Dietary macro- and micronutrient requirements of endurance athletes

Energy expenditure and dietary intake during high-volume and low-volume training periods among male endurance athletes

The primary purpose of this study was to examine dietary intake in endurance-trained athletes during a week of high-volume and a week of low-volume training while measuring exercise energy expenditure (EEE), resting metabolic rate (RMR), and nonexercise activity thermogenesis (NEAT). In addition, compliance with current American College of Sports Medicine/American Dietetic Association nutrition and performance recommendations for macronutrients was evaluated. Energy expenditure and dietary intake were measured in 15 male endurance athletes during 2 nonconsecutive weeks resembling a high-volume and a low-volume training period. Anthropometric measurements were taken and percentage body fat was determined at the beginning and end of each week of training. Total daily energy expenditure (TDEE) was calculated by summing RMR, NEAT, and EEE. Dietary intake was assessed with an online food-frequency questionnaire completed at the end of each week of data collection. Despite significant differences between TDEE and energy intake, no difference in body composition between the beginning and end of either week of training was observed, suggesting underreporting of caloric intake. Further, no changes in total caloric intake or macronutrient intake occurred even though TDEE increased significantly during the high-volume training. Reported carbohydrate intake (4.5 g·kg(-1)) and fiber intake (25 g·day(-1)) were below recommendations, whereas fat intake (1.3 g·kg(-1)) was slightly above recommendations. In summary, no short-term dietary adjustments occurred in response to differences in training regimen. Because these athletes were generally consuming a Western diet, they may have required some support to achieve desirable intakes for health and performance.

Brisk walking offsets the increase in postprandial TAG concentrations found when changing to a diet with increased carbohydrate

We tested the hypothesis that 30 min of brisk walking daily would offset the increase in plasma TAG concentrations associated with substituting dietary fat for carbohydrate. Fourteen subjects (six males) aged 57 (sd 5) years underwent three 4 d trials in a counterbalanced order: (i) 4 d on a typical UK diet (40 % energy from fat, 45 % carbohydrate and 15 % protein); (ii) 4 d on an isoenergetic diet but substituting fat for carbohydrate in line with the present recommendations (30 % fat, 55 % carbohydrate and 15 % protein); (iii) 4 d on the same recommended diet with 30 min of brisk walking each day. The food provided for the first 3 d of each trial was isoenergetic with each volunteer's previously determined daily energy intake. On day 4, the subjects consumed breakfast, lunch and an early evening meal, equivalent in total to 90 % of their daily energy intake. Blood samples were collected and substrate utilisation and energy expenditure were determined in the fasted state and for 9 h postprandially. Substrate utilisation differed significantly among trials (P = 0.003); RER was higher on the recommended diet trial than during either of the other two trials (P = 0.012 and 0.021 for the UK diet and recommended diet with walking, respectively). The rise in plasma TAG concentrations over the day was steeper on the recommended diet trial than on the other two trials (trial x time interaction, P = 0.040). The increase in postprandial TAG concentrations associated with substituting dietary fat for carbohydrate was offset by 30 min of brisk walking daily.

Dietary conjugated linoleic acid increases endurance capacity and fat oxidation in mice during exercise

Ingestion of CLA activates beta-oxidation and causes loss of body fat in rodents. We investigated the effects of dietary CLA on endurance capacity and energy metabolism during exercise in mice. Five-week-old male BALB/c mice were fed a control diet containing 1.0% linoleic acid or a diet containing 0.5% CLA that replaced an equivalent amount of linoleic acid for 1 wk. The maximum swimming time until fatigue was significantly higher in the CLA-fed group than in the control group. During treadmill running, the respiratory exchange ratio was significantly lower in the CLA-fed group, but oxygen consumption did not differ significantly between groups, suggesting that FA contributed more as an energy substrate in the CLA-fed mice. The muscle lipoprotein lipase activity was significantly higher in the CLA-fed group than in the control group. These results suggest that CLA ingestion increases endurance exercise capacity by promoting fat oxidation during exercise.

Consumo de carboidratos e lipídios no desempenho em exercícios de ultra-resistência

A nutrição é uma importante ferramenta dentro da prática desportiva. Dentre as modalidades esportivas, a nutrição exerce uma grande influência nos chamados "esportes de desafio", que são as provas de ultra-resistência ou de longa duração. O custo energético de uma prova de ultra-resistência pode variar de 5.000 a 18.000kcal por dia. É amplamente aceito que o consumo de carboidratos antes e durante exercícios prolongados irá retardar o aparecimento da fadiga, poupando o glicogênio hepático e muscular e fornecendo glicose diretamente para os músculos em atividade. Recomenda-se que a dieta de atletas de ultra-resistência possua 70% ou mais, ou de 7 a 10 gramas por quilo de peso corporal de carboidratos. Porém, apesar da melhora apresentada com a nutrição bem planejada, alguns pesquisadores procuram desenvolver novas intervenções nutricionais, visando a melhora do rendimento, que continuam a ser estudadas, como a suplementação com lipídios, através do consumo de triglicerídeos de cadeia média (TCM) ou de dietas ricas em lipídios nos dias que antecedem a competição. Sendo assim, esta revisão possui como objetivo elucidar como os carboidratos e os lipídios podem influenciar o desempenho nos exercícios de ultra-resistência.

Chronic (-)-hydroxycitrate administration spares carbohydrate utilization and promotes lipid oxidation during exercise in mice

(-)-Hydroxycitrate (HCA) is an active ingredient that is extracted from the rind of the Indian fruit, Garcinia cambogia, which is available as an herbal supplement and is used to lose weight. In this study, the acute and chronic effects of HCA on energy metabolism were examined in male Std ddY mice. Mice were placed into metabolic chambers and administered 10 mg HCA or water (control) orally. Serum free fatty acid levels were significantly higher 100 min after administration in the HCA group, but the respiratory exchange ratio was not different from that in the control group. The concentration of glycogen in the gastrocnemius muscle was higher in the HCA group 16 h after administration, and in a separate study, the maximum swimming time until fatigue was slightly longer (P: = 0. 21) than that in the control group on d 1. The difference was significant on d 3 after 3 d of HCA or water administration. Other mice were administered 10 mg HCA or water orally twice a day for 25 d. On d 26, they were placed into metabolic chambers after administration and allowed to rest for 1 h, followed by 1 h of running at 15 m/min. Respiratory gas was monitored. The respiratory exchange ratio was significantly lower in the HCA group during both resting and exercising conditions. These results suggest that chronic administration of HCA promotes lipid oxidation and spares carbohydrate utilization in mice at rest and during running.

Low doses of dexamethasone suppress pituitary-adrenal function but augment the glycemic response to acute hypoxemia in fetal sheep during late gestation

Despite the widespread use of antenatal glucocorticoid therapy in obstetric practice, little is known about the effects of synthetic glucocorticoids on the fetal capacity to respond to episodes of acute hypoxemia, such as may occur during labor and delivery. This study investigated the effects of prolonged fetal exposure to low concentrations of dexamethasone on the fetal ACTH, cortisol, and glycemic responses to an episode of acute hypoxemia during the period of dexamethasone treatment in sheep. At 118 d of gestation (term is approximately 145 d), 11 fetal sheep had catheters implanted under halothane anesthesia. From 124 d, five fetuses were infused i.v. continuously with dexamethasone (1.80 +/- 0.15 microg x kg(-1) x h(-1) in 0.9% saline at 0.5 mL/h) for 48 h, and the other six fetuses received saline solution i.v. at the same rate. At 45 h of infusion, acute hypoxemia was induced in all fetuses for 1 h by reducing the maternal inspired fraction of oxygen. During glucocorticoid treatment, fetal plasma dexamethasone concentrations increased to 3.9 +/- 0.2 nM by 24 h and remained elevated for the rest of the infusion period. During hypoxemia, a similar fall in fetal arterial PO2 occurred in both saline-infused and dexamethasone-treated fetuses. In control fetuses, significant increases in plasma ACTH and cortisol concentrations and in blood glucose concentrations occurred during hypoxemia. Dexamethasone treatment prevented the increases in fetal plasma ACTH and cortisol, and augmented the blood glucose response, induced by hypoxemia. These data indicate that prolonged fetal exposure to low concentrations of dexamethasone suppresses pituitary-adrenal function, but augments the glycemic response, to acute hypoxemia in fetal sheep during late gestation.

Interaction of physical activity and diet: implications for lipoprotein metabolism

OBJECTIVE

To consider how physical activity interacts with diet to modify lipoprotein metabolism and comment on implications for human health.

DESIGN

An overview of lipoprotein metabolism is followed by a summary of the main effects of physical activity on lipoprotein metabolism. Interactions with dietary practice and the disposition of dietary lipid are reviewed, with comment on links with body fatness.

SETTING

Literature is reviewed in relation to the risk of atherosclerotic disease.

SUBJECTS

Although some data are presented on athletic groups, evidence relating to individuals with normal physical activity habits is mainly discussed.

RESULTS

Physical inactivity is a risk factor for cardiovascular disease and one mechanism may involve changes to lipoprotein metabolism. The consensus is that aerobic activity involving an expenditure of > or = 8 MJ week(-1) results in an increase in HDL cholesterol and probably decreases in fasting triacylglycerol. These changes Occur despite the spontaneous increase in the proportion of dietary energy from carbohydrate which accompanies increased exercise. For this reason, exercise may be a means of reducing the hypertriglyceridaemic and HDL-lowering effects of low fat (high carbohydrate) diets. Decreases in total and low density lipoprotein cholesterol are sometimes, but not always, reported in sedentary individuals beginning exercise. One mechanism linking all these changes may be alterations to the dynamics of triacylglycerol-rich particles, particularly in the fed state.

CONCLUSION

The expenditure of considerable amounts of energy through regular, frequent physical activity increases the turnover of lipid substrates, with effects on their transport and disposition which may reduce the progression of atherosclerosis.

Basic principles for compounding all-in-one parenteral nutrition admixtures

Parenteral nutrition admixtures are complex pharmaceutical entities. The more closely they are examined, the more physico-chemical interactions emerge that could potentially affect stability. The move towards large scale hospital or commercial preparation, with a requirement for extended shelf life, and the increasing use of admixtures as vehicles for drugs and pharmaconutrients have created new formulation challenges for pharmaceutical scientists.