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!