The effect of pre-exercise nutrient intake on metabolism

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.