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The Circadian Code book summary

The Circadian Code book cover

This is a fairly quick read for information that could create a step function improvement in your health and well being. In short, your body runs best when it adheres to its internal clock. Going against it could have profound negative implications on your long term health, physically and mentally.

Human bodies run on a circadian rhythm

  • It has been well documented that shift workers experience more health problems than non–shift workers, particularly gastrointestinal diseases, obesity, diabetes, and cardiovascular diseases.
  • ...found that almost every aspect of our daily life is rhythmic. Although humans don’t flower, or migrate over long distances, we do have circadian clocks that time almost every aspect of our daily health to the right moment of the day or night.
  • The melanopsin protein is most sensitive to blue light waves and is less sensitive to red light. When melanopsin is activated by registering blue light, it sends a signal to the brain that any light is present, and the brain responds by thinking it is daytime, regardless of what time it really is.
  • ...every organ in an animal has its own clock, and these clocks don’t need instructions from the brain in order to function.
  • ...in every organ, thousands of genes turn on and off at different times in a synchronized fashion. Every gene in our genome has a circadian cycle. However, they don’t cycle at the same times, and some cycle only in one organ. This means that for every tissue there is a hidden time code to our genome.
  • Cellular activity in our bodies that occurs in a cyclic manner:
    • The nutrient-or energy-sensing pathways—cell’s hunger and satiety pathways. Every cell in every organ has such a mechanism that makes the cell hungry and opens the door to let nutrients flow in during the day; and when the cell has enough energy, it closes the door so that it does not get overstuffed.
    • The energy metabolism pathway is circadian, affecting cellular function and metabolism of all key nutrients. The use and storage of carbohydrates, fat, or protein is not a continuous process. When sugar is absorbed from the blood and converted to fat or glycogen for future use, the body’s fat-breakdown function is shut down. Only after the sugar is depleted does fat breakdown resume.
    • Cellular maintenance mechanisms. Every chemical reaction, particularly when the cells make energy, produces a mess known as reactive oxygen species. Cells have a timed mechanism to clean up after themselves. This also includes the detoxification process.
    • Repair and cell division. Our body is being repaired and rejuvenated every day. This repair, through the production of new replacement cells, does not happen randomly; rather it occurs at a specific time of the day: at night, when we’re asleep.
    • Cell communication. Our organs need to communicate with each other, and this happens within a distinct rhythm. These communications are stronger at certain times and they weaken at other times of the day.
    • Cell secretion. Each cell produces something of value for its neighbor or for the whole body.

Our master clock and how to regulate it

  • Scientists found a small cluster of cells that function as a master clock. These cells, collectively known as the suprachiasmatic nucleus, or SCN, are strategically located at the hypothalamus, the center of the base of the brain, which houses the command centers for hunger, satiety, sleep, fluid balance, the stress response, and more. The 20,000 cells that make up the SCN are indirectly connected to the pituitary gland, which produces growth hormone; the adrenal glands, which release stress hormones; the thyroid gland, which produces thyroid hormones; and the gonads, which produce reproductive hormones. The SCN is also indirectly connected to the pineal gland, which produces the sleep hormone melatonin.
  • We are programmed to maintain at least a 9-hour sleep pattern when we are babies and a 7-hour sleep pattern for the rest of our lives, yet the overall clock system dampens with age and becomes less effective. As we age, the internal drive to have consolidated sleep or wakefulness slowly breaks down, and we wake up more easily when disturbed by light or sound and have difficulty getting back to sleep. This is when nurturing a body clock with better habits becomes critically important.
  • In Kenya, I was exposed to lots of light during the day, no light at night, less noise, relatively cooler temperatures at night, and earlier dinner. Each of these factors has been shown to contribute to better sleep.
  • Just like the first light of the morning resets our brain clock, the first bite of the day resets our organ clocks. In fact, food timing can be a powerful cue to override the master signal from the SCN master clock.
  • Using the circadian clock, each organ is programmed to process food for a few hours starting from breakfast. If your breakfast was at 8:00 a.m., then the system works optimally for about 8 to 10 hours.
  • After about a 10-hour window, the gut and metabolic organs will continue to work on your food, but their efficiency slowly goes down as they are not programmed to be open for business 24-7.
  • For most people, our circadian clock takes almost 1 day to adjust to each hour of time-zone shifting
  • ...your last bite of food or drink has to be part of the digestive process for 2 to 3 hours before the body can begin its repair and rejuvenation mode.
  • People who can eat all of their food within an 8-to 11-hour window most days will reap the most health benefits.

Fat storage and utilisation

  • Our cells cannot make and break up body fat at the same time. Every time we eat, the fat-making program turns on and the cells in our liver and muscles create some fat and store it. The fat-burning program slowly turns on only after the organs realize no more food is coming their way, and that takes a few hours after your last meal. And it takes a few more hours to deplete a good portion of stored body fat.
  • ...when eating occurs at random times throughout the day and night, the fat-making process stays on all the time.

Cardio and respitory system

  • Our lungs and heart are both muscles that have a circadian variation—we have a relatively higher heart rate and heavier breathing during the day, and both slow down at night. The higher heart rate and breathing help distribute oxygen and nutrients throughout our body, including to our muscles during the day, priming us for physical activity. At night our muscles don’t need the same levels of nutrients and oxygen as they do during the day, when we are more likely to use them. This may be one reason why heart rate and breathing slow down at night, which helps the body cool down so we can sleep better.
  • All of the studies have come to the same conclusion: Physical activity improves sleep.


  • Compare your last bite/sip time with your bedtime. The difference should ideally be 3 hours or more.
  • Great sleep is created when there are cycles of quiet sleep and active sleep. The quiet sleep takes place in three stages that occur in a specific sequence: N1 (drowsiness), N2 (light sleep), and N3 (deep sleep).
  • Within that 7-hour period, there is a critical 4-hour window. You may notice that between the hours of 10:00 p.m. and 2:00 a.m., or in the first 4 hours after falling asleep, you get some of your best sleep. This is because these first few hours go toward paying back your sleep debt. They neutralize the urge to sleep or the tiredness you feel before going to bed. This is why it may be harder to go back to sleep if you wake up after that 4-hour period: You no longer have the sleep debt that was making you tired in the first place. The next 3-plus hours of sleep go toward nurturing your brain and body, giving it the additional time it needs for repair and rejuvenation.
  • ...a sleep-deprived brain, or one exposed to bright light at night, craves excessive calories that it does not need, resulting in weight gain.
  • In fact, even a sleepy brain may work better without adding food to the mix for hours at a time. Research in Mark Mattson’s lab at the National Institutes of Health has shown that mice that undergo a longer fasting period have better brain function, as keeping to a restricted eating time strengthens the connections or synapses between brain cells. A stronger connection between neurons means the brain can think better and remember better, regardless of how rested we are.
  • Eating late at night is not only bad for metabolism, it also affects sleep. This habit interferes with both falling asleep and maintaining deep sleep. In order to fall asleep, our core body temperature must cool down by almost 1°F. But when we eat, our core body temperature actually goes up as blood rushes to the gut (the core) to help digest and absorb nutrients. So, eating late at night prevents us from getting into a deep sleep. To have a good night’s sleep, we should have our last meal at least 2 to 4 hours before going to bed to ensure that the body is able to cool down.
  • Mouth breathing reduces the amount of oxygen that goes into the brain. That also puts the brain in a hypoxic, or low-oxygen, state, which can increase the chance of getting dementia and various brain-related problems like memory loss.

When to eat

  • We believe that a shortened feeding period provides the digestive system the right amount of time to perform its function uninterrupted by a new influx of food, and enough time to repair and rejuvenate, supporting the growth of healthy bacteria in the gut.
  • ...individuals who spread their calories over a long period of time—meaning they eat the same number of calories but eat later into the night—did not lose much weight. However, people who ate bigger meals during the day and refrained from eating at night actually lost a substantial amount of weight. This means that regardless of which kind of calorie-restricting diet you follow, when you eat is more important than what type of food you eat.
  • While the science at 12 hours is impressive, lowering your window (to as few as 8 hours) is significantly advantageous. Time-restricted eating is never about counting calories; it is just about making you more disciplined about timing. We’ve found the best results for weight loss come with eating within an 8-or 9-hour window, and you can maintain this pattern until you get the desired results. Most of your body’s fat burning happens 6 to 8 hours after finishing your last meal and increases almost exponentially after a full 12 hours of fasting, making any amount of time fasting past 12 hours highly beneficial for weight loss. Once you’ve achieved your desired weight loss, you can go back to an 11-or 12-hour window and maintain that body weight.
  • We’ve found that it’s healthiest to eat breakfast as early as possible. The reason is that the insulin response is better in the first half of the day and worse in late night. Besides, if you start early, you are also likely to end early, or at least 2 to 3 hours before going to bed. This is important, as melatonin levels begin to rise 2 to 4 hours before your typical sleep time. Finishing your meals before melatonin begins to rise is necessary to escape the interfering effect of melatonin on blood sugar.
  • In general, the gut’s activity slows down at night. So, when you eat late into the evening, slow movement of food, or movement in the wrong direction, can cause stomach problems.

What to eat

  • When your melatonin level begins to rise in the evening and you eat, the food triggers the insulin response to begin. The insulin helps your liver and muscles absorb glucose from your blood so that your blood glucose doesn’t rise too high. But later at night, since insulin production is slowed down, there won’t be enough to soak up all the glucose from the food. This will leave your blood glucose levels high for a long period of time. At the same time, your body might store the excess sugar in the blood as fat instead of using it as fuel.
  • All plants and animals require amino acids, which is why they occur in all food sources. Plants can create amino acids through sunlight and water, while animals (including humans) can create only some. There are additional amino acids we must get from the foods we eat.
  • The rule of thumb is your daily intake should be 0.36 grams of protein per day per pound of body weight.
  • Excessive protein intake stresses your metabolism, which is hard on your kidneys, and you really would like to go through life with two working kidneys.
  • Foods high in fiber are predominantly carbohydrates, but they are good choices because your body can’t digest fiber and it scrubs your intestines as it leaves the system. Fiber helps detox your body and provides nutrients for a healthy gut.

Oxidative stress and inflammation

  • The most common threat inside a cell is oxidative stress, which occurs as a direct result of additional oxygen molecules entering the cell. These molecules produce dangerous free radicals, electronically unstable oxygen molecules that must scavenge electrons from whatever sources they can find in order to become stable molecules. The sources of electrons can include cellular DNA, cell membranes, important enzymes, and vital structural or functional proteins. When these important cell parts and substances lose their electrons and bind to free radicals, their function is altered.
  • One of the central roles of the circadian clock is to control oxidative stress. After eating, when every cell in our body uses nutrition to make energy, cells produce reactive oxygen species. The clock acts as a sensor of this oxidative state inside the cell and coordinates antioxidant defense mechanisms to clean up the damage. Since eating used to happen predictably during the daytime for millions of years, this function of the clock is very fundamental to cellular health. Scientists believe this predictable rise and fall of oxidative stress between day and night might have been one of the primary instigators of the evolution of the circadian clock.
  • Having a healthy circadian rhythm under TRE serves several important functions in reducing systemic inflammation. A strong circadian rhythm supports better repair of the skin and gut lining so that there is less opportunity for undigested food particles, disease-causing bacteria, or allergy-causing chemicals to enter our body and activate the immune system.
  • A stronger circadian rhythm reduces oxidative stress and the production of inflammatory chemicals. With a reduction in external agents gaining access to our body and a reduction of our body’s own inflammatory chemicals, the immune cells are less activated and thereby create less systemic inflammation under TRE.

Brain health

  • ...adult brains have special stem cells that produce new neurons throughout our lifetime. These new neurons replace damaged or dead neurons through a process called adult neurogenesis, and the ability to regenerate is very important for maintaining a properly functioning brain well into old age. A reduced ability for neurogenesis contributes to a range of brain health dysfunction, from forgetfulness and memory loss to dementia.
  • ...many benefits of a ketogenic diet on brain health can be tapped by eating all your food within 8 to 10 hours. Eating at the same time every day and maintaining a long period without food synchronizes the circadian clocks in your brain and body.
  • Exercise increases brain-derived neurotrophic factor (BDNF), which strengthens the connection between neurons and improves memory. BDNF can further augment repair of stressed or injured neurons—the process that also occurs when a strong circadian clock is present in the brain.

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