Artificial light regulates fat mass: no bueno.

“despite not eating more or moving less”

We’ve seen this time and time again: LIGHT IS A DRUG.


above quote is extrapolated from this rodent study: “Prolonged daily light exposure increases body fat mass through attenuation of brown adipose tissue activity.”


Artificial light impacts nearly every biological system, and it doesn’t even take very much to have an appreciable effect (think: checking your smart phone or watching a television show on your iPad in bed at night).  In this study, adding 4 hours to the usual 12 hours of light slammed the autonomic nervous system, disrupting sympathetic input into brown adipose leading to a significant increase in body fat  “despite not eating more or moving less.”



Circadian arrhythmia pwns CICO —- remember the adipose-specific Bmal1-knockouts?  “they burn fewer calories to do the same amount of work, similar to weight-reduced humans”   …inducible leptin-resistance?



Funny thing, this resulted in a direct effect on heat production via uncoupling (ie, can’t be “out-exercised”), in a system that could be band-aided with cold exposure.  Take a page out of Jack Kruse’s handbook and have a cold bath?  …or just tune out the artificial light & tech devices.


Excess artificial light is a circadian disruptor: same diet & exercise will have a very different impact on someone with circadian misalignment.  IT WON’T WORK UNTIL CIRCADIAN RHYTHMS ARE FIXED.  #Sisyphus.



actigrams and circadian periodicity



Don’t say it’s a stupid rodent study, Arlet Nedeltcheva showed the same thing in humans: hypocaloric diet + circadian disruption = lose more lean mass and less fat mass.


muscle and fat loss



Translation: don’t go into a caloric deficit or try to lose weight until AFTER you’ve done everything possible to improve circadian rhythms —– get plenty of sleep, don’t skip or delay breakfast in the morning, wear blue blockers at night, sunlight all day (or a bright light device if necessary).  If these boxes aren’t checked PRIOR TO your weight loss efforts, then more muscle and less fat is lost; so even if you start paying attention to circadian rhythms later in the game, you’re already significantly handicapped.


calories proper


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  • rs711

    i’m cheering!

    • Jack Kruse

      ancestral health isn’t

      • rs711

        A missed opportunity then. I couldn’t care less because ‘ancestral health’ (social movement) ? evolutionary biology.

      • Jack Kruse

        This is especially true when the evidence you believe is missing key parts of nature’s truth. Light and dark cycles always trump ideas about food.

        • Dan Ordoins

          But when combined in the right context each one complements and enhances the other. – Light and dark cycles coupled with eating within seasons and food circadian rythm (durning light cycles) and food choices (high seafood based diet).

          • Optimal health = ALL the boxes must be checked 🙂

      • bradjkovacs

        Why would this be at odds with ancestral health proponents? I’ve seen Paleo advocates talk about this same issue. If their suggested etiology is about diseases of modernity and a mismatch with evolutionary biology, inappropriate light cycles and circadian rhythm fits into their ethos.

  • This Old Housewife

    I’m sending this to Hubby at work–he and I have serious differences about when to go to bed, in spite of my speechifying about blue light, circadian rhythms, and how all this relates to diabetes.

  • TechnoTriticale

    Since the fulltext appears to be paywalled, I can’t answer this for myself:
    what type of light was used?

    And would the blue content even matter? Do mice have ipRGCs?

    • white fluorescent light, intensity ~85 uW/cm2… and yes blue light matters for mice; they have ipRGCs.

      • TechnoTriticale

        re: … white fluorescent light …

        Thanks for reporting that. Most fluorescent lamps have a nasty peak down around the key ipRGC wavelengths, but we’d need lamp brands and model numbers to nail down an SPD.

        This suggests that nutrition studies have yet another major confounder (test cell light spectral power distribution), which, like incep gut biome status and prebiotic content of the chow, has probably been entirely overlooked in most trials to date.

        Studies which couldn’t be confirmed, or saw wildly varying results upon attempt at another lab, may easily have fallen victim to these factors.

        Sometimes I’m amazed that we’re at the moment able to learn anything at all about the effects of diet and personal environments.

        • “we’d need lamp brands and model numbers to nail down an SPD”
          I’m working on it!

          but yeah, this is a major problem in some labs… the lights fail to turn on or off at the right times and no one even notices. We monitor this with light sensors 24/7, but it’s still not perfect…

        • “Sometimes I’m amazed that we’re at the moment able to learn anything at all about the effects of diet and personal environments.”

          it’s nice when clinical trials match up with rodent data, rare as it may be… but fortunately, it seems like a lot of the studies on rodents vs. light exposure, meal timing, circadian arrhythmia, etc., appear to match up…

      • Jack Kruse

        and this is why studies on mice need to be avoided……if you do not control lighting you can tell nothing about ubiquitination rates and how this controls their carbon flows. Obesity researchers never have this insight at all

        • fwiw, we rigorously control the lighting (color, duration, timing, etc.)… but admittedly, this isn’t even on the radar in most vivaria.

          • Jack Kruse

            Bill this needs to be the first question of peer review…….and they dont ever think to ask. Guyenet linked studies are horrendous because of this issue. I have been in contact with someone who worked in his lab. Light is never controlled for. In fact fake light is often left on all night long. FYI.

          • “In fact fake light is often left on all night long.”

            SOOO MUCH #FAIL

            seriously, that really sucks

          • Wendy

            Aren’t mice nocturnal?

          • mice are nocturnal.
            Some experiments are conducted twice: at night and during the day.

  • Paul Crothers

    There a real simple solution to this. Sleep outside in a light colored tent. You get cold and get light as soon as the sun comes up. And its fun. Good luck getting anyone to join you, except the kids might.

  • jasmine johend

    Bill, I cannot do breakfast..period…it sets me up to EAT all day. Have tried and tried..non bueno

    • you’re not alone… fortunately, meal timing is only a small piece of a big puzzle.

      I’d say try different foods or meal planning strategies, but it sounds like you’ve been down these rabbit holes before. High protein breakfasts work for some, whereas Jane Plain & Rosemary prefer higher fat in the AM. Ymmv.

      • jasmine johend

        Yes will def work on blue blockers and more am sunlight. Working up CT with brief cold water exposure on back after shower.

        • you could take that to the next level by easily progressing into more advanced CT…

    • Paul Crothers

      Have you tried the big a** breakfast? 50g of protein. I’m doing it and it tends to last until dinner.

      • jasmine johend

        Even worse, almost killed myself driving to work fell asleep at wheel, raises blood sugar.

    • Wendy

      Try protein and fat only and vegies instead of fruit, no carbs. Carbs will set you up to crave food and more carbs especially all day and night.

      • jasmine johend

        I don’t eat carbs apart from veggies. Fat, protein, makes no difference, some people can’t eat breakfast, doesn’t work for them.

  • Thomas Hemming Larsen

    Another good one Bill! You should make a post about the ‘optimal’ day. I know a girl who could help you do an infographic 🙂

    • I could make some infographics, but they’d be different depending on geography & season, people’s individual environments, etc., etc……….

      • P.S. I <3 infographics… would probably get obsessed with the project until it completely overtook all of my free time! lol 🙂

        • Thomas Hemming Larsen

          Haha. Honestly I think it could a good idea. I’m completely aware of the caveats, hence I wrote ‘optimal’. It could be a combination of flow chart and infographic. Its just after I saw the infographic following Panda’s study I think they are so good at conveying a message 🙂

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  • Ken

    Can you elaborate on what you mean by “in a system that could be band-aided with cold exposure.” Any clarification or links would be awesome, Bill.

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  • “An important point is that LIGHT affects fish growth via better food conversion efficiency, not just increased food intake.”

  • Ken

    Bill, when you say Blue Blockers at night, do you mean at sunset or do you usually put them on a few hours before bed?

    • the rule of thumb is ‘sunset,’ but if your bedtime is around that time, it might help to wear them a little earlier. Ymmv.
      Eg, if you find you’re waking up sooner than desired, then try wearing them later (*after* sunset)… and vice versa: if you’re still tired/sleepy when you wake up in the morning, then it might be better to start wearing them earlier.

  • Mindbody Medic

    I have a pair of amber glasses but how does one know if they are working? is there an agreed standard without having to investigate specific wavelengths of light or is it based on colouration of the lense alone?
    Also they aren’t the best but having trouble in UK getting decent cheapo blueblockers. Has anyone hacked ordinary clear glasses using sticky amber film or painting on resin/something that would work?

    • Amber is usually ‘good enough.’ Uvex Skypers are available via
      I know people have tried sticky amber films, but I still recommend Skypers because they’ve been clinically tested.

      • Mindbody Medic

        Thanks a bunch and thanks for this site. A treasure trove of useful info!

    • TechnoTriticale

      re: I have a pair of amber glasses but how does one know if they are working?

      Look away from the sun at the blue of the sky. This is the blue we respond to. If it turns gray with the glasses, you’re all set.

      Alternatively, find a blue indicator LED on one of your appliances or devices. View it with and without the ambers. If they are working as well as a Uvex, the blue will either turn green or appear to extinguish entirely.

      If in doubt, Uvex eyewear is only US$10 or so on Amazon.

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  • barry

    isnt the screen of a laptop bright enough? lol

    • it is! you can dim it, and use something like F.Lux to reduce the blue light.

  • Wendy

    My doctor told me that adults do not have brown adipose tissue, only white. He said only infants have the brown adipose tissue which disappears after that.

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