Firing Up The Furnace

Over the last couple of weeks, I have been talking about increasing the ability to burn fat as a source of energy. Basically what it comes down to is reducing the amount of high carb foods you eat, so the body is not constantly trying to reduce the sugar load on the body. Also in enabling the body to oxidize fat, we are reducing our fat stores, great for some of us struggling to lose those extra inches off the waist, and increasing our endurance. If we burn more fat for energy, we are burning less carbs and rely less on carrying fuel on the long runs.

But there was one technique to boost your fat oxidation rate that blows all the other methods out of the water. This method has allowed many runners to run marathons and some ultras without fuelling at all. Sound interesting? Well the method to boost your fat burning metabolism is called ketosis. Now some of you who know diabetics may be freaking out at this term as diabetics can go into a state called keto acidosis which is quite a dangerous state to be in. But it is like comparing a paper cut to losing a limb. Sure they are both cuts, but only one is life threatening.

Ketosis is basically something the human race has used to survive all through the hunter gatherer phase of evolution until farming was invented. You see, in nature, high carb foods are not readily available all year round, so when they are readily available, we burn glycogen/sugar for energy as they are in abundance. But when winter comes and the crops stop growing, we need some way for our bodies to get its energy. This is when ketosis kicks in.

To put it simply, it’s a complex chemical process where we produce acetoacetate to be converted into beta hydroxybutyrate (BOHB) which breaks down the fat molecules in our body to be burnt as energy. The only way to achieve this state is purely by carbohydrate restriction replaced by more fat. The body need roughly 130 grams of carbohydrate every day to function on a basic level (ie fuelling the main organs like the heart and brain) and anything under this amount needs to be produced by other means.

Going into ketosis is not something that happens overnight. There is an adaption phase which varies for the individual, although 2 weeks is considered long enough for the average person to “adapt” to it. During this time, endurance and energy levels can and most often reduce. There have been many studies to see if fat can be used as a reliable energy source, but most are flawed. Most of them study people who have been on a high fat diet for 5 to 10 days, where they concluded that endurance reduced on a high fat diet. But there is a couple of researchers by the names of Jeff Volek (PhD) and Steve Phinney who have gone further than most to study these effects.

In one study they recruited 5 bike racers who were quite lean and very fit. They were asked to ride a stationary bike at 60% of peak aerobic power until exhaustion while only consuming water (no outside sources of energy). While on the high carb diet, they averaged 147 minutes. After a 4 week adaption to a ketogenic diet where they ate 15% of their calories from protein, 80% from fat and minimal amounts of carbohydrate (about 10 grams per day), they were again tested. Peak power output was unchanged, and in the endurance test they managed 151 minutes. A slight improvement, but with further adaption, it is believed they can still improve.

The main difference was in the second test, the muscle glycogen was half of the first test and they only oxidized half of that. Meaning they only used a ¼ of the glycogen compared to the previous test. The rest came directly from their fat stores, even though they were relatively low in fat stores to start with.

We don’t need to go to the extremes that these cyclist went through to get into the fat burning zone. Their diet was extreme, even by ketogenic standards. But eating 50 grams of carbs per day for the average Joe and 70-80 grams per day for athletes is readily accepted as sufficient. Protein intake should be around 1-1.5 gram per day per Kg of lean body mass and the remainder from fats. It may sound quite gross to be eating this much fat, but actually becomes quite tolerable after a short time provide the right fats are chosen.

The advantages are many and varied for us athletes, but to go into them all would require another full blog from me. If you are interested into seeing how any of the diets I have mentioned over the past few weeks work, feel free to message me with your questions.

Run Well

Chris O’Driscoll

Leave A Reply (10 comments so far)

  1. shane
    3 years ago

    Great article Chris. I went strict Paleo for some time & had outstanding results. I have since fallen off the wagon hahaa. Anyway my question is, I still have trouble working out grams per day of carbs?

    Is it simply say 50grams of dry pasta shells = 50 grams of carbs or would it be 50 grams cooked??

    Or something completely different

    Cheers Shane

  2. Antony Daamen
    3 years ago

    I am about 68-70kg so that means 70 – 105 gram of fat…

    That is about a serve of chips or a serve of KFC ? 🙂 joking of course. I realize that these are probably the wrong fats.

    Avocado I know is good, but what else is there? Nuts?

  3. Amanda
    3 years ago

    A great insight into using fat as fuel and your blogs couldn\’t have come at a better time as we are currently shifting to a more high fat, low card weighted diet. Being a plant based athlete we are getting our fats from avocado, flaxseed oils (to name just one) and nuts such as Brazil, macadamia and almonds. We have never felt better, lighter and less bloated.

    Thanks for keeping us well informed & quenching our thirst for further knowledge about how to fuel these bodies of ours all the while still running & enjoying being healthy.

  4. Taz
    3 years ago

    I have been gradually shifting away from carbs to a higher fat diet, but had been advised recently that a high fat diet in women can affect hormone levels. Particularly where cortisol levels are already too high. Thoughts?

  5. Chris
    3 years ago

    Hi Shane, get back on the wagon again!
    With measuring out quantities of dried foods, it generally is the dried product that is measured since when you have re hydrated it, most of it is water.
    Hope that helps,

  6. Chris
    3 years ago

    Hi Antony, for your reply I have to make a few assumptions as I don’t know your height, age or activity levels. But for the purpose of the exercise, let’s just say you need 2,600 calories per day. If you are to be ketogenic, you would need about 70% of your calories to be from fat which is 1,820 calories. Divide that by 9 (9 calories per gram of fat) and you get 200 grams of fat per day.

    Now on the topic of quality, yes the oils KFC and other similar burger chains use are polyunsaturated which are very unstable at high heat and go rancid quite quickly. To combat this, they use anti foaming agents and a host of other chemicals to help keep it stable. Saturated fats are actually quite heat stable and are least likely to go rancid. I prefer to stick to the naturally occurring fats like monounsaturated from avocado, olives, nuts etc and the saturated from animal sources and coconut oil. As you are metabolizing so much fat on this diet, the cholesterol problems just aren’t an issue, not that they have ever been proven to be anyway. Have a read here for more info –

    Hope this helps,

  7. Chris
    3 years ago

    Hi Amanda,

    No problems at all, glad to hear you are getting good results from increasing the fats in your diet.
    Love the positive feedback!


  8. Chris
    3 years ago

    Hey Taz,

    If you have high cortisol levels, I would first look into the reason behind this. Cortisol is a stress hormone and as athletes, we are constantly putting stress on our bodies. But if your life is already full of other stresses, they can get out of control and the cortisol levels will stay elevated constantly rather than reducing once the cause of the stress has passed. This can definitely cause hormonal problems in women.

    In regards to a high fat diet such as the ketogenic one, there is some evidence to show that it raises cortisol levels, but is only temporary until you are “fully adapted”. Although in a more Paleo type diet, the fat levels don’t need to be so high as keto. Also make sure you are eating the right fats, as some (such as processed polyunsaturated oil) are highly inflammatory and will not do you any favours.

    Make sure you get plenty of good quality sleep, meditate, or just take some time out to look after yourself. You could also look into something like ashwagandha, an adaptogenic herb that relieves stress.

    Feel free to email me at if you have further questions.
    Hope this helps

  9. Ian
    3 years ago

    For those that find ketosis hard to maintain another option is to improve your metabolic flexibility – your body\’s ability to switch between glucose and fat as its primary fuel source. Having tried both I prefer working on improving my metabolic flexibility, but ketosis is certainly very effective when done correctly.

  10. Chris
    3 years ago

    Thanks for your comments Ian, some great points there.

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