Testing for Fat Adaption

I have heard the term "I am fat adapted", a number of times over the years and although embarking on this experiment of lower carbs, moderate protein, higher fat (LCMPHF) diet for only a short time, I was beginning to wonder if this concept could be proven. How would I know when I am "fat adapted"? Can I improve on my ability to burn fat as fuel?

So I decided to do what I normally do, and find a gadget that could give me this type of data and quantify it. I approached one of my colleagues from Morph Performance to conduct the test (known as a fuel efficiency test) and I was certainly surprised at the results. The test itself is relatively easy and it clearly answered my questions. The test consists of a progressive treadmill effort that increases in speed every 2 minutes. You are monitored using a heart rate strap and also a respirometer (a device that measures respiratory quotient by analysing the air you breath). The total test time is about 20 minutes plus the set up time. 

The Results

Although I have nothing to compare it to, I was surprised as to how I continued to burn fat throughout the test. Only embarking on the lower carb, higher fat diet about 5 weeks ago, I didn't think that there would be a result other than the "high intensity exercise equals almost all carbs as fuel" picture. I was pretty shocked to see that I could utilise 20% of my energy from fat at just above threshold levels, which equates to around 198 calories per hour (about 2 gels per hour of carbs equivalent). It also demonstrated that my intuition of my "fat burning zone" or aerobic zone was estimated correctly (around the 140 bpm and below). What it also emphasised was that carbohydrates are still an important energy source. Here are some of the stats...

At around the "easy" level that I have been training at (about 138 bpm), I burn an estimated 28 grams of fat per hour. Since fat delivers around 9 calories per gram, this equates to around 252 calories per hour. Compared with carbohydrate, 1 gram delivers around 4 calories for a total of 428 calories per hour. As a percentage, it was around 37% of fat, 63% carbs. As you can see, when I went faster, this stayed between 35%-37% until the "cross over" as seen on the graph below, where carbohydrates significantly take over and fat utilisation starts to drop. One thing I would likely do differently next time is to start faster and push to a much higher intensity to see whether fat drops off more (mine seemed to rebound a bit back up near the end).

So how do I use this information in training?
Firstly, I have to say that I was pleased to see that my intuition during training was pretty close to the zones reported. I knew that I could train for long periods in a fasted state if I stayed  under 140 bpm and the results backed up my estimate. During these sessions, I have grown confident that I would need minimal fuel and I would not "bonk" (run out of energy). Typically these "long" sessions were between 2-5 hours, but it did take a while to get used to and I had to be strict on not going above this (i.e. I walked up hills). I have only just started some higher intensity efforts while fasted and have been using carbs during these sessions as a top up (based on feel).

The second piece of information that I feel can be easily overlooked, is that carbohydrates still supply a significant portion of energy so I will certainly not be completely eliminating these from my diet. Actually what I will likely be doing is calculating roughly how much training I do and use this test as a guide to see how much needs replacement. Eg a hard session for 1 hour may use up to 200 grams of carbohydrate.

Will I continue to try and become more "Fat Adapted"? Will I stay LCMPHF? In short, I feel that boxing up my eating habits into one particular group is not truly reflective of what I do, nor is it a good guide to eating and training effectively. By saying "only eat 50 gram of carbs per day" or "you must have 2.5g or protein per kg of body weight" is overly simplified and doesn't take into account the many variables and individual needs, not to mention the stage of training you are in or the session goals. Also, recognising that high intensity does require high carbohydrate supplies is an important aspect to understand. What I like about this test is that it gives me more detailed guidance about the use of energy and the energy sources at specific intensities for me at this moment in time... I plan to repeat this test and see if it is something that can actually be trained. I will likely use this guide and continue as I have been doing, "going by feel, measuring outcomes and making adjustments".

Special thanks to Courtney from Morph Performance for conducting the test.