Last week I introduced the topic of fat burning as an energy source compared to glycogen. I explained how they both had their shortcomings and both had their advantages. But what I didn’t explain was the fact that we generally don’t just use one or the other. There is always a certain amount of fat burnt and a certain amount of glycogen burnt, depending on many factors, including diet, training intensity and fitness levels. So the question is, how do you adapt to predominantly one side or the other?
There are many different ways to encourage your body to burn or oxidize fat for your energy supplies. One of the more common ways is using the Maffetone (Phil Maffetone) way, which through eating less high carb foods and training at maximum aerobic intensities, you will oxidize far more fat than the average Joe. This is great if you are someone who runs road Marathons or Triathlons where the intensity tends to be quite consistent. But if you’re a trail runner, where the intensity is constantly changing and you are very likely to go anaerobic for short periods on the hills, it’s not necessarily the best option.
There is no doubt that reducing your carbohydrate consumption will contribute to your body oxidizing fat more effectively. But to keep your caloric intake high enough to prevent issues associated with long term caloric deficits, you need to replace it with something else. Protein is not advised as the upper limits we can tolerate are in the range of 30-40%. So we must increase our fat intake (click here for some information on doing this).
High carbohydrate diets limit our fat oxidation as our bodies really hate high blood sugars. We eat high carb, our body stores what it can in glycogen, a small amount in our blood and the rest as converted fat. Keep doing this day in day out and we not only gain weight, but our body kind of forgets how to burn fat as it’s constantly trying to keep all this carbohydrate in the system in check. Which ends up for many of us, a double edged sword. We keep storing the fat and struggle to burn it off.
Running first thing in the morning before breakfast (fasted), is one way to encourage fat oxidation. Our glycogen levels are quite low at this time of the morning, so your body is forced to use more fat. Studies have shown that doing this does increase the amount of fat you oxidize, it does not however increase performance, nor does it decrease it. Although the study was done on subjects doing <1hr sessions. I believe that it would be more benefit to runners in training sessions or races of 2hrs+ where the benefits of fat burning are more obvious.
The way I like to keep my body burning fat is definitely through dietary methods along with the fasted training. I eat plenty of foods containing carbohydrates through the day, although they are all medium to low carb foods. But after a training session, especially the longer ones, it’s a different story. After running, our body is in severe energy depletion, especially after long sessions or if you have run in a fasted state.
We actually have a ½ hr window after any reasonable training session where our body is in a state known as insulin sensitivity. Generally when we eat a high carb food, our body reacts by producing a heap of insulin to reduce our blood sugar levels. It can quite often over react and reduce the sugar levels too far, leading to a crash. We then crave something sweet and the roller coaster of sugar highs and crashes begins. But after training, our glycogen levels are very low and we need very little insulin to get the energy back into the muscles at this point in time. So we can get away with eating grains, especially the sprouted ones which I use, without the negative effects we normally get from high carb foods throughout the day.
Hope this has cleared the picture up a bit more for you, and next week I will explain a way we can really go into fat burning overdrive which can work great for races like ultras.