Fat burning for endurance athletes

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Fat burning for endurance athletes

Postby Skip » Fri Apr 13, 2018 2:15 pm

When we exercise, we use carbohydrate and fat as fuels to power us. Sometimes marathoner's "bonk" around the 20 mile mark. Bonking refers to the idea that your body has used up all of the glycogen stores and you have to stop running because you have no perceivable energy left to continue. If we train ourselves to burn more fat and less carbohydrates when we train, we won't bonk because the amount of energy we store as fat is way less limited than the amount of energy we have stored from glycogen. I'd imagine this is definitely important for those ultra long distance races, like ultra runs that can be 100 miles long.

Maffetone teaches us that we can increase our aerobic capacity by training at heart rates in an aerobic range of 65-85% of the maximum heart rate. By training in this range, we train our body's to be more adapt at burning fat while burning less glycogen.

The ketogenic advocates argue that their bodies will become more adapt at burning fats if more fats are consumed while decreasing the carbohydrate consumption. Unfortunately, they usually talk eating lots more animal fats and protein while limiting carbohydrates. I'm wondering if anyone has tried to remain on a starch based diet while decreasing the starch and increasing the fat intake (like more nuts, seeds, and avocado etc......but no oil). I'm thinking like suppose your breakdown is 80% carbs, 10% fat, and 10% protein and then you try something like 60% carbs, 30% fat and 10% protein. I know that fat you eat is the fat you wear, but the idea here is to use that fat that you wear as an energy source for ultra endurance athletes.

These thoughts occured after reading https://idmprogram.com/fasting-and-exercise-fasting-23/
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Re: Fat burning for endurance athletes

Postby geo » Fri Apr 13, 2018 8:18 pm

Great questions Skip! There are 3 different questions here that are interesting:

1. Does aerobic training in the 65-80% of MHR range cause the body to adapt to useing fat stores more efficiently for aerobic type exercise?

2. Does eating a LCHF diet (LC/Paleo/Atkins/etc...) cause the body to switch/adapt/become more efficient at using fats as primary energy source instead of glycogen?

3. Does increasing Fat in a Starch based diet cause the body to burn more fat for energy or more efficiently or in greater proportion to glycogen stores?

All very interesting questions. I don't have the answers. I've seen a lot of the hypothesis low carber's make on these things, but I've not seen any of the science behind it. My thoughts though are more about what mechanisms might possibly be a cause for such if they are true. We know the body has limited glycogen stores and will switch to fat stores for energy when needed. But how effiecient is that mechanism? Can it create energy to be readily used for bodily processes as fast as glycogen stores can? Does the body have any efficiency mechanism's to recycle, revitalize glycogen stores when they become or start to become depleted? Is there some point of glycogen depletion wherein the body says...time to start using fat stores? If so, can it keep up with the rates of glycogen depletion? Can fat stores be converted to fill glycogen stores? By what mechanisms? At what rates of efficiency?.

And thats just a small start of questions that need to be looked at. I don't know the science in this area. But I do know what this program has done for my energy levels and I do know that exercise does increase efficiency of energy utilization. I also know that fat is not a good thing to eat for the body beyond the very small need for EFA's. Personally I wouldn't risk my health to find out the answers to the above but I do think its a fascinating question and if anyone has more insight into any studies in this area I'm interested to hear them as well.
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Re: Fat burning for endurance athletes

Postby Skip » Sat Apr 14, 2018 9:27 am

geo wrote: We know the body has limited glycogen stores and will switch to fat stores for energy when needed. But how effiecient is that mechanism? Can it create energy to be readily used for bodily processes as fast as glycogen stores can? Does the body have any efficiency mechanism's to recycle, revitalize glycogen stores when they become or start to become depleted? Is there some point of glycogen depletion wherein the body says...time to start using fat stores? If so, can it keep up with the rates of glycogen depletion? Can fat stores be converted to fill glycogen stores? By what mechanisms? At what rates of efficiency?.


When we exercise we are using glycogen and fat stores at the same time. As we do more aerobic exercise, we burn more fat and as we do more anaerobic exercise we burn more glycogen. Suppose when I run aerobically, that I am burning 40% fat and 60% glycogen. If, by training and (perhaps diet), I may be able to change that ratio so I am burning more fat and less glycogen (say 75% fat and 25% glycogen), then I am far less likely to bonk. So the answer to #1 is yes, I believe.
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Re: Fat burning for endurance athletes

Postby geo » Sat Apr 14, 2018 12:58 pm

This article has a lot of info in it on the subject, but all its links to the data and graphs is broken :-(

http://sciencedrivennutrition.com/fat-a ... -exercise/

However it is based a lot on this study from back in 1993: https://www.ncbi.nlm.nih.gov/pubmed/8214047

Basically it seems, the lower the intensity of exercise, the more fat is burned than carbs and as intensity and or endurance increases a greater proportion of carbs is burned. Basically it says that the regulation of carb burning seems to be a simple function of endurance and intensity of exercise. While fat burning regulation is more complex and not well understood in terms of exercise. There are also some interesting comments at the end of the article concerning research on LCHF diet utilization.

Now I dont know the science well at all so I cant say whether the article is accurate or not but it seems to make sense and seems reasonable.

But again ultimately is your health worth following a LCHF diet to possibly improve some athletic improvement?
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Re: Fat burning for endurance athletes

Postby EvanG » Tue Aug 28, 2018 9:09 am

vegpedlr had lots of posts on the Maffetone method.

I did some ultra endurance events prior to switching to a McDougall style diet. I did a 24 hr race and a 600 km bike ride successfully, and learned a bit about fueling those types of events. Basically, you can only digest about 300Cals/hr of carbs, and you can burn them much faster. You can store about 2500 Cals in your liver and muscles. The more you train and the more carbs you eat, the better your carb stores will be. If you want to last through a 24 hr event, you will have to conserve your carbs by riding or jogging at the appropriate rate. You will benefit from eating 300 Cals / hr from the start of such a race, even if you are not hungry. People bonk or hit a wall toward the end of a marathon, because they run out of stored carbs. That is because they ran too fast for their ability level. The people who bonk are the ones who train and learn to pace for shorter distances. Then they race for a longer distance, and they don't slow their pace down enough, so they bonk.

In my experience, heart rates of 180 bpm were fine for an hour or so. At the end of a 24 hr race, the most effort I could exert gave me a heart rate of 145 or so. My interpretation was that I just could not maintain an energy burn rate to need the extra oxygen that a higher heart rate would provide. My glycogen stores were depleted, and I could ingest about 300Cals/hr of carbs. The rest had to come from fat, and you just cannot metabolize (burn or oxidize) fat as fast as you can sugar. You may be able to train yourself to run more efficiently on fat (oxidize it faster) by training slower. Another option might be to go out and exercise in a fasted state (in the morning) without eating. But the biggest benefit may be that you are really just practicing exercising in that state. You will learn how to pace yourself in that situation, and you will learn what it feels like. There are other limits like muscle endurance that people might test in such events.

From a practical perspective none of this has any bearing on normal modern life, where you want to be energetic throughout the day and fuel some moderate exercise. It only applies to ultra endurance type events.
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Re: Fat burning for endurance athletes

Postby Lyndzie » Tue Aug 28, 2018 5:47 pm

I would love to hear more about this. My dad does an annual 24 hour bike race, and might appreciate the information.
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Re: Fat burning for endurance athletes

Postby EvanG » Fri Aug 31, 2018 4:34 am

Lyndzie,

The only other things I might mention are that I used to drink hammer perpetuem, and tried to eat snacks that roughly matched that percent carbs. I preferred real food to the gu sugar packs that people like to carry. 24 he races are nice, because you can pick up some food on each lap, so you don't have to worry about logistics. Most people in the race I did started too fast, but I don't know how common that is.
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