Dietary supplements in sport.

Studies of the dietary practices of athletes report that nutritional supplements are commonly used. Supplementation practices vary between sports and individual athletes; however, there is evidence that at least some athletes use a large number of supplements concurrently, often in doses that are very high in comparison with normal dietary intakes. In exploring supplementation practices we propose a classification system separating the supplements into dietary supplements and nutritional erogogenic aids. The dietary supplement is characterised as a product which can be used to address physiological or nutritional issues arising in sport. It may provide a convenient or practical means of consuming special nutrient requirements for exercise, or it may be used to prevent/reverse nutritional deficiencies that commonly occur among athletes. The basis of the dietary supplement is an understanding of nutritional requirements and physiological effects of exercise. When the supplement is used to successfully meet a physiological/nutritional goal arising in sport it may be demonstrated to improve sports performance. While there is some interest in refining the composition or formulation of some dietary supplements, the real interest belongs to the use or application of the supplement; i.e. educating athletes to understand and achieve their nutritional needs in a specific sports situation. The sports drink (carbohydrate-electrolyte replacement drink) is a well known example of a dietary supplement. Scientific attitudes towards the sports drink have changed over the past 20 years. Initial caution that carbohydrate-electrolyte fluids compromise gastric emptying during exercise has now been shown to be unjustified. Numerous studies have shown that 5 to 10% solutions of glucose, glucose polymers (maltodextrins) and other simple sugars all have suitable gastric emptying characteristics for the delivery of fluid and moderate amounts of carbohydrate substrate. The optimal concentration of electrolytes, particularly sodium, remains unknown. Most currently available sports drinks provide a low level of sodium (10 to 25 mmol/L) in recognition that sodium intake may promote intestinal absorption of fluid as well as assist in rehydration. The sodium level of commercial oral rehydration fluids (used in the clinical treatment of diarrhoea and dehydration) is higher than that of the present range of sports drinks. However, even if research indicates that intestinal glucose transport is optimally stimulated at higher sodium concentrations, concern for the palatability of sports drinks may impose a lower ceiling for sodium levels. Commercial viability of a sports drink requires that it provide a refreshing and palatable fluid replacement across a wide variety of sports and exercise situations.(ABSTRACT TRUNCATED AT 400 WORDS)

Dietary intakes and food use of groups of elite Australian male athletes.

The present study conducted dietary surveys of four groups of Australian male athletes: triathletes, marathon runners, Australian Rules football players, and Olympic weightlifters. Their training diets were assessed via a 7-day food record from which mean daily intakes of energy, macronutrients, and key micronutrients were estimated. The data were compared between groups as well as to recommendations in the literature for athlete nutrition. Results showed major differences between groups. The contribution of carbohydrate to total energy intake was greater for triathletes and marathon runners than for the other two groups. There was no difference between all four groups in the total amount of fat consumed, yet its contribution to total energy intake was significantly lower for triathletes and marathon runners. The football players and weightlifters consumed a similar fat:energy ratio as the typical Australian diet. Furthermore, the micronutrient density of the football players' diets was significantly lower than that of the other groups.

Sports nutrition. Approaching the nineties.

A sophisticated appreciation of the role of nutrition in athletic performance has been made possible by increasing knowledge of the physiology of exercise. The nutritional issues of training are of primary importance, since this occupies most of the athlete's effort. The nutritional support of an intense daily training programme includes an appropriately high energy intake, predominantly in the form of carbohydrate in order to continually replenish muscle glycogen stores. Recent review of the protein needs of athletes indicates that requirements may be substantially above those of sedentary subjects, to account for the oxidation of amino acids during exercise as well as the retention of nitrogen during periods of muscle building. However, these increased requirements are likely to be met by the generous protein intakes anticipated in a high energy diet. The same would seem to hold true for micronutrient considerations, although there is no evidence that vitamin requirements are considerably increased by exercise. Nevertheless, a high energy diet chosen from a sufficiently varied range of foods should allow micronutrient intakes well in excess of population recommended dietary intake levels. Current interest is focused on the mineral status of athletes, particularly that of iron and calcium. In the case of iron, there is a possibility that the increased level of loss by some endurance athletes will not be met by their usual dietary patterns. Screening for early signs of iron deficiency, and appropriate supplementation and dietary counselling seem warranted in high risk groups. Competition poses the challenge of identifying possible factors limiting performance, and taking steps to delay or reduce these. Of paramount importance is body temperature regulation through the maintenance of hydration levels. This issue has long been recognised, but recent studies of gastric emptying and the benefits of carbohydrate supplementation during exercise have caused an update of the advice to athletes regarding fluid intake during exercise. It now seems possible to simultaneously achieve fluid and carbohydrate requirements for endurance exercise within a wide range of choice of beverages containing up to 10% carbohydrate. Concern about the adequacy of carbohydrate fuel stores in endurance exercise situations is also well known. The recognition that training achieves various physiological adaptations to enhance the lifespan of fuel stores has taken away some of the attention previously focussed on carbohydrate-loading techniques.(ABSTRACT TRUNCATED AT 400 WORDS)

A study of dietary patterns of elite Australian football players.

This report describes the dietary patterns of 56 elite Australian Rules football players. Data collected included an anthropometric profile, training information, and measurements of haemoglobin and blood lipids. Information on dietary practices, for training and game preparation, was collected by interview and food diary. Analysis of training diets showed a mean energy intake of 14.2 MJ/day (0.17 MJ/kg/day). Mean protein intake was 126 g/day (1.5 g/kg/day). The proportions of dietary energy contributed by the macronutrients were carbohydrate, 44%; fat, 37%; protein, 15%; and alcohol, 4%. Mean daily intake of selected vitamins and minerals from food sources was: retinol activity, 1439 mg; thiamin, 1.7 mg; riboflavin, 2.8 mg; niacin equivalents, 45.1 mg; vitamin C, 139 mg; iron, 19.6 mg; and calcium, 1016 mg. Carbohydrate intake was considered low, but overall intake of nutrients studied was adequate.

A study of carbohydrate loading techniques used by marathon runners.

Carbohydrate loading techniques were studied in a survey of 76 marathon runners. It was found that these runners practised a variety of methods that they believed would achieve carbohydrate loading. Analysis of records of food use showed that the diets actually used by runners did not reach the level of carbohydrate specified in the high carbohydrate phase of the glycogen loading regimens reported in the literature. It is suggested that in a free-living situation, without specific instructions or a knowledge of nutrition and food composition, runners are limited in their ability to achieve the dietary requirements of carbohydrate loading.

Diet Patterns of Elite Australian Male Triathletes.

In brief: The triathlon makes heavy demands on the body and especially on glycogen supply. This article describes the self-reported diet practices of 25 elite Australian male triathletes during training and racing. They consumed a mean of 4,095 kcal/day, 59.5% of which was carbohydrate, 13% protein, 27% fat, and 0.5% alcohol; glycogen and protein intakes met or surpassed recommended levels. Intakes of five vitamins and two minerals also exceeded recommendations, and iron status was satisfactory. The athletes ate carbohydrate mostly in complex form, snacking frequently to get enough for energy needs. Few subjects trained deliberately to build up a tolerance for consuming food and fluids during competition.

Faster assay of H2 in breath by dedicated instruments compared with conventional gas chromatography.

Recently available instruments dedicated to the clinical assay of hydrogen in breath were tested and the results compared with those from a conventional thermal conductivity gas chromatograph. We found the Quintron Model 12 Microlyzer and the GMI Exhaled Hydrogen Monitor to give much faster and more sensitive results than the Gow-Mac 550 conventional gas chromatograph, and their readout is digital rather than graphical. Linearity of response, accuracy, and precision were similar for all those instruments. Maintenance requirements and performance characteristics of the three instruments are compared in detail and practical advice is given on daily operation.

Seasonal changes in body composition in Australian Rules footballers.

Anthropometric measurements were collected from a group of Australian Rules footballers at the start and end of the competitive season. Eighty-nine players were studied, drawn from a top level professional league team, a second level association team and an A-grade amateur association team. Changes in the physical profile of these players during the season were observed. A small but significant gain in fat-free body mass in the top level players was observed (0.9 kg, p less than 0.01), but no change in body fat. The intermediate level players showed no significant change in body mass and a tendency toward a slight loss in body fat, while the lower level players showed a significant loss in body fat during the season (1.8 kg, p less than 0.001) without significant change in fat-free body mass.

Substrate aggregation and cooperative enzyme kinetics: consideration of enzyme access with large aggregates.

Consideration was given to a system in which an enzyme substrate indefinitely self-associates according to a general model with f sites of aggregation and a single intrinsic binding constant k. Where enzyme attack occurs at random points on the substrate surface, surface regions will be obscured from enzyme access by aggregate formation. The significance of reduced surface access for the infinite array of different size aggregates which co-exist was explored through use of a reacted site probability function, PA: the proportion of total substrate surface which is accessible to the enzyme was estimated as the fraction of total sites for aggregation which are unoccupied. The effective substrate concentration was thereby specified in terms of total substrate concentration (mA) by the simple expression mA = (1 - PA)mA. Plots of simulated v versus mA data were examined for a Michaelis-Menten enzyme of maximal velocity Vm and Michaelis constant Km to reveal deviations from expected enzyme behaviour; corresponding Hofstee (v/mA versus v) plots were found to be convex to the v axis as is characteristic of a negatively cooperative enzyme. As self-association is known to occur widely with large or small molecules in solution, the experimenter should be aware of the potential for these phenomena in kinetic studies to produce pseudo-allosteric effects, or to mask true allosteric behaviour.

Australian Rules football: an anthropometric study of participants.

Anthropometric measurements and personal data were collected from 119 Australian Rules footballers from Victoria. A top level professional league team, a second level association team, and an A-grade amateur association team were observed, representing three levels of ability. The profile of physical features of these athletes at the beginning of the season is presented. A gradation of body size was observed between teams. The players in the top level team were slightly taller and heavier than those in the other teams. They had less body fat, as shown by lesser skinfold thicknesses, a smaller percentage body fat as determined by prediction equations, and a greater fat-free mass. The intermediate level team showed an intermediate level of body fat and the lower level team had the highest proportion of fat.

Plasma insulin response and food intake in pseudopregnant rats.

1. Plasma insulin response to an intravenous glucose injection was measured in anaesthetised pseudopregnant and non-pregnant rats. Food intakes and body composition were also compared in pseudopregnant and non-pregnant animals. 2. The insulin responses and food intakes were greater in the pseudopregnant group. 3. Pseudopregnancy increased the fat-free dry weight of the animals and there was a tendency for the proportion of fat to be increased. 4. The results provide further evidence to indicate that in the rat progesterone plays a significant part in increasing insulin secretion during pregnancy.

Bacteriocin of a group A streptococcus: partial purification and properties.

The production of bacteriocin-like inhibition by certain strains of group A streptococci was demonstrated during the growth of these organisms on solid nutrient media. Active bacteriocin could not be recovered from broth cultures, possibly because of its inactivation by streptococcal proteinase. The bacteriocin, streptocin A, produced by Streptococcus pyogenes strain FF-22 was partially purified by chemical precipitation and chromatography on carboxymethyl-cellulose. Streptocin A inhibited the growth of various gram-positive organisms but none of a wide range of different gram-negative strains. The bacteriocin was inactivated by proteolytic enzymes and, although labile in alkali, it was extremely stable to heating in mild acids.