loss efforts. Your metabolism is most efficient in the morning, peaking around mid-day. As evening approaches, your metabolism will be less active as your body winds down in preparation for sleep. 

Jenny Craig’s innovative Rapid Results program utilizes the science behind the circadian rhythm. The program is designed to work naturally with your body’s metabolism by providing you with more calories in the morning when you’re most active, and tapering calories in the evening when it’s not as efficient. By paying attention to when and what you eat, you may be able to work with your rhythm to maximize your weight loss.16

Circadian rhythms are a complex and vital part of everyday life, working behind the scenes to keep the body’s processes in sync. Abrupt changes to your schedule – working nights, traveling, or even transitioning to a new season – may influence your rhythms and affect your health. One of the simplest ways to support your natural circadian rhythm is to maintain a healthy lifestyle. Eating nutritious meals, exercising regularly and getting sufficient sleep nightly are a few ways to help your body to stay on track.

Discover the many possible benefits of eating with your circadian rhythm with the new Jenny Craig Rapid Results program. Book your free appointment with a coach today! 





[1] https://www.nigms.nih.gov/education/pages/Factsheet_CircadianRhythms.aspx

[2] https://pubs.niaaa.nih.gov/publications/arh25-2/85-93.htm

[3] https://www.scribd.com/document/191231252/Sleep-Wake-Cycle

[4] https://jamanetwork.com/journals/jama/fullarticle/2589344

[5] https://www.health.harvard.edu/blog/resetting-your-circadian-clock-to-minimize-jet-lag-2016090810279

[6] https://www.who.int/ith/mode_of_travel/jet_lag/en/

[7] https://www.mayoclinic.org/diseases-conditions/jet-lag/symptoms-causes/syc-20374027

[8] https://www.kpbs.org/news/2010/mar/08/studying-biological-clock/

[9] https://pdfs.semanticscholar.org/5bc6/db312c2bfc69d528868d8d2b2e3fdbfba6fe.pdf

[10] https://www.cdc.gov/niosh/topics/workschedules/default.html

[11] https://www.bls.gov/careeroutlook/2015/article/night-owls-and-early-birds.htm#Through the night

[12] http://care.diabetesjournals.org/content/41/4/762

[13] https://www.endocrine.org/news-room/current-press-releases/diabetes-control-is-more-difficult-for-night-shift-workers

[14] https://www.hopkinsmedicine.org/digestive_weight_loss_center/conditions/diabetes.html

[15] https://www.sleep.org/articles/circadian-rhythm-body-clock/

[16] Lifespan.” Cell Metabolism, vol. 23, no. 6, 14 June 2016, pp. 1048–1059., doi:10.1016/j.cmet.2016.06.001.

Stephanie Eng-Aponte

bio-photo-stephanie.jpg.eef213ad82f6fc52f4126898595992fc.jpgStephanie Eng-Aponte is a copywriter for Jenny Craig, based in Carlsbad, CA. They’ve focused on writing within the health and wellness space for the last several years, but have dabbled in the tech and environmental industries. Stephanie graduated from Rutgers University with a Bachelor of Arts degree in Journalism and Media Studies. Stephanie employs a “eat first, write later” approach to food blogging and enjoys the occasional Oxford comma. Outside of writing, you can find Stephanie photographing a muttley crew of rescue pups, brewing kombucha, or exploring San Diego.


Favorite healthy snack: Green apple slices with sunflower butter.




This article is based on scientific research and/or other scientific articles and was written by an experienced health and lifestyle contributor and reviewed by certified professionals.


Our goal at Jenny Craig is to provide the most up-to-date and objective information on health-related topics, so our readers can make informed decisions based on factual content. All articles undergo an extensive review process, and depending on the topic, are reviewed by a Registered Dietitian Nutritionist (RDN) or Nutritionist, to ensure accuracy.


This article contains trusted sources including scientific, peer-reviewed papers. All references are hyperlinked at the end of the article to take readers directly to the source.


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