The effect of pre-exercise nutrient intake on metabolism

Abstract

English: In the exploration for methods to advance athletic performance, current interest has focused on numerous nutritional actions which may hypothetically promote fatty acid oxidation, ease the rate of muscle glycogen depletion and ultimately improve exercise capacity. Numerous factors are known to influence the selection of fuel for exercise, and there can be noteworthy interactions between several of them. These factors include: substrate availability, nutritional status, diet, mode, intensity, duration of exercise, muscle fiber type composition, physical fitness, the effect of training, drugs, and hormones and environmental factors (temperature and altitude). Furthermore, dietary manipulating strategies aimed at improving the metabolism of fat could have clinical significance in terms of body composition and obesity. An understanding of the factors that enhance or reduce fat oxidation is vital. One of the unanswered questions which served as basis for this investigation is the following: Does pre–exercise nutrient intake within the hours prior to exercise have an effect on macronutrient metabolism of man during subsequent exercise? Not only will newly-gained knowledge in this domain serve those individuals who would like to promote well-being (correct body composition by reducing fat mass) but will also provide constructive information for athletes on fuel utilization to improve athletic performance. Accordingly, the primary purpose of this investigation was to evaluate the effect of pre-exercise nutrient intake on fat and carbohydrate metabolism during exercise in man. The secondary purpose of this investigation was to investigate whether nutrient intake within the hours prior to training influence the physical work capacity (PWC). Newly-gained perspectives on these research objectives may also provide information for other researchers who wish to explore this field of study further and this could also explain contrasting research results presented in the peer reviewed scientific literature on weight loss or athletic performance that has been presented to date. In a double blind cross-over protocol design fasting, fat intake, caffeine intake, fat in combination with caffeine intake and carbohydrate intake prior to a graded exercise test served as interventions to validate the effect of pre-exercise nutrient intake on metabolism. Indirect calorimetry by means of an automated computerized breath-by-breath analysis system (Jaeger: Oxycon Pro; Masterscreen CPX Ergospirometry-Germany) coupled to a Technogym short range radio telemetry heart rate analyser was used when 12 subjects (6 trained and 6 untrained) were subjected to a graded incremental treadmill running test up to the point of voluntary fatigue. A Technogym RUNRACE 1200HC treadmill was used for this purpose. The findings presented here suggest that all trained subjects and untrained subjects did not respond to the various interventions to the same extent. Various foodstuffs ingested at specific time intervals prior to exercise influence fat and carbohydrate oxidation and the PWC significantly. The findings revealed by this investigation also suggest that trends towards increased levels of fat oxidation (-13 to 47%) coinciding with decreased level of carbohydrate oxidation (1.85- 55.5%) and a trend towards a decrease in the RER (-9.3 -0.2%) during the initial phases [(first 7 minutes of the exercise regime); (treadmill speeds between 4-12 km/h)] coincided with an improvement in the PWC. In 83.3% [(43.6%-97.0%) population proportion] of trained subjects an increase in the PWC is observed when fat, in combination with caffeine, is consumed compared to the intervention responsible for the worst PWC. Pertaining to the aforementioned variables (and in many cases also the interventions) the opposite seems to rule for the untrained group of subjects. Depending on the quantity, quality and time-intake of foodstuffs within the hours prior to exercise, it affects fat oxidation rates significantly. Furthermore, training at a prescribed treadmill speed or heart rate to promote fat loss, is deceptive for both trained and untrained individuals. Conclusion: Although exercise duration and intensity are very important regulators of fat metabolism, the findings of this investigation suggest that pre-exercise nutrient intake within the hours prior to exercise affects metabolism during subsequent exercise and could impact on the well-being status (obesity), physical work capacity and the validity of “fitness testing results” when individuals are subjected to numerous evaluation protocols. The rationale of this investigation also indicates the importance why it is necessary to combine diet and exercise in the well-being and sporting industries.

Afrikaans: In die strewe na metodes om sportprestasie te bevorder is die huidige belangstelling gefokus op verskeie voedingskundige aspekte wat hipoteties vetsuuroksidasie bevorder en glikogeensparend intree om die oefenkapasiteit te bevorder. Dit is bekend dat verskeie faktore die seleksie van brandstowwe vir verhoogde fisieke aktiweiteit beïnvloed, ook dat daar interaksies tussen verskeie van hierdie faktore onderling kan wees. Hierdie faktore sluit die volgende in: substraatbeskikbaarheid, voedingstatus, dieet, duurte van oefening, spierveseltipering, tipe oefening, fiksheid, effek van oefening, farmakologiese agente, hormone en omgewingsinvloede (temperatuur en hoogte bo seespieël). Verder kan dieet-manipulerende strategië wat beoog om die vetmetabolisme te verbeter ook klinies relevant wees in terme van liggaamsamestelling en obesiteit. Dit is dus noodsaaklik om die faktore wat vetoksidasie bevorder of demp te verstaan. Een van die onopgelosde vraagstukke wat as die basis vir die huidige ondersoek dien is die volgende: Bëinvloed die inname van voedingstowwe in die ure voordat oefening ‘n aanvang neem die makronutriënt metabolisme gedurende oefening by die mens? Nuwe kennis in hierdie terrein sal nie net insig verskaf vir individue wat hul welstand status wil bevorder nie maar ook konstruktiewe informasie rakende brandstofverbruik aan atlete kon verskaf om prestasie te bevorder. Dienooreenkomstig was die primêre doel van hierdie ondersoek om die effek van voedingstofinname voor oefening op die vet- en koolhidraatmetabolisme te ondersoek. Die sekondêre doel van hierdie ondersoek was om te kyk of die inname van voedingstowwe voor oefening ‘n aanvang neem, die fisieke werksvermoë beïnvloed. Nuutgefonde perspektiewe m.b.t. die huidige navorsingsdoelwitte kan ook nuwe inligting aan ander navorsers verskaf om hierdie studieveld vêrder te verken of om weersprekende navorsingsresultate rakende gewigsverlies of sportprestasie in geakrediteerde joernale uit te klaar. Die invloed van vas, kaffeieninname, vetinname, vet en kaffeieninname en koolhidraatinname is op ‘n dubbelblind-oorkruis manier as intervensies aangewend om die effek van voedingstofinname voordat oefening ‘n aanvang neem op die metabolisme te ondersoek. Deur gebruik te maak van indirekte kalorimetrie is 12 mense (6 geoefende en 6 ongeoefende mense) aan ‘n standaard geoutomatiseerde en gerekenariseerde “asem vir asem” analitiese sisteem (Jaeger: Oxycon Pro; Masterscreen CPX Ergospirometry-Germany) gekoppel met ‘n harttempo analiseerder (Technogym short range radio telemetry heart rate analyser) aan ‘n gegradeerde trapmeultoets onderwerp. ‘n Technogym RUNRACE 1200HC-trapmeul was hiervoor gebruik. Die bevindinge wys daarop dat alle geoefende en ongeoefende individue nie tot dieselfde mate teenoor die verskeie intervensies reageer en vetoksidasie en die fisieke werksvermoë betekenisvol beïnvloed nie. Die huidige bevindinge suggereer ook dat neigings tot ‘n verhoging in vetverbranding (-13 to 47%) en ‘n verlaging in die RER (-9.3 -0.2%) gepaard gegaan het met ‘n afname in koolhidraatverbranding (1.85- 55.5%) gedurende die eerste fases [(eerste 7 minute); (trapmeulspoed tussen 4-12 km/h)] van die oefenprotokol by geoefende individue met ‘n verbetering in die fisieke werksvermoë gepaard gegaan het. In 83.3% [(43.6%-97.0%) populasie proporsie] van die geoefende gevalle is ‘n toename in die fisieke werksvermoë aangetoon indien vet in kombinasie met kaffeïen ingeneem word en met dié intervensie wat die slegste fisieke werksvermoë opgelewer het, vergelyk word. Die teendeel m.b.t. van voorafgenoemde veranderlikes (en baie van die intervensies) geld vir die onongeoefende groep persone. Afhangende van die kwantiteit, kwaliteit en die tydsduur van inname van kossoorte voordat oefening ‘n aanvang neem, kan vetoksidasie betekenisvol beïnvloed word. Dit blyk verder dat ‘n voorgeskrewe trapmeulspoed of harttempo by beide groepe individue misleidend tot die werklikheid staan indien dit die intensie is om vetverbranding te bevorder. Gevolgtrekking: Alhoewel die intensiteit en duurte van oefening belangrike reguleerders van die vetmetabolisme kon wees, stel die huidige bevindinge voor dat voedingstofinname voordat oefening ‘n aanvang neem, die metabolisme tot so ‘n mate beïnvloed dat dit impak op die welstandstatus (obesiteit) van die individu, fisieke werkverrigtingsvermoë en die geldigheid van fisieke evalueringstoetse waaraan sportlui onderwerp word, kon uitoefen. Die rasionaal van die huidige resultate dui ook op die noodsaaklikheid om oefening en voeding gelyktydig en gesinkroniseerd in die welstand- en sportindustrië aangespreek moet word.