Intermittent fasting has gained huge popularity in the past few years, and in my own opinion, it is for a good reason.
Unlike other diets or diet fads with strange or arbitrary rules, intermittent fasting isn’t really a diet at all. With my own words, I would describe it as smart way or strategy to manage your calorie intake whilst gaining some great additional health benefits. You could call it a lifehack.
There is a lot of people on the internet providing information on intermittent fasting and some of the information is exaggerated and hyped.
This is especially true when it comes to losing weight.
In this post, I will refrain from doing that, and I will instead do my best to relay what is backed up by science and research on intermittent fasting and weight loss.
The Cause Of Weight Loss
No matter what, when or how you are eating, gaining or losing weight is essentially a question of energy balance. In order to gain weight, you need a calorie surplus, and in order to lose weight, you need a calorie deficit.
There are of course other factors that influence weight loss and can make things more complicated, especially whether the weight loss includes muscle or not, but that should not distract you from what is by far the most important thing – the calorie deficit.
What Is Intermittent Fasting?
As mentioned intermittent fasting is not really a diet because it is not related to what you eat, but it is instead related to when you eat. Technically it is an eating schedule or pattern that cycles between periods of fasting and periods of eating.
There are different variations of intermittent fasting, some more popular than others. Below are three of the variations I believe to be most popular.
Fasting 16 Hours Followed By 8 Hours Of Eating (16:8)
This is by far the most popular way to do intermittent fasting, probably because it is relatively easy to implement. Simply skip breakfast and eat a late lunch every day. E.g. your last meal in the evening is at 20.30 and your first meal next day is at 12.30.
Meal frequency doesn’t matter, but since you are eating in a “window” of 8 hours it will probably not be more than 2-3 meals.
This way of doing intermittent fasting was popularized by Martin Berkhan (Leangains). Martin Berkhan also recommends structuring meals according to the time of training and cycling carbs and fats. This means you should have a higher carb intake on training days and a higher fat intake on non-training days.
A modified version that can be described as more relaxed was arguably later popularized by Greg O’ Gallagher (Kinobody). Again it is about skipping breakfast, but being looser regarding the 16:8 hours’ structure and simply focus on pushing the first meal as late into the day as comfortably possible.
Fasting 24 Hours Once Or Twice A Week
This method is definitely tougher, but instead, it is only once or twice a week. The other days you eat normally.
E.g. your last meal in the evening is at 20.30 and your first meal the next day is again at 20.30.
For fasting beginners, it is recommended that you start out with fasting fewer than 24 hours and then slowly work towards the full 24 hours as you become more familiar with fasting.
This method was made popular by Brad Pilon in his book “eat stop eat”.
“Fasting” 20 Hours And Eating 4 Hours
Also known as the warrior diet by Ori Hofmekler, this method is technically not fasting. It instead a period of undereating for 20 hours and then a period of overeating for 4 hours.
The key to this is eating very light in the day and not get a lot of calories. You could eat a few servings of fruit or vegetables or a bit of protein. This should ensure that you are kept highly alert and focused.
At night you would then eat the large majority of your calories in a 4-hour eating window.
According to Ori Hofmekler, the ideal eating order in the 4-hour window is first to eat vegetables, protein, and fat. After that eat your carbohydrates, but only if you are still hungry.
This method can be great if you find the ability to snack on some fruits helpful, but you sacrifice the health benefits from fasting which first starts kicking in after not consuming any calories for about 10-14 hours.
Health Benefits Of Intermittent Fasting
In the past few years, many studies have been conducted on intermittent fasting. Perhaps the reason is the increased popularity of intermittent fasting.
Below you will see a list of the major benefits which research has given evidence to, but please understand that the more thorough research of intermittent is still in its early stages.
All these benefits first start kicking in when you are in a fasted state which your body normally enters after 10-12+ hours after last meal.
- Human growth hormone (HGH) skyrockets benefiting muscle gain/retention.
- Insulin levels drop which makes burning body fat easier. There is some proof that this can help burn “stubborn” body fat.
- Increased release of the hormone noradrenaline which it easier for your body to convert fat into energy and also makes you generate more body heat
- Can help reduce insulin resistance protecting against type 2 diabetes
- Stabilizes blood sugar
- Cells start repairing themselves and recycle materials. A process called autophagy.
- Changes to genes that promote longevity and protection against diseases.
- Some studies have shown reduction of inflammation
- Possible reduction in LDL cholesterol
- Lowering insulin resistance, LDL cholesterol and inflammation can help improve heart health.
- Intermittent fasting has been shown to extend the lifespan of rats and it is therefore to have an anti-aging effect
- Increases in the brain hormone (BDNF) that may aid in the growth of new nerve cells.
TL;DR: Intermittent fasting results in a number of changes to hormone levels, cell functions and gene expressing that are proven to have benefits to overall health. It makes it easier for your body to burn fat, and actually slightly increases your metabolic rate. Additionally, depending on your current health these changes give rise to potential benefits to heart, brain and cellular health and is possibly anti-aging.
Intermittent Fasting For Weight Loss
When we are talking about losing weight, it is important to distinguish between weight loss and fat loss. As I point out in my other post, you should always be focused on fat loss and not just weight loss. The truth about weight loss not everyone is telling is that it is very likely to include your muscle mass unless you are smart about your diet and training.
Intermittent fasting has been proven in studies to be a successful weight loss tool and to be especially good for burning fat since the participants saw a significant drop in waist circumference which is an indicator of losing fat rather than muscle.
To understand why intermittent fasting can be a good tool to help you burn excess body fat, you have to understand how insulin levels affect your body’s choice of fuel source. Your body can either burn glycogen (carbs) or ketones (fat) as a source of energy. Described very simple (I will talk more about insulin another time), as long as insulin levels are high your body wants to burn glycogen.
When you have consumed a meal your body immediately starts digesting and absorbing that meal which usually takes about 3-5 hours. This is technically referred to as the fed state and this is where insulin levels peak.
After your body has processed the food insulin levels start declining. The body is now in what is referred to as the post-absorptive state which lasts for 10 – 12 hours after last meal. It is after that time your body finally enters was is known as the fasted state. In this state insulin levels are low enough that your body is able to burn fat as fuel easily.
Because of the traditional meal frequency, most people rarely enter this optimal fat burning state, and that is why intermittent fasting can be a very useful fat loss tool.
There is even some evidence that some fat storages in the body are hardly accessible at all until insulin levels are low. This could be fat storages like your stubborn belly fat.
There is also the fact that intermittent fasting slightly increases your metabolic rate
This is not the same as saying that intermittent fasting will magically help you burn a ton of calories, but it does indeed have an effect.
As I pointed out in the beginning, gaining or losing weight is a question of energy balance. Fasting doesn’t break basic physics.
Intermittent Fasting And Muscle Loss
A calorie deficit no matter what the cause is very likely to cause muscle loss unless you take the right preventive measures. It is very important to lift weights and get enough protein and fat.
However, there is a study indicating that a calorie deficit done together with intermittent fasting causes less muscle loss than a calorie deficit without intermittent fasting likely due to the huge rise in human growth hormone.
Tips On Doing Intermittent Fasting For Weight Loss
Drink plenty of water throughout your fast. Keeping hydrated is super important, it helps flush out toxins which might increase when fat is used as a fuel source (your body likes to store toxic stuff in your body fat).
Also, when you are not eating you are missing out on liquids from food. Hunger and thirst can easily be mistaken, and keeping hydrated will prevent this. Additionally, drinking excess fluids can help suppress hunger but should not be overused as it will lead to having to go to the toilet a lot, also taken to the extreme it can be unhealthy.
Schedule a part of your fasting overnight. It is much easier to fast when you are sleeping and not thinking about food.
Work on your mindset towards eating and familiarize yourself with the difference between physical and psychological hunger.
Physical hunger being the “real hunger” which usually always arises gradually but can be postponed easily. With psychological hunger, I mean the hunger that is spontaneous e.g. you suddenly become hungry because it is 1 pm and your usual time for lunch, or because you watch other people eat. In eat stop eat fasting is reframed as simply having a break from eating.
While fasting keep yourself busy with tasks that require a high level of focus and cognitive function. You will be surprised by how easy you can “forget” that you are hungry when focusing on other things and you will reap the benefits of higher alertness and focus that comes from fasting.
Do strength training, ideally full-body heavy weight training to avoid muscle loss. Check out my two posts on why weight training for weight loss is best and how to use weight training to lose weight.