On the impact of diet on circadian phase setting

We’ve seen that meal size and frequency can influence circadian rhythms, but here are some examples of how nutrients can, too.

Circadian phase advance: going to bed earlier, waking up earlier.  Blue blockers at sunset, bright light at sunrise.  Flying east.  Autumn.

Circadian phase delay: staying up late, sleeping in.  Flying west.  Spring.  Using smart phones, tablets, and iPads in bed at night.  Light pollution.

Relative to adolescents, infants and children are circadian phase advanced.  This is part of what is fueling the movement to delay high school start times.  Kids are mentally better prepared to work later in the day.  With early school start times, performance is down in the morning, but they kill it on video games after school.  Delaying start time by an hour won’t totally fix this, but could help.



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  • Jack Kruse

    Nice job yet again, Bill. There is a reason the Leptin Rx uses the BAB. (big assed breakfast) The key point is to consider what might happen to your health when you advocate a “old type of diet” when your environment moves forward because of modern technology

  • Dan Ordoins

    Nice one Bill. Thanks.

  • Another excellent blog entry, Bill.

    One point of contention. Although daylight savings time acutely causes a phase advance in fall and a phase delay in spring, the net effect on the human brain of these season changes is opposite. As light becomes progressively later (during the fall -> winter solstice) , total light exposure is decreased and the timing becomes later and later. The human brain is shifted toward a phase delay, sleeping and waking later. This is a depression trigger, and a major reason so many mood disorder pts struggle in fall.

    Spring is the inverse. The spring ahead is a phase delay, but the progressive earlier light all the way into the summer solstice and longer days are profoundly advancing. Many people get “spring cleaning” energy and bipolar patients may go manic from the circadian effect on neurotransmitters and alertness.

    Is minor point but an important one because the circadian system is very important to regulate for anyone with endogenous mood problem, and “fall” clusters with delay triggers for a reason (and depression). This will help other readers who have similar mood problems make sense of their symptoms and how to control them.

    If the keto diet is phase advancing this is powerful evidence to further support its role in mood disorders especially bipolar II with a preponderance of depression, or endogenous depression. Phase advancing is antidepressant.

    (FYI, lithium promotes a phase delay, which may also influence antimanic benefits)

  • Eric CFB

    Cold thermogenesis can also effect circadian issues.

    I’ve had serious sleep issues my whole life. Always used to miss school, morning college classes, dayshift jobs, cause I could never fall asleep at nite, or subsequently wake up the next morning.

    Cold thermogenesis has gone a long way to fix that. I’ve seen two ways this seems to happen.

    Doing CT at nite can help one get to sleep. First there is the catecholamine ‘dump’ one may experience, the rush and high of initial CT, followed by the ultra-mellow later on. And of course, CT lowers body temp, arguably mimicking the effects of melatonin:


    But then last year I started experimenting w/ morning CFB sessions (usually fasted or PSMF), and noticed that I would get sleepy that nite sooner, more tangible. It was as though the CT functioned to “wake me up” early, almost analogous to bright light therapy for nite shift workers.

    I’ve lost track of the amount of feedback reporting that the CFB/CT has helped them get a deeper sleep, but they’re all using it at nite, before bed. I’ve found that morning sessions can be just as effective, especially if you’re a “night owl” type.

    I suppose it causes “circadian phase advance.”

    • epic.
      This is very interesting! Thanks, Eric.

  • “‘Social Jet Lag’ and the Teenager”


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  • School start times for adolescents.


    The American Academy of Pediatrics recognizes insufficient sleep in adolescents as an important public health issue that significantly affects the health and safety, as well as the academic success, of our nation’s middle and high school students. Although a number of factors, including biological changes in sleep associated with puberty, lifestyle choices, and academic demands, negatively affect middle and high school students’ ability to obtain sufficient sleep, the evidence strongly implicates earlier school start times (ie, before 8:30 am) as a key modifiable contributor to insufficient sleep, as well as circadian rhythm disruption, in this population. Furthermore, a substantial body of research has now demonstrated that delaying school start times is an effective countermeasure to chronic sleep loss and has a wide range of potential benefits to students with regard to physical and mental health, safety, and academic achievement. The American Academy of Pediatrics strongly supports the efforts of school districts to optimize sleep in students and urges high schools and middle schools to aim for start times that allow students the opportunity to achieve optimal levels of sleep (8.5-9.5 hours) and to improve physical (eg, reduced obesity risk) and mental (eg, lower rates of depression) health, safety (eg, drowsy driving crashes), academic performance, and quality of life.

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