As the name suggests, intermittent fasting (or IF for short) is a technique that involves abstaining from food for various periods of time. The idea goes against conventional wisdom for health and weight loss - yet it remains a popular (and effective) technique.
What is Intermittent Fasting?
Unlike most lifestyle and diet approaches, intermittent fasting isn't about what you eat instead it is all about when you eat.
Specifically, you're choosing to not eat for specific times or days. There are many variations - which we'll go into later on. But first, let's look at how intermittent fasting can help you.
We've long been told that being hungry is a bad thing - including the idea that it can slow down metabolism and put us into 'starvation mode'.
Yet, research suggests that fasting can be powerful because it promotes autophagy.
This process is promoted by hunger, so it occurs more often when people fast. Indeed, research has highlighted a range of key benefits that occur in the body during fasting, including the following:
Intermittent Fasting and Weight Loss
Intermittent fasting does offer health benefits - but most people follow it as a way of promoting weight loss.
Not only does intermittent fasting help with weight loss but many people actually find it easier. One reason is that you're eating over a smaller time period, which naturally reduces the number of calories you consume.
For example, if you do 16:8 intermittent fasting, there is only an 8-hour eating window each day.
You're unlikely to get three full meals plus snacks in that period. Instead, some people eat smaller meals, while others may have two large ones instead.
Either way, your calorie intake ends up naturally lower. You also lower snacking as a side effect, along with many bad eating habits. For example, there is less temptation to snack during a movie if it is outside of your eating window.
In fact, the patterns of intermittent fasting mean that you'll often lose weight without changing the type of food you eat or how many calories you have in a given meal.
That's a major advantage.
The role of intermittent fasting on weight loss isn't just behavioral either. Instead, fasting has some direct benefits for weight loss. The ability to boost human growth hormone levels is one aspect (15) and lowering insulin is another (16,17,18). Short-term fasting also releases a specific hormone, called norepinephrine, which is thought to increase fat burning (19,20).
What About Metabolism?
The largest argument against intermittent fasting is the potential impacts on metabolism. In particular, fasting is meant to slow down the metabolism, making it harder to lose weight. That pattern was why eating 5-6 small meals a day became so popular for a while.
And yes, dramatically restricting calories in the long-term will slow your metabolism.
But, that's not the same as intermittent fasting. After all, intermittent fasting typically means your fasting a day at a time, or less. For that matter, the 16:8 variation isn't dramatically longer than the overnight fast that we normally do.
Additionally, even if there are undesirable metabolism impacts, they're likely to be very small. As a result, any negative aspects would be outweighed by how intermittent fasting promotes weight loss.
It's clear that there are benefits to intermittent fasting, especially for weight loss. But, there are a few additional topics to mention.
First of all, intermittent fasting does make it harder to get enough nutrients. After all, you're eating over a shorter span of time. This can also mean you're eating two meals instead of three. As a result, you have to plan around that issue and make sure the meals you do eat are nutrient dense.
Options like bone broth and red meat are key ways to do so, as are healthy fats and protein. Likewise, you often need to train yourself to have larger meals, to help ensure you get enough nutrients.
That pattern is particularly important for maintaining lean body mass and you need to be sure that you're getting enough protein. Doing this is achievable but it will typically take some planning.
Even if you're eating large enough meals and aren't short on nutrients, intermittent fasting can come with some side effects. For one thing, some people simply don't fare well when they are hungry. This could result in headaches, poor mood, low energy, difficulty concentrating and similar problems.
In many cases, such issues would decrease as you got used to the diet. However, that won't be true for everybody. Instead, some people are low on energy, hungry and cranky the entire time.
Sure, you could push through that. But, you're better off finding an approach that matches your needs.
Intermittent fasting can also cause problems for women. This happens because fasting will affect hormones, potentially leading to hormonal imbalance. The issue doesn't affect everybody but it's important to be aware of.
As a result, you can turn to the following resources for more insight into intermittent fasting for women:
At present, the research into fasting for females is fairly sparse and it's hard to know what the precise effects will be. Because of this, the best answer is to pay attention to your body and the way that it responds when fasting. Honestly - that's what you should be doing anyway.
Types and Variations of Intermittent Fasting
Intermittent fasting is a highly personalized approach, with countless options. After all, people have different needs than one another and biological responses also vary. The styles below are all different examples of ways to approach intermittent fasting.
However, you can also vary these based on your own needs and lifestyle. For example, many people do a style of intermittent fasting that basically involves skipping breakfast and eating lunch and dinner roughly as normal. The approach can be easy to achieve, especially if you don't like breakfast.
Some of the most common styles are as follows:
16:8 Intermittent Fasting
This style is also called daily intermittent fasting or the Leangains model.
Here, you're fasting each day. Doing so typically involves an 8-hour window where you eat and a 16-hour fast.
Precisely when you eat and fast is up to you, although the idea is to remain consistent each day.
One common approach is to skip breakfast and have your first meal around noon. After that, you could eat until 8pm. Missing breakfast like this suits many people, as breakfast is the least social meal.
But, you can tailor the idea as you please - making it perfect for anyone with unusual sleeping patterns.
Even though this sounds tough, 16:8 intermittent fasting is very easy to get used to. After all, it's just a slight variation on regular eating patterns. For many people, this is the best way to get started.
The time factor can also be varied. For example, some people do a 18:6 alternative, where they have a longer fasting period. Alternatively, women will often choose a longer faster window, such as a 14:10 ratio of fasting to eating. So, you can choose the window that suits you best.
Weekly (or Monthly) Fasting
This style involves a longer fast but less frequently. So, instead of fasting every day, you're doing a 24-hour fast every week or every month. The most common way to achieve this is to start at noon one day and go to noon the next, meaning you still get at least one meal every day.
This type of fast does offer benefits, including many of the ones discussed earlier. However, it is less relevant for weight loss. After all, you're not decreasing your food intake all that much.
Once again, you can make your own variations, such as increasing the length of the fast or the specific times that you fast to and from. Another variation is 5:2, where you would fast two days each week and eat normally the other five days.
Alternate Day Fasting
Alternate day fasting can be considered a step up and it works like the name suggests. With it, you're fasting on alternate days - typically three days a week.
So, you may be fasting on Monday, Wednesday and Friday, then eating normally the other days.
Because this style involves a longer fast, it takes time to adjust to.
Theoretically, doing so offers more benefits, as you're in the fasting state for a longer period of time. On the other hand, there are more challenges too and any negative effects (such as low concentration) are likely to be more pronounced.
This version is fairly common in research but it doesn't seem to be done much in practice.
One reason is that it is harder. It takes much more planning to miss food for 24 hours at a time and still get the nutrients you need. The pattern has social limitations as well, especially if you follow it strictly. As a result, it might be impractical in many situations.
Bulletproof Intermittent Fasting
The Bulletproof variation is a little different because it isn't strictly intermittent fasting. Basically, it is a form of the 16:8 approach, where you are having Bulletproof coffee in the morning - rather than nothing.
You can have black coffee on regular intermittent fasting but Bulletproof coffee is a little different. This is coffee that uses butter or ghee, along with either coconut oil, MCT oil or Brain Octane Oil.
Doing so leads to fairly calorie-dense coffee that is great for energy.
In terms of intermittent fasting, the coffee will break your fast, so you lose some of the benefits. It may also be less effective for weight loss, as you're consuming more calories.
But, the idea does work well for people who struggle with regular intermittent fasting, particularly for women. As such, it is another option, although it's better to try intermittent fasting itself first.
Intermittent fasting is all about when you eat. But, the food you choose is still relevant. For one thing, you do need sufficient nutrients. You also want to be eating healthy food overall. As a result, intermittent fasting is often combined with other diet and lifestyle approaches.
A common example of this is the ketogenic or ketosis diet. With ketosis, you're dramatically cutting down carbs and obtaining most of your fuel from fat.
Many people find that ketosis naturally fits with intermittent fasting. In fact, intermittent fasting can make a ketosis diet easier (and vice versa).
There are also some powerful guides that show you how to combine the two and why you may want to.
It is worth reading these in depth if you're considering ketosis and intermittent fasting. The combination is effective but there are additional considerations, especially as ketosis has significant impacts on your energy source and on metabolism.
I have also seen intermittent fasting on other diet approaches, such as paleo and a low carb non-keto diet. Some examples of guides are below:
Overall, the principles of intermittent fasting are easy to apply to any diet.
Personalizing Intermittent Fasting
As all of these areas show, intermittent fasting is a very flexible approach. You can basically combine it with any type of diet, along with informal eating patterns.
Likewise, you can choose from the various styles like daily, weekly and alternative day fasting. Plus, you can tweak your eating times and days based on your own needs.
You can also choose how strictly you want to follow the diet. There are no set rules.
Some people choose to follow their eating periods rigorously, never eating outside of them regardless of the circumstances. Others take a more relaxed approach. For example, if your eating period was 11am to 7pm and you were invited to a friend's place for beer and snacks at 9pm - you could still go and eat.
That's a personal decision and everybody is different.
Another change to consider is whether you do a true fast or not. If you completely fast during the non-eating periods, you will see many more benefits. But, some people do choose to do extremely low calorie days instead (such as 500 calories per day).
This is also the key advantage of intermittent fasting - you can heavily personalize the diet. This aspect alone makes it a realistic and achievable idea for many people.
Intermittent Fasting and Resources
Intermittent fasting is a little different than most other lifestyle approaches. After all, the diet is all about when you eat, rather than your specific food choices. As a result, there isn't the same avenue for amazing recipes and Pinterest food posts that there is for techniques like keto.
In a similar vein, there aren't many resources or sites that specifically focus on intermittent fasting. Instead, the topic tends to be a subsection. Nevertheless, a range of sites do talk about intermittent fasting to some degree and there are some great resources out there. Key examples include:
I would normally also feature products that help you with intermittent fasting.
But, to be honest, there aren't very many. Instead, you'd just be wanting products to prepare food and recipes, which is the same for any eating pattern.
If you plan to follow a specific approach along with intermittent fasting, then there may be more products to consider.
You can find more information about some of the key approaches in the list below:
For that matter, the best approach for intermittent fasting may be to think about your eating choices first. In particular, what lifestyle or diet do you plan on following? It doesn't need to be a strict approach but you do need to consider whether you're going to focus on protein and healthy fats as your primary energy source and whether you are going to decrease your intake of sugar and processed foods.
Intermittent Fasting Posts
You can find out more about intermittent fasting and its implications in the posts below.