Subject: Optimal diet for endurance athletes

Note: The following is from the USENET newsgroup rec.sport.triathlon and is part of an ongoing discussion about diet and athletic performance. Barry Sears, Ph.D is an advocate of, and has commercial interests in, the 40/30/30 diet. Andrew R. Coggan, Ph.D is an exercise physiologist and a multi-sport endurance athlete.

Dr. Sears' comments are preceeded by, ">>" Dr. Coggan's comments are preceeded by, ">"

From: Andrew R. Coggan, acoggan@beach.utmb.edu

Date: 24 Aug 1995 19:09:19 GMT

In article<41iip0$78u@atlantis.utmb.edu>Andrew R. Coggan, acoggan@beach.utmb.edu writes:

>>Dr. Barry Sears wrote: >>For the past two years at Dave Scott's Triathlon camps held at Vail, I >>give the nutrition lectures on the hormonal effect of diet on physical >>performance. I can assure you that Dave does sit in on my lectures.

>Dr. Coggan: > It is good to know that Dave takes an active interest in the information >presented at the camps bearing his name. However, the fact that he attends such >lectures does not prove that he in fact follows your recommendations. Moreover, even >if he (or any other elite athlete) does follow your recommendations, their >performance cannot be used as evidence as to the validity of such recommendations. >What counts is good science (see below).

>>Dr. Barry Sears wrote: >>Current nutritional wisdom predicts that the greater the levels of muscle >>glycogen, the greater the performance of any endurance athlete. >>Unfortunately there are no controlled studies in the scientific literature >>to support this statement if the diet is held constant for more than seven >>days.

>Dr. Coggan: > You are quite correct in pointing out that the literature contains a paucity of >studies that have altered dietary composition for more that 1-2 weeks. We made this >same point is our review (1). However, I am aware of at least 3 studies in humans >that altered dietary CHO intake for periods of 4-6 weeks and measured endurance >performance pre/post: > Phinney et al (2) measured time to fatigue during treadmill exercise in 6 women >consuming a low CHO diet. Their endurance decreased by 23% after 1 week, but was >actually *increased* by 32% after 6 weeks. At first, these data would therefore >appear to support the idea that duration of adaptation is key. Unfortunately, these >obese subjects lost nearly 25 pounds during the study; as a result, the exercise was >considerably easier (requiring only 60% of VO2max after training, compared to 75% of >VO2max before training) after the diet. This, and not adaptation to the diet, >probably explains the increase in performance.

> Bogardus et al. (3) essentially repeated the above study, except that >performance was measured on a cycle ergometer, where changes in body weight are much >less important. Time to fatigue fell by 50% after both 1 and 6 week. *Importantly, >changes in muscle glycogen concentration were highly correlated (r=0.79) with >changes in performance.*

> Finally, in another study Phiney et al. (4) measured time to fatigue and muscle >glycogen levels in 5 cyclists consuming a low CHO diet for 1 month. Although >performance on average was not affected by the diet, this was due entirely to the >aberrant response of one subjects, whose performance increased by 57% (in my >opinion, and those of many others, such large changes in performance are not >believeable, suggesting that the pre-diet performance of this individual was greatly >underestimated). In the other 4 subjects, performance fell in conjunction with a >decline in pre-exercise muscle glycogen concentration.

>>Dr. Barry Sears wrote: >>In fact several of these studies in which the diet has been >>controlled for at least seven days have demonstrated statistically >>significant decreases in oxygen transfer for the athletes on a >>high-carbohydrate diet. This decrease in oxygen transfer negates many of >>the potential benefits that should be observed with the increased muscle >>glycogen storage which is a consequence of the high-carbohydrate diet. >>

>Dr. Coggan: I am uncertain exactly what you mean by "oxygen transfer". If you mean VO2max, >I am unaware of any solid data suggesting that VO2max is reduced by a high CHO diet. >If you mean VO2 during submaximal exercise, it is true that several studies have >found VO2 to be lower during exercise when CHO intake is higher (or vice-versa). >This, however, is a beneficial adaptation, resulting in less stress on the >cardiovascular system to deliver O2 to the tissues. While in part this may simply >reflect the greater metabolic efficiency of metabolizing CHO, the magnitude of the >difference is such that other factors must be involved. Probably a major component >of the higher whole-body VO2 observed during exercise following a low CHO diet is >due to increased VO2 by the liver, necessary to meet the great energetic demand of >elevated rates of gluconeogenesis.

>>Dr. Barry Sears wrote: >>There is a distinct difference between the hormonal consequences of the >>diet (especially in terms of eicosanoid modulation) and the caloric >>effects. Of the two, I believe and the existing literature strongly >>supports that the hormonal adaptation to the diet is the stronger of the >>two influences.

>Dr. Coggan: > Stronger in terms of? Certainly not performance.

>>Dr. Barry Sears wrote: >>Finally, I believe the study which you refer to in your e-mail was >>conducted by Munio et al. and published in 1994.

> > The study I was alluded to was not that of Muoio et al. (5), but one sponsored >by Bio-Foods, Inc. (Not yet published; my mistake. I also apologize if I have >confused some of the corporations/personalities involved in the "balanced" diet >movement). The study by Muoio et al. (5), though, is an excellent example of how the >results of poorly controlled research can create apparent controversy where none >really exists. This study attempted to manipulate the diets of members of a >university track team; unfortunately, since the athletes' season was about to >commence, at the request of their coach the treatment sequence (normal diet, low CHO >diet, high CHO diet) was not randomized (as required for good science), but given in >that order. Food was not supplied to the athletes; rather, they were given a dietary >checklist. Although the authors of the study attempted to monitor compliance via >questionaire, such tools are notoriously unreliable. Time to fatigue during exercise >was reported to be longest on the low (50% of calories) CHO diet; however, time to >fatigue during VO2max testing did not differ across the treatments. The latter >finding is not consistent, however, with the fact that VO2max was reportedly >significantly higher on the low CHO diet and significantly lower on the high CHO >diet (findings which themselves are quite unusual; see above). In short, the >experimental design and methods of this study have so many flaws and shortcomings >that one cannot trust the data, especially since they run counter to numerous >previous well-designed and well-executed experiments. Yet, I am sure that this study >will be cited in support of the concept that endurance athletes should reduce their >CHO intake below currently recommended levels.

>>Dr. Barry Sears wrote: >>That study was not sponsored by PR Nutrition, Inc. >>In fact, I am unaware of any study that PR Nutrition has ever sponsored.

>Dr. Coggan: > I apologize to everyone (and to PR Nutrition, Inc. in particular) if I appeared >to imply that corporate sponsorship *per se* invalidates the results of a scientific >study. Clearly, many times science could not proceed without the generous financial >support of corporations. My point, though, is that one must be an educated consumer >of the scientific literature, just as one needs to be an educated consumer in other >areas. When evaluating claims based on "science", one must ask, where does the data >come from? Were the studies carefully designed and executed? Are the results >published in an accepted, peer-reviewed journal? Are they corroborated by other >data, ideally from other researchers? And, unfortunately, does somebody have an axe >to grind or something to sell? Only by addressing such questions will one be able to >separate the wheat from the chaff, and discover scientific "truth" (if such a thing >really exists).

> > >References: > >1. Coggan, A.R., and L.A. Mendenhall. Effect of diet on substrate metabolism during >exercise. In: Perspectives in Exercise Science and Sports Medicine, Vol. 5: Energy >Metabolism in Exercise and Sport. D.R. Lamb and C.V. Gisolfi, eds. Dubuque, IA: >Brown and Benchmark, 1992, pp. 435-464.

> >2. Phinney, S.D., E.S. Horton, E.A.H. Sims, J.S. Hanson, E. Danforth, and B.M. >LaGrange (1980). Capacity of moderate exercise in obese subjects after adaptation to >a hypocaloric, ketogenic diet. J. Clin. Invest. 66:1152-1161.

> >3. Bogardus, C., B.M. LaGrange, E.S. Horton, and E.A.H. Sims (1981). Comparison of >carbohydrate-containing and carbohydrate-restricted hypocaloric diets in the >treatment of obesity. Am. J. Clin. Invest. 68:399-404. >

>4. Phinney, S.D., B.R. Bistrian, W.J. Evans, E. Gervino, and G.L. Blackburn (1983). >The human metabolic response to ketosis without caloric restriction: preservation of >submaximal exercise capability with reduced carbohydrate oxidation. Metabolism >32:769-776.

> >5. Muoio, D.M., J.L. Leddy, P.J. Horvath, A.B. Awad, and D.R. Pendergast. Effect of >dietary fat on metabolic adjustments to maximal VO2 and endurance in runners. Med. >Sci. Sports Exerc. 26:81-88, 1994.