There are five key elements to weight loss from a circadian point of view: Timing of Meals; Light Exposure; Sleep; What to Eat, When; and Genetic Variants. All of these can come together in our modern world to give you a propensity to gain weight – and all can be hacked to help you lose weight.
Timing is everything when it comes to our bodies.
Midnight snacks, a bowl of cereal before bed, or even ‘saving’ desert until 9 or 10 pm. All of these are fairly normal behaviors these days. Just open up the fridge and pop something in the microwave to heat it up, anytime day or night. Modern convenience at its best; not something our ancestors would have been able to do.
This penchant for eating at any time, day or night, is one factor driving the obesity epidemic.
The simple solution is to eat earlier in the day and to not snack at night. This is easier said than done, for some of us. So make a plan for your meals for a few days. Yes, actually sit down with a pencil and paper and come up with ideas for shifting your calories to the morning hours. If you are a habitual TV watcher at night (with a subsequent bowl of popcorn and a beer), plan out a couple of evening activities to get you out of the house for a few evenings while you break the snacking habit. Perhaps go for a walk, go see a movie and avoid the overpriced snacks, or dust off your bowling shoes for a quick game.
While this all may sound a bit cut-and-dried, we really are flexible creatures, able to withstand periodically eating at different times without drastic effects. The bigger picture is the chronic effects of eating at the wrong time, rather than just the one-off change up of our daily eating habits. So don’t beat yourself up if you nibble on something at an evening event. Just get back on track for the rest of the week.
Light is also important to weight gain. While it seems strange to think about, again the research on this topic seems to point to an incontrovertible conclusion that light – both bright light exposure in the daytime and no light exposure at night – makes a significant difference to our weight.
In Circadian Rhythm Connections, Part 1: Mood Disorders, I explained how light at a specific wavelength (~480nm, blue light) hits melanopsin containing photoreceptors in our eyes, signaling to our core circadian genes (CLOCK, BMAL1) in the brain that it is daytime.
Our body has both the strong central circadian clock in the suprachiasmatic nucleus in the brain as well as what are known as peripheral clocks in our organs. These peripheral clocks include the timing of functions in the liver, pancreas, etc.
The core clock genes are mainly entrained through the cycle of light and darkness, while the peripheral clock in the liver is more quickly reset, or entrained, by food intake. But the core clock genes do still affect the peripheral clocks.
The core circadian clock is located in a region of the hypothalamus called the suprachiasmatic nucleus (SCN). The SCN signals to the adrenal system to increase adrenal glucocorticoids (e.g. cortisol is a glucocorticoid hormone) production just prior to waking. “This promotes arousal and alertness by enhancing liver gluconeogenesis (from amino acids and fatty acids), promoting the release of liver glucose to the blood, and increasing its uptake in the brain and muscles. Adrenal glucocorticoids have been implicated as a peripheral humoral cue for the entrainment of oscillators such as the liver.” [ref] The SCN also controls the circadian rhythm of the hormones insulin, glucagon, and adrenalin.
That may sound like science mumbo-jumbo, but it has practical implications. For people waking up at 3:30 or 4:00 am every night, this could be caused by the circadian spike in cortisol levels. Personally, I used to see 4:00 am on the clock quite often. Blocking blue light in the evenings, going to be at a reasonable hour, and cutting out snacking after dinner has eliminated the 4 am wake-up for me.
What does light at night do to people? Shift work is a very well-studied risk factor for obesity. One study of rotating shift workers (Canadian men) found a 57% increase in the risk of obesity.[ref] Another study of shift workers (Korean women) found a 63% increased risk of obesity.[ref] Numerous other studies have similar results.
Solving this problem is as simple as shutting off that night light, getting some blackout curtains, and eliminating all the glowing LEDs from chargers in your bedroom.
Make getting outside during the morning a priority. Drink your coffee on the porch, walk or bike to work, take a morning break outside, and eat lunch outside if possible.
Sleep is something that every health guru out there puts on their lists of “Top 5 ways to improve blah, blah, blah.” But does it really affect our weight and metabolism that much? Is the benefit worth the trade-off – e.g. is it worth going to bed before 11:00 each night rather than staying up late, having fun with friends or working long hours? Quick answer: Yep. Research shows that it really does make a significant difference.
So that was just three studies; there are hundreds of more studies on this topic showing similar results. The science is clear and unambiguous on this topic.
There are several players involve here, with melatonin being an important one. Melatonin, a hormone that rises and peaks at night while we sleep, is important to our basal metabolism for a couple of reasons that I will go into below. Light at ~480nm (blue wavelength of light) hitting the retina of our eye stops melatonin production. It is surprisingly quick, with 15 seconds of light stopping melatonin production for over 30 minutes and two minutes of blue light suppressing melatonin for more than 45 minutes.[ref] Thus, turning on the bathroom light in the middle of the night means it will take a long time to fall back to sleep.
First, let’s take a look at a 2003 study that just kind of makes logical sense. The study looked at medical students who were ‘nocturnal’ – e.g. staying up until 1:30 am and sleeping in until 8:30 am – vs. those who were ‘diurnal’, which would be going to bed well before midnight and getting up when it is light. The nocturnal med students skipped breakfast and ate more of their calories later at night. This caused glucose impairment as well as decreased melatonin and leptin secretion.
It has been known for decades that people are more insulin sensitive in the morning (again why we shouldn’t eat a big meal at night).[ref] Another study states: “Multiple studies have shown that in healthy humans, both insulin sensitivity and beta-cell responsivity to glucose are lower at dinner than at breakfast”. It goes on to explain that mouse models show that deleting one of the core clock genes (BMAL1) in the pancreas causes insulin resistance.[Multiple studies have shown that in healthy humans, both insulin sensitivity and beta-cell responsivity to glucose are lower at dinner than at breakfast] Circadian disruption is intimately coupled with poor glucose metabolism and insulin resistance.
Blue light at night effectively shuts down melatonin production, so you need to block all blue wavelengths for a couple of hours before bed. You may be thinking… “ha! I don’t need to wear silly looking blue-blocking glasses because I have night shift enabled on my phone/tablet.” Well, it turns out that researchers studied the night shift mode at a couple of different settings, and it did very little to prevent melatonin production from being suppressed. So either (shock face!) put away electronic devices a couple hours before bed or get a pair of blue-blocking glasses.
It takes a couple of weeks to get your body’s melatonin production up to optimal after you start blocking blue light at night. In the meantime, you could increase your consumption of foods that contain melatonin. Foods high in melatonin include tart cherries, grapes, and almonds. Interestingly, melatonin levels fluctuate in plants as well, so the time of harvest, season, and other environmental conditions may affect the levels found in plants.
Why not take a melatonin pill instead of blocking blue light at night? Well, your body’s production of melatonin (without unnatural light) is a bell-shaped curve. Taking a pill gives you a big dose immediately that then gets metabolized and eliminated. Most people are better off with increasing their natural production of melatonin.
The liver coordinates our metabolism through the synthesis of lipids from carbohydrates and storage of both fats and carbs as glycogen. The liver’s peripheral circadian clock is powered by both the SCN (core clock) and by feeding timing. CLOCK and BMAL1 genes are thus involved in the rhythm of glucose metabolism and release.
A study of 93 overweight women looked at the effects of either a higher calorie breakfast or a higher calorie dinner over a 12-week diet plan. The results showed that those eating the higher calories at breakfast lost 2.5 times the amount of weight as the high dinner group. The higher calorie breakfast group also had a decrease in triglycerides by 33% compared with the high-calorie dinner group which had an increase in triglycerides.
What time of the day should you do TRE?
A time-restricted feeding study for an 8 week period had participants eating their normal amount of calories during a 4-hour window in the evening (5 – 9 pm). Participants did lose a little weight, but they also had increased fasting blood glucose levels and impaired glucose tolerance.[ref] This seems to indicate that a time restricted feeding plan at any time does work to reduce weight, but the feeding window needs to be earlier in the day so as to not impair glucose tolerance.
The research really is good on the effectiveness of a time-restricted eating program. If you are the type of person likes experimenting and who needs to set some rules for yourself, try a TRE program. Example: eat a good breakfast at 7:30 before heading out the door to work; lunch around noon; and then finish up with a light meal around 6:30 pm. This gives you an 11-hour eating window. Simple. And shown to be effective.
Of course, I have to talk about genetics here. We are all different, and our genes play a role in our natural circadian rhythm. I’ve written other articles on this topic as well, so I won’t go too in depth here.
The most obvious example of genes affecting our circadian rhythm and our propensity to gain weight is the aptly named CLOCK (Circadian Locomotor Output Cycles Kaput) gene. This is one of our core circadian genes, setting the daily rhythms for the rest of our body.
Another study of this variant showed that morning gastric motility may be slower in C allele carriers. Variant carriers also had somewhat lower morning diastolic blood pressure.[ref] This may play a role in timing for breakfast, with C allele carriers perhaps wanting to eat breakfast an hour or two later.
Around 30 – 40 percent of the population carries this CLOCK gene variant. For these people, it may be even more important to watch your blue-light exposure at night so that you aren’t fighting a lack of melatonin alongside your natural propensity for staying up a little later. Get into a good routine for getting to bed at a reasonable hour, and, if possible, shift your morning work schedule a little later to allow you to get enough sleep. Yes, I know that is easier said than done. While you may not be the person who wants to get up at 6:30 am, this variant is more of an hour or two shift rather than an ‘I should sleep in until noon’ excuse.
Blue-blocking Glasses: Why? Which ones?