D3 recently partnered with Nick Suffredin, a former Scientist at the Gatorade Sports Science Institute, in an effort to bring more clear and useful information regarding nutrition to our athletes. As we all know nutrition is a major part of race day and training and can make the difference between a great day and just finishing. We hope you find his information helpful in your daily training and racing. Suffredin has been a life long athlete and is competing in his first Ironman at IM Wisconsin. If you have specific questions that you would want answered, please direct those to aj@d3multisport.com.
We first asked Suffredin to explain in more detail the theory of training your body to burn fat rather than carbs for long distance athletes. This topic has been a hot one lately with many different ideas being thrown around. He gave us some great information and good tips to use.

D3: In the tri-world fat burning is the new idea and many athletes get tested to see where their fat/carb burning point is. Do you have any thoughts on trainability of the body's ability to burn fat as a fuel source rather than carbs? It's also been said to not eat for the first 90 minutes of a long steady ride and to eat more "good" fats. What does the research tell us?

Nick Suffredin: The “train-low, compete-high” fad has been gaining steam due to some research results that have been published that look very promising. The problem is there are flaws in that research which show these positive results. It is a great concept in theory, but has yet to be proven in an endurance or trained athlete for improved athletic performance. Before we get into the heart of this theory I will provide some background to help make sense of it all (10).

There are two main sources of fuel endurance athletes utilize during exercise: carbohydrate (glycogen and glucose) and fat (triglyceride). Something to note is that research has proven repeatedly for years that maintaining carbohydrate levels in the body is a key factor that will not only increase performance, but also decrease muscle fatigue (1, 4).

If you are exercising at ~70% of your VȮ2max, your primary fuel source is carbohydrates with the rest of your energy coming from fat, but once above that moderate zone there is a shift that takes place where your body will utilize a lot more carbohydrates. Reason is that fat takes too long to break down as a fuel source. Carbohydrates are a more efficient source of energy and optimal for performance.

The theory of “train–low and compete-high” states, if an endurance athlete periodically trained with low glycogen stores, meaning they train in a carbohydrate exhausted condition in hopes of oxidizing (burning) more fats as a fuel source. This is done in order to “compete-high” referring to the athlete being able to compete on a full tank of stored glycogen and burn fat more efficiently in a race to enhance their overall performance.
This theory sounds great but does it work? If you deplete your liver glycogen stores during exercise, your blood glucose will drop. If this happens you will be in for a new level of pain, you will “bonk”. What happens is your body will start decreasing exercise intensity and speed because your fuel source is changing from carbohydrates to the slower utilized fats. Basically your pace may slow significantly or even stop completely because triglycerides cannot be metabolized quickly enough for high intensity exercise.

What is funny about this theory is that you are possibly already training this way without even knowing it. If you wake up in the morning and decide to have a quick workout without eating anything for breakfast, meaning it has been about 7-10 hours since having some type of carbohydrates, you are training in a depleted state. The other way to look at it is if you perform two workouts a day, one early and one later, you may not take in enough carbohydrates to replenish and refuel what you have lost in your first workout, so your second workout will be in a depleted state, further diminishing your glycogen stores.
Carbohydrate dominated diets are essential to continue to preserve glycogen stores at high levels during multiple sessions of intense exercise. These diets have also been shown to provide optimal training improvements and significantly increase athletic performance.
Endurance athletes will allow themselves to exercise longer by increasing the rate of oxidation of fat because their glycogen stores typically become depleted. The longer the duration of your exercise, your body will eventually not be able to provide enough carbohydrates to keep up so it will start utilizing more fat as a fuel source. But the more you train you increase your ability to train harder, faster, and longer. These adaptations are best suited with maintaining carbohydrate feeding before, during, and after exercise because oxidizing fat alone will not allow your muscles to perform optimally (2, 7, 9).
The second part of the question asks “what about waiting 90 minutes to feed during exercise?” The duration of exercise and time between eating carbohydrates before exercise are two things that play a role in the sensitivity of fat oxidation during exercise. If you eat earlier in your work out, your fat oxidation will decrease because there are more carbohydrates available in your blood to be used as fuel. What this shows us is that the human body prefers carbohydrates during high intensity exercise if they are available. But as the exercise time increases, the body will then begin to increase fat oxidation to maintain energy to perform the workout. In order to improve overall performance and training quality eating carbohydrates before and during will have a more positive effect than relying on fats as your fuel source. The carbohydrates being available in the blood will also help prolong muscle glycogen stores (2, 3).
There was a study completed with a high-fat vs. no or low-carbohydrate diet that was conducted on endurance athletes. The idea here was to increase fat-oxidation, and it did so during moderate exercise intensity 60-65% VO2max. The diet did reduce muscle glycogen stores by only 50%, and did increase fat oxidation at moderate exercise intensity. Problem with the diet as it shows in the study is that it did not prolong the length of time that exercise could be maintained, and it also showed that the subjects could not perform at high-intensities. These results tell us that muscle glycogen as a source of fuel cannot be replaced by means of fat oxidation (5, 8).
Basically fat supplementation and special diets have limited ability to increase fat oxidation, especially during races. Body fat stores and higher fat diets, or fasting are not adequate ways to replace or save muscle glycogen and blood glucose for durations of intense exercise. We don’t have a full understanding of fat metabolism during exercise but there is enough evidence so far in research casting doubts on many claims from products that have already been made to increase fat and reduce carbs. There may be some benefit to training in a low-state, but if you choose to try this theory out, do so with caution and only with low-intensity workouts, and be sure that your intense workouts and races are completed with enough carbohydrate in-take for optimal performance (6).
So simply, just trust your carbs.
References:
1. Carey, A.L., Staudacher, H.M., Cummings N.K., Stepto, N.K. Nikolopoulos, V., Burke, L.M., Hawley, J.A. (2001). Effects of fat adaptation and carbohydrate restoration on prolonged endurance exercise. J. Appl. Physiol. 91:115-122.
2. Costill, D.F., E.F. Coyle, G. Dalsky, W. Evans, W. Fink, and D. Hoopes. (1977). Effects of elevated plasma FFA and insulin on muscle glycogen usage during exercise. J. Appl. Physiol. 43: 695-699.
3. Coyle, E.F., A.R. Coggan, M.K. Hemmert, R.C. Lowe, and T.J. Walters (1985). Substrate usage during prolonged exercise following a preexercise meal. J. Appl. Physiol. 59: 429-433
4. Harger-Domitrovich, S.G., McClaughry, A.E., Gaskill, S.E., Ruby, B.C. (2007). Exogenous carbohydrate spares muscle glycogen in men and women during 10 h of exercise. Med. Sci. Sports. Exerc. 39: 2171-2179.
5. Hawley, J.A., Brouns, F., Jeukendrup, A. (1998). Strategies to enhance fat utilization during exercise. Sports Med.25: 241-257.
6. Hulston, C.J., Venables, M.C., Mann, C.H., Martin, C., Philip, A., Baar, K., Jeukendrup, A.E. (2010). Training with low muscle glycogen enhances fat metabolism in well-trained cyclists. Med. Sci. Sports. Exerc. (Epub).
7. Montain, S.J., M.K. Hopper, A.R. Coggan, and E.F. Coyle (1991). Exercise metabolism at different time intervals after a meal. J. Appl. Physiol. 70(2):882-888.
8. Phinney, S.D., Bistrian, W.J. Evans, E. Gervino, and G.L. Blackburn (1983). The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation. Metabolism 32:769-776.
9. Simonsen, J.C., W.M. Sherman, D.R. Lamb, A.R. Dernbach, J.A. Doyle, and R. Strauss (1991). Dietary carbohydrate, muscle glycogen, and power during rowing training. J. Appl. Physiol. 70: 1500-1505.
10. Yeo, W.K., Paton, C.D., Garnham, A.P., Burke, L.M., Carey, A.L., Hawley, J.A. (2008). Skeletal muscle adaptation and performance responses to once a day versus twice second day endurance training regimens. J. Appl. Physiol. 105: 1462-1470.

About Nick Suffredin:

Professional:

Previously I was an Associate Scientist at the Gatorade Sports Science Institute (GSSI). My primary responsibility was to support the GSSI physiology research program. I assisted with laboratory-based research projects focused on product efficacy and innovation to stay up to date on the emerging science in sports nutrition as it relates to physiological and performance responses. I primarily worked in the Human Performance Laboratory incorporating components such as sports nutrition, sport psychology, exercise physiology, motor behavior, biomechanics, and strength and conditioning. I also worked on testing elite professional athletes to enhance their hydration practices and nutrition intake to improve their performance. I was involved with research where I helped lead and design projects involving exercise/muscle recovery, exercise/athletic performance, carbohydrate metabolism, rehydration and dehydration, stress testing, body composition, gastric emptying, sensory perception, along with aerobic and anaerobic performance testing. I have been on human performance advisory boards to ensure and improve quality exercise programs and nutritional assessments with clear communication involving proper training and education.

Education:

Originally I am from the suburbs of Chicago. I received his undergraduate degree in Movement Sciences from the University of Illinois at Chicago. After graduation I began an internship at GSSI where he helped assess the physiological and metabolic responses to fluid and nutrient intake before, during, and after exercise. I am currently working to earn my M.S. in human nutrition and food science with concentrations in sports nutrition and metabolism and then an M.S. in Applied Exercise Physiology with a concentration in thermoregulation.

Personal:

I am married to my beautiful wife Melanie who also shares my passion with endurance sports and coaching. I was a collegiate athlete playing men’s varsity soccer. In my leisure time I am a competitive runner while also enjoying weightlifting, and playing soccer. I have coached elite endurance athletes along with providing them nutrition guidelines to follow.