Intermittent Fasting Stages And What You Should Expect [Hour-By-Hour]
Updated: Jan 20
If you're new to Intermittent Fasting, you're probably wondering what you should actually expect, hour-by-hour, with Intermittent Fasting. In other words, what are the Intermittent Fasting stages? When do you burn fat, when should you eat, when should you stop?
Today, I'm breaking down the details of what's happening in the body at each Intermittent Fasting stage and what you can expect.
What Are The Stages Of Intermittent Fasting?
Intermittent Fasting is broken down by whether or not you're eating. When looked at with this perspective, Intermittent Fasting can really be broken down into just two stages: fasting and feeding. But in order to understand exactly what's happening while you're using Intermittent Fasting for the first time, I've broken down the first 48 hours of Intermittent Fasting into 5 stages.
Stage 1: 0-12 Hours (Fasting)
The first stage of Intermittent Fasting is your first eating window. This begins with the last bite of food that you took the night before. For example, if you stopped eating at 7pm on Friday, your first 12 hours of fasting will take you to 7am Saturday morning. As you can probably see, for most people, this first 12 hours of fasting might not be too different from your current routine. Around 8 hours of your first fasting window is when you're sleeping, so this first 12 hour fasting period should be fairly simple. Not to mention, naturally higher levels of cortisol (our stress hormone) in the morning helps to increase energy levels without needing to eat breakfast right away.(1)
However, the real perks of Intermittent Fasting begin after you have fasted for 12 hours. This is where stage 2 of Intermittent Fasting begins...
Pssst - wondering what type of fasting is best for your goals? Click below for my free Intermittent Fasting Schedule quiz to find out!
Stage 2: 12-16 (Fasting)
Around 12 hours of fasting is when your body starts to ramp up fat burning. Anytime insulin (our storing hormone) levels drop, the fat burning process called lipolysis kicks in. And insulin levels tend to naturally decrease when we stop eating (aka while fasting). During this time, your cells also start to "clean house" through a process called Autophagy. With autophagy, the body gets rid of dysfunctional mitochondria (energy systems within cells) to make way for new, higher functioning ones.(2) In fact, this cleaning process even appears to be happening in the brain!(2) This is likely why so many people explain that they experience increased energy levels with Intermittent Fasting.
Autophagy benefits increase the longer you fast, but daily short term Intermittent Fasting bouts appear to have these "house cleaning" perks with your cells as well.
During this phase, your body turns on another cleaning process called the Migrating Motor Complex, aka the MMC. This is one of my favorite perks because this process helps to reduce bloating. The MMC cleans out your GI tract of left behind food and bacteria that would typically lead to fermentation and bloating. The MMC only turns on when we're not eating for at least 3 hours and 45 minutes.(3)
However, if you're new to Intermittent Fasting and you find that you're getting hungry during your eating window, you can still receive the fat burning perks of your fasting period (with a lesser autophagy and MMC perk) by sipping on Keto Coffee or Keto Tea. Because it doesn't contain any protein or carbohydrates to spike insulin, this fat burning drink can still keep your body in a state of lipolysis (aka fat burning) without feeling hungry.
Stage 3: 16-24 Hours (Eating)
A common eating window is an 8 hour eating window. This allows you to get 2-3 highly satiating meals within your window to support your weight loss and wellness goals. But you don't need to have an 8 hour eating window. In fact, something I teach in the Complete Intermittent Fasting Bundle Program is the importance of choosing an eating window that fits your lifestyle and schedule. Otherwise, you won't be able to reap the benefits long term if you can't maintain a schedule that works for you.
During this "eating window", your body is no longer fasting. You're now breaking down and absorbing nutrients. This means autophagy and the MMC are turned off. During this eating window, it's crucial to be getting enough protein, fat and fiber to trigger satiety hormones and prevent hunger during your next fasting period. Amino acids from the protein you eat will also be used to repair muscles from a workout earlier in the day.
Stage 4: 24-40 Hours (Fasting)
Once you've finished the last bite of your last meal, you have now begun your second fasting window. The amount of time you fast will depend on the length of time you choose to have as your eating window. Exercise can also be utilized during your fasting window. In fact, as we know, fat burning is turned on during the fasted state, so exercising during this time can help your body directly use fat as fuel. However, it's extremely important that you slowly ease back into exercise. You can check out my step-by-step details on exercise and Intermittent Fasting with my article below.
Stage 5: 40-48 Hours (Eating)
In this final stage of Intermittent Fasting, we're now at your second eating window. If you found that the previous day's meals were not satiating enough for you, you can tinker with the amount of protein, fat and fiber in your meals in order to adjust your intake to your needs. Some days you might find that you need a bit more protein or fat because you had an intense exercise earlier in the day. Others you might find that you don't need as much. It's important to take it day-by-day and reassess how you're feeling so that you can continually provide your body with the nutrients it needs in order to maintain fat burning and achieve your wellness goals.
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Autumn Elle Nutrition