RMI Expeditions Blog

On The Map

On The Map

On The Map

This is the second of a two part series looking at the benefits of improving rates of fat metabolism to prevent or delay bonking in endurance sports. For week one of the series, click here.

Last week, we introduced the idea of training or developing fat metabolism to preserve glycogen stores, utilize our body’s largest energy store, and ultimately prevent “bonking” while climbing. This week we’ll look at how to accomplish it!

There are two main components that we can alter to affect our body’s use of fat: diet and training. The two work hand in hand – a change in diet without a focus on aerobic training volume is of little use, as anaerobic workouts require glycogen by definition, and aerobic training volume while continuing to eat a high carbohydrate diet will cause little change in your body’s metabolic pathways.

Diet

The key to training fat metabolism is to adjust your diet to take in more calories from fat than carbohydrates. This doesn’t mean you need to take in more calories overall, but instead, shift the nutritional balance of your diet. These diets have taken on the moniker LCHF or low carb high fat in studies and the media. There are a number of specific diets out there that align with this description (the paleo diet, the Atkins diet) but the specific diet is less important for the purposes of an athlete than the nutritional balance. Some articles suggest about 15% of your daily calories coming from carbohydrates, which is a significant shift for those of us that have trained under the paradigm of carbohydrate loading!

Changing our diet to make carbohydrates more scarce, and fats more plentiful accomplishes several things that will ultimately help our fat oxidation rates. The first is that when sugar is present in the bloodstream at high levels, insulin is released to control rates of blood sugar—extremely high rates of blood sugar are treated as a toxin by the body—and consequently insulin is a fat oxidation inhibitor, as the body wants to burn off the excess sugar and uses the opportunity. If we keep our levels of blood sugar lower with diet, our body releases less insulin, and fat oxidation rates are not suppressed.

Second, while sugar is easily transported across cell membranes and into cells, fats require transport by specific enzymes. Reducing our blood sugar and allowing fat oxidation to take place stimulates the production of these fat transport enzymes, so that fat can be brought into the cells at higher rates and utilized.

Finally, mitochondria are responsible for oxidizing fat and producing the ATP that fuel our cells. By reducing our carbohydrate fuel and relying more on fat, we stimulate the growth of mitochondria in the cells. Studies of athletes that are efficient fat oxidizers vs. sugar burners show a significant increase in mitochondrial density in the muscle cells.

Training Type

Our body is able to burn fat as fuel during aerobic exercise – those workouts and efforts that stay at level 3 or below. Once we cross the anaerobic threshold into lactate production, glycogen is the only fuel source that the body uses for energy production, so the stimulus to oxidize fat is gone. Thus fat oxidation is best trained during an aerobic base or volume phase, when the preponderance of workouts focus on relatively lower intensity, higher volume (hours or miles).

This isn’t a process that can be changed overnight. The cellular development that is required to shift your metabolic pathways takes time and sustained stimulation to change. With dedication to diet and training, studies show marked improvement in rates of fat oxidation after 8 to 12 weeks, so stick with it!

It’s often tempting as athletes to take things too far: if more of something is better, even more of it must be better still. Fat oxidation alone isn’t enough to keep up with our energy demands when we are training heavily for a climb. Therefore, maintaining some carbohydrates in your diet is important. Think of it as replenishing the fuel you spend: a workout of harder intensity will deplete your glycogen stores more; a 4 hour workout will require some carbohydrate fuel intake during the workout to prevent depleting glycogen stores as well. For those who want to really dig into the numbers, Alan Couzens has a calculator for balancing your nutritional intake depending on the phase of your training plan, hours, etc. It is designed for ironman triathletes, but can provide some interesting numbers for us as climbers as well!

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For more reading Alan Couzens has a number of interesting blogs on the subject. A good one to start with is Improving Fat Oxidation. Also see Deborah Schulman's Fuel on Fat for the Long Run.

Questions? Comments? Share your thoughts here on the RMI Blog!

On The Map

Climbing is a long and demanding endeavor, with a typical summit day on Rainier or Denali stretching for twelve to fifteen hours. Every time you take a step, your muscles require energy in the form of ATP to be able to fire. ATP is created within the muscle cells by mitochondria from two main nutrients: carbohydrates and fat.

For many years, athletes have focused on their carbohydrate intake as the key to performance. Carbohydrates provide a readily accessible and easily digestible energy source for your body, which is the reason that they are the main content in most sports foods; just look at the labels of shot blocks, Gu’s, bars, energy drinks, and the like, and you will see a heavy focus on sugar. There is a good reason for this: your body has a limited ability to digest food while exercising (digestion requires energy of its own), and carbohydrates and sugars are the easiest to digest, requiring little to be done to the glucose components before they enter the bloodstream and are carried to the cells.

The main issue with a reliance on carbohydrates is that your body has the ability to store a finite supply of glucose in the muscle cells and the liver in the form of glycogen. For trained athletes that are efficient with their energy usage, that store still only lasts for about 2 hours of sustained hard effort. If you aren’t familiar with the term “bonking,” it’s that feeling when your performance drops off a cliff; you don’t feel like you are working that hard aerobically, but you can’t possibly go any faster or harder. You’ve run through those glycogen stores and your muscles are out of fuel. Eating while you exercise can help to delay bonking, but your body can only process about 250 Kcal of sugar per hour, far less than you expend over the same period. Even though we are replenishing our sugar fuel, we dip further and further into those reserves as summit day goes on. At the same time, even the leanest among us carries over 24 hours of energy in the form of fat stores. Wouldn’t it be nice to recruit those stores while you are climbing?

Fatty acids are the most energy dense nutrients in our diet and our body stores them readily. They create more ATP per unit than sugars, and our body’s ability to store them can leave us with a huge reserve energy supply. The problem is that when fatty acids and sugars are both present, our metabolisms preference burning the sugars for energy. Julia Goedecke is a sports scientist who has been examining the influence of fat oxidation (metabolism) in endurance athletes. In examining rates of fat oxidation in athletes at different intensity levels, she found a vast difference in overall rates of fat oxidation. Some burned nearly no fat at rest, while others metabolized nearly 100% fat at rest, but while there were differences in overall rates of fat metabolism, those who metabolized more fat at rest derived more of their energy from fat at all intensity levels too. This would suggest that if we can train our metabolism to derive a greater percentage of our energy from fat, it will continue to do that as we up our intensity climbing, and we will use our sugar reserves more slowly, and hopefully avoid the dreaded “bonk!”

Now that we’ve introduced the idea of developing your fat metabolism, stay tuned next week as we get into the details about how to accomplish it.

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For more reading Alan Couzens has a number of interesting blogs on the subject. A good one to start with is Improving Fat Oxidation.

Questions? Comments? Do you have experience applying LCHF nutrition to endurance sports? Share your thoughts here on the RMI Blog!