As more and more studies appear on the benefits of intermittent fasting, more and more people are giving it a try. People are using intermittent fasting for weight loss among other benefits. If you’ve never tried it, it might seem a little intimidating at first, but intermittent fasting is actually nothing to fear. In fact, it might become something you enjoy once you start reaping the myriad of benefits.
What is intermittent fasting?
Intermittent fasting (IF) is a pretty simple concept — it shortens your eating window and lengthens your fasting window. It basically rearranges your eating schedule to allow your body to go anywhere from 12 to 18 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 snacks. When doing intermittent fasting however, regimented meal times are no longer rule your way of eating, and the “fasting window” between meals is extended.
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 doing intermittent fasting, the fasting window extends to 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.
5 different ways to do intermittent fasting?
There isn’t just one way to do it to do intermittent fasting. It lends itself to a wide variety of schedules compared to the typical eating pattern of +3 meals given the longer fasting windows. We all vary somewhat in how we respond to fasting but we’re all able to do it and benefit from it. So choosing the method that works best for your body is important. Here are a couple of the most popular ones.
- 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.
- Breakfast n’ Dinner – 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 during working hours. For example, it could mean having a 6-7am breakfast and an 8-9pm dinner. It even gives you time for a quick workout after work, before sitting down for dinner.
- 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.
- The 5:2 Method — Here you’d eat normally five days a week but restrict calories to 500-600 the other two days.
- 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 deciding which way is best. Test and adjust.
Never push yourself to a point where you feel as though something isn’t right. However, keep in mind that if you’re 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 interrupted at any point if something feels off or your body isn’t responding how you want. If in doubt, start with smaller fasting windows and gradually increase them as your body adjusts.
Is there a normal eating pattern and frequency that everyone should aim for? It won’t be possible to derive a universal rule, but aiming for 2 meals a day, on average, leaves your body with lots of time to derive the benefits of the un-fed (aka low insulin) state. This style of fasting usually sets you up for the 16/8 method by nature. But keep in mind that you should learn to listen to your body in order to distinguish cravings from hunger — some days you might feel satisfied with one meal, while on others you may be genuinely more hungry and will have a small additional meal to your usual two. In the end, it all balances out.
While all of the methods have their advantages and disadvantages, 5:2 method is not one we recommend. This is because it doesn’t truly get you away from the regimented 3 meals a day. It’s on-again off-again pattern will require a lot of discipline. 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, something that’s much easier to accomplish when eating food steak and avocado instead pizza and donuts. We want you to really tune into your body and learn your hunger cues. This works when we fix our biology through proper choosing quality foods, eating them not too regularly and timing them appropriately, rather than exerting will power as a first resort.
How can intermittent fasting help for 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 for weight loss:
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. This business of turning food into ATP is actually pretty costly in terms of energy! 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.
What, when and how much you eat impacts your ‘readiness’ to exercise and be mentally on point.
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, also known as fat stores. When there is no circulating glucose to provide an immediate source of fuel, the body taps into stored glucose, found in the liver as glycogen. This happens before you tap into stored body fat located in fat tissue all throughout the body. 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. People on a ketogenic tend to feel like they’re appetite is improved  and that they no longer crave a third meal. This naturally puts you into a pattern of intermittent fasting.
Furthermore, 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 our bodies making it for us, through the process of gluconeogenesis (creating glucose from protein and fat). It’s a much more fine tuned way of regulating our blood glucose than by relying on eating fast-absorbing dietary carbs. Secondly, we extended the fasting window that is too short, now more fully benefitting from a process called autophagy . This ‘cleans out’ the body — i.e. gets rid of old, damaged or worn-out cells and structures which would otherwise accumulate and damage us. Think of it as your body recycling some of these parts to make room for new, younger better functioning ones.
Now that you understand how intermittent fasting works, here’s why it can be a great tool for weight loss specifically:
Accelerates fat loss. Not only does intermittent fasting reduce your feeding window such that you’re likely lower your excessive calorie intake, but you’re also forcing your body to tap into fat stores. Tapping more fully into fat stores carries additional metabolic benefit, on top of the obvious reduction in 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 who ate the same amount of calories .
Weight-loss independent benefits. Intermittent fasting for weight loss isn’t just about losing fat but also about feeling better and having better blood markers which can predict disease risk. 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 optimize the levels of 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 fast-absorbing 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 favorable 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 an improved body composition in terms of muscle-to-fat ratios and general health status (especially mental health). Indirectly, these benefits in other areas of lifestyle could help improve weight-loss goals (e.g. better sleep). Studies have shown that working out in a fasted state leads to better metabolic adaptations (increased training stimulus) and improved metabolic responses to post-workout meals, which are critical for recovery [9,10,11]. 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 – it certainly counts, but it must be contextualized with other measures, such as symptoms (e.g. headache) and blood markers (e.g. fasting blood glucose). 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 may be you, partaking in intermittent fasting, possibly following a ketogenic diet and especially resistance training, can be great tools to get yourself out of the skinny fat rut and onto a healthier track. That way intermittent fasting for weight loss works for you.
Are there any dangers or side effects?
There are no inherent dangers to intermittent fasting for weight loss, but when you do it as someone coming from a standard American diet and lots of medications, the combination does require some caution which a knowledgeable doctor can help you navigate. Intermittent fasting can lower your blood pressure, blood glucose and blood insulin levels such that medications affecting all of these levels can be adjusted accordingly. Intermittent fasting may also cause slight diuresis at first, which can flush out certain electrolytes. If you’re metabolically inflexible, you will most likely go through this so-called ‘keto flu’ or ‘fasting flu’. This happens upon withdrawal of most dietary carbohydrates from your diet – especially fast-absorbing refined carbs. This extended fasting window is, in effect, a low-carbohydrate and low-energy state. If you’re already quite metabolically flexible, you’re less likely to experience these adaptation effects.
In rare cases such as people with rare fatty acid oxidation mutations, any way of eating that increases reliance on fatty acid oxidation like extended fasting windows or ketogenic diets are not recommended.
About The Author:
Raphael Sirtoli is the co-founder of Nutrita, a website helping people grasp cutting-edge nutrition science. Nutrita is also a mobile app that helps people follow well-formulated low-carb diets as well as reach their health and performance goals. Raphael has an MSc in Molecular Biology and is currently pursuing a PhD in Health Sciences at the University of Minho. His day job however is neuroscience research at the Behavioral n’ Molecular Lab where he studies the metabolic effects of antipsychotics in rodent models of schizophrenia. His understanding of metabolism, nutrition and clinical medicine forms the base upon which Nutrita derives its evolving knowledge. He loves open scientific debate, Crossfit, football, hiking, psychedelic medicine, cold water immersion and cooking for loved ones.