Five Ways Circadian Rhythms Regulate Life

Savannah Helm

By: Alicia Jerome MS, RDN

In the realm of biology, there exists a fascinating, hidden world that governs the ebb and flow of our daily lives. This world is governed by circadian rhythms, often referred to as our body's internal clock. Russell Foster, a renowned neuroscientist, explores this captivating subject in his book "Life Time." In this blog, we'll delve into the five ways circadian rhythms regulate life, as revealed by Foster's insights, as well as how registered dietitians can use this information to benefit their clients.

  1. Sleep-Wake Cycle

Perhaps the most well-known function of circadian rhythms is regulating our sleep-wake cycle. These rhythms dictate when we feel alert and when we naturally become tired. The master clock, located in the brain's suprachiasmatic nucleus (SCN), aligns our internal body clock with external cues, such as daylight and darkness. This synchronization ensures that we are awake and alert during the day and prepared for restful sleep at night.

Foster's research emphasizes the importance of respecting our body's natural rhythms. He explains that disruptions, such as those caused by shift work or frequent jet lag, can lead to a host of health issues, including sleep disorders, mood disturbances, and even chronic diseases.

Possible application: Dietitians can use this information to make a case for a consistent sleep schedule as part of their wellness prescription, especially for those combatting chronic nutrition-related diseases.

  1. Hormone Regulation

Circadian rhythms play a pivotal role in regulating hormone production and release. For instance, cortisol, often referred to as the "stress hormone," follows a distinct circadian pattern. Cortisol levels typically peak in the morning, providing us with the energy needed to start our day, and decrease in the evening, promoting relaxation and sleep. Irregular sleep can promote increased levels of cortisol which in turn lower leptin (satiating hormone) levels and increase ghrelin (hunger hormone) levels.

Additionally, melatonin, the hormone responsible for inducing sleep, is produced in higher quantities at night. This hormone regulation ensures that our bodies are in the right physiological state at the right time. Interestingly enough, beta-blockers have been shown to cause an 80% reduction in melatonin production – something to consider if clients struggle with good quality sleep.

Possible application: A dietitian can offer basic sleep hygiene recommendations or refer to a sleep specialist for those clients who may struggle with eating in response to higher baseline anxiety levels.

  1. Metabolism and Nutrition

Circadian rhythms also influence our metabolism and eating patterns. Foster's work highlights that our bodies are more efficient at processing food during certain times of the day. For instance, we tend to burn calories more effectively during the day than at night. Eating out of sync with our circadian rhythms can lead to weight gain and metabolic disturbances.

Moreover, studies have shown that when we consume most of our calories earlier in the day, it can improve insulin sensitivity and aid in weight management. Foster's research underscores the importance of aligning our eating habits with our internal clock for optimal health. 

Additionally, the quantity of sleep can also affect the desire for certain foods. When study participants were limited to only 4 hours of sleep their affinity for high carbohydrate foods increase by 32%.

Possible application: Dietitians can use this information to support a meal plan with a larger breakfast, medium lunch, and smaller dinner. They can also make clients aware of the need for more sleep when combatting cravings or trying to adhere to a prescribed meal plan.

  1. Cognitive Performance

Our cognitive abilities are not constant throughout the day; they ebb and flow with our circadian rhythms. Foster's book highlights that alertness, concentration, and memory tend to be at their peak during the late morning and early afternoon. This information has significant implications for education and productivity.

Understanding our cognitive rhythm can help us make better decisions about when to tackle demanding tasks, study, or engage in creative pursuits. By aligning our activities with our cognitive peaks, we can enhance our overall performance and efficiency.

Possible application: Dietitians may suggest to their clients to focus some of their most challenging tasks in the late morning or afternoon. Examples might be: meal prep mid-day on Saturday or Sunday, write out the next week’s menu during this peak concentration time, or schedule a challenging workout during this alert window.

  1. Mood and Mental Health

Lastly, circadian rhythms have a profound impact on our mood and mental health. Disruptions in these rhythms can contribute to conditions such as depression and bipolar disorder. Foster's work emphasizes the importance of maintaining a stable daily routine and getting regular exposure to natural light to support healthy circadian rhythms, which in turn can promote better mental well-being.

Possible application: Dietitians may supplement their nutrition recommendations with suggestions to eat at regular times and to take advantage of eating in natural light.


Russell Foster's book, "Life Time," provides a compelling exploration of how circadian rhythms regulate our lives in myriad ways. From our sleep-wake cycle to hormone regulation, metabolism, cognitive performance, and mental health, these internal clocks play an essential role in our overall well-being.

Understanding and respecting our circadian rhythms is not just a matter of curiosity; it is a vital component of a healthy and fulfilling life. By syncing our daily activities with our body's natural clock, we can unlock the potential for improved health, productivity, and overall happiness. Foster's research serves as a reminder that within the rhythm of life, we have the power to find balance and thrive.



Foster, R. G. (2022). Life Time: your body clock and its essential roles in good health and sleep. Yale University Press.

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