Originally with the help of the First Endurance Research Board we posted an article about the benefits of low carbohydrate training which helps athletes modify their substrate utilization to become more efficient at burning fats. This topic has become quite popular among endurance athletes. First Endurance Board Member Bob Seebohar MS RD CSSD, CSCS, is one of the leading authorities on the subject and uses this for his clients. Bob Seebohar send the following information to help clarify some misconceptions about this topic.

The original Low Carbohydrate Program can be found here.

To fully understand the metabolic efficiency concept, it is first important to understand some history and background information. The crossover concept describes the relationship between exercise intensity and the use of carbohydrate and fat. It dates back to the 1930s and has been widely accepted among exercise physiologists with research to support it.
You know it as this: as exercise intensity increases, the body prefers to use carbohydrate for energy. The basic message of the crossover concept is that the body prefers to use carbohydrate at increasing intensities while the reliance on fat significantly decreases.
The goal of improving metabolic efficiency is to extend that crossover (“push” it to the right) as much as possible by teaching the body to use more of its fat stores at higher intensities. This will allow more area under the curve where a greater percentage of fat is being utilized at higher intensities. This will benefit any athlete in any sport of any duration both in the short and long-term.
Aerobic Training
Prior aerobic training results in cellular adaptations that can increase fat oxidation and decrease sympathetic nervous system activity. These adaptations can improve the ability of the body to use all of the energy substrates, but overall, the adaptations will favor more fat than carbohydrate oxidation.
With higher intensities of exercise, certain biochemical adaptations contribute to the increased use of carbohydrate. These adaptations include contraction induced muscle glycogenolysis (the breakdown of stored glycogen to glucose so the body can maintain blood sugar and use glucose for fuel), increased recruitment of more skeletal muscle with a greater proportion of fast twitch fibers and increased sympathetic nervous system activity. Norepinephrine (similar to adrenaline which constricts the blood vessels and increases blood pressure and blood glucose levels) may stimulate both liver glucose production and lipolysis (the breakdown of fat stored in fat cells). Epinephrine (adrenaline) signals the heart to pump harder, opens the airways in the lungs and increases blood flow to the major muscles. This intensifies the contraction induced rate of muscle glycogenolysis which leads to a higher lactate formation. The acidic effect of lactate and hydrogen ion development inhibits free fatty acid transport by inhibiting a key enzyme, carnitine palmitoyl transferase, which reduces fat uptake into the mitochondria.
Training the body to oxidize fat at higher intensities will delay the accumulation of lactate which means athletes will be able to maintain a higher power output or velocity longer. Yes, aerobic training does help improve this process; however, the dietary manipulation is even more powerful and more realistic for athletes to implement considering that you
may not have adequate time to put in the aerobic training or you may not be in the proper training cycle.
I have proven with athletes that metabolic efficiency can be improved during a high intensity training cycle. Bold statement I know. How is this done? By keeping the daily nutrition plan in check and controlling blood sugar and insulin. It is really not too difficult but for some reason, athletes and coaches believe that the only way to improve the body’s ability to burn fat is only through aerobic training. That is not correct.
Nutrition Impact
In addition to lower intensity, aerobic training, metabolic efficiency can be further manipulated through proper macronutrient partitioning and by following a nutrition periodization program. Eating a highly refined carbohydrate diet leads to an increase in carbohydrate oxidation. While the benefits of eating more carbohydrate may be justified during the competition season, this type of eating can work to your disadvantage at lower training load times (transition and early preparatory season) because it will not allow the body to fully reap the benefits of increased fat oxidation.
Eating too many refined carbohydrates or eating a large amount of carbohydrates with a lower protein and fat intake at one time leads to an increase in carbohydrate oxidation. This decreases the body’s ability to oxidize fat due to a higher insulin response experienced. As insulin increases, fat oxidation significantly decreases because insulin inhibits lipolysis (the breakdown of fat) by activating protein phosphatase 2A which dephosphorylates hormone sensitive lipase and inhibits its activity.
Therefore, to properly teach the body to use fats more efficiently, carbohydrate intake should be held at moderate levels in the preparatory and transition training cycles and depending on the athlete, sport and number of competitions, possibly even during the competition season. Controlling blood sugar through proper food selection is the key nutrition take-home message.
The goal is to balance macronutrient intake so proper metabolic changes can happen and since a large number of athletes eat an unbalanced daily diet (too high of a refined and processed carbohydrate load), it is important to bring them back into balance to control blood sugar and insulin levels. Research proves that eating lean protein and fiber together has a blood sugar stabilizing effect as well as being very successful in weight loss strategies.
Back to Basics
As stated previously, the concept of metabolic efficiency centers on the control and proper management of blood sugar. When blood sugar is high from eating an imbalanced macronutrient diet, insulin levels will increase which will inhibit the breakdown of fat. It is really as simple as controlling your blood sugar to teach your body to burn more fat and preserve carbohydrates.
However, contrary to what many non-health professionals believe about the concept of metabolic efficiency, starvation training sessions are NOT a piece of this puzzle. In my professional opinion, these should not happen nor be encouraged.
In fact, when implementing a metabolic efficiency training nutrition program, an athlete should not go hungry or starve themselves. It counteracts the entire purpose of the concept which is to control blood sugar and the hormonal response of insulin to encourage the body to burn fat instead of turning off the mechanism of burning fat. Better blood sugar management is seen when correctly using the metabolic efficiency concept and this leads to controlling hunger better without starving the body.
The concept of metabolic efficiency supports an athlete eating a small metabolically efficient snack comprised of carbohydrate, protein and fat PRIOR to a workout so proper fuel can be supplied to the working muscles and prevent being in a catabolic state. Then, and only then, if the training session is less than 2-3 hours, is it satisfactory to only consume water and electrolytes because physiologically, the body has enough carbohydrate stores to fuel this amount of moderate intense exercise. After this amount of time, some calories are needed.
Don’t believe the hype that you may read. You do not have to starve yourself, teach your body how to handle bonking or follow a high fat diet to improve your body’s ability to use fat at higher intensities. That is just plain ridiculous! You also do not need to train your body to consume as many calories that it can stand during training. This is not necessary and will only increase the risk of GI distress, increase the need for simple sugars and may even predispose you to insulin resistance and metabolic syndrome.
Improving your body’s ability to burn fat at higher intensities requires a combination of diet and training program manipulation. One alone does not cut it.
I hope that has cleared up some of the confusion surrounding this very exciting topic.
As a resource to the athletic community, I have formed a Facebook page for Metabolic Efficiency so successes and challenges can be shared amongst athletes and coaches implementing the concept of metabolic efficiency. The goal is for everyone to share their strategies, ideas and metabolically efficient recipes so all athletes can benefit from them. Here is the link:
Feel free to contact me at coachbob@fuel4mance.com if you have questions or comments. By the way, my qualifications include the following to show that I have some background in this subject and am not just throwing around some fancy words in an article:
-Undergraduate degree in Exercise and Sport Science -Masters degree in Health and Exercise Science (emphasis on metabolism) -Masters degree in Food Science and Human Nutrition -Registered Dietitian -Exercise Physiologist -Board Certified Specialist in Sport Dietetics -Past Director of Nutrition, University of Florida -Past Sport Dietitian, US Olympic Committee -2008 Team USA Olympic Sport Dietitian -2008 Olympic Triathlon Team Sport Dietitian and Exercise Physiologist -Published author -Nationally recognized expert in sports nutrition