Intermittent fasting (IF) is a form of eating that emphasizes when you eat, rather than what you eat - it's a time approached eating pattern. It's become extremely popular in the fitness and health world due to the benefits it has been linked to, including helping lower blood pressure, cholesterol, inflammation, and even helps with weight loss.  It's no wonder so many people have taken up fasting! Despite its many benefits, it's important to know how to get started with intermittent fasting to maximize its effectiveness.
The most popular fasting method is known as the 16:8 method, which involves a 16-hour fast and an 8-hour eating window. But to the average person, a 16 hour fast sounds scary and nearly impossible. You can certainly work your way up to it, but it still may not be a sustainable fasting schedule. There's another, a possibly better method that involves timing your meals so that they are in line with your body's internal clock. This method is known as circadian rhythm fasting and typically involves fasting for 12-14 hours. This form of intermittent fasting is not only more sustainable than other forms, but it also has added benefits that can make all the difference on your fitness journey!
What is circadian rhythm fasting?
Also known as the circadian rhythm diet, this form of fasting involves timing your meals with the rise and fall of the sun. To understand this fasting method, let's take a step back to learn a little about circadian rhythms...
Circadian rhythm refers to our internal body clock (or sleep/wake cycle), we operate on this rhythm in which our body goes through physical, mental, and behavioral changes in a 24-hour cycle. It impacts our hunger, sleep patterns, and can cause hormone fluctuations. The circadian rhythm works this way because it's controlled by the hypothalamus, an area in your brain that is extremely sensitive to light. So, when the light shines in this area, it sends out signals to the body it's time to wake up. When it gets dark, it signals your body to start winding down for sleep. Not only that, but it regulates your eating schedule! Circadian rhythms can cause certain hormones to fluctuate, two of those are cortisol and melatonin. When exposed to light, your circadian clock signals to your body to get up by causing your cortisol levels to rise, giving you an increased level of energy. At night, your cortisol levels dip while melatonin levels gradually increase.
But, what does this have to do with when you eat your foods?
Cortisol has a significant effect on your thyroid hormones which affects your metabolism. This means when your cortisol levels rise in the morning, so does your metabolism which means it's the best and most effective time to eat! When your metabolism is up and running, your body is able to efficiently use the food you eat as energy. When cortisol begins to dip as the sun sets, your metabolism starts to slow down which can cause an increased risk of your body storing food as fat. To be clear, this only refers to normal cortisol levels. Chronically high stress/cortisol levels can actually contribute to an increase in body fat - so keep your stress levels managed to keep your cortisol levels normal.
Basically, our cells and organs have clocks that determine when they should be on and off. Most processes, like digestion, are turned off when it gets dark, while repair and reparation turn on. This is what gives circadian rhythm fasting an edge that other fasting methods don't have! It forces you to eat during daylight hours when your metabolism is functioning at its highest and to fast when it slows down at night. The key to this form of fasting is to eat larger meals at the start of your day and eat smaller and lighter meals at the end of the day. This will help you reap the most benefits. Speaking about health benefits, what even are they...
The effects of intermittent fasting are undeniable. Many claim to feel more energetic, focused, and even develop better eating habits which result in improving your immune system. But as we said earlier, circadian rhythm fasting has a bit of an advantage over other approaches to fasting, one of them being that you fast less than 14 hours! Aside from that, there are other health benefits you can reap by using this meal timing method, including:
- Weight loss:
Evidence suggests that following a circadian rhythm diet when combined with regularly working out and a healthy diet, can lead to weight loss.  Intermittent fasting is known to be effective at burning fat, especially when paired with a high-fat diet, but meal timing around the day and nighttime has the advantage of eating when your metabolism is at its highest and fasting when it's not, this reduces the risk of your body storing food as fat.
- Avoid late-night insulin spikes:
Insulin rises several times throughout the day, but an insulin spike at night (due to eating late at night) can disrupt your circadian rhythm. This can lead to an increased risk for health problems, including heart disease, obesity, and type 2 diabetes. Eating a carb-heavy meal late at night will spike your insulin levels during a time of day in which your digestion and body are resting. This can have a negative impact on a number of things, including your quality of sleep, mood, and energy levels, and can even cause negative eating habits that lead to weight gain. Unlike other intermittent fasting methods, circadian rhythm forces you to stop eating when the sun is down which will help you to avoid late-night insulin spikes that can be detrimental to your health.
- Improved digestion:
The circadian rhythm diet can enhance your digestion because it forces you to stop eating when your digestive system is "off".
- Increased energy:
Breaking an overnight fast in the morning when your cortisol levels are up, metabolism is up and running, and insulin sensitivity is high will lead to better energy levels. Your insulin response is much better in the daytime, so when you eat in the morning you pump out more insulin which tells your cells to store glucose. Glucose is responsible for controlling blood sugar levels and providing your cells with energy, thus giving you better energy throughout the day.
It's important to know that research surrounding intermittent fasting and circadian rhythm fasting is still in the early stages. Despite studies showing great benefits, a lot of them are small and short-term. Don't let this discourage you from trying this fasting method! There is no denying that eating before bed can cause serious digestive issues and even weight gain. So, if this is something you struggle with and want to give fasting a shot then the circadian rhythm diet is your best bet because it requires only 12-14 hours of fasting, opposed to 16+, and it works harmoniously with your sleep/wake cycle.
How to start a circadian rhythm diet
There are no food rules surrounding intermittent fasting, there are no off-limit foods or a caloric/ food intake limit... However, if you want to achieve weight loss, other fitness goals, or simply want to reap the benefits of fasting, then you have to implement a healthy eating and training plan. You can't expect to get results if you're eating highly processed foods that are low on essential nutrients! So, remember to prioritize nutrient-dense foods along with working out 3-5 times a week (depending on your goals).
Aside from that, follow these tips to help you reap the most out of a circadian rhythm diet:
- Make your first meal the biggest:
Your metabolism is revved up and ready to convert food to energy in the morning, so within two hours of waking up have a big breakfast! But choose your food wisely. Your breakfast should consist of plenty of fiber, lean protein, and healthy fats.
- Eat fewer carbohydrates on your last meal:
Aim to have dinner before 7 p.m., or at least four hours before bed! Avoid foods that will disrupt your sleep and natural circadian rhythm, this includes starchy carbs, sugar, and anything processed. Stick to protein, healthy fats, and veggies for your dinner.
- Limit your snacking:
Snacking can easily lead to overeating in a short period, so aim to eat at most three nutrient-dense meals. Since this form of fasting requires a shorter fasting window, you'll have enough time in the day to have three meals. Making sure that you build nutrient-dense meals will help reduce your chances of snacking.
- Set a good morning and nighttime routine:
You don't want to negatively affect your natural circadian rhythm, doing that will throw your hormones out of wack. You want to eat with your natural sleep/wake cycles, and to do that you need to wake up and go to sleep around the same time every day. So, set a sleep schedule that works harmoniously with your eating schedule. Try to go to bed between 9-11 p.m. and wake up between 5-8 a.m. And make sure you're getting good, deep sleep by reducing artificial light at night and shutting off electronics an hour before bed! This will not only reduce sleepiness throughout the day but will also ensure that your muscles are recovering and repairing effectively for better growth.
In summary, meal timing around your circadian clock can have amazing benefits! Including, weight loss, improved sleep, energy, digestion, and so much more. Intermittent fasting is a hit or miss for many, but the circadian rhythm diet takes a different approach that works harmoniously with your sleep/wake cycle and only requires a 12-14 hour fast, making it a more sustainable fasting approach.