The Circadian Theory of Obesity


For many years it was hypothesised that losing weight was as simple as calories in vs calories out. If you wanted to lose weight you would simply consume less calories than you expended in a given day. On the flip side, if you wanted to gain weight you would do the opposite and consume more calories than you expend.

To some extent calories matter but what matters more according to the food gurus, is macronutrients, this is the proteins, fats and carbs you eat and how these foods affect your hormones. Jason Fung hypothesises that obesity is a hormonal dysregulation of fat mass. That is, there is a hormonal signal from the body that controls fat mass.

Jason turned my head many years ago when it came to understanding what we eat can affect our fat mass and when it comes to aesthetics and fat mass regulation, its hormones that matter first. Correct your hormones and weight loss will become a simpler task.

Jason argues that by limiting carbohydrate intake and by only consuming fat and protein you can regulate hormones and lose weight. Insulin is controlled, the pancreatic hormone that regulates blood sugar levels, and in environments of low insulin we supposedly lose weight easier.

What Jason is saying is in many ways correct but it is not the full picture. I wholeheartedly agree with Jason in that hormones are the key drivers to weight gain, but where Jason hasn’t completed the story is he only briefly touches on the fact that hormones can be controlled by proper sleep. It is the reason we see people in the keto communities struggling to break weight loss plateaus, they are not looking at fat gain from a circadian standpoint and they need to open their eyes. Jason has covered some of this in an article on sleep and hormones so let’s explain it further from a circadian perspective.

 Circadian Rhythms

A circadian rhythm is a roughly 24-hour cycle in the physiological processes of living beings

Circadian rhythms are endogenously generated, although they can be modulated by external cues such as light and temperature.

Circadian rhythms are important in determining sleeping and feeding patterns.

Circadian rhythms regulate hormones and when circadian rhythms are disrupted by incorrect feeding patterns or mismanagement of light at the wrong times of day our hormones become out of whack.

What is contributing to fat gain? Unbalanced hormones.


Insulin is a key regulator of fat mass. The food gurus believe that this system is purely controlled by the amount and type of carbohydrate you ingest. But, I proved in my article “Is Insulin Resistance a Disease of Light?” that exposure to artificial light after dark and whilst you sleep is causing insulin resistance.

We know that insulin resistance creates an inability to handle glucose in the blood stream so eating excess protein or carbohydrates will create an inability to handle the glucose and could lead to fat gain and/or diabetes. Fix your light environment and consequently your hormonal profile and you can then enjoy seasonal carbohydrates without worrying about fat gain.

In the carnivore community, the lab results of Shawn Baker suggests that he is boarder-line insulin resistant. Is this because of the amount of gluconeogenesis caused by eating tonnes of protein? Or is it the fact that he works out under artificial light, has a disrupted circadian clock and eats a lot of protein? The evidence points to the latter being a more logical explanation rather than the simplistic food only theory.

Let’s take a look at an example below from the literature. Please note that further studies can be found in this article here

Light Exposure During Sleep May Increase Insulin Resistance

This study from 2018 shows that just one night of blue light exposure causes can increase in insulin resistance.

Twenty healthy adults ages 18 to 40 were randomized into Dark-Dark or Dark-Light groups and run in parallel for a three day and two-night stay. Participants had eight hours of sleep opportunity each night starting at habitual bedtime determined from one week of actigraphy with sleep diary. The Dark-Light group slept in the dark < 3 lux on Night 1 and slept in overhead room light of 100 lux on Night 2, while the Dark-Dark group slept in the dark <3 lux on both Nights 1 and 2.

To put this into perspective street lamps give off at least 100 lux and if you do not have black out curtains this level of lux is shining into your room whilst you sleep. This is a common problem and also, if you or your partner gets up to use the bathroom in the night you will also be exposed to even higher levels of lux which will cause insulin resistance.

Results showed that a single night of light exposure during sleep acutely impacts measures of insulin resistance. Insulin resistance is the diminished ability of cells to respond to insulin action transporting glucose out of the bloodstream and precedes the development of type 2 diabetes.

Leptin and Ghrelin

Leptin and Ghrelin are very important hormones when it comes to regulating fat mass and hunger.

Increased levels of leptin suppress appetite, so it makes sense that you want to be eating when levels of leptin are higher. i.e. the morning under sunlight.

Ghrelin is the hunger hormone; higher levels of ghrelin makes you feel hungrier and you therefore eat more food.

The below study shows what happens when we eat under artificial blue enriched light.

Morning and Evening Blue-Enriched Light Exposure Alters Metabolic Function in Normal Weight Adults

In this study in 2016 the researchers took 19 healthy adults and randomly assigned them to be exposed to bright blue enriched light either 0.5 hours or 10.5 hours after waking. Both groups were tasked with eating during this exposure as well.

The researchers then took subjective measures of sleep and hunger, as well as blood samples to measure glucose, cortisol, insulin, leptin and ghrelin, and compared these with the results when the participants were subjected to dim light. The findings showed that exposure to light, which was blue-enriched, in the morning and evening both led to higher insulin resistance.

Basically, if you eat your breakfast and dinner under artificial lights, scrolling through your smart phone or whilst watching television you are going to have a harder time digesting carbohydrate which will lead to weight gain and eventually diabetes.

In a 2004 study entitled short Sleep Duration Is Associated with Reduced Leptin, Elevated Ghrelin, and Increased Body Mass Index. The study showed that lack of sleep caused leptin and ghrelin to become unbalanced and increased fat mass in the participants.

Lack of sleep is caused by a disrupted circadian rhythm.

When you eat is so important. Bill Lagakos wrote a short blog showing that eating under sunlight increased leptin and reduced fat lipid particle size, because, well, melanopsin of course!

Going back to Jason Fung’s work, he does make a connection to sleep and hormones, he does state that sleeping for 4 hours increases ghrelin by 28% and decreases leptin by 18%, really not a good combination for satiety and weight management. We just need to get the food gurus to understand more that its not just sleep, but light and dark cycles that control our hormones.

When we sleep leptin turns our body fat into fuel to run the clearance of adenosine from the brain and run growth and repair processes. A poor night’s sleep will impair this process and you won’t be burning body fat when you should be and struggle to lose weight. This process can only be done in complete darkness otherwise the hormonal cascade of melatonin secretion will impair leptin’s ability to utilise fat stores for fuel during sleep. 


Cortisol is the hormone that makes you feel alert and awake. In the morning, we get a rapid rise in cortisol and this is what gets us out of bed.

However, chronically high levels of cortisol have been shown to contribute to weight gain. Also, just one night’s bad sleep can double cortisol levels.

It has been shown that exposure to blue and green light after dark leads to chronically elevated cortisol levels. Being “stressed” and alert before bed is not a good thing, this is the time when we need to be relaxing before bed. Therefore, you might want to put the smart phone down and watch your favourite TV show wearing some blueblocker glasses!

Also, chronically high cortisol levels can lead to impaired insulin secretion, which we have discussed is not good for your waist line.

The Circadian RX for Healthy Weight Management

  • Watch the sunrise each morning to produced serotonin and dopamine (high levels of dopamine will reduce your cravings)
  • Eat your largest meal at sunrise, ideally outside. Leptin will be optimal and sunlight will allow for a decrease in lipid particle size.
  • Make sure your food is in season, do not worry about macronutrients, just eat what is in season and stop when full.
  • Exercise in the morning, outside, because of the above but one
  • Get regular breaks from work, outside, to increase dopamine
  • Watch the sunset to ready the body for melatonin release and cortisol suppression
  • Put on your blueblockers once the sun has set. Grab some here. This will start the release of melatonin (sleep hormone and powerful anti-oxidant)
  • Do not eat after dark, artificial light will increase insulin resistance and digestion will impair sleep
  • Put down the smart phone 1 hour before bed to reduce cortisol
  • Go to bed early, make sure you get at least 8 hours sleep
  • Make sure you install black out curtains or wear a silk sleep mask to melatonin and leptin can go to work
  • Rinse and Repeat


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