Endurance Skating

Training, Racing & LCHF Fueling For Skating And Endurance Sports

Fat Adaption For Athletes 101

Pork rinds > GU

Pork rinds: superior to GU.. and tastier.


In case it hasn’t registered with you already, I will openly state that I’ve spent the best part of a year turning myself into a fat-adapted skater & runner. As a professed nerd and self-experimenter, I have been a fan of Low-carb/Atkins/Paleo/Primal/Realfood – call it what you want.. they all have 80-90% commonality – for a very long time and have always believed it to be the “correct” interpretation of how the food pyramid should have been written. For sure, down the years, I haven’t always paid as much care to my own diet as I sometimes should, but at least I have a very clear understanding and interpretation of the healthiest way to eat for my own body (everyone is different, of course, and we are all experiments of n=1).

However, I had not until recently investigated in any detail the bridge between diet/health and athletic performance. The population of people who practice a Real Food approach and it’s implications for health is small; the number of those who further understand the implications for athletic performance is much smaller still, but for those who can successfully implement a fat-adapted way of eating and training, it offers a huge competitive advantage over the traditional high-carb model.


What is “Fat Adaptation” and “Metabolic Efficiency”, and why would I want to become Fat Adapted?
You body stores both glucose and fat, and can convert both of these fuels to produce Adenosine Triphosphate (ATP), the chemical that actually powers your muscles. It’s ordering of preference of which fuel to use is not just by random chance; it is trainable and prgrammable, which is the whole point of this article.

In sports science, there are many synonyms which describe similar states. “Fat Adaptation”, or at least my interpretation of it, simply describes a metabolic preference for one’s body to use its own internal fat stores as the preferred fuel for exercise, rather than dietary and stored glucose/glycogen. “Metabolic efficiency” is a term coined by endurance coach Bob Seebohar that has become popular and describes the body’s ability to use the most appropriate fuel substrate for the desired outcome – while we may be splitting hairs here if we are talking about substrate usage for your typical marathon age-grouper, I consider metabolic efficiency to be a more encompassing term, as there are times when you might want to purposely change your pace and exertion even during a long endurance event – for example, to produce a finishing surge at the end of a race.

Note that in the practical terms, there are no clear dividing lines here – you can’t categorically state that at a precise point your body switches from using fat to using carbs, because the truth is that everyone – even the most carb- or fat-adapted – uses a mix of these substrates at nearly all levels of exertion, but the framework is that at rest we all use almost 100% fat, and at maximal exercise capacity we all use almost 100% carbs. The key is understanding and manipulating what the body does inbetween these two extremes.

But why would you want to become fat-adapted in the first place? Even if we accept that carb restriction can ben helpful for fat loss, and general health, what advantage does it offer for athletes?

Firstly, as I have already pointed out, weight is an important issue for athletes, and many who don’t have tight control of their metabolism are usually carrying excess pounds of fat that penalizes performance.


Me in 2013, again

Me in 2013 – not bad, room for improvement

Me in 2014

Me in 2014; a lean, mean, metabolically efficient endurance machine


But the game changer for most fat-adapted athletes is the size of the fuel tank you are able to access, and this why it is gaining so much traction within endurance sports such as Ironman and Marathon/ultrarunning. Your muscles and liver can store 2,000 calories of carbs. That is enough to fuel you for perhaps 3 hours of moderate exercise. For many endurance events that is not enough – If we are reliant on this fuel tank and can’t replenish it quickly enough, we run the risk of “bonking” – hitting the wall, call it whatever you like. Your brain shuts down your body in an act of self-preservation, and you literally cannot do anything except lie down feeling like you’re on the verge of a coma, while your body figures out a way to access more fuel. I have personally never experienced a bonk, and neither do I want to.

In contrast, each lb of bodyfat contains 3,500 calories of energy. On a slender 150lb person with a modest 10% body fat, that still works out at over 50,000 calories, or theoretically over 25 times the size of the carb fuel tank; enough to keep you going for.. well, many marathons.

The irony is that athletes who are carb-dependent are barely able to access their body fat for fuel, certainly not at any degree of moderate exercise intensity. By contrast, the fat-adapted athlete who sources most of their energy from fat, is able to keep going and going without the need to top up the fuel tank, and with no fear of bonking.

In addition, as well as being less energy dense in and of itself, carbs must also be stored with 2 parts water to 1 part carbohydrate, so it is a far less dense store of energy as compared to fat.

And lastly, fat adaptation produces less oxidative damage in the form of free-radicals than carbohydrate oxidation. What does this mean? You preserve lean tissue better, and recover better after exercise. If you understand the important of periodisation and recovery within a structured training plan then you will know that this is a huge advantage to have.


Wait! What?! Don’t you need carbs to exercise?

Negative, not even close to true. But even amongst those who understand that a calorie is not a calorie, there is a still a wrongly held misconception that our body can only use carbohydrates for energy, and that a carb-restricted diet will leave you with no energy for anything more than a 5 minute walk to the shops.

We already know that when switching to lo-carb for general living there is an adaptation phase, perhaps 2-3 weeks where you can feel a bit rough. This shouldn’t really be surprising, when you consider the drastic changes that you are forcing your body to adapt to. Furthermore, I often hear lo-carbers complain they don’t have any energy for exercise even after this 2-3 week initiation period…. and so the belief becomes entrenched that while lo-carb may be good for weight loss and even good for one’s health (both true), you have to sacrifice any athletic ambitions on this diet. In fact, nothing could be further from the truth once you are fully adapted.

I do confess that this seems to be a common and very real complaint for many people, but my own interpretation of it is that your body is so used to using carbohydrates as its default energy store that when you begin exercising on lo-carb and your body automatically goes looking for its carbs and doesn’t find any… of COURSE it’s going to rebel and you’re going to feel lousy.. the energy deficiency is still very real. Simply put, just as it took some time to reprogramme your body to use fat during normal daily activities, so it takes yet more time to reprogramme it to use fat as the primary fuel source during exercise. If you are a lo-carber lacking in energy during exercise, take it as positive confirmation of how metabolically inefficient you were and still are.

The solution is simple – (no, don’t add the carbs back, you doofus), it is simply a matter of allowing your body more time to become fat-adapted during exercise. Even doing whatever regular exercise your energy levels allow, you should not expect to be anywhere near fat-adapted for 2-3 months, and even at 6-12 month your body will be making continual adaptations. Becoming fat-adapted is not something that happens overnight – as I am fond of saying: if it was easy, everyone would do it. However, the reverse is unfortunately not true – it’s very easy to quickly destroy a fat-adapted metabolism with the rapid introduction of too many dietary carbs.

In my own experience, for new lo-carbers you will find that at the start of an exercise session you will take longer to warm up and get “into the zone” as your body discovers that it a) has no carbs, and b) has to switch to and ramp up fat oxidation – this might take 15-20 minutes at first, however as the weeks and months go by and you slowly become more adapted, you will find this sympton disappearing and will eventually be able to hit the ground running as your brain and body automatically goes straight for the fat engine – that’s when you know that you’re fully fat-adapted 😉


How do I become Fat Adapted, then?

90% Diet; 10% training.

In the presence of sufficient dietary carbs, your body will use this as its primary fuel source. That is the metabolic norm for most athletes who follow the standard high-carb diet. They are so used to sourcing their energy primarily from carbs that their metabolic pathways to using stored fat during exercise are virtually blocked. We all know some “skinny fat” friends who do plenty of exercise and yet still carry excess fat, right? That’s because they simply can’t access their fat due to their diet.

Conversely, restrict your carbohydrate intake and your body has no choice BUT to use fat – dietary AND your own internal fat cells – for both rest and exercise. How many carbs you can consume and stay happily in this state is difficult to say and probably a topic for another blog post, and as I said there are no clear dividing lines, but carbohydrates are so plentiful in the standard western diet that unless you are actively restricting your carbohydrate intake, you will not be anywhere near well a fat-adapted state.

Additionally Spending training time at the appropriate intensity zones that promote fat-burning is also a factor – as we know, as intensity increases, so will your body’s propensity to switch over to carbs for fuel. But really, it’s mostly all about the diet.


How do I know how Fat Adapted I am?
The best way to really quantify exactly how fat-adapted you are is to take a metabolic effciency test. The science requires a bit of explaination here – your body produces different levels of respitory carbon dioxide when it metabolizes fat to when it does carbs. By collecting and analysis O2 and CO2 levels before and after it has entered and left your lungs (via a strap-on mask), we can compare before & after gaseous ratios and calculate the Respitory Exchange Ratio (RER, sometimes also called the Respitory Quotient, or RQ) which tells us – very precisely – exactly how much carbohydrate and how much fat we are oxidizing.

An RER of 0.7 means that you are using exclusively fat, while a RER of 1.0 means you are using exclusively carbs (yes, that’s correct you produce less CO2 output for any given amount of O2 when you are oxidizing fat compared to carbs).

Combine several snapshots of your RER at different levels of exercise intensity via a stepped treadmill test or a cycle powermeter test, and you can build a very good image of your energy substrate breakdown at different levels of exercise intensity.


My N=1 Experiment

I personally didn’t take much convincing. I have always believed in the power of carb restriction and real food, and as soon as I looked into the topic of low carb and endurance sports I began to uncover names like Timothy Olson & Zach Bitter, a “new breed” of openly low-carb runners who are making a big name for themselves in the world of ultrarunning.

It all makes *perfect* sense – eat ancestral real food, programme your body to use fat as fuel, and become a metabolically efficient endurance machine, and never have to rely on an energy gel ever again.

I began in November 2013 to eat a ketogenic diet. Immediately, as I have always responded, I dropped a lot of excess weight and my body composition changed drastically. My BMI went from 28 to 23 within the space of 6 months, and my body fat fell to roughly 8%. I took a metabolic efficiency test in April 2014 which confirmed that I had a good fat-adapted metabolism.


My metabolic efficiency test results

My metabolic efficiency test results – note that at a zone-3 heart rate of 162, I am still using 91.7% fat.

Even though I was starting from a pretty high knowledge base, I refined and improved my diet even further, replacing much protein for fat, replacing polyunsaturated fat with saturated fats like butter and coconut oil, and increasing my intake of really nutrient-dense foods such as organ meat, and dark leafy greens such as kale and spinach. You can never stop learning or improving.

Depending on your choice of sport and how lucky you are with your genes, many people can get away with sub-optimal eating and fueling. Some of us aren’t so lucky, or as we age we lose the ability to eat anything and remain as thin as a rake. But in the realm of endurance events, these topics become critical if you want to achieve your potential. Now that I am fat adapted, the longer the race, the better, as far as I am concerned!

This isn’t rocket science, you just have to be willing to self-experiment, and let the results rather than the dogma lead the way.


Further reading

I hope that I’ve summed up the key points, but you can go as deep into this as you like, as I did, and immerse yourself in the science and theory of the low carb diet for endurance athletes. Here are some of the resources that I used along the way.

Peter Attia – The Eating Academy

Steve Phinney & Jeff Volek – The Art & Science of Low Carbohydrate Performance

Tim Olson – Western States 100 record holder

Zach Bitter – American 12 hour record holder

PaleoRunner – Paleo/running podcast

Sami Inkinen -Becoming a Bonk Proof Triathlete: Fat Chance!?

Timothy Noakes

Bob Seebohar

Cycling Tips – High-fat, low-carb diets: good for you and your cycling?




4 comments on “Fat Adaption For Athletes 101

  1. Penny
    January 22, 2015

    So, what should we eat during a long race, say 12hrs race ? Just water ? I have been searching on the web for some time, looks like it is a “secret” …..


    • Van
      January 22, 2015

      I’m going to write about in-race fueling in much more detail., but it’s a highly individualised thing because it depends on what your stomach can handle. I will use UCAN, as well as calorie dense real foods.. salami sticks, nuts, boiled eggs. Chicken soup or coconut-milk smoothies are great too.

      Liked by 1 person

  2. Pingback: In-Race Fueling Part 1: Is Your Ego Writing Cheques Your Body Can’t Cash? | Endurance Skating

  3. Pingback: Lab Ratting: Maximum Aerobic Heart Rate & Substrate Usage | Endurance Skating

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This entry was posted on July 16, 2014 by in Endurance, Food, Nutrition, Science.

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