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.
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