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Intermittent Fasting

Posted on November 28th, by Gary in Diet, Featured. 65 comments

Intermittent Fasting

Intermittent fasting is a popular concept that involves periods of no food followed by a short eating phase. This method has been shown to be extremely effective in accelerating fat loss, normalising insulin sensitivity and improving your mental clarity.

From a paleo standpoint, our bodies have evolved to deal with periods of little or no food. Until the introduction of agriculture, this irregular eating pattern would have been the norm as there was no guarantee of food when hunting.

What is intermittent fasting?

The basics of intermittent fasting (IF) are that you alternate between a fasted state and a feeding window in which you eat your daily calories. This can be as simple as skipping breakfast in the morning or it may be a longer fast that lasts up to 24 or 48 hrs. There are many approaches to intermittent fasting, each with different fast/feed timings and varying diet restrictions. One of the the most popular ways of fasting is Martin Berkhan’s LeanGains method which uses a 16/8 hour fast/feed.

It goes against popular advice to skip meals but in fact humans genetically evolved with this way of eating. Our hunter-gatherer ancestors lived in unforgiving habitats where food was not guaranteed. This meant our bodies had to become adapted to periods without eating. It was likely that early man was regularly in a fasted state and the result is that our bodies are very good at storing body fat to cope with times when food is scarce.

In the Western world nearly all of us have access to food 24/7. People will also tell you we need small regular meals to feed your metabolism like some sort of coal fire. This constant pattern of feeding can lead to overeating and is well out of line with our evolutionary background. Intermittent fasting gives us an opportunity to engage our primitive eating habits and reap the rewards.

Benefits of intermittent fasting

IF has been shown to provide the body with a wide range of physical and cognitive benefits. These include:

  • Increased fat loss while retaining lean body mass
  • Improved fat burning and metabolic adaption with fasted training
  • Increased release of human growth hormone, essential for building muscle
  • Improved metabolic markers including reduced triglyceride and LDL cholesterol levels
  • Improved cognitive function and mental clarity
  • Normalised hunger levels
  • Reduced insulin levels and normalised insulin sensitivity
  • Reduced risk of heart disease
  • Reduced inflammation and oxidative stress
Emerging research in animals also indicate that intermittent fasting may help combat cancer, diabeties and aging.

Why it works

After eating, it takes around 6-8 hours for your muscles to use up reserves of muscle glycogen and turn to body fat as a primary fuel source. By fasting, we extend this period in which we are burning body fat. Giving our bodies a break from food makes it a lot easier to use fat as an energy source. Fasting will also reduce your body’s level of insulin hormone, high levels of which can block fat loss.

You get an additional fat burning boost from raised levels of catecholamine when fasting. These are the hormones that activate your body’s fight-or-flight response. An increase will raise your metabolism as your body prepares for physical activity, allowing you to burn fat more efficiently.

Which IF method should I use?

The first step in intermittent fasting is to decide what sort of timings you will use for your feeding and fasting windows. Some people like to use fasting spontaneously when they just don’t feel like they need to eat a meal. If you wake up one morning and can get by without eating then maybe try fasting till lunch or dinner. Other people prefer a more scheduled approach and will dedicate certain days a week to fasting. There are a few popular intermittent fasting methods you can try that include:

Each of the approaches is usually accompanied by some guidelines so if you’re interested in some further reading please check out the sites/books and experiment with a fasting style that suits you. The important thing is to remember there are no hard and fast rules and you don’t have to follow a “branded” approach. Pick something which fits well with your lifestyle, work commitments and goals.

Self experimentation is the most interesting and accurate way to discover what really works for your body. I’ve tried the Leangains method which I found to be really effective and consistent in results. I’m currently testing with some 24 hour fasts and want to try a 36 & 48 hour fasts in the near future. Experimenting with how and when you eat adds a whole new dimension to your diet rather than just focusing on what you eat.

During the fasting window, the general consensus is this should be a zero calorie period. Water, green tea, black tea/ coffee are all OK. There are a few notable exceptions. Dave Asprey from The Bulletproof Executive starts the day with a Bulletproof Coffee as part of his Bulletproof Intermittent Fasting. Paul Jaminet of Perfect Health Diet also advocates coconut oil and bone broth during the fasting period.

With the first few times you try fasting it’s not uncommon to get feelings of hunger, irritability or sluggishness. This is a physiological and psychological response to skipping a regular meal. I found that my hunger pangs were controllable by the fourth day. They still come but feel a lot milder, disappear quicker and are easily manageable.

Once you break your fast you are free to eat your daily food how and when you want. Some people like to begin the feeding window with a large main meal, others may prefer 3 smaller meals throughout the rest of the day. Again, the frequency and size of your meals is something for you to experiment with. Eating paleo fits in well with intermittent fasting as it’s designed around foods that satiate hunger and help you maintain energy levels. This should allow you to skip meals without much thought. The combination of a paleo diet framework with varied intermittent fasting gives us an eating guideline that is much more relevant to our human biology.

It’s important that you keep the irregularity of the fasting. Skipping breakfast every single day is not intermittent. Instead you may want to vary your fast types to get a more accurate primal eating pattern. This might involve skipping breakfast a few days a week and then a 24 hour fast every fortnight. You could also include a 48 hour fast 2 or 3 times a year.

Many people also use fasting when travelling or when only sub-optimal foods are available. Rather than partake in the office team breakfast of bagels and croissants you can choose to fast.

Fasted training

You can choose to train in a fasted state for increased results. Training while fasted boosts your metabolism and will also encourage the human growth hormone (HGH) to be released. This further maximises your ability to use body fat as the primary source of fuel instead of muscle glycogen. The great advantage is that fasting allows you to retain your muscle mass while dropping body fat. Most people will train towards the end of the fasting window and then break the fast with their main meal of the day.

Fasted training works by adding an additional layer of stress to your body. Without food, you will learn to adapt on lower fuel reserves. This is akin to the principle of breaking down muscles so they repair stronger. Once you revert to a fed state, your body will be more efficient thanks to your fasted training.

While training fasted has benefits, research is mixed on fasted competitive performance. Some people experience no detrimental effects whilst other studies have shown a degradation in performance. Our gut feeling is that if you’re going into a race or competition, you would want to go in fuelled. If you’ve got any experience in competing while fasting, we’d be interested to hear.

Is fasting for everyone?

Nearly all healthy folk should have no problem integrating some form of intermittent fasting into their diet. They should however, be well dialled in with their sleep, stress levels and training schedule. Intermittent fasting is not something you want to try on top of inadequate rest or any chronic stressors.

There has been quite a lot of talk about whether intermittent fasting is suitable for women.  Stefani Ruper of Paleo for Women discussed the issue in depth here and Mark Sisson of Mark’s Daily Apple has offered this advice:

“As it stands right now, I’d be inclined to agree that pre-menopausal (and perhaps peri-menopausal) women are more likely to have poor – or at least different – experiences with intermittent fasting, at least as a weight loss tool. That said, it appears to be a potentially gender-neutral therapeutic tool for chemotherapy, cancer, and age-related neurodegeneration patients.”

“Most of all, though, I’d simply suggest that women interested in fasting be cautious, be self-aware, and only do so if it comes naturally. It shouldn’t be a struggle (for anyone, really).”

Like Mark says, the bottom line is that intermittent fasting should not be a grind for anyone. The only way to gauge your own suitability is to self-experiment a good number of times and note the results. If you find that intermittent fasting gives you significant negative side-effects then listen to your body and stop.


Intermittent fasting allows you to break from rigid meal times and gives you an insight to your own hunger signals and body function. Once you’re past the hunger pangs of the first day or two you’ll find that you have a lot more control of your appetite. You won’t be tied to 3 meals a day at set times and you can skip meals without the feeling you’re under-fuelled and about to keel over from hunger. You are exercising your primal nature and engaging your body’s natural fat burning ability.

Fasting can also provide an amazing head-clearing stimulant like effect. You become focused with controlled energy which is great for when you need to be concentrating, maybe at work or during meditation. It gives you a chance to focus on other matters without counting down to your next meal.

Combined with a paleo diet, intermittent fasting is a useful tool if you want to reduce body fat or just aid concentration. It is what our bodies are genetically adapted for and can be an excellent way to develop your own sense of resilience and virility.

Image courtesy of: lisalovesdesign

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65 thoughts on “Intermittent Fasting

  1. Great article.

    It’s useful to have an overview of all of the IF approaches. It’s been a topic of interest recently as I have found myself eating less and less. Now I am at the stage where I am regularly skipping breakfast and only eating two meals a day. This has given me a better level of focus and helped me dial in to my natural appetite.

    Keen to try a few of the other approaches and see what kind of benefits they offer.

  2. Great write-up on intermittent fasting Gary. I’ve had it in mind to give it a go since starting to eat Paleo a few months ago. My personal worry is weight loss: I lose weight very very quickly if I don’t keep up a good level of food intake (fast metabolism?) I worry that IF might lead to more undesirable weight loss, which can’t really afford!

    Mind you, I’m not complaining: nice to have the opposite problem to most people eh? ;)

    • Cheers Dave. Yeah I’m pretty similar, so it’s important that I get a decent amount of calories in during the feeding window. It gives you more of a re-composition effect while training and you can still get the other benefits of IF without dropping weight.

  3. Excellent article on IF. I think we come nearest to the leangains pattern
    as we seldom eat breakfast until noon and have finished our evening
    meal by 9pm. Not hungry in the mornings with paleo eating and so much
    more clear headed.

  4. I’ve tried Eat Stop Eat while on a GI diet but with no weight loss. Although I was more clear headed and so I wanted to loose weight. I was doing it for two 24 h periods a week. But I will try this again with a paleo diet and doing CrossFit.

  5. did anyone see the documentary i think it was on bbc called eat, fast and live longer, it was very interesting and prompted me to give fasting a try, scientific data suggests its very good for the body which would make sense as its part of mans natural rhythum. I like to have a day of not eating at least every couple of weeks but i want to start doing it every week, think i will also have a go at missing meals out when appropriate. Its funny how people are so programmed into 3 meals a day as when i discuss the topic with people they just dont get it, food is definately an addiction for them. Great article keep up the good work.

  6. Thanks Mark. I missed that program but just found it on Vimeo so I’ll check that out tomorrow. I think there is plenty of supporting evidence out there as well as the fact that many cultures for centuries have used fasting to improve health & longevity.

    A lot of people find it hard to break the mindset that they can operate without food for a few hours. It can take a few goes to get used to but the benefits kick in pretty quickly. It’s something I think is really worth experimenting with.

  7. Is drinking tea and coffee with milk ok when fasting? Im new to fasting and don’t no of its just water you should drink.

  8. Hey Col. The general opinion I’ve read is that it’s not that big a deal and you should be fine with a splash of milk/ coconut milk/ coconut oil etc. You could always leave it out for a week or two and see if you notice any difference. Here’s some good info from Mark Sisson:

    Can I drink coffee or tea during a fast? How about adding cream or coconut oil to it – will that take me out of the fasted state?

    Coffee is actually beneficial for fat-burning, especially during a fast. One study found that an infusion of epinephrine – a hormone which coffee increases – during “starvation” enhanced its lipolytic and thermogenic effects. In other words, fat-burning and metabolism up-regulated in response to epinephrine (more so than usual). Epinephrine also lowers appetite, which can be extremely helpful for people trying to stave off hunger during a fast. Tea, and anything non-caloric, is also fine.

    Adding a pure fat source won’t “take you out” of the fasted state, and it may take the edge off the hunger, but it will reduce the body fat you burn by a bit.

    Read more: http://www.marksdailyapple.com/fasting-questions-answers/#ixzz2OegKbZur

  9. Nice post. I learn something new and challenging on blogs I stumbleupon on a daily basis.
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  10. Enjoyed this article. You say “Skipping breakfast every single day is not intermittent.”, however Dr Mercola (who advocates fasting) uses this approach and he says it works fine for him.

    I’ve been doing this fairly consistently (perhaps occasionally have a light breakfast if I’m starving) and find it is the easiest way for me to fast. If I tried doing 24 hours or more, I think I’d be very unhappy!

    Having a warm bone broth in the morning keeps me going till lunch time.

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