This brings several benefits with it. The more you can train your body to burn fat while running, the less you have to eat, which means less chance for GI distress. You will also have less chance of running into the horrible feeling of “bonking” when your carb stores get low, feeling low energy, depleted mental state/focus/mood/energy, and feeling ravenously hungry. It is also possible you will have more energy to run-on, since you have faster ability to process fat for fuel.

Potential Downsides to Fat Adaptation

Some of the downsides to fat adaptation training are that you may be getting less aerobic adaptation than you would otherwise, since you won’t be able to run as hard while focusing on fat adaptation. You may also lose some “carb-adaptation” which, depending on your goal race distance, could be very helpful.

Who should consider focusing on fat adaptation for part of your training?

Very experienced runners, who have done a lot already to improve their muscle strength and aerobic systems.

OR inexperienced runners with a long time until their goal-event. and who can tolerate a longer term approach to improvement.

And in both cases, it would especially benefit runners training for longer events (longer than 2 hrs).

So, how do I do this?

There hasn’t been enough research on this to provide really solid guidelines for the “best” way to do this, but we do have some ideas about changing how hard, how long, and when you run, and then also what you eat before/during/after running.

This, like other aspects of your training can be periodized in some way, which means there are seasons, (days, weeks, or even months) focused on fat adaptation, and other seasons where you are not focusing on it as much. I think this helps promote a more balanced approach, where you aren’t always trying to cut something out of your diet, or stress your body in a certain way, but during certain times you focus on increasing fat-burning, and other times you focus on gaining strength, and other times you focus on improving your aerobic system, and you can eat differently for each period of your training.

Also, this may be very different from what you have been doing, and might feel really bad if you try too extreme of an approach at first. So be gradual with it to start, avoiding ever making yourself totally miserable, and just trying to stress your body a little more every time in this respect.

So, one way of thinking about improving fat adaptation is about decreasing carb dependance, then your body responds with increased fat adaption. To do this, you want to use a strategy focused on training with low carbohydrate availability, or “training low.”

Ways of "Training Low"

Training long without eating much/any carbs When you are going really long, it’s probably still a good idea to eat a little bit of slow-digesting carbs to help prevent muscle wasting

Training Fasted Running in the morning without breakfast means that liver glycogen is low (even though muscle glycogen should be normal)

Training twice a day. First run lowers muscle glycogen, then without eating carbohydrate in between, the second run is done in a low-glycogen state.

Not eating carbs after runs Delaying providing yourself carbs after a run, during recovery

Sleeping low Similar to not eating carbs after runs, but you exercise later in the day, then go to bed without consuming additional carbs.

Long term low-carbohydrate stores Longer term low-carb, or even ketogenic diets, for weeks or even months at a time.



My Experience

I first tried Low carbohydrate availability during long runs. When I first started trying this, I could only go 1.5 hrs or so before I would get really hungry and not feel so good, but eventually I could go over 4 hours (as long as I maintained a slow pace) without feeling fatigued or hungry.

Currently I am trying some fasted runs (even at relatively faster “maximum aerobic” paces), not eating carbs after runs (as long as they are relatively easy and shorter runs), and partial days or whole days of very low carb.

Zach Bitter’s Periodized Nutrition

You also might want to check out Zach Bitter’s strategy, and he has some good blog posts on this. Zach Bitter holds the 12 Hour World Record and the 100 Mile American Record. Also he was apart of the “Faster” study and tested with higher fat oxidation rates than previously thought possible, so clearly his strategy has worked for him.

He breaks down his nutrition strategy into 3 distinct phases

Recovery or rest, and low to moderate volume base building, done after a race or heavy training block Lowest carb intake (less than 5%), and highest fat intake (between 65-85 percent). Peak phase of base training. In this phase he targets hitting peak mileage, but retains a lower intensity More carbs, but still only 10-15% of diet. And most of these additional carbs are timed for days with the highest volume, but still eats fat and sometimes protein along with the carb sources. “Specified phase” this phase there are two main targets: Aerobic threshold and higher shorter intensity workouts. Highest amount of carbs, but still only 15-30%, and keeping 50-75% fat in the die Highest carb intake happens near the times of hardest workouts. And times of recovery has the highest fat and protein intake. "I always aim to include a fatty source of fuel along with any of the concentrated sources of carbohydrates during this phase. I want to continue to encourage my body to maintain a sense of fat as being the primary fuel."

Read more at zachbitter.com/blog