The Circadian Code: Lose Weight, Supercharge Your Energy, and Transform Your Health from Morning to Midnight

The Circadian Code: Lose Weight, Supercharge Your Energy, and Transform Your Health from Morning to Midnight

by Satchin Panda

Reset your body and your life by optimizing your biological rhythms. This book will teach you everything you need to know about your circadian code: the internal clock that governs all aspects of your biology and health. Learn how to enhance and support sleep, nutrition, digestion, physical activity, motivation, alertness, productivity, and much more: all through the science of circadian timing.

Summary Notes


“A good night’s sleep synchronizes all of your internal clocks so that your whole body is working at peak performance.”

Sleep is probably the single greatest barometer of and contributor to our physical and mental health. Its importance cannot be overstated. Although we lose consciousness and are unaware of what actually happens to us when we sleep, the brain and body are tremendously active during this period. 

All of the necessary processes that support life occur in sleep: detoxification and cleansing of brain and body structures; repair of micro-damages and the ‘wear and tear’ that we accumulate in waking life; digestion and absorption of nourishment from food; growth and transformation of various tissues; organization and coordination of sense impressions and memories…

Without good quality and quantity of sleep, we suffer in innumerable ways—such as through weight gain and digestive problems like IBS and reflux; systemic inflammation and joint pain; increased stress, moodiness and irritability; hormone imbalances; high blood pressure and heart rate; brain fog and neurodegenerative disease; poor motor and impulse control; increased likelihood of chronic illness like diabetes and cancer; and so on. Every system in our body is reliant upon sleep to function properly. Optimizing your sleep is the most important thing you can do for your overall health, and it can have truly astonishing benefits. 

Human bodies are rhythmic in nature, and follow a master cycle known as the circadian (meaning ‘around a day’) code. We are programmed to sleep at night and be awake and active during the day. Many of our internal processes—like those described above—are triggered and timed by the circadian rhythm. Because sleep is so crucial, we could say that each circadian ‘day’ actually starts at night, when we go to bed and sleep. Good sleep has a positive domino effect: it sets us up to wake feeling refreshed, to be alert and productive during the day, to digest food and eliminate toxins properly, to be able to engage in healthy physical activity, and so on. 

Establishing a strong sleep-wake rhythm supports the overall health of the whole body. On average, an adult needs 7-9 hours of sleep per night, while children and teens need ten or more hours. 

There are many lifestyle choices and habits we can adopt to support enhanced sleep quality and quantity. These include getting proper light exposure during the day, avoiding light exposure at night, keeping sleep timing consistent, optimizing your sleep environment, and avoiding caffeine and late-night eating or drinking. These habits will program the circadian clock to know when to wind down and wake up. They will also support deep, rejuvenating sleep of the kind that leaves us refreshed and ready to face the day.

Actions to take


“Our circadian rhythms are designed to adapt to the natural cycle of light and darkness. Your brain needs light to turn on all of its functions.”

Light is one of the keys to the circadian rhythm—it is like a master reset button on our internal clock. Viewing bright light at any time, whether sunlight or blue-wave artificial light, sends a signal to the brain that indicates it is daytime. This signal then cascades through the body, acting as a wake-up call to our organs and muscles and priming them for the day’s activity. Being in darkness, or the absence of light is the signal that triggers winding down and sleep.

Light can be measured in a unit called lux, where 1 lux is the light of a candle within a 1-foot radius. Natural light on bright or sunny days is around 100,000 lux, and even on a cloudy day usually surpasses 2,000 lux. In contrast, the typical indoor office, even with a large unshaded window, is around 1,000 lux or less. Brightly lit places like hospitals and shopping malls average 100-1,000 lux, while classrooms, living rooms, and bedrooms are usually between 10 and 100 lux. 

When we view bright light (>1,000 lux) in the morning and throughout the day, we are more likely to experience an elevation in mood, heightened alertness and focus, increased motivation and drive, and better physical and mental performance. However, many of us get very little light exposure even during the day, as we spend a lot of time indoors. We need at least 1 hour of natural light exposure per day to experience the cascade of signals that keep us alert, motivated, and awake. This is why it is inadvisable to wear blue-light blockers during the day—they dampen the wakefulness signals and can lead to a kind of ‘jet lag’ fugue state of low mood, fatigue, and even depression.

In the natural world where we evolved, the light fades as we approach evening and night. It is the absence of light that primes and prepares us for sleep. As it gets dark, the hormone melatonin is released from the brain, making us feel sleepy and prompting us to head to bed. If we expose ourselves to bright blue light from artificial sources in the evening and night, the brain is tricked into thinking it is still daytime, so we don’t feel sleepy. 

Our sensitivity to light increases throughout the day and is highest at night, so even a small amount of light at night can trigger wakefulness signals. This pushes our bedtime later and later–negatively impacting our ability to fall asleep, as well as our sleep quality. 

A circadian lifestyle involves setting up our homes and lives to mimic the natural rhythms of daylight and darkness. This means getting lots of natural light exposure during the day, either by going outside, sitting next to large windows, or using bright overhead lights. Then, from dusk onwards, switch to low-level warm-tone task lighting (desk and floor lamps) to support sleep. 

Special care should be taken for children and teens, who are more sensitive to light than adults. Bright light is also emitted by digital devices and screens, which can be mitigated by using blue-light filters or blockers.

Actions to take


“Regardless of which kind of diet you follow, when you eat is more important than what type of food you eat.”

Along with sleep and light exposure, food intake or digestion is one of the main rhythms of the circadian code. Like sleep, digestion is also a circadian process—most active and powerful during the day and least efficient at night. 

While light exposure and sleep rhythms are largely governed by the brain, digestion is governed by our internal organs. Each organ has its own clock, which turns it on and off at certain times of day, given certain inputs like food and drink and in relation to the activity of other organs. The digestive process is highly complex and carefully calibrated, like an orchestral symphony or an ensemble dance. 

Digestion is a highly time-, energy- and resource-intensive process. While we digest food, the body has to devote all its attention to breaking down and absorbing nutrients. It cannot do anything else like repair cellular damage, detoxify organs or rebuild muscles and bones. 

Every time you take a bite, your body has no choice but to immediately divert attention to digestion, even if it was already in the middle of other rest-and-repair processes. For optimal health, digestion cannot and should not be happening continuously, or it will take valuable time and energy away from all the other necessary internal functions that sustain health and life.  

Most nutritional advice focuses on the content of food, i.e., what we eat, but largely neglects the enormous importance of the timing of our food, i.e., when we eat. Timing is actually the dominant variable when it comes to nutrition and digestion. In other words, when we eat is just as important, or even more important, than what we eat. 

The best approach to food timing is known as time-restricted eating or TRE, sometimes also called intermittent fasting. This entails restricting all food intake to a certain portion, or ‘window,’ of the day and fasting for the remainder of the 24-hour period. The fasting period gives the body enough time to focus properly on efficient digestion, as well as on other internal rest-and-repair processes. The optimal window for digestive health, fat metabolism, and sleep quality are 8-10 hours of eating, followed by 14-16 hours of fasting. As with sleep, TRE mimics the eating rhythm that would have been observed by pre-industrial humans living in the natural world.

Unfortunately, most people normally eat throughout the day—an almost-continuous 15-16 hour digestive window throughout the day. Many people are also prone to eating or snacking late at night, right when the digestive process is primed to slow down and switch off. This mismatch in rhythm can lead to all sorts of problems like acid reflux, indigestion, stomach cramping, and insomnia. 

In the long-term, random or all-day eating is linked to increases in weight and body fat; a greater likelihood of chronic diseases including diabetes, cancer, and heart disease; reductions in brain health and longevity; and increased inflammation throughout the body. 

On the other hand, TRE has been shown to reduce weight and body fat, boost muscular endurance and strength, reduce inflammation, improve sleep quality, protect against chronic diseases like diabetes, cancer, and heart disease, and support brain and organ health. Along with sleep, it is one of the most underrated and valuable tools to bring about sustainable change in one’s health.

Actions to take

Physical Activity

“Exercise has a circadian effect, improving sleep and mood. It is one of the best medicines.”

Physical activity is the third of the three core rhythms that make up the circadian code, along with sleep and food. Human bodies are designed to move frequently and regularly. Incorporating physical activity every day is strongly recommended for all as it can positively impact both our physical and mental health. It’s important to remember that all kinds of movement and physical activity can be beneficial, including taking walks, gardening, and doing house chores. Exercise does not have to be rigorous or complicated to be good for you—as long as you’re moving regularly, your body is getting something good out of it.

The relationship between exercise and circadian rhythm is a two-way street: physical activity is affected by circadian rhythms and acts to reinforce or re-align our circadian rhythms. Applying the principles of the circadian code to the timing and scheduling of exercise will enhance the overall benefits of physical activity. 

In general, humans are designed to be more physically active during the day when our body temperature and heart rate increase and muscular contraction and motor coordination improve. In contrast, our bodies cool down at night, our heart rate and breathing slow down, muscles become more relaxed, and motor coordination declines. 

Certain periods within the day are specially optimized for movement and physical exertion: these include the early morning and the afternoon/early evening. At these times, we are at peak physical performance and get the most out of movement and exercise. 

The afternoon/early evening period is particularly suited to vigorous exercise as motor coordination and strength are at their peak so that we can achieve maximum benefits with minimum injury. Exercising at this time also lowers blood sugar and reduces appetite, making us less likely to overeat at dinner. 

The early morning period is also ideal for taking a walk or any form of outdoor exercise; the combination of natural light exposure and physical activity will set and reinforce a strong circadian rhythm. 

Exercising late at night is not ideal, as it heats and stimulates the body, making it harder to fall asleep. However, these effects can be mitigated by keeping late-night exercise light to moderate in intensity, avoiding exercising under bright lights (like in gyms), and taking a shower to cool off before going to bed.

Physical activity also supports the other rhythms of the circadian code: sleep and digestion. Following a regular exercise regimen reduces appetite and can help with hunger pangs and cravings, particularly in transitioning to a TRE schedule. Exercising when you’ve fasted in cool or cold environments further enhances weight loss and fat burning. Physical exertion can also elevate mood and increase alertness, making it an ideal substitute for caffeine and other stimulants. Regular physical activity also primes the body for good quality and duration of sleep.

Actions to take

Integrating Circadian Rhythms

“Circadian clocks time almost every aspect of our daily health to the right moment of the day or night… Our entire sense of health is guided by our daily rhythms.”

The circadian code governs and affects the vast majority of our physical health and even our mental well-being. It has far-reaching impacts on areas such as sleep, mood, alertness, digestion, weight, chronic diseases, and physical activity. Understanding how the body’s rhythms work gives us a wide array of tools to optimize various parts of life. For example, applying the circadian code can enhance productivity at work or in learning environments. 

By combining all the different elements of the previous sections, we can successfully boost our focus, enhance motivation and drive and set ourselves up for a productive day of work or school. Use the following section as an inspirational guide or template to explore how you can best apply the circadian code to your life and your specific goals and needs.

Actions to take

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