Metabolic Efficiency: Friend and Certainly Not Foe

This is a follow-on post to my colleague’s recent blog, which you can read here.

Having worked with Bob and metabolic efficiency training principles for the past ~5 years, I encounter many of the same misconceptions about the concept that he expressed in his blog.  Granted, swimming against the current is often part of any paradigm shift and it takes time for new and different approaches to take hold. Additionally, nutrition is a very touchy and emotional subject for many people, particularly athletes. Yet, I often see individuals who are new to this concept become quickly confused because they either are given incorrect information by other health professionals, coaches, etc. OR there is an inadequate understanding of the potential application of metabolic efficiency in the context of that specific individual. 

My inclination to expand on Bob's blog stemmed from a recent nutrition symposium I attended that was targeted to Sport Dietitians and Registered Dietitians. To be honest, one of the presentations given at the symposium perpetuated a lot of the ongoing misconceptions (or lack of understanding) about ‘low carb’ and metabolic efficiency.

So, here are my additions to Bob’s post:

Statement #1: The crossover point (where the body switches from burning predominantly fat to burning more carbohydrate) happens at about 65% of VO2max. Competitive endurance athletes compete at an intensity higher than this, hence they rely on carbohydrate stores almost exclusively.

Comments:  This statement is based on physiological data and while still valid in the context of training manipulations (i.e., “building the aerobic base”), it does not consider the influence of nutrition training. We, at eNRG Performance (formerly Fuel4mance), have shown through manipulation of athletes’ diets and metabolic efficiency assessments (using a state of the art metabolic cart) that the crossover point can actually be moved far above 65% VO2max. This means athletes can burn more fat below AND beyond the 65% VO2max level. Fat can easily become a more usable energy source, even at high intensities, while glycogen stores are preserved for the highest intensity bouts.

Statement #2: Low carb diets do not support high intensity exercise or team sports with intermittent hard efforts because the working muscle must use glycogen.

Comments:  After you remember there is no standard definition for what a low carb diet is (other than in the context of nutritional ketosis), refer to the first point above. We can make the body more efficient at preserving its glycogen stores so that this fuel source IS available for high intensity exercise.  Secondly, we are not advocating for zero carbohydrate consumption during high intensity training and team sports. The fact is that the metabolically efficient athlete may need less of this supplemental carbohydrate during these activities.

Statement #3: Fat only burns in a carbohydrate flame and the metabolism of fat is slow compared to carbohydrate.

Comments:  While true the body oxidizes carbohydrate faster than fat, we have also learned that fat can be converted into energy much faster than what was believed just a few years ago.  Additionally, we are not advocating for zero carbohydrate consumption during training and racing. Did I say that already?  There is still a need to provide calories to the endurance athlete and yes, this often includes carbohydrate sources! They just may not need as many carbohydrates as the carb-dependent athlete, nor will they necessarily need to feed as frequently.

Statement #4: The low carb methods of “Train Low, Race High” popularized by Louise Burke and nutritional ketosis from the study done by Phinney et al. in 1983 did not show a performance benefit in athletes.

Comments: As Bob mentioned, there are several research papers that have been published since 1983 to show that performance is not negatively affected by low carb diets. But you must really understand that this notion of ‘low carb' is not universally the same throughout research studies.  I also want to mention that there are actually more than just these two methods of making an athlete metabolically efficient, which you can read about in the Metabolic Efficiency Training book. And although many of you want science to "prove it works”, even the renowned Dr. John Hawley recognized that the tools used in the laboratory setting may not be sensitive enough to detect performance improvements such as what athletes are seeing in real life.

Lastly, what is almost always missing in the naysayers’ anti-metabolic-efficiency talk is the importance and role of nutrition periodization.  This is another area where every single athlete may have a unique nutrition plan based on what their individual needs are in the context of health and athletic performance. This cannot be neglected, but sadly, those who are not knowledgeable of the concept are doing a disservice to their athletes by only focusing on the subject of "To Low Carb or Not".