Dr. Satchin Panda is a pioneer in time-restricted eating and an expert on circadian rhythms. Dr. Panda is a professor at the Salk Institute and runs a laboratory with high-impact studies that have a major impact on public health.
Circadian rhythms are daily timetables that repeat every day. Almost every organ and cell in the body has its own circadian rhythm, including hormones, digestive juices, brain chemicals, and genes.
The brain has a narrow window in the first half of the day when it has the best cognitive ability and problem-solving ability. Sleep is crucial for peak cognitive performance, and caffeine only wakes up the brain but doesn’t necessarily improve clear thinking.
Neurotransmitters, their receptors, and the systems that recycle them all have circadian rhythms, influencing our moods throughout the day. Some people are natural early risers, while others are night owls.
Understanding circadian rhythms and their impact on sleep and cognitive performance is crucial for overall health and well-being.
The amount of sleep a person gets is more important than whether they are early risers or night owls. Sleep scientists agree that adults need around seven hours of sleep. Night owls may have difficulty functioning at peak performance if they cannot get enough sleep. Night owls who have difficulty sleeping may need to avoid caffeine and bright light exposure in the evening. Melatonin, a sleepiness hormone, is inhibited by blue light, so avoiding blue light exposure in the evening and seeking it out in the morning can help regulate circadian rhythms. Blue light sensors in the retina are responsible for detecting blue light and adjusting to changing day lengths.
Research has shown that light, particularly blue light, plays a crucial role in regulating our circadian clock and sleep patterns. The melanopsin receptor in our retina senses bright light during the day and blue light from electrical lighting. This signal is then sent to our brain to either tell it to reset our circadian clock or to regulate the release of melatonin, the sleep hormone.
To take advantage of this information, it is recommended to dim down light in the evening to allow melatonin to rise naturally and signal to the body that it is time to wind down and go to bed. Changing the color of light, such as using a night shift feature on electronic devices, can also help in this process. Additionally, it is important to get a good dose of bright daylight in the morning to put a strong break on melatonin and increase alertness.
There is a balance to strike between protecting our eyes and getting enough blue light. It is important to consider the amount of light exposure, such as 100,000 to 200,000 lux of light on a sunny day, and adjust accordingly. For example, wearing blue filtering eyeglasses in the evening can help improve sleep, while avoiding sunglasses early in the day can ensure activation of the melanopsin receptor for circadian clock resetting.
The impact of UV light exposure on the human body can vary depending on the environment. Singlet oxygen produced by blue light can be damaging to the skin and cornea. Melatonin supplementation is not regulated in the US and its long-term effects are not fully understood. Clinical studies have shown that while melatonin can help with sleep latency, it may not sustain sleep throughout the night. Endogenous melatonin rises gradually before sleep and maintains a peak throughout the night, whereas a pill will cause a spike shortly after consumption.
Research on melatonin dosing has shown that it is difficult to find low doses of melatonin in drugstores, with common doses being around three to five milligrams. When taking these higher doses, there is a risk of a significant spike in melatonin levels, which can stay elevated for an extended period of time, affecting insulin production in the pancreas and leading to high blood glucose levels. Studies have shown a connection between melatonin and blood glucose levels, with high melatonin levels making insulin-producing cells less responsive to glucose, resulting in elevated blood sugar levels. Therefore, it is recommended to avoid eating close to bedtime when melatonin levels may be high, in order to help regulate blood glucose levels. This has been supported by experimental evidence dating back to the 70s and 80s, which demonstrated the impact of evening eating on blood glucose levels.
It is recommended to wait for an hour or two after waking up for the nightly melatonin levels to return to daytime levels before eating. Similarly, at night, it is best to avoid consuming carbohydrates or glucose two hours before bedtime.
Consider consuming a higher fat meal in the morning rather than something with a high carbohydrate or glucose content. For example, if the blood sugar level is 100 milligrams per deciliter, adding one gram of sugar will raise it to 120 milligrams per deciliter, which is indicative of diabetes.
It is important to be cautious about recommending dietary choices, as most foods, except for pure fat, contain carbohydrates. Even a seemingly low-carb option such as boiled eggs with toast can still trigger a significant rise in blood sugar.
Many individuals experience altered circadian rhythms due to factors such as shift work or travel to different time zones. The definition of shift work includes staying awake for two to three hours between 10 pm and 5 am for 50 days in a year. This can disrupt the body’s internal clock and lead to a 40-50% disturbance in circadian rhythm for the week.
The anthropogenic world built in the post-industrial era lacked knowledge of the significance of circadian rhythm, leading to personal choices that disrupt natural sleep patterns. The lack of awareness about circadian rhythm led to the acceptance of shift work, late-night socializing, and binge eating as momentary discomforts, similar to the misconception about the safety of lead and asbestos in the 1970s.
To mitigate the negative effects of shift work, individuals should be cautious with caffeine and alcohol consumption, as they can disrupt the sleep-wake cycle. For night shift workers, it is important to maintain consistent eating and sleeping times, even on off days. Some countries implement continuous night shifts followed by off days to allow the body to adjust to the night shift.
As a new field of science, researchers are still learning how to develop personal habits, family rituals, and societal norms to reduce circadian rhythm disruption. It is essential to adopt habits that promote resilience against circadian rhythm disruption.
It is common for personal sleep patterns to be influenced by external factors, such as parental responsibilities and evening entertainment choices. Individuals should be mindful of the impact of stimulating activities on their sleep and make conscious decisions to prioritize healthy sleep habits.
The discussion centers around managing sleep patterns and creating an environment conducive to good sleep. The importance of managing free time in the evening and finding a balance between personal enjoyment and health is highlighted. It is emphasized that having control over the bedroom environment, including darkness and noise, is crucial for quality sleep. Napping is suggested as a way to catch up on lost sleep, and the physiological reasons behind feeling sleepy after lunch are briefly discussed. Overall, the conversation focuses on practical strategies for improving sleep quality.
There are many new technologies and architectural designs coming into play for office design. Open office design and large windows are part of this new scheme. Glass manufacturing has advanced to the point where glass can be both aesthetic and load-bearing. This allows for large walls of glass to let in natural light, reducing the need for artificial lighting and lowering energy bills.
At night, innovations in office space design include light layering, which allows for personalized lighting using dimmable LED lights. The lighting industry is a $27 billion industry, and there is now near complete control over the quality, quantity, and timing of light in the workplace or at home.
In countries with little winter daylight, there are lights available to simulate daylight, with different flavors of light for different times of day or seasons. The use of blue-shifted indoor light in winter can uplift mood and alertness, while in summer, orange-shifted light can simulate evening time for better sleep.
Circadian rhythms play a significant role in the body, including organs involved in metabolism. Time-restricted feeding, or eating within a specific time window, has shown to be beneficial for health.
Intermittent fasting, as defined in scientific literature, refers to alternate day fasting, fasting for two days in a week, or periodic fasting, where individuals fast for four or five days every two to three months. The term “time-restricted eating” generally refers to eating within a specific number of hours, usually between eight to 12 hours, without explicitly reducing calorie intake.
Circadian rhythms are important as they help the body repair and rejuvenate itself. Unlike a car, our bodies need time to repair and rejuvenate, and this process occurs during sleep. Just as the brain repairs and rejuvenates during sleep, every organ in the body also needs time to repair and resist external input. Food is one of the main external inputs that affects our organs, as it influences hormone levels and nutrient processing.
After eating, it takes at least five hours for the stomach to digest food, and even longer for nutrients to be absorbed and distributed throughout the body. This means that our organs do not get the necessary time to rest and repair if we are constantly eating. By limiting the hours of eating to eight to ten hours, the body can get roughly eight hours of rest and repair, which is essential for overall health.
The experiment was conducted on mice and fruit flies to control eating patterns. Mice were given unlimited access to food and consumed 70 to 85 percent of it during nighttime, leading to weight gain, diabetes, and other health issues. However, when the same number of calories was consumed within an 8 to 10-hour window, these diseases were prevented and even reversed. Molecular studies revealed improved metabolism and mitochondrial function. These findings are being translated to human studies, with promising results from pilot studies. Randomized clinical trials are ongoing and results are expected from 2021 onwards.
It was also observed that people generally eat within a 15-hour window, impacting their circadian rhythm. An app called “My Circadian Clock” was developed to capture eating patterns and revealed that 50% of adults have an eating window of 15 hours or longer. This highlights the importance of understanding not just what people eat, but also when they eat.
The researchers have developed an app to measure when people eat, in addition to traditional methods of tracking food intake. Research shows that nearly 50% of adults eat for 15 hours or longer, while only 10% eat for 12 hours or less each day. People’s perceptions of how long they eat differ from their actual eating habits, with only 5% of respondents accurately reporting their eating window. This discrepancy indicates a need for further study on the timing of human nutrition. The researchers also found that the timing of the eating window can influence the types of food consumed, with later eating windows correlating with higher consumption of unhealthy foods. Therefore, the researchers suggest ending the eating window earlier to reduce the likelihood of consuming unhealthy food and to allow for better sleep. The researchers also discuss the potential impact of social influences on eating habits, emphasizing the need for further research into this area.
The impact of eating patterns on sleep has been studied, with evidence showing that late night eating can lead to fragmented sleep. Caffeine, such as black coffee, has been shown to reset the circadian clock, but consumption after 2 o’clock in the afternoon may disrupt sleep. However, exceptions are made for individuals who require alertness for their job, such as those in the entertainment industry. Studies on the impact of caffeine intake on sleep patterns are ongoing.
Time-restricted eating is a broad term, and it is suggested that pregnant or breastfeeding individuals do not attempt to restrict their eating times for medical risk reasons. However, adopting good habits during pregnancy or breastfeeding can have long-term impacts on the family’s eating habits.
Overall, time-restricted eating for individuals aged five and older can be done without significant adverse effects, unless they have type 1 diabetes. It is compared to brushing teeth for maintaining good health. However, a 10-hour eating window may be too restrictive for pregnant or breastfeeding individuals.
Scientific evidence suggests that timing of exercise can impact muscle tone, joint flexibility, and risk of injury. Late afternoon or evening may be the best time for exercise due to higher heart rate, warm core body temperature, and better muscle tone and flexibility. For people with diabetes, late afternoon exercise has been shown to help reduce blood glucose levels, as opposed to exercise in the morning. This research highlights the importance of considering circadian rhythms when planning exercise routines for optimal health benefits. Additionally, maintaining a 12 to 13-hour eating window for children can be achieved through sleep hygiene and bedtime rituals, aligning with general recommendations for sleep and fasting periods.
The pancreas produces more insulin in the morning or the first half of the day, and the second half of the day, even in the absence of melatonin. It doesn’t produce as much insulin as well as in the morning. This means that any health in managing glucose independent of insulin is much better in the evening. When we exercise, our muscles actually take up a lot of glucose without the help of insulin. This might be one reason why late afternoon or early evening exercise, or even brisk walking, may be much more beneficial for people with diabetes in managing their blood sugar levels. The bottom line is that late afternoon or early evening exercise is better. But at the same time, if you have time to exercise only in the morning, then you should not stop exercising. A recent study showed that fat oxidation was about almost 13% higher in the afternoon compared to the morning. Participants who took in a large amount of caffeine 30 minutes before exercise in the morning had fat oxidation equivalent to someone who exercised in the afternoon without any caffeine. There was another study showing that athletic performance varies depending on when a person wakes up. The peak performance was very different for early risers versus late risers. An ideal circadian day might be to sleep for eight hours consistently every night, try to avoid food for one to two hours after waking up, have your first bite within 8-12 hours, avoid food and bright light for 2-3 hours before bedtime, and take a 30-minute brisk walk during the day.
Satchin Panda’s ongoing crowdsourced data using the MyCircadianClock app has been extremely useful for many ongoing and future studies. There are nearly 10 different clinical studies going on in parallel on the MyCircadianClock platform. The book “My Circadian Code” has been translated into 10 different languages and has helped Satchin understand how to think of his experiments in the light of public health.