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Bulletin #62 – Ultimate Endurance Performance

It is well known that endurance exercise performance is highly dependent on carbohydrate fuel availability. Inges-tion of a high carbohydrate (CHO) diet prior to exercise, and supplementation of carbohydrate during exercise, have both repeatedly proven to improve endurance performance. Furthermore, the onset of fatigue during prolonged exercise corre-lates highly with muscle glycogen deple-tion. However, the rate of oxidation of orally supplemented CHO seems to have a maximum limit around 1.0 to 1.1 grams per minute (1). Even when ingestion of oral carbohydrate during exercise is in-creased to a rate of 2 grams per minute, the rate of oxidation of this carbohydrate supplement did not exceed 1 gram per minute. Thus there seems to be an upper limit to how fast the body can digest, ab-sorb, transport, and oxidize carbohydrate. In simple terms, your body cannot digest and absorb carbs fast enough to keep up with the rate of carbohydrate oxidation during prolonged exercise performed at moderately high intensity .

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What this means is that you can’t keep up with the energy demand simply by supplying extra carbs while you exer-cise—your body can’t absorb them fast enough. If you try, you’ll just get a full stomach and a belly ache. So this means that muscle glycogen will be consumed and eventually when it is depleted you will “hit the wall.” So another strategy to improve endurance performance would be to supply another fuel source that could be used at the same time as carbo-hydrates, possibly sparing muscle gly-cogen and delaying the onset of fatigue. There are several theoretical reasons why medium chain triglycerides, such as Cap-Tri®, might help in this regard. CapTri® is a special kind of engineered fat that is processed by the body differently from conventional fats (2). CapTri® is absorbed directly into the bloodstream from the gut and is transported to the liver where it is largely metabolized into ketone bodies. CapTri® is absorbed and metabolized as rapidly as glucose and serves as a source of immediate energy. The liver converts CapTri® into ketone bodies, which are fat breakdown products, which are then transported to the muscles and burned as fuel.

Importantly, the availability of carbohydrate does not seem to suppress the use of CapTri® as a fuel source (2,3). This means that if we add CapTri® to the fuel mix it will be burned at the same time we’re burning carbohydrate, and this extra source of added energy should help relieve the demands on the carbohydrate depot. In theory, this should improve en-durance performance. CapTri® has a number of oth-er interesting metabolic properties that makes it well suited as an energy sub-strate for exercise. It is very rapidly di-gested and absorbed, and does not require transport via the lymphatic system, as do conventional fats (2,4,5,6,7). Further-more, medium chain fatty acids (MCFAs) do not require the carnitine transport system for entry into mitochondria, which further enhances their availability as an immediate energy source . Medium chain fatty acids are thus oxidized as rapidly as glucose itself (2) which is truly remark-able. What this all means is that we have an alternative fuel source which can be burned just as fast as glucose and which can be burned at the same time as glu-cose. Since there is a limit to how fast we can digest and absorb energy from car-bohydrate (about one gram per minute) this represents an excellent way to further enhance supplemental energy intake dur-ing exercise. CapTri® has a very high thermogenic effect, which means it is preferentially burned as a fuel source, and also has very little tendency to be stored as body fat (4,5,6,7).

MCFAs (includes MCTs) have been shown to produce as much energy as glucose when isocaloric quantities of MCFA or glucose was in-gested prior to exercise (8).A recent study was undertaken to examine the effects of MCFA supplementation on endurance exercise performance (8). Six male cyclists all with three years or more of serious training experience at 300-500 km/week were studied. Each subject com-pleted three successive trials consisting of two hours riding at 60% of peak VO2 (60% of maximal intensity) followed im-mediately by a 40 km time trial. Each of these trials were separated by ten days during which time the subjects ate and trained as usual. Before the experimental trials the cyclists consumed either a 10% solution of short chain glucose polymer, an isocaloric 4.3% MCT solution, or else a solution providing a mixture of 10% glucose polymer plus 4.3% MCT. These test formulas were called CHO, MCT, or CHO+MCT, respectively. During the exercise sessions the subjects’ blood and respiratory gases were measured to moni-tor fuel metabolism. When comparing the three for-mulas in terms of average speed to com-plete the 40 km time trial, it was found that the fastest average speed was for the CHO+MCT formula, in the middle was the CHO alone, and the cyclists per-formed the slowest when supplementing with MCT alone (8).

This makes perfect sense if you think about it. We know that the preferred fuel for intense exercise per-formance is carbohydrate, and that endur-ance performance correlates with carbo-hydrate availability. So we would expect that cyclists supplementing with carbo-hydrate alone would perform better than those supplementing with MCT alone, and this is exactly what was observed. Furthermore, we would expect that taking both CHO and MCT together at the same time would result in better endurance performance than either one separately, and this also is what was found. This is because MCFA can be used as fuel at the same time as glucose, thus increasing the overall pool of available energy substrate beyond what can be obtained from car-bohydrate alone. Conventional fats just don’t seem to be very effective at this, apparently because they are metabolized too slowly. When some of the specific me-tabolites were looked at, it was found that both of the supplemental formulas which provided carbohydrate suppressed the rise in endogenous free fatty acids normally seen during prolonged exercise. What am I talking about?

This is simply saying that if you use a carbohydrate-containing supplement before or during exercise this will decrease your use of body fat as a fuel source during the exercise session. Logical, right? If you eat a bunch of carbs right before you train, you’ll burn less body fat than if you train on an empty stomach. This is why it’s so important to define your training goals and know what you’re trying to accomplish. If you what to maximize endurance performance you should supplement with carbohydrate (and even better, with carbohydrate plus CapTri®) before and during training, but if you want to maximize body fat loss during the training session you should do it on an empty stomach. Or if you’re wor-ried about maximizing lean body mass, refer back to the “Next Level” articles in the September and October issues of The Press, where we explain how branched chain amino acid supplementation (Mus-cle Amino Formula™, Hi-Protein Pow-der™, 50/50 Plus™ or Optimized Whey Protein™) can help prevent muscle loss during training . In contrast, the addition of CHO to the MCT-containing formula did not reduce the rise in plasma-free medium chain fatty acids. So while carbohydrate availability seems to reduce the oxidation of long chain fatty acids (which includes both body fat and conventional dietary fats) it does not suppress the use of MCFAs (includes MCTs) (2,8,9).

This is another reason why conventional fats just don’t work well as energy supplements during endurance exercise. If you want the biochemical explanation: carbohy-drate metabolism generates an intermedi-ate called malonyl-CoA which inhibits the activity of the carnitine shuttle. This is the transport system which is required to carry long chain fatty acids inside the mitochondria where they are burned. This means that as long as carbohydrate fuel is available for exercise you won’t burn much fat. It’s only as the carbohydrate stores become depleted that fat burning picks up. On the other hand, MCFAs such as CapTri® do not need the car-nitine shuttle to enter mitochondria, so for this reason they can be burned at the same time as glucose. This is one of their special properties that make them so well suited as an energy source for athletes. Of note, the rate of carbohy-drate oxidation was lower in the MCT and CHO+MCT trials than in the CHO trial after 90 minutes of exercise. Overall the rate of carbohydrate oxidation was highest for the CHO formula, moderate for the CHO+MCT, and lowest for the MCT alone. This also is exactly what we might have expected. The addition of MCT to the CHO formula represents an alternative fuel source which can be used at the same time as glucose . So you would expect this to help the glucose last longer, which it did.

And the rate of glucose oxidation is lowest for the pure MCT supplement because no supplemen-tal glucose is provided in this formula. Equally as important, the decrease in carbohydrate oxidation which occurred as a result of MCT supplementation seems to have been due to decreased oxidation of muscle glycogen, rather than just a decrease in oxidation of plasma glucose. There are two very important findings from this study which will help endurance athletes . First is that the addi-tion of MCT to a CHO beverage supple-ment ingested during exercise signifi-cantly increased cycling speeds during a 40 km time trial done after a two hour “pre-exhaustion” ride at 60% intensity. This means that the MCFAs significantly improved performance at the end of a long (approximately three hours total) endurance event. Second, the MCTs also seemed to spare muscle glycogen at the end of this simulated race. This may in fact be the mechanism by which perfor-mance was improved. At Parrillo Perfor-mance we have noticed for some time that our athletes seem to be stronger and perform better for a longer period when supplementing with CapTri®. We always believed the reason for this to be two-fold. One part of the explanation is that CapTri® provides an additional energy source which can be burned at the same time as glucose, thereby providing greater overall energy delivery to muscles. Also, this additional energy substrate seems to spare muscle glycogen, thereby delaying the onset of fatigue. So you not only can perform faster, you can perform faster longer.

This is the first formal laboratory experiment which has been performed to scientifically prove that these theories of ours actually do work in experienced athletes . I should mention that other ex-periments have been done in the past which failed to demonstrate any decrease in carbohydrate oxidation as a result of MCT supplementation . These trials used doses of MCT around the 30 gram level (about 2 tablespoons), which doesn’t seem to be enough to demonstrate a statistically significant decrement in CHO oxidation. The protocol reviewed here (8) employed an MCT dose around 86 grams, which is equal to 6 tablespoons, administered in a beverage consumed gradually during exercise over 3 hours. So to get this effect you would need to consume about 2 table-spoons of CapTri®per hour. This should be mixed with Pro-Carb™, a slow-release complex carbohydrate, to generate a fairly dilute solution. We suggest two scoops of Pro-Carb™ mixed with two tablespoons of CapTri® in one-half to one liter of water to be consumed gradually during each hour of intense endurance exercise. During a three hour endurance event this would amount to a total of six scoops of Pro-Carb™ and six tablespoons of Cap-Tri® in a total of 1.5 to 3 liters of fluid. Adjust the amount of fluid to suit your particular needs. This will vary somewhat depending on ambient temperature and humidity.

Remember that water replace-ment is just as important, if not more so, than carbohydrate supplementation. This formula will provide a total of 1,320 calories split roughly equally between carbohydrate and MCFA. Also, be sure to experiment extensively with this for-mula before an actual competitive event. Some people experience mild nausea or stomach cramps the first time they use MCT, particularly in fluid form. So break yourself into it before a real competitive event. In summary, this study confirms some of our theories and observations that we’ve been talking about for the last eight years or so. That is, MCFAs like Cap-Tri® improve endurance performance. This seems to be the result of both the availability of a secondary energy source which can be rapidly oxidized along with glucose, thus increasing energy deliv-ery to cells, and also by sparing muscle glycogen oxidation and delaying fatigue. Don’t forget you heard it here first. For a refresher course on MCFA biochemistry and metabolism, get a copy of our Sports Nutrition Guide which is filled with great information on CapTri® and energy utili-zation during exercise.


1. Jeukendrup AE, Saris WHM, Brouns F, Halliday D, and Wagenmakers AJM. Effects of carbohydrate (CHO) and fat supplementation on CHO metabolism during prolonged exercise. Metabolism 45: 915-921 (1996).

2. Bach AC and Babayan VK. Medium chain triglycerides: an update. Am. J. Clin. Nutr. 36: 950-962 (1982).

3. Jeukendrup AE, Saris WHM, Schrau-wen P, Brouns F, and Wagenmakers AJM. Metabolic availability of oral medium chain triglycerides co-ingested with car-bohydrates during prolonged exercise. J. Appl. Physiol. 79: 756-762 (1995).Ultimate Endurance Performance

4. Baba N, Bracco EF, and Hashim SA. Enhanced thermogenesis and diminished deposition of fat in response to overfeed-ing with diet containing medium chain triglyceride. Am. J. Clin. Nutr. 35: 678-682 (1982).

5. Geliebter A, Torbay N, Bracco EF, Hashim SA, and Van Itallie TB. Over-feeding with medium chain triglyceride diet results in diminished deposition of fat. Am. J. Clin. Nutr. 37: 1-4 (1983).

6. Seaton TB, Welle SL, Warenko MK, and Campbell RG. Thermic effect of me-dium-chain and long-chain triglycerides in man. Am. J. Clin. Nutr. 44: 630-634 (1986).

7. Hill JO, Peters JC, Yang D, Sharp T, Kaler M, Abumrad N, and Greene HL. Thermogenesis in humans during over-feeding with medium chain triglycerides. Metab. 38: 641-648 (1989).

8. Van Zyl CG, Lambert EV, Hawley JA, Noakes TD, and Dennis SC. Effects of medium chain triglyceride ingestion on fuel metabolism and cycling perfor-mance. J. Appl. Physiol. 80: 2217-2225 (1996).

9. Jeukendrup AE, Saris WHM, Van Dis-sen R, et al. Effect of endogenous carbo-hydrate availability on oral medium chain triglyceride oxidation during prolonged exercise. J. Appl. Physiol. 80: 949-954 (1996).

2018-03-13T11:10:33+00:00 June 9th, 2009|Technical Supplement Bulletins|

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