What is Intermittent Fasting and How To Use It for Weight Loss and Energy

By Raphael Sirtoli

Posted 2 years agoHEALTH

As more and more studies appear on the benefits of intermittent fasting, more and more people are partaking in it. And while it might seem a little bit intimidating if you’ve never tried it, intermittent fasting is actually nothing to fear and might actually become something you enjoy.
What is Intermittent Fasting and How To Use It for Weight Loss and Energy

What is intermittent fasting?

Intermittent fasting (IF) is a pretty simple concept — it refers to the idea of rearranging your eating schedule to allow your body to go anywhere from 12 to 16 hours without food throughout the day.

Typically, people eat anywhere from three to five times per day, that is generally three meals and a couple of snacks. When intermittent fasting, however, regimented meal times are eliminated and the “fasting window” is extended between meals. 

For example, a person who eats breakfast around 7-8am, lunch around 12-1pm and dinner around 5-6pm (with snacks in between) would stop eating after dinner (6pm). They’d then break their fast anywhere from 8am-10am depending on the length of their fasting window. 

For most people, the fasting window extends about 14-16 hours — roughly three times as long as people who don’t fast. However, there are no strict times on intermittent fasting so the length will vary from person to person.

What are the different ways to do intermittent fasting?

When it comes to intermittent fasting, there isn’t just one way to do it. We all vary somewhat in how we respond to fasting but we’re all able to do it and benefit from it. So finding and choosing the method that works best for your body is important. Here are a couple of the most popular ones.

  1. The 16/8 Method — This method restricts the eating window to a period of 8 hours and extends the fasting window to 16 hours each day. For some, the fasting window can range from 16-20 hours, further restricting the eating window.
  2. The 2-a-day – This pattern of eating is a great way to free up some time. Executives and entrepreneurs love it as they can get more work done. For example, it could mean having a 6-7am breakfast and an 8-9pm dinner.
  3. Alternate Day Fasting — It involves rotating between eating the classical 3 meals a day and fasting for the whole day on others. For example, eat normally Monday, Tuesday, Wednesday, Friday, and Sunday, but fast the whole day Thursday, and Saturday.
  4. The 5:2 Method — Here you’d eat normally five days a week but restrict calories to 500-600 the other two days.
  5. 24-Hours or OMAD — The 24-hour fasting or One Meal A Day method is simply having one meal every 24-hours. For example, eating dinner at 7pm and not eating again until 7pm the following day.

It’s important to remember that some methods of intermittent fasting are better than others and will elicit more desirable results or outcomes. There’s also quite a bit of margin for you to experiment and see what pattern of eating and fasting you feel best with. It’s crucial that it fits with your schedule. In fact, intermittent fasting should make your schedule easier to handle, not harder. It’s also important to listen to your body and see how it responds to IF before setting any precise way in stone.

Never push yourself to a point where you feel as though something isn’t right. However, keep in mind that if you’re eating used to eating three meals a day plus snacks, it’ll take some time for your internal body clocks to adapt to the new eating schedule – maybe a couple of days, or a week. In any case, an intermittent fast can be broken at any point if something feels off or your body isn’t responding how you want. If in doubt, start with smaller windows and gradually increase your fasting window as your body adjusts.

At Nutrita, we believe intermittent fasting is great standard practice to partake in. We suggest aiming for 2 meals a day, on average. This style of fasting usually sets you up for the 16/8 method by nature. But keep in mind that you should always listen to your body — some days you might feel satisfied with one meal, while others you may need to have a snack after a meal to feel good. In the end, it all balances out.

While all of the methods have their advantages and disadvantages, we don’t recommend the 5:2 method. The reason is that it’s hard to follow; getting your body on and off of the three meals a day pattern repeatedly is pretty stressful. We don’t want a method to heavily rely on discipline, as this is a limited resource.

We encourage people to eat when they are hungry and stop when they are full; we want you to really tune into your body and learn your hunger cues. This works when we fix our biology through proper eating rather than exerting will power.

How can intermittent fasting help with weight loss?

There are an abundance of studies showing favorable results for intermittent fasting in terms of weight loss, but why?

Here’s a little snippet behind how intermittent fasting works:

When your body is in the fed state, it operates differently to when it’s in the fasted state. That is, after you’ve consumed a meal, your body will absorb and metabolize what you’ve ingested in order to convert it to a readily available source of energy (ATP) capable of fuelling your cells.

Turning food into ATP is actually a pretty energy costly process! This is why you may hear people refer to the ‘rest and digest’ state and why people prefer to exercise on an empty stomach so that energy is directed to their muscles rather than their digestive system.

However, when you’re in a fasted state there is no ‘incoming energy’ to draw on. In this case, your body must draw from another pool — stored energy. When there is no circulating glucose to provide an immediate source of fuel, the body taps into liver glycogen stores (stored glucose) before it will tap into stored body fat.

If you’re following a strict ketogenic diet, however, liver glycogen stores will be lower than when on a standard diet, so you can tap into body fat stores more quickly and intensively. This ‘forced’ reliance on body fat is characteristic of both intermittent fasting and keto, making them excellent fat-loss tools.

Additionally, during the fasting window, we are doing two interesting things. First, we’re not taking in any calories for a specified period of time and thus forcing our bodies to rely much more on fat and less on glucose (carbs).

We still get all the glucose we need from the process of gluconeogenesis (creating glucose from protein and fat), a much more fine-tuned way of regulating our blood glucose than by relying on dietary carbs. Secondly, we extended fasting windows help ramp up a process called autophagy . This  ‘cleans out’ the body — i.e. gets rid of old, damaged or worn-out cells and structures. Think of it as your body recycling some of these parts to make room for new, more youthful ones.

Now that you understand how intermittent fasting works, here’s why it can be a great weight loss tool:

  • Accelerates fat loss. Not only does intermittent fasting reduce your feeding window such that you’re likely consuming fewer calories, but you’re also forcing your body to tap into fat stores to provide the body with energy, thus reducing your fat stores.
  • Calorie restriction independent benefits. Intermittent fasting is most probably the eating frequency our biology is most comfortable with. A study looked at alternate day fasting (a kind of intermittent fasting) found that insulin levels and measures of insulin resistance were more improved in the alternate day fasting group compared to the classically calorie restricted group.
  • Weight-loss independent benefits. Intermittent fasting isn’t just about losing fat but also about feeling better and having better blood markers. One study found that cardiometabolic markers improved in the early time-restricted feeding group (a kind of intermittent fasting) who ate within a smaller eating window (6 hours) compared to other one eating within a more extended window (12 hours).
  • Improves glucose uptake efficiency and insulin sensitivity. Intermittent fasting helps to increase insulin mediated glucose uptake rates into tissues that are able to use it for fuel, for example muscle. It also helps to decrease and/or normalize certain biomarkers that are associated with chronic diseases, like insulin and glucose. Fat fasting is also a great way to improve insulin sensitivity, as well as deepen the extent of ketosis if you have also chosen to follow the ketogenic diet.
  • Normalizes/decreases appetite. When your body is running off of your main energy store, body fat, rather than frequently incoming glucose carbs, your body is using a stable and well-regulated supply of energy. Intermittent fasting has been shown to help people eat less in the evening, as well. As the day proceeds, our metabolic responses to incoming food aren’t as favourable compared to earlier in the day. As such, it may, therefore, be healthier to increase food consumption during the day when our bodies can metabolize and use energy more efficiently.
  • Improves athletic performance. While it may not seem like a method of ‘weight loss,’ it’s obvious that an improved ability to exercise contributes to improved body composition and improvements in general health status (especially mental health). Studies have shown that working out in a fasted state leads to better metabolic adaptations (increased training stimulus), higher sensitivity to growth factors (muscle synthesis) and improved metabolic responses to post-workout meals, which are critical for recovery. With that said, when our bodies are able to be more efficient during workouts and recovery, we can train better, harder, and see more improvements in body composition.

It’s also crucial to understand that physical appearance isn’t always a marker of health. Someone may look thin or in-shape on the outside, but internally, they’re on par with someone who is obese; essentially they are ‘metabolically obese.’

For this, we use the term “skinny fat,” and it’s just as dangerous, if not more, as being physically obese. If you think this maybe you, partaking in intermittent fasting, and possibly following a ketogenic diet, can be a great tool to get yourself out of the skinny fat rut and onto a healthier track.

How can intermittent fasting increase your daily energy levels?

Often times, you hear people who follow a standard American diet (SAD) complain of feeling lethargic, fatigued, bloated, foggy-headed, and the like. The quality and type of food you’re eating, among a few other factors, play a significant role in why people feel like this. 

You can think of your body, or your metabolism more specifically, as functioning a bit like a car. When you put fuel into a car, the engine burns it to allow the car to move. We fuel (feed) our cars (bodies) with food but essentially have two engines — one that runs on glucose and one that runs on fat and ketones. 

If you give the body sugar (from carbs) it will burn that before it burns fat. This is known as oxidative priority. Sugar acts as an immediate source of energy. However, if you deprive the body of glucose, as with the keto diet and IF, it will shift over to burning fat to provide energy. Thus, when insufficient glucose is coming in through diet, the body can easily switch over to burning body fat without experiencing any nasty side effects and a drop in blood sugar.

When we run primarily on the sugar-burning engine and we don’t refuel with sugar multiple times a day, our blood sugar drops and we experience the symptoms associated with hypoglycemia — mood swings, fatigue, hunger, irritability, shakiness, etc.

This is a vicious cycle that will continue until wearing habits are changed: you eat, your blood sugar and insulin spike, you have a bit of energy, and then you crash, which leads to irritability, ‘hanger,’ and more cravings for sugar. Long-term, this leads to weight-gain, low energy, fatigue, high cholesterol, insulin resistance, and adrenal fatigue.

After all, our stored form of sugar (glycogen) is tiny compared to our stored form of fat (adipose tissues), so it’s not that surprising that we have better energy levels when relying on fat than on carbs.

So how do you avoid the sugar roller coaster? Train your body to burn fat for fuel.

When our bodies burn fat – or ketones, which derive from fat – instead of glucose, one of the two main side effects we experience is more stable and even increased energy levels.

This is partly because fat is the most energy-efficient and energy-dense fuels available to our body. Since our brain needs a significant amount of energy to function, our brains love to function on a fat-fuelled system. When our glucose stores are low, the brain is able to function at its best given its preferred fuel requirements. Thus, a brain that can function optimally means a body that is energized.

The other side effect we get from intermittent fasting is stable blood sugar levels and appropriately low insulin levels. When we’re constantly bombarding the body with food, particularly with sugars and flour products, our blood sugar levels are constantly spiking and dropping as is our insulin, effectively wreaking havoc on our energy levels.

By removing the blood sugar spikes as well as the large and frequent insulin spike we experience when eating refined carbs from, we essentially stabilize energy levels. We’re no longer getting those highs and lows that we usually experience when following SAD (standard American diet).

Should you combine keto with intermittent fasting?

Realistically, keto and intermittent fasting go hand in hand, so the answer is YES! If you’re just starting out with keto and haven’t quite got yourself into ketosis, intermittent fasting can do wonders to get you there just a little bit quicker. 

While fasting alone is a great practice, there is a chance that it might not be enough to get your body producing the optimal level of ketones. Think of it this way: if you’re doing intermittent fasting to burn more body fat in order to lose weight, but your meals are carb-heavy, you’re likely engaged in an uphill battle.

On the other hand, if you’re doing keto and so refeeding after fasting with nutrient-dense high-fat foods, your body essentially has no choice but to use the fat to fuel your body. This glucose restriction allows the body to get into ketosis that much quicker than when you’re following SAD.

The great thing about keto and intermittent fasting is that when following a ketogenic diet, people naturally tend to extend their fasting window due to its highly satiating nature. So if you’re already keto, you may find fasting quite easy. This is because our body already knows how to burn fat and ketones for fuel.

So rather than switching between burning fat and glucose, the body relies on one main source of energy — fats and ketones. Don’t worry though, you remain perfectly capable of burning glucose as the body needs; this is the premise behind metabolic flexibility.


Whether you’re looking to increase your energy, improve sleep, lose body fat and/or weight, or improve your athletic performance, intermittent fasting is a great method to try out. While it may seem slightly daunting at first, there’s no need to be afraid of it.

As each individual is unique, there’s a different type of IF that will suit your lifestyle and your body’s needs — the 16/8 method, OMAD, 2-a-day, 5:2 or alternate day fasting.

Regardless of the type, you partake in, you’ll reap all the amazing benefits that intermittent fasting has to offer. And if you’re already following keto, IF should slide into your eating schedule with no problems. Just remember, each body is different and therefore each body will react and adapt differently, so ease into it, experiment, and see how it works for you.

About the author Raphael Sirtoli

Raphael Sirtoli has an MSc in Molecular Biology and is a PhD candidate in Neuroscience at the Behavioral n’ Molecular Lab in Portugal. He is the co-founder of Nutrita, a Health & Nutrition app helping people reach their goals with a well formulated low-carb or keto diet. He loves open scientific debate, Crossfit, football, hiking and cold water immersion.

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