Food timing resets the metabolism circadian clocks, not the time of day, level of light exposure or regulation by the brain.
I practice intermittent fasting (IF) or ‘time-restricted eating’. One of the reasons why I choose to do so, why IF is good for your health, has to do with circadian clocks, or your body’s ‘circadian rhythm’.
Our bodies contain several circadian clocks that are biochemical oscillators that cycles with consistent patterns and are ideally synchronised with daylight and time of day. Such clock’s in vivo period is necessarily almost exactly 24 hours and our sleep-wake cycles.
These internally synchronised circadian clocks make it possible for all plants and animals to anticipate daily environmental changes corresponding with the day-night cycle and adjust its biology and behaviour accordingly.
In 2017, the Nobel Prize in Physiology or Medicine was awarded to Jeffrey C. Hall, Michael Rosbash and Michael W. Young “for their discoveries of molecular mechanisms controlling the circadian rhythm” in fruit flies. Other researchers in the field include Dr Satchidananda ‘Satchin’ Panda, who wrote ‘The Circadian Code: Lose Weight, Supercharge Your Energy and Sleep Well Every Night‘ that a lot of the content in this post is based on.
The term circadian derives from the Latin circa (about) diem (a day), since when taken away from external cues such as environmental light and, as we will discuss, food intake.
Without light, they do not run to exactly 24 hours. Clocks in humans in a lab in constant low light, will average about 24.2 hours per day.
Circadian clocks are the central mechanisms that drive circadian rhythms. They consist of three major components:
- a central biochemical oscillator with a period of about 24 hours that keeps time;
- a series of input pathways to this central oscillator to allow entrainment of the clock;
- a series of output pathways tied to distinct phases of the oscillator that regulate overt rhythms in biochemistry, physiology, and behaviour throughout an organism.
Circadian clocks or oscillators are in every tissue of the body where they are synchronised by both the central clock and external signals to regulate tissue and organ activity throughout the day in a tissue-specific manner.
When you eat affects your circadian clock. The circadian clocks main goal is to optimise energy intake and survival.
What happens to the system when food timing does not match the circadian clock?
Experiments in rodents models, who are nocturnal, found if food is available only during the daytime, they start waking up an hour before the food arrives to search for food. That is, they figure out a mechanism to anticipate food.
After eating their food, they go back to sleep then wake up and mobilise around at night. In other words, their circadian clock that controls their daily sleep-wake cycle continues to work fine except during a brief period during the day when they wake up to eat food.
What happens to the food when mice eat when they are not supposed to? Does it get digested and metabolised in the liver where the circadian clock regulates metabolism?
In 2009, researchers took some nocturnal mice and fed them only during the daytime. They found that their liver function changed. Almost every liver gene that turns on and off during the day completely tracked the food and ignored the timing of light exposure.
That meant that it was the food that reset the liver circadian clock, not the time of day, level of light exposure or regulation by the brain. This finding completely changes how we think about circadian rhythms in how we think about light and food.
Instead of thinking that all timing information is taken in from the outside world has to go through the blue light sensors, it was now known that the body can respond to other cues. Just like the first light of the day resets our brain clock, the first bite of the day resets our organ circadian clocks. In fact, food timing can be a powerful signal to override the master circadian clock.
Think about your breakfast. Have you ever noticed that you get hungry at the same tie every morning, regardless of what you ate for dinner the night before?
This happens because our brain huger centre tells us when we should be hungry. At the same time, the brain tells the intestines to get ready for a rush of breakfast. The pancreases readies to secrete insulin. The muscles ready to soak up some glucose. The liver is ready to store some glucogen and make some fat then send it off to be stored.
If you usually eat breakfast at 8am, you set a meeting with your stomach, liver, muscles, pancreas and other organs to process the breakfast. This first bite of food is also one of your bodies links to the outside world.
Breakfast is the cue that sinks the internal clock with the outside time. As long as you eat breakfast at 8 am every day, your internal clock will be in sync with the outside world.
What happens if you change your usual food timing routine?
Imagine you need to catch an early plane flight and your schedule is disrupted. Instead of eating at 8 am, per usual, you need to eat at 6 am. After all, you’ve been taught that breakfast is the most important meal of the day.
When you sit down in front of your bowl of cereal, you will notice that you are not really hungry. Your brain has not sent the signal to your stomach to get your digestive juices flowing to get ready for the food. Your liver and the rest of your organs are not ready either, but you ‘need to eat’ so you eat anyway.
The first bite will signal your stomach to switch on its emergency mode to process the food. Your body has to stop everything else it is usually supposed to do at 6 am including cleansing itself and running on fat stores.
It will give its attention to the incoming meal. If it does not, the food will stay undigested in your stomach for a couple of hours. Usually, the body chooses the first option. It stops its usual activities like cleansing and burning fat, two things that are essential for good health and ageing.
The body uses fresh food for fuel. At the same time, the food regulated circadian clocks in your pancreas, gut and muscles will also pay attention to the unexpected meal and get confused. These food circadian clocks will believe that it is 8 am.
To make up for the lost two hours, the clocks in these organs will speed up to make up for lost time, like a factory or office workers who suddenly realise that they have two fewer hours to do their work for the day.
The problem is that it is very hard to make up for lost time due to the many parts of the circadian rhythm. Getting all the parts back into alignment is very difficult. You circadian clocks can usually adjust themselves by one hour per day.
When you show up for breakfast the next day, it is 8 am in whatever city you are now in. But your body still thinks it’s whatever time it was in your home city so the stomach is still not ready for the food. It again kicks into emergency mode and tries to process your food.
Again, it tries to speed up the clocks. Assuming only a few hours time difference, by day four your body has adjusted to your current location. But, guess what, when you return home, maybe a week or so later, when you sit down to breakfast at your usual 8 am, your body thinks it’s whatever time it is in the place of your trip.
This time, the organs were probably ready for food a couple of hours earlier but did not get any food so they started the next task on their to-do lists. As soon as you eat anything, your stomach, liver, pancreas and muscles have to stop what they were doing or divert some attention to processing your breakfast. This time, they likely choose to multi-task.
Again, the food regulated circadian clocks try to reset to the new breakfast time by slowing down for the next few days. This example shows how an erratic breakfast time confuses your organs and makes them less effective.
Using the food regulated circadian clock, each organ is programmed to process food for a few hours starting from your first meal of the day, usually called breakfast, regardless of what you eat. If your breakfast was at about 8 am then the system works optimally for about eight to ten hours.
Every time we eat, the entire process of digestion, absorption and metabolism takes a couple of hours to complete. Even a small bite of food takes a couple of hours to process.
After approximately a ten-hour window, the gut and metabolic organs will continue to work on your food but their efficiency slowly goes down because they are not programmed to be open for business 24 hours per day.
The food circadian clocks in different organs are not that efficient. Your gastric juice and gut hormones are produced at different rates. Your digestion slows down giving you a sense of indigestion or acid reflux.
Just like a late breakfast interferes with the other tasks your organs have to accomplish, a late dinner will too. This time the disruption is more severe. The same food that would have taken two hours to digest at 6 pm takes longer to digest at 8 pm because, if you ate at 8 am, you are outside that optimal 10 hours window.
This extra digestion work interferes with the next tasks the organs need to do by delaying or even completely removing that task from the to-do list.
Who cares? I’m sleeping anyway. Right?
The problem with that statement is that our cells can not make and break up body fat at the same time. We can not be in catabolic (breakdown) and anabolic (building) at the same time. That is why it is very difficult to lose weight and build muscle at the same time, and why bodybuilder cycle periods of time ‘bulking’ and ‘cutting’.
Everytime we eat, the fat making programme turns on and the cells in our liver and muscles create some fat and store it. The fat burning programme only turns on slowly after the organs realise that no food is coming their way, which occurs a few hours after your last meal. It takes a good few more hours to deplete a good proportion of stored body fat.
If you have your dinner at 8 pm and finished at 8:30 pm, the food circadian clocks start to tick, the fat-making processes slowly wind down. Around 10:30 pm, you have an urge to snack. A piece of fruit. A piece of cake. A bag of crisps. A handful of nuts. It does not matter.
As soon as that food gets into your stomach, the circadian clock that has already signalled that food has stopped, has to get ready to work and process your snack.
That same food in the morning would have been processed in an hour or so, but with the stomach unprepared to receive more food, it will take a few hours to process.
Your fat-making process continues past midnight and the fat burning process won’t begin until the morning, but when you eat your breakfast, the switch turns again to making fat.
What’s the big deal? Aren’t we talking about just a few ounces of fat gain after a late-night snack? Won’t my metabolic rhyme come back the next day?
Actually, it’s worse than you think. It is hard enough for the body to monitor hormones, genes and food circadian clocks for someone with a strict eating routine. For someone who eats erratically throughout the day and night, the fat-making process stays on all the time.
Concurrently, glucose from digested carbohydrates floods the blood and the liver becomes inefficient in its ability to absorb glucose. If this pattern continues for a few days, blood glucose level (BGL) continues to rise and reaches the danger zone of pre-diabetes or even diabetes.
So, if you have wondered why diets have not worked for you before, the timing might be the reason. Even if you were following a calorie-controlled diet, routinely exercising, avoiding refined carbs and sugar, and ensuring you are getting enough protein to feed your muscles, it is very likely that you were not respecting your circadian clocks.
If you eat late at night or have a different morning routine, for example on the weekend or shift workers, you are constantly throwing your body out of synch.
Don’t worry, the fix is very simple. Just set an eating routine and stick to it. Timing is everything!
Enjoy!
Scott
Read more… Best Practices for “Time-Restricted” Eating / Intermittent Fasting and Whom It Could Benefit
Delay eating breakfast and eat dinner early if you want to lose body fat
Intermittent fasting could help tackle diabetes – here’s the science
Intuitive eating: a ‘diet’ that actually makes sense
What Is The Pareto Principle – 80:20 Rule – of Lifestyle Choices?