The Circadian Code by Dr. Satchin Panda

The Circadian Code by Dr. Satchin Panda

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A book about your body's natural rhythm and why it's better to be in sync with it rather than fight it.

The book in a few sentences

This book explains the natural rhythm of our bodies and what we should do to align with that rhythm. It also explains the implications that can happen when we fight that rhythm.

Who Should Read It ?

  • Anyone looking to improve their heath
  • Anyone looking to understand our circadian rhythm
  • Anyone looking to get into intermittent fasting

How the Book Changed Me

This book taught me the importance of being consistent with my eating and sleeping times. That what we do is just as important as when we do it. It also taught me how easy it is to disrupt our natural rhythm by eating or sleeping at the wrong time.

Summary + Notes

Part 1: The Circadian Clock

Chapter 1: We Are All Shift Workers

Don't matter how we try to fight it, all of us are shift workers. We have to abide by certain shifts every day. Whether that is our wake/sleep cycle or our eating cycle

The circadian rhythm in large is affected by light. Bright light in the morning triggers some part of our circadian rhythm and so does the absence of light in the evening.

It governs from when we feel hungry to when we feel sleepy. That is why it is important to view sunlight as early in the day as possible

Windows and indoor lighting are not strong enough to active the melanopsin cells to trigger a strong circadian rhythm. Even if we think indoor lighting is very bright, it cannot compete with the sun. There is a significant difference between perceived and actual light brightness.

Chapter 2 : How Circadian Rhythms Work

The Circadian clock governs these activities:

  • Getter Energy (Food)
  • Balancing the use of the energy vs preservation of energy
  • Protecting itself from harmful bacteria and agents
  • Repairing itself
  • Reproducing

The cycle cannot be sped up or slowed down drastically. It is largely in tune with the 24 hour cycle, it may teeter back and forth a few hours but it is largely governed by the day.

Every organ has their own clock:

  • When we eat is circadian
  • Our energy metabolism system is circadian
  • Cellular maintenance mechanisms are circadian too
  • Repair and cell division is circadian
  • Cell communication is circadian
  • Cell secretion is circadian
  • Even drug targets are circadian, which means there are specific times of the day where drugs are the most effective

SCN: The Master Clock

All the organs above are controlled by a master clock which is controlled by our suprachiasmatic nucleus (SCN) and is circadian

However, depending on the circumstances, organ clocks are allowed to override the master clock.

The eating cycle mentioned above is circadian but when food is ingested outside the cycle, the body does not reject it because that signifies a huge potential loss for energy.

This means that there are three core rhythms in the body

Three Core Rhythms


Our brains will nudge us to sleep after about 12 hours of being awake and then to very sleepy after 16 hours of being awake


Ingesting any food will kick start the cycle of digestion again which forces all the other organs to work overtime if done outside regular hours.

I like to think of it as organ office hours. Some times they have to work late but it shouldn't be done al the time Knowing this, it could be a good idea to use eating to reset one's circadian rhythm especially if they are travelling to help with jetlag

Physical Activity

Most of our muscles are more efficient in the day than night.

Even our gut motility which is more active during the day than night. Therefore, eating something late in the night can cause indigestion

Chapter 3: Track and Test: Is Your Circadian Rhythm in Sync?

Questions to test how in-sync you are

Physical Health

  • Has your doctor told you that you are overweight? Y/N
  • Have you been diagnosed with either prediabetes or diabetes? Y/N
  • Are you taking prescription medication for a chronic disease, such as heart disease, blood pressure, cholesterol, asthma, acid reflux, joint pain, or insomnia? Y/N Are you taking over-the-counter remedies for acid reflux, pain, allergies, or insomnia? Y/N
  • Do you have an irregular menstrual cycle? Y/N Do you have hot flashes or disrupted sleep related to menopause? Y/N
  • Do you have a decreased libido?
  • Have you been diagnosed with a disease linked to chronic inflammation, such as multiple sclerosis or inflammatory bowel disease? Y/N
  • Do you have frequent lower back pain? Y/N
  • Have you been diagnosed with sleep apnea? Y/N
  • Do you snore? Y/N
  • Do you wake up feeling congested or with a stuffy nose? Y/N
  • Do you have frequent abdominal pain, heartburn, or indigestion? Y/N
  • Do you have frequent headaches or migraines? Y/N
  • Do your eyes feel tired at the end of the day?

Mental Health

  • Do you feel anxious? Y/N
  • Do you feel low or have frequent blue moods? Y/N
  • Do you struggle with attention and focus? Y/N
  • Do you experience brain fog or poor concentration? Y/N
  • Do you frequently lose items, like your glasses, a charging cable, or keys? Y/N
  • Are you forgetful of names and faces? Y/N
  • Do you rely on a calendar or to-do lists? Y/N
  • Do you get tired in the afternoon? Y/N
  • Do you wake feeling tired? Y/N
  • Have you been diagnosed with post-traumatic stress disorder (PTSD)? Y/N
  • Have you been diagnosed with attention deficit hyperactivity disorder (ADHD), autism spectrum disorder (ASD), or bipolar disorder? Y/N
  • Do you have food cravings? Y/N
  • Do you feel like you have a lack of willpower over food? Y/N
  • Have you been told that you are irritable? Y/N
  • Do you have trouble making decisions? Y/N

Behavioral Habits

  • Do you take less than 5,000 steps a day? Y/N
  • Do you spend less than an hour outdoors under daylight each day? Y/N
  • Do you exercise after 9:00 p.m.? Y/N
  • Do you spend more than an hour on the computer, your phone, or watching TV before bedtime? Y/N
  • Do you have one or more alcoholic drinks (cocktails, wine, or beer) after dinner? Y/N
  • Do you forget to drink water throughout the day? Y/N
  • Do you drink coffee, tea, or caffeinated soda in the afternoon or evening? Y/N
  • Do you consume chocolates, high-carb foods (doughnuts, pizza), or energy drinks to improve your energy level? Y/N
  • Do you binge on foods late in the day regardless of hunger? Y/N
  • Do you drink or eat anything (other than water) after 7:00 p.m.? Y/N
  • Do you sleep with a light on? Y/N
  • Do you set aside less than 7 hours for sleep and rest every day? Y/N
  • Do you need an alarm clock to wake up in the morning? Y/N
  • Do you typically catch up on sleep on the weekends? Y/N
  • Do you eat whenever food is presented to you, even if you are not hungry?

Assessing Your Responses

Saying yes to a few of the questions would mean that we have some form of circadian disruption but it is normally fine unless you answered yes to a lot of them.

Your Ideal Circadian Code

We are all different human beings with unique circadian codes. Some parts of it will be similar but all of us will have our own ideal circadian code.

The easiest way to find that out, is to take a month long vacation with nothing plan. Then track and observe what are the times we want to wake up, eat, reproduce and sleep. This will be our natural state of being.

Tracking the Circadian Rhythm

One of the easiest ways to track how in-sync you are with your circadian rhythm is to keep these questions in mind daily


  • When (and How) You Wake Up (You should try to wake without an alarm)
  • When is/was your first bite of the day or first drink with calories of the day
  • The End of your last meal/Drink
  • When do you go to sleep ?
  • What Time do you shut off all screens. (Ideally 2-3 hours before bed)
  • What Time did you exercise ?

Assessing your response

If all six times change by +/- 2 hours or more, then you have to improve on the consistency of the timings.

Some notes on the 6 questions.

  • You should be getting 7 hours of sleep, 9 for children
  • Even a meager 3/7 days of poor sleep could throw the cycle off
  • Look at the amount of hours your stomach is at work (Time you last ate - time you first ate)
  • It should be less than 12 hours, a 8-11 hour feeding window is ideal
  • Compare your last bite/sip time with your bedtime. Should be about 3 hours.
  • For the most optimal result, also compare when you first wake against first bite/sip

Part 2: The Circadian Lifestyle

Chapter 4 : A Circadian Code for the Best Night's Sleep

For a person with good sleeping habits, you should be able to fall asleep within 20 minutes of lying down in bed with no aid ( Meaning no book, lights or phone)

If you need longer than that, there is some form of disruption happening, this could be:

  • Stress
  • Too much food, which keeps the body temperature too high to sleep
  • Too little physical activity
  • Too much time spent in light in the evening

Waking up 4-5 times a night is bad for your sleep too. The main causes for this are :

  • Dehydration
  • Ambient temperature is too high or too low
  • Acid Reflux from eating too late in the night
  • Pet
  • Sounds
  • Snoring

Chapter 5 : Time-Restricted Eating: Set Your Clock for Weight Loss

We know that our eating window is circadian, therefore, it is best to time our meals within the same window each day.

Because of this, it is important that we also keep this eating regime through the weekends. Even not following the same regime for 1 day in a week can throw off your circadian rhythm

Chapter 6: Optimizing Learning and Working

The Optimal Workday

Most of us get our best work done between 10:00am to 3:00pm or more specifically a couple of hours after your body's temperature low (which should be a couple of hours before you wake up)

This is a very good reason, to have a speedy lunch or just quick lunch break and then get back to work to stay within this period of efficiency

Master Light, Master Productivity

Staying up into the night working is not a good idea because it sends us down this spiral of bad productivity where your brain cannot focus for long

Therefore, we want to optimize our rhythms, so that we get a good working day and that we are able to get majority of our work done when the sun is still up.

Work with a lot of sunlight in the morning and afternoon. Which normally means try to work next to a window in the office or at home. Minimize light exposure in the evening, to get ready for sleep.

Chapter 7: Syncing Your Exercise to Your Circadian Code

The three types of physical activity

  • Aerobic
  • rhythmic in nature and includes anything that gets your heart rate up that you can sustain for a period of time
  • think long runs, marathons, etc.
  • Strength or resistance training
  • FRC (Functional Range Condition) or stretching

The two best times to exercise

Early in the morning

  • from sunrise until 2-3 hours after sunrise
  • More sunlight exposure
  • Higher cortisol in the morning means better sleep at night

Late in the afternoon

  • 3:00pm onwards
  • Better performance which prevents injury

Part 3: Optimizing Circadian Health

Chapter 9: The Clock, the Microbiome and Digestive Concerns

Digestion itself is circadian and therefore should be treated with equal importance to sleeping. That also means we should try and not eat/drink outside our regular hours.

When we eat is just as important as what we eat.

Gut Microbiome

We also need a diet that benefits us as well as our gut microbiome. This includes eating fermented foods and fibre from leafy vegetables.

Foods with lots of preservatives can damage our gut's mucosal lining.

Chapter 11: Enhancing the Immune System and Treating Cancer

Because most cell activity associated with repair and defense is circadian, we can use this to our advantage. Maximizing on our circadian rhythm could lead to better defense.

This also means that we can schedule surgeries and medicinal intakes at specific times of the day to get the most use out of them. Generally these are times when your body doesn't need to rest, which is when the sun is up.

Final Thoughts

I really liked this book because it made me understand that consistency is just as important as what we do. It's better off to do small good things consistently rather than one big "healthy" thing every once in awhile. It also helped me understand that being consistent with sleeping and eating has large benefits and I should be doing that more often.