Report on The Circadian Code

This book opens on a preface by the author Dr. Satchin Panda. Dr. Panda grew up in India and spent his childhood split between two places. The first place (his home during the school year) was in the city near his maternal grandparents. The second place (his home during winter and summer breaks) was a farm owned and run by his paternal grandparents. His maternal grandfather worked as a goods clerk at the local train station, often working the night shift. His paternal grandfather worked his own farm and, importantly to this story, he lived in sync with the rhythms of nature. As Dr. Panda’s grandparents aged, his maternal grandfather developed dementia shortly after retiring and died at the age of 72. These symptoms were not noticed in Dr. Panda’s paternal grandfather and this, among other experiences, led Dr. Panda towards researching circadian rhythms. If you are not aware what a circadian rhythm is, it’s simply a biologically determined timing of organ function, behavior and other physiological mechanisms. “Circa” means around in latin and “diem” means day, so circadian is referring to a rhythm that revolves around a 24 hour daily cycle. Dr. Panda proposes that this circadian rhythm can become out of sync if an individual does not operate in a well timed day/night pattern. Once this occurs, he claims that people are predisposed to higher rates of chronic disease and other maladies. Throughout this book, Dr. Panda will detail why it's important to readjust your lifestyle to work with your natural rhythms of light exposure, activity and even eating times. This field of research is small and short-lived but Dr. Panda believes that he has started to crack the circadian code, so let's dive in.

Dr. Panda opens his first chapter by describing the current human condition in regards to shift work. He claims that everyone is a shift-worker, or is at least negatively impacting their circadian rhythms by behaving similar to a shift worker. The official European definition of a shift worker is someone who “stays awake for more than 3 hours between 10:00 pm and 5:00 am for more than 50 days a year. Dr. Panda highlights how things like jet-lag, social jet-lag (later sleep/wake schedule on the weekends), digital jet-lag (chatting with people online who are on different time zones), being a performance artist or being a new mother can all impact your health in the same way that shift work can. If you are wondering why Dr. Panda is making such a big deal of shift-work and shift-work mimicking lifestyles, here are some facts about the health of people who work these poorly aligned shifts. A single night of shift work can impact a person’s cognition for a whole week. On top of a loss of memory and attention, shift work can affect appetite and the type of foods a person craves and the individual may not be the only one affected. Dr. Panda describes research done in 2013 that claims that the children of shift workers were also likely to have cognitive and behavioral problems as well as an increased incidence of obesity. Needless to say, circadian rhythms are important and people need to start monitoring their current patterns in order to optimize their own rhythms. Dr. Panda uses the rest of this chapter to detail the circadian rhythms of humans. Briefly explained, the human body has multiple physiological responses throughout a day/night pattern. Starting in the morning, the body raises its internal temperature by half a degree, our blood pressure rises as our heart rate increases and breathing becomes faster. In order for these functions to occur, the pineal gland must stop its production of melatonin. The body essentially replaces (not exactly) melatonin with the hormone cortisol in order to awaken consciousness to a level that allows an individual to start the search for food. Nearing the end of the day, the human muscle tone is at its peak. As the day winds down, the body temperature starts to drop and the pineal gland begins producing melatonin as cortisol levels lower. During the night, the brain is actively consolidating memories, flushing out toxins and creating new neural connections. The body is also healing and releasing growth hormone in order to heal and grow (which is one reason why kids need adequate sleep to grow up healthy and strong). When we are newly born, our circadian rhythms are not as powerful. Babies wake up during the night making bowel movements and feeling hungry. As they adjust to the light/dark cycle they start to have more regularity in their sleep/wake/eat/poop schedule. One of the main things that the baby uses to regulate its rhythms in light exposure. Dr. Panda’s lab (and other researchers) discovered a light sensing protein in the retinal cells of the eye called melanopsin. This protein regulates the body's circadian rhythm in accordance with exposure to blue light. Once these proteins are exposed to the blue-light spectrum (from the sun or artificial sources) the production of melatonin is down-regulated (suppressed in response to an outside stimulus). Orange or red lights don’t have the same effect on melanopsin so using these colors of the light spectrum at night can be helpful for producing enough melatonin for adequate sleep.

The second chapter of this book details how circadian rhythms actually work. Dr. Panda begins the section by discussing how every living thing has to abide by the cycle of light and dark or day and night. During the day when it is light out, living organisms spend their time gathering food, protecting themselves, repairing or growing and reproducing. Dr. Panda describes how plants oscillate their leaves up (during the day) and down (during the night) to optimize photosynthesis. Even molds use timing to dictate when to bloom so that they can capitalize on the time of the day with the strongest winds. The circadian rhythm of a living creature is dependent on particular genes. These genes code for the creation of certain proteins that can act as enzymes (such as enzymes that digest food), building blocks or even hormones. From research done on fruit flies, scientists were able to find the particular genes in these flies that controls their circadian rhythms. These genes are called period genes or “per” genes. These per genes turn on and off throughout a 24-hour cycle and this will dictate the amounts of particular proteins throughout the day and night. There are more than a dozen per genes in animals, including humans. These per genes become important for understanding how circadian rhythms affect one's health once you consider that the timing of protein creation is important for various functions such as digestion, sleep and even muscle tone. Before, it was thought that the per genes were all located in the brain, but it turns out that every organ has its own per gene, which was another discovery from fly research. A team of scientists put a glow-in-the-dark tag on flies per genes and noticed that even when the flies were separated into various body parts, the body parts kept to the same rhythm of glowing and not glowing that they had when they were one fly. It turns out that thousands of genes turn on and off over time in a synchronized fashion. It’s important to understand that your body can’t perform all of its various functions at the same time, it needs to be coordinated. For example, you can’t burn fat and store fat at the same time. These are two separate processes that are driven by different genes. Other examples of coordinated systems are nutrient absorption pathways, cellular maintenance, repair and cell division, cell communication, cell secretion, and almost every drug target (specific area that a drug affects). So the body is essentially an orchestra of physiological functions that are conducted by genes which turn on and off at specific times. Now that you understand how all organs have an individual gene expression, it’s important to know that all of these genes are controlled by a master clock. This master clock is a small cluster of cells located at the hypothalamus called the suprachiasmatic nucleus or SCN. The hypothalamus is the command center for hunger, sleep, satiety (feeling full), fluid balance, stress response and more. The SCN is indirectly linked to the other main glands in the body (namely the pineal gland, pituitary gland, gonads, adrenal glands and thyroid gland). In lab animals that have had the SCN removed, scientists have noted that they lose all sense of time and their behaviors become random and erratic (eating when they should be sleeping, exercising when they should be resting etc). The SCN is made up of only 20,000 cells and when it is exposed to blue-light, it resets all of the glands that I mentioned before, along with the functions they relate to. The other clocks in the body (such as the liver clock) create a rhythm based on light exposure and the timing of eating. The SCN is still indirectly in charge of eating times as well since it regulates when the body feels hunger. Dr. Panda finishes up this section by describing the three core rhythms: sleep, nutrition and activity. He warns the reader that if any one of these core rhythms becomes out of sync, individuals health will suffer. In the section describing the first core rhythm “sleep”, Dr. Panda claims that morning larks and night owls are largely a myth. He describes how the sleep cycle changes over time from needing more sleep and sleeping earlier in the evening as a newborn to slowly needing less sleep and sleeping later in the evening as an adult. There are some cases of people who had genetic mutations that forced them to sleep in odd patterns (like 7pm to 2am) against their will. However, this is highly unlikely and most people are able to make changes to their sleep patterns by altering environmental and lifestyle factors. One study that Dr. Panda discusses brought a group of self proclaimed “night owls” out into the wild for a few nights of camping. After 2 days of sleeping in the wild these “night owls” began producing melatonin at earlier times and started falling asleep at a normal hour (just a few hours past sun-down). Dr. Panda actually experienced this first hand after camping in Kenya. Once he got back to San Diego to continue working in his lab, he fell back into his old habits and noticed that his sleep quality was worse than when he was in Kenya. He chalks this down to a few factors: being exposed to more light during the day (especially blue-light from the sun), no light at night, less noise, relatively cooler temperatures at night and an earlier dinner. All of these factors should be taken into consideration to improve sleep and quality of life in general. The second core rhythm in this section is nutrition. Dr. Panda claims that blue-light sensors aren't the only thing that can influence circadian rhythms. If we are looking at the clock in various organs, food can actually have a more powerful influence than light. Simply put, your organs plan to digest your meals according to the schedule you make by eating at the same time each day. If you usually eat breakfast at 8:00, then that is when your organs will be ready to eat. If you eat before that time, your body may not finish its other functions (like detoxification or repair) because it will usually switch its function to digestion (as this takes priority over most functions at rest). Eating late can also be problematic since your gut moves slower at night and especially once it's past your usual dinner time. If you are eating midnight snacks then you are putting food into a digestive system that is not very receptive. This can lead to poor sleep and indigestion. Not to mention it will make fat loss more difficult since you will be using your late-night snack energy at night instead of your body fat energy or stored glycogen (glucose stores). Simply put by Dr. Panda; “Your fat-making process continues past midnight and the fat-burning process won’t begin until the morning, but when you eat your breakfast, the switch turns again towards making fat”. The third and final core rhythm is the rhythm of activity. This is a short section and in brief terms it is essentially saying that those who exercise experience more robust circadian rhythms. A study on mice who were given total access to an exercise wheel showed that the well exercised mice got better sleep and were less tired during the day. Similar studies have shown similar results with teens and even older adults (who need less activity for the same benefits). So to summarize this section, create an environment and habits that are conducive to sleep and light exposure, eat on a set schedule so that your organs can function properly and get some exercise!

The third chapter and final section of part 1 revolves around tracking your circadian rhythms and understanding why it is important to do so. Dr. Panda uses most of this section to illustrate our lack of resilience once our rhythms have been broken. He includes constant reminders that misaligning your rhythms can lead to pretty much any chronic disease you have ever heard of (primarily cancer, heart disease, type 2 diabetes and liver disease). To provide some scientific context for how weak our bodies become under chronically poor circadian rhythms, Dr. Panda describes a study in which 8,000 workers of 40 different companies were compared to see how much worse off a shift worker will be. This study found that shift workers were more likely to become ill with anything from the common cold to stomach infections. He takes the topic a step further to describe how crossing over time zones or staying up later and sleeping later on the weekends (social jet-lag) impacts health. Dr. Panda claims that for every time zone you cross over it will take a whole day to adjust your rhythms (although using tricks like blue-light blocking glasses and altering your eating schedule before you leave can impact your recovery time). Some people may also experience jet-lag more than others. To understand how sensitive you are, note how long it takes you to recover from daylight savings or crossing over one or more timezones. The first symptoms of circadian disruption are very common amongst the general public. People with poor circadian functions experience things like migraines, sleepiness or restlessness, lack of focus, bloating/stomach pain, constipation and poor blood glucose regulation. If left unchecked these issues can translate into chronic disease. After attempting to convey the importance of resetting your circadian rhythms, Dr. Panda uses the rest of the section to give the reader various things to look out for and tools to help assess your current levels of circadian disruption. The main questions he wants you to ask are as follows:

What time did you wake up?

What time did you go to sleep?

What time did you take your first bite/sip of the day (anything that’s not water)?

What time did you take your last bite/sip of the day?

What time did you shut off all screens?

What time did you exercise?

So you can have an idea as to what the ideal numbers are, here are the most optimal answers (P.S. its ok if you aren’t perfect on any of these, we can get there eventually). Optimal sleep/wake times depend on your schedule and genetics but generally adults should get anywhere between 7 and 9 hours of sleep every night (or you can think of getting 35+ hours a week). Your first and last bite should be anywhere from 11 to 8 hours apart. Once you are past 12+ hours of eating during the day, your body will have a harder time regulating your rhythms. Your last bite should be at least 2 hours before bed but 3 hours tends to be optimal. Light exposure (especially blue light) should be limited at least 2 hours before bed. The rule for exercise depends on the intensity, but in general, you should avoid strenuous exercise 3+ hours before bed (stretching and breathwork/meditation can be done closer to bedtime for optimal sleep). Dr. Panda recommends tracking all of these measures to know where you stand on circadian disruption. He and his team have also developed an app called mycircadiancode where you can track your rhythms and they will be saved in a database to use for future and current research. So, if you are interested in keeping yourself accountable while helping expand scientific exploration I would download it right away! Please note that they will not share any of your information with third party organizations, all data will be used to research purposes only.

The first chapter of part 2 is all about sleep. Dr. Panda believes that the first step towards a better nights sleep should be observing and then managing your nightly activities (essentially how you spend your time once the sun goes down). Dr. Panda uses the first portion of this chapter to describe the various sleep stages in these terms:

N1: drowsiness stage, where you lose awareness of your surroundings but can still be easily woken up.

N2: light sleep, your eyes don’t move and your heart and breathing rate slow down.

N3: deep sleep, you are least aware of surroundings and your blood pressure falls as your heart rate slows to 20-30 percent its waking rate. Your brain also measurably cools as less blood is directed there.

REM (Rapid Eye Movement): Heart rate and breathing return to waking levels as your eyes dart back and forth in your skull. The body is usually completely immobilized as you are dreaming so don’t act out your dreams while sleeping (unless you are a sleepwalker).

A full sleep cycle occurs in around 90 to 120 minutes and as the night goes on you spend more and more time in REM and less time in the deep sleep stages. So if you only sleep for 5 or so hours you will miss out on your REM-heavy sleep which can impact memory consolidation, behavior and more. Dr. Panda recommends giving every adult at least 8 hours of sleep opportunity (being in bed ready to sleep) and giving children 10 hours of sleep opportunity. If you get less than the required amount of sleep you will experience “sleep debt” which is the difference between how much sleep you got and how much you needed. Your body has an ability to pay off this debt through napping and extending sleeping time but it is still not a wise strategy to try and catch up on sleep during the weekends as this still leads to social jet lag. To get a clear picture of your sleeping quality, Dr. Panda asks the reader to ask these three questions.

When do you go to bed, and how long does it take for you to fall asleep?

A healthy sleeper can fall asleep within 20 minutes of laying down. If you take longer than 30 minutes to fall asleep consider these 4 important lifestyle factors:

Stress levels: are you ruminating in bed because you are anxious/depressed?

Too much food: are your meals not fully digested? This will keep your core temperature too high to allow for adequate sleep.

Too little physical activity: did you not get your wiggles out during the day? There are hormones produced through activity that aid sleep.

Too much bright light at night or too little night during the day: proper light exposure is critical for sleep onset and duration.

How many times do you wake up during the night?

Fragmented sleep is not conducive to full sleep cycles and will not lead to high quality sleep. Here are the main causes of sleep fragmentation according to Dr. Panda:


Ambient temperature being to hot or cold

Acid reflux by eating too late in the evening

Sleeping with a pet

Snoring/sleep apnea

Other noise

Do you feel rested when you wake up?

Probably the most tell tale sign of proper sleep is waking up feeling rested. If you feel foggy or need coffee to wake up fully than it's pretty much guaranteed that your sleep is not good enough.

In summary, here are the main tips to consider in order to improve sleep.

Make sure your food is digested enough before you try to sleep (give it 2-3 hours)

Limit light exposure before going to bed (use blue-light blockers and avoid screens)

Limit stress at the end of the day (leave work for the morning and enjoy your evening)

Don’t stress over last nights poor sleep, take it one night at a time

Use your bedroom for sleep and love making only (don’t watch TV or work on your bed)

As soon as you are up get some light exposure, get outside and get moving (consistently)

Be active during the day (being lethargic and acting like it's nighttime during the day will confuse your clock)

Once you start sleeping better, your other rhythms will be easier to manipulate. Good sleep will affect other aspects of your life such as eating times, since sleep affects the production of hunger and satiety hormones. Better sleep can also lead to better dietary choices. Make sure you are considering sleep quality and quantity when you are making your optimum circadian schedule.

Chapter 5 is focused around time-restricted eating or TRE. Dr. Panda begins this chapter by discussing the main themes of nutrition, quantity and quality. The quantity of calories consumed is known to have a bearing on weight loss and overall health, which lead to “healthy” people who count their calories. The quality of foods consumed is a more controversial topic but it is mainly understood through mouse studies that have one group eating a balance of macronutrients (fat, carbs and protein) and another group eating a high sugar/high fat diet. This has lead to the notion of a “balanced” diet in which all macronutrients are consumed in adequate (but not excessive) amounts. Dr. Panda took these mouse studies and introduced a time element to see how timing affects the “unhealthy” diets outcomes. Dr. Panda created studies using mice who consumed a high sugar/fat diet either within 8-12 hours or throughout a full 24 hour cycle. The mice who ate the poor diet within 8-12 hours (primarily 8-9 hours) were protected from the negative health outcomes of unhealthy eating. These mice who used a proper TRE schedule had better blood sugar and cholesterol, better hormone function, lower weights and even an improved gut microbiome (population of bacteria in the gut). Similar studies have been done on humans and while it is harder to test for every health outcome the one thing that is clear is that proper TRE schedules equates to greater weight loss, according to a group of Harvard scientists. Obviously, it is still a good idea to eat whole foods and avoid excess sugar or excess of any kind. That being said, these studies highlight the power of improved circadian timing for health and weight loss. Dr. Panda also covers food intake timing in greater detail by highlighting when you should consume certain macronutrients. For example, protein intake creates a large amount of acid production in the stomach. If one were to eat a lot of protein before bed and then lay down, they may experience acid reflux. Another example of timing your macronutrients has to do with sugar consumption (or carbs in general). Your body is most insulin sensitive in the morning so you will end up utilizing the sugar in your blood better in the morning. As melatonin is produced in the body, insulin secretion goes down which can leave a lot of excess sugar in your blood (which can lead to atherosclerosis and heart attack/stroke). If you are attempting to alter your eating schedule to one that better fits your circadian rhythm, Dr. Panda recommends giving it 2-4 weeks before your body accepts the new schedule. You may notice that you are hungry or have cravings during the times you used to eat, especially if you were a chronic late night snacker. Dr. Panda uses the remainder of the chapter to answer ten frequently asked questions.

Is TRE for everyone? You can start at 12 hour TRE by the age of 5. Anyone 5 and older can benefit from TRE. The length of the eating schedule will vary from person to person.

Can I choose any 12 hours I want? In short, yes. The benefits from TRE are most potent when the TRE starts earlier in the day (mainly due to the insulin affect mentioned earlier). That being said, some schedule is better than random eating.

Can I combine TRE with other diets? Yes, TRE is not a diet but a lifestyle and a pattern that works even better when you add other healthy behaviors along with it.

Can I combine TRE and periodic fasting (such as a 5:2 diet) or a fasting-mimicking diet? TRE works as a kind of daily cleanup for your body while prolonged fasting or additional fasting protocols can add to the detoxification process. That being said, make sure that you are generally consuming enough calories to sustain energy and function. Make fasting a conscious behavior and not just laziness with cooking and preparing food.

Is there any downside? What are the potential dangers? The dangers are only seen in certain cases with people who physically can’t go longer than 12 hours without food. These special cases should consult with their general practitioner in order to move forward. Slight stomach rumbling and hunger aren’t really issues and should eventually lessen as you stick with it. The only other possible danger comes from not working your way in gradually. Don’t go from eating 16 hours a day to eating 8 hours a day in one step. Take your time and start off with an 11-12 hour eating window.

What are the potential distractions? Most people who quit tend to do so around the 6 week mark since the benefits may not yet be obvious. Staying consistent will eventually yield positive results so be patient. The people in your life can also pose a threat to being consistent but if you can convince the people in your life of the benefits they may be tempted to join you in becoming more healthy. A 12 hour TRE will usually allow you to enjoy meals with friends and family without seeming too weird,

What about medications? Medications are not to be considered food, so discuss with your doctor as to when to take them. Some drugs work better at different times of the day so try to learn about an effective time window to take it.

What about coffee? Coffee counts as a breaking of the fast, especially with sugar and cream. If you need coffee to wake up you may not be sleeping well and the coffee isn’t helping. Instead of relying on coffee try instead to rely on your natural rhythms.

Can I stay on TRE forever? Yes, but it may be wise to fluctuate between 8 and 12 hours. Sometimes a schedule change can require an altered eating schedule. Also, these requirements for food and food intake timing will change with age.

How often can I cheat? TRE is still beneficial even if you take a day off during the week. It is up to you to decide if you can take a day or two off on any given week. It is always best to air on the side of caution and stay within 12 hours but life happens and it won’t ruin your life to go out every once and awhile. In mice studies, the mice were able to have essentially the same benefits with only 5 days of strict TRE a week. If you are recovering from illness or an older individual you may want to consider sticking to it more regularly.

Dr. Panda finishes up this section by talking about what foods are best for TRE. This is not his area of expertise so I will leave it at whole foods from both plant and animal sources. Try to get some fiber and keep the glycemic load low. Other than that try to focus more on your TRE. Dietary changes are harder to make and may not yield the same amount of benefits.

Chapter 6 focuses on using timing to optimize learning and working. Dr. Panda describes the 7 criteria for learning as follows:

Attention: Described as the ability to stay focused and complete a task without distraction. Attention is greatest during the day and fades once the sun goes down. Being tired or being out of rhythm can lead to poor attention due to the distraction of sleepiness.

Working memory: The form of memory in charge of absorbing information, retaining that information and connecting it to information you already know. Sleep deprivation affects working memory through slowing reaction time. You will not respond as quickly to a stimulus you have a learned response to (such as seeing a car pull out in front of you).

Positive Reward Assessment/Negative Reward Assessment: These assessments are how we use attention and working memory to make decisions. When your circadian rhythms are off you are more likely to make poor decisions. This is something to consider if you are trying to make better dietary choices or better choices in social situations.

Hippocampal Memory: The hippocampus is involved in consolidating short-term and long-term memories. Poor sleep leads to less memory consolidation.

Alertness: Your brain is most alert in the morning and it starts to become less alert towards the end of the day. Higher levels of cortisol lead to this increase in alertness and cortisol production decreases at night as the body prepares for sleep.

Mood: Better access to light during the day can lead to more positive moods. It has been shown in animal studies that insufficient light can lead to depressive moods and imparied learning.

Autonomic Function: You heart rate, breathing patterns and hormonal balance are important in learning. Making sure to align your rhythms is important for adequate timing of these autonomic functions.

Dr. Panda believes that the brain is functioning optimally between 10am and 3pm (there may be some variance depending on your sleep/wake time). He urges that you take advantage of this time instead of taking a long lunch and grinding past dinner or late into the night. In order to maximally productive, Dr. Panda believes that sleep and proper light exposure are the keys to success. Light exposure during the day will keep you awake and alert, while limiting blue/white light at the end of the day will help you feel sleepy and ready for bed. The minimum amount of daylight you should expose yourself too is an hour but more is better. Some tricks for this could be to eat your breakfast by a window or park your car further away from where you are going so that you can get some sun on your short walk. Other things to consider when trying to have a fully functioning brain are eating and exercise. Your brain works best on an empty stomach or after exercise. Think about the last time you ate too much and didn't move around, your brain was probably feeling pretty foggy right? The last thing I’ll mention from this chapter is on Coffee. While coffee can help you feel more alert it does not alleviate sleep debt, it merely pushes it back later. Try to make sure that coffee is an added bonus to your alertness instead of being the only thing keeping you awake. Good sleep and light exposure should be all you need in order to be fully awake.

The next chapter is on the timing and benefits of exercise. Most people know that exercise has many benefits but what many don’t understand about exercise is that timing influences these benefits greatly. For instance, morning exercise is a great way to increase alertness and energy levels. If you are someone who “needs” a cup of coffee to fully wake up in the morning try going for a walk or jog outside. This gets you exposed to more light in the morning and it helps increase cortisol levels which is a good thing when you need to wake up (not so much before bed). As the day goes on, your body gets ready for higher intensity exercise. Your muscle tone is at its highest in the afternoon around 3pm until dinner time. This makes the afternoon an optimal time for performing at peak levels. A study on Monday Night Football games noted that teams travelling from an opposing coast had a higher likelihood of winning a game that started at 9pm, potentially because their circadian rhythms were set to behave as though it were 6pm (when muscle tone and cortisol levels are higher). After dinnertime, or around 7-9 pm, cortisol levels are intended to drop in order to prepare the body for sleep. If you have to get your exercise in this late in the day, consider activities like yoga or qigong that are not as stimulating as HIIT training or sports. This will give you the benefit of exercise while still allowing for adequate sleep. Speaking of sleep, exercise has been shown to increase sleep quality. This is partially done by a molecule produced by exercising muscle cells called Interleukin-15 (IL-15). Rabbits who were injected with IL-15 were shown to have deeper and better sleep. The takeaway from this article is that exercise is a critical pillar of health that feeds into a larger network of healthy behaviors. Even if you can’t make it to the gym or go on a long hike in the sun, just move when you can. Once exercise has become apart of your life, use the concepts above to time your activity accordingly.

Chapter 8 takes a deep dive into light exposure and in particular, screens and their ability to produce circadian disruption. Improperly timed light exposure is linked to many health issues including cancer, heart disease, metabolic disease, gastrointestinal issues and more. In fact, light exposure is one of the main reasons that shift work is now classified as a carcinogen. While shift work is one of the reasons that people are improperly exposed to light, late night screen time is becoming increasingly common. Using devices late at night has a strong influence on circadian rhythms and in a study involving 600 children, increased screen time led to higher instances of poor sleep quality and problem behaviors. Young people are the ones who are most at risk from late night screen use. Dr. Panda uses this chapter to cover some techniques and concepts for getting proper light exposure. In regards to screens, there are various programs and apps that allow you to reduce the blue-light that you screens emit. F.lux is an app that can be downloaded to your device (I use it on my computer) and will gradually emit less blue light as the sun goes down. Newer Apple products have a similar feature called nightshift, look up your particular devices to see what programs are compatible. As for lighting your home, there are new bulbs on the market that can actually change color and dim through a timer. These lights are more expensive than regular bulbs but if you are someone who struggles with sleep and alertness it may be a worthwhile expense. A cheaper option (and one that I use every night) would be to use blue-light blocking glasses. These glasses range in price but I was able to get a pair for under $30 dollars on Amazon. They are very simple to use, just put them on once the sun goes down or at least a couple of hours before bed. You may notice that your eyes are able to relax and you feel more sleepy before bed. Dr. Panda recommends getting these glasses on right after you finish dinner (remember that dinner should be completed 2+ hours before bed). Optimal light exposure doesn’t just mean limiting blue-light at night, it also means getting enough light exposure during the day. If you are someone who regularly experiences under an hour of direct daylight it may be best to avoid wearing sunglasses during those times (if that can be avoided). Sunglasses can decrease the intensity of light from seven to fifteen fold, bringing the daylight inside your car from 5,000 lux (unit of brightness) to 330-700 lux. During the day, you want to get as much light exposure as your skin tone can tolerate. I try to make sure that I get 2-3 chunks of light exposure a day; first thing when I get up, then when the sun is brightest (around noon) and lastly as the sun goes down. This strategy helps educate my circadian rhythms to the time of day so it can understand when it is truly nighttime. Then once it is dark, I keep the light exposure as limited as possible to prepare for sleep.

Congratulations! You have reached the final third of this book report. The first chapter of this section (chapter 9) focuses on the gut. Dr. Panda wants his readers to understand that the gut does not work like a boiler that is always hot and ready for fuel. Your digestive system has operation hours and procedures for starting up and closing down. One of the most important parts of opening up your guts “shop” is salivation. Your body is set to salivate during the day and salivates less and less towards nighttime. If you are eating late at night your body may not produce enough saliva to properly digest your food. This lack of saliva production also has other implications when you consider the next step in digestion which is acid production in the stomach. The stomach is not constantly filled to the brim with acid and digestive enzymes. These enzymes and acids require signals (food ingestion) in order to populate the gut. Stomach acid production increases later in the evening which is another reason to avoid late night eating. In combination with a lack of saliva production, high stomach acid production can lead to acid reflux. Eating right before you lay down for sleep (losing the benefit of gravity) is almost a guaranteed formula for acid reflux and GERD (Gastroesophageal reflux disorder) in the long run. The final reason for not eating late that I will discuss is a decrease in gut motility. Gut motility is the motion of your intestines to move food through your stomach. Your intestines move like a worm on a treadmill (enjoy that visual). This wave-like motion of contracting smooth muscles is at its peak during the day and is very slow during sleep. If you eat before bed you can guarantee that your food will stay in your intestines longer than you would want, which can lead to indigestion and subsequent stomach pains. Depending on the amount of food you ingest, your stomach can remain filled for 2 to 5 hours. Remember that your body needs to cool down in order for you to get adequate sleep at night. If your stomach is full of food you can guarantee that your body is directing more blood in that area which will keep your internal body temperature higher than you want. Toy around with different feeding times and note how you feel when you wake up. For some people, 2-3 hours might be enough to get food far enough along the gastrointestinal tract. For others, it may take more than 3 hours (especially after big meals, like on holidays). Also, it’s important to note that not all foods are digested at the same speed. Since bile needs to be created (in the liver and stored in the gallbladder) and shuttled to the small intestine in order to digest fats. Fat can take much longer to digest and absorb than carbohydrates and proteins. So the composition of your meals will determine how fast they are digested and absorbed as well as the size. As you can probably tell from how exhaustive this paragraph is, digestion can be complex and taxing on the body. Your gut lining actually replaces 10-14% of its cells every day just to keep up with the wear and tear of digestion. So, be easy on your gut by following these simple rules:

Skipping a meal will not kill you

Don’t eat breakfast unless you are hungry

Don’t snack because you are bored

Avoid unnecessary late night meals or snacks

Hunger comes in waves and it will fade if you give it time (very rarely have I ever experienced hunger pangs that keep me up)

Give your gut adequate rest between meals

Allow your stomach to empty before bed (remember 2-5 hours)

These are the main takeaways from this chapter. Your gut needs rest just like the rest of your body. Digestion and absorption are active processes that actually require energy. If you are experiencing gut issues currently, talk with your doctor about rescheduling your meals to adequately fit your circadian rhythms.

Chapter 10 is all about metabolic diseases and how TRE can improve the symptoms of each disease (diabetes, heart disease and obesity). I am going to try and keep this one short and sweet since there are only a few concepts involved in how this works. Fat loss is a huge component of improving metabolic disease symptoms. TRE assists in fat loss by allowing you adequate time in a fasted state, which will allow an individual to use energy from their stored fat. Your body cannot add to itself and subtract from itself simultaneously, these are two separate processes. That being said, you will never lose weight if you don’t eat fewer calories than you burn. TRE merely makes it easier to eat less. It also helps you make better decisions about the food that you do eat. Think back to a time when you ate an ungodly amount of junk food. I would put money on it being later in the evening while in front of the TV. TRE limits your ability to live a lifestyle that allows for late night snacking like this. With the concepts of fat loss out of the way, I want to discuss glucose metabolism. Your bodies ability to utilize and store glucose is very important for remaining healthy. Excess glucose will be converted to fat. If your body takes too long to convert the glucose into fat or store it as glycogen in the liver or muscle cells, it will run rampant in your blood vessels. High levels of blood glucose for long periods of time will lead to arterial damage which can manifest as anything from kidney disorders to strokes and heart attacks. When you eat within a shorter window, your body will have an easier time regulating glucose so that it doesn’t damage your blood vessels. One other thing to understand in regards to glucose metabolism is that your body manages glucose better in the morning than in the evening. Insulin sensitivity is at its peak in the morning which is good for reuptake of glucose from the blood. As melatonin is secreted in the evening, it inhibits the production of insulin, which causes your blood glucose to reach higher levels when compared to the same meal consumed in the morning. If you are struggling with any metabolic disorders, discuss implementing TRE with your primary care physician.

Chapter 11 is titled “Enhancing the Immune System and Treating Cancer”. This chapter rather complicated so I am going to simplify it as well as I can. Your immune system can be described as having two modes, surveillance and attack (followed by repair and clean up). TRE and other ways of improving circadian rhythms help keep the immune system from being in a constant state of attack. Strong circadian rhythms prevent higher levels of oxidative stress. A good example of this involves eating. When you consume food, your body produces free radicals (the molecules that cause oxidative stress). If you are eating food for longer than 12 hours a day, then your body is producing free radicals for that entire period. When you limit the amount of time spent eating, oxidative stress is limited and the immune system can spend more time in surveillance mode. There are many other concepts that are brought up in this chapter that are above my pay grade and I will advise you to watch Dr. Satchin Panda’s podcast episodes on the Found My Fitness podcast with Dr. Rhonda Patrick to get a better idea of what’s going on. The cells of the body undergo many processes of death, breakdown and recycling which are optimized under strong circadian conditions. When the body is not timing itself optimally, these dead cells and their components become a part of the problem (especially in the case of cancer). This is obvious in regards to prevention of diseases like cancer, but what Dr. Panda describes in this section is that circadian rhythms even play a role in the treatment of these diseases. An example in the book comes from a study of 500 patients with rheumatoid arthritis. In this study, patients were given anti-inflammatory medication to help with stiffness and pain in the morning, around noon and in the evening. Since the inflammatory process of rheumatoid arthritis is most active after midnight, the patients who took their medication in the evening saw the best results. Dr. Panda brings up many situations like this with examples from chemotherapy to surgery, the timing matters. Discuss with your doctor how to optimize the timing of your treatments.

The second to last chapter is on brain health and how it relates to circadian rhythms. Almost all brain regions have a circadian clock embedded in them. Circadian rhythms are involved in four main themes that Dr. Panda discusses in this chapter:

Inability to replace dead neurons with new ones: The birth of a new neuron and its nutrition is dependent on a circadian timing. With improper rhythms, the body will not supply the compounds that are necessary for a stem cell to become a functioning neuron.

Poor wiring of neurons: Poor light/dark and sleep/wake cycles can lead to improper brain development in young brains. Dr. Panda argues that these poorly timed cycles can lead to disorders like ADHD and autism spectrum disorder.

Accumulation of damage with insignificant repair: The brain’s circadian clocks need to properly scheduled for repair to be optimal. With poorly regulated clocks, neurons are more likely to become stressed, damaged and eventually die off.

Chemical Imbalance: With poorly timed clocks, neurons produce levels of neurotransmitters that negatively impact mood and behavior. This is shown in studies with mice that lack brain clocks. They end up creating too much dopamine, leading to manic mice with too much energy.

To summarize the impact that circadian rhythms have on the brain in mainly breaks down to sleep. Obviously, if the body doesn’t know what time of day it is, sleep will suffer. When sleep suffers, the brain suffers because most of its repair and maintenance occurs during the various sleep cycles. Improving circadian rhythms can prevent, improve and potentially treat many brain illnesses from bi-polar disorder to parkinson’s disease. For more information on brain health, check out my other book report on “The Concussion Manual”.

Dr. Panda uses the last chapter to describe his perfect circadian day. But since this has already been such an exhaustive read into what a perfect circadian day is, I am going to do something different. I want to make sure that you understand that even though this sounds like an incredibly easy fix for every health issue known to man, it is only one piece of the puzzle. Throughout this book, Dr. Panda emphasizes the importance of exercise and proper nutrition and I want to echo that here. Just because a person who eats garbage for 12 hours a day will be healthier than someone who eats garbage for 15 hours a day doesn’t mean you should be eating garbage. Obviously, you should take into account all of the other health knowledge at your disposal to optimize your lifestyle. Circadian rhythm optimization could be the thing that you were missing. Having added it to your tools for better health, you may find yourself feeling better than ever. I hope you found this information useful and please check out Dr. Panda’s other work at the Salk Institute by searching his name on their website.

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