High Carbohydrate Availability Research Articles

Accuracy of a continuous glucose monitoring system applied before, during, and after an intense leg-squat session with low- and high-carbohydrate availability in young adults without diabetes.

The aim was to assess the accuracy of a continuous blood glucose monitoring (CGM) device (Abbott FreeStyle Libre 3) against capillary blood glucose measurement (BGM) before, during, and after an intense lower body strength training session in connection with high- versus low-carbohydrate breakfasts. Nine adults (22 ± 2 years) completed a strength training session (10 × 10 at 60% 1RM) twice after high-carbohydrate and twice after low-carbohydrate breakfasts. CGM accuracy versus BGM was assessed across four phases: post-breakfast, pre-exercise, exercise, and post-exercise. Overall fed state mean BGM levels were 84.4 ± 20.6mg/dL. Group-level Bland-Altman analysis showed acceptable agreement between CGM and BGM across all phases, with mean biases between -7.95 and -17.83mg/dL; the largest discrepancy was in the post-exercise phase. Mean absolute relative difference was significantly higher post-exercise compared to pre-exercise and exercise phases, for overall data and after the high-carbohydrate breakfast (all p ≤ 0.02). Clark Error Grid analysis showed 50.5-64.3% in Zone A and 31.7-44.6% in Zone B, with an increase in treatment errors during and after exercise. In this group of healthy participants undergoing strength training, CGM showed satisfactory accuracy in glucose monitoring but varied substantially between individuals compared to BGM and fails in meeting clinical criteria for diabetic monitoring. CGM could aid non-diabetic athletes by tracking glucose fluctuations due to diet and exercise. Although utilization of CGM shows potential in gathering, analyzing, and interpreting interstitial glucose for improving performance, the application in sports nutrition is not yet validated, and challenges in data interpretation could limit its adoption.

Continuous Glucose Monitoring in Endurance Athletes: Interpretation and Relevance of Measurements for Improving Performance and Health

Blood glucose regulation has been studied for well over a century as it is intimately related to metabolic health. Research in glucose transport and uptake has also been substantial within the field of exercise physiology as glucose delivery to the working muscles affects exercise capacity and athletic achievements. However, although exceptions exist, less focus has been on blood glucose as a parameter to optimize training and competition outcomes in athletes with normal glucose control. During the last years, measuring glucose has gained popularity within the sports community and successful endurance athletes have been seen with skin-mounted sensors for continuous glucose monitoring (CGM). The technique offers real-time recording of glucose concentrations in the interstitium, which is assumed to be equivalent to concentrations in the blood. Although continuous measurements of a parameter that is intimately connected to metabolism and health can seem appealing, there is no current consensus on how to interpret measurements within this context. Well-defined approaches to use glucose monitoring to improve endurance athletes’ performance and health are lacking. In several studies, blood glucose regulation in endurance athletes has been shown to differ from that in healthy controls. Furthermore, endurance athletes regularly perform demanding training sessions and can be exposed to high or low energy and/or carbohydrate availability, which can affect blood glucose levels and regulation. In this current opinion, we aim to discuss blood glucose regulation in endurance athletes and highlight the existing research on glucose monitoring for performance and health in this population.

Valorization of lipid-extracted spent coffee grounds: The synthesis of levulinic acid by thermochemical process

Due to increased coffee consumption, spent coffee grounds (SCG) are an ever-growing waste management concern, despite the opportunity to recycle and reuse this valuable bioresource. SCG is an attractive feedstock for the production of bio-based compounds due to its high carbohydrate content and availability. This study developed the thermochemical conversion using an acid catalyst for the production of valuable platform chemicals (levulinic acid and formic acid) from lipid-extracted SCG. Conversion condition was optimized using statistical methodology and the reciprocal interactions between the reaction factors were analyzed. As a consequence of optimizing conversion conditions, the maximum yields of levulinic acid and formic acid were achieved at 190 °C, 10 % lipid-extracted SCG, 0.4 M sulfuric acid, and 60 min: 15.6 % and 7.73 %, respectively, based on biomass weight. Furthermore, in the reciprocal interactions of reaction factors, larger LA yields were achieved when the temperature was elevated, the catalyst concentration was decreased, and the reaction time was prolonged under the experimental ranges. According to these findings, lipid-extracted SCG has high potential as a sustainable and renewable feedstocks for the synthesis of bio-based platform chemicals in the biorefinery sector.

Analysis of walnut fruit quality based on source-sink relationships

In the paper, we investigate the relationship between the walnut fruit quality and the leaf-to-fruit ratio (LFR). The LFR had a significant effect on the physical quality of walnuts (P < 0.05), and the fruit volume, fruit fresh weight, fruit dry weight, nut dry weight and kernel dry weight increased with an increasing LFR. However, the LFR had no significant effect on the crude protein and crude fat kernel contents (P > 0.05). The number of cells per unit area and the cross-sectional area of the green husk cells with 5L : 1F were significantly higher than those with 1L : 3F and 2L : 3F (P < 0.05). The number of cells per unit area of the kernel with 1L : 3F and 2L : 3F was significantly higher than that with the other LFRs (P < 0.05). There was no significant difference in the NDW between the natural and girdled fruit-bearing shoots with 2L : 1F (P > 0.05). We concluded that the high carbohydrate availability with the high LFR augmented the fruit size by increasing the number of cells in the green husk and kernels. There was no change in the crude protein and crude fat contents in the kernels, possibly due to the proportion of the sugar to the fat distribution not affected by the LFR. Two leaves with good light were necessary to ensure the normal growth and development of one walnut fruit on girdled fruit-bearing shoots.

Ecological impacts of fungal wood decay types: A review of current knowledge and future research directions

AbstractI summarize current knowledge about the ecosystem functions of wood decomposition in forests with a particular focus on the effects of fungal wood decay types (traditionally categorized into white‐, brown‐, and soft‐rot) on the community composition of saproxylic organisms, forest tree regeneration, and carbon sequestration. Deadwoods of different decay types show markedly different physicochemical and biological properties. High carbohydrate availability in white‐rotted wood promotes the activities of nitrogen‐fixing bacteria; thus white‐rotted wood is a good dietary source for many wood‐eating invertebrates. In contrast, brown‐rotted wood is unattractive to saproxylic communities due to the high recalcitrance of accumulated lignin, low nutrient content, and low pH. Nevertheless, some species have adapted to these conditions and form distinctive communities on brown‐rotted wood. Tree seedlings that are associated with brown‐rotted wood are symbiotic with arbuscular and ericoid mycorrhizal fungal species, but not ectomycorrhizal species. Thus, the diversity of fungal communities associated with a variety of wood decay types produces habitat diversity for saproxylic communities and promotes biodiversity in forest ecosystems. Wood decay type also affects carbon sequestration in forests as brown‐rotted wood might be more instrumental in soil organic matter accumulation than white‐rotted wood. An important aspect of wood decay type is that the wood decay activities of fungi can have indirect long‐lasting cascading impacts on forest biodiversity by altering the physicochemical properties of deadwood. Including the effects of wood decay type in ecological models is thus important for predicting the long‐term dynamics of biodiversity, vegetation, and carbon cycling in forest ecosystems.

Carbohydrate for endurance athletes in competition questionnaire (CEAC-Q): validation of a practical and time-efficient tool for knowledge assessment

PurposeDespite unequivocal evidence demonstrating high carbohydrate (CHO) availability improves endurance performance, athletes often report under-eating CHO during competition. Such findings may be related to a lack of knowledge though currently there are no practical or time-efficient tools to assess CHO knowledge in athletes. Accordingly, we aimed to validate a novel questionnaire to rapidly assess endurance athletes’ knowledge of competition CHO guidelines.MethodsThe Carbohydrate for Endurance Athletes in Competition Questionnaire (CEAC-Q) was created by research-active practitioners, based on contemporary guidelines. The CEAC-Q comprised 25 questions divided into 5 subsections (assessing CHO metabolism, CHO loading, pre-event meal, during-competition CHO and recovery) each worth 20 points for a total possible score of 100.ResultsA between-group analysis of variance compared scores in three different population groups to assess construct validity: general population (GenP; n = 68), endurance athletes (EA; n = 145), and sports dietitians/nutritionists (SDN; n = 60). Total scores were different (mean ± SD) in all pairwise comparisons of GenP (17 ± 20%), EA (46 ± 19%) and SDN (76 ± 10%, p < 0.001). Subsection scores were also significantly different between the groups, with mean subsection scores of 3.4 ± 4.7% (GenP), 9.2 ± 5.2% (EA) and 15.2 ± 3.5% (SDN, p < 0.001). Test–retest reliability of the total CEAC-Q was determined in EA (r = 0.742, p < 0.001).ConclusionTaking ~ 10 min to complete, the CEAC-Q is a new psychometrically valid, practical and time-efficient tool for practitioners to assess athletes’ knowledge of CHO for competition and guide subsequent nutrition intervention.

Sustained Exposure to High Carbohydrate Availability Does Not Influence Iron-Regulatory Responses in Elite Endurance Athletes.

This study implemented a 2-week high carbohydrate (CHO) diet intended to maximize CHO oxidation rates and examined the iron-regulatory response to a 26-km race walking effort. Twenty international-level, male race walkers were assigned to either a novel high CHO diet (MAX = 10g/kg body mass CHO daily) inclusive of gut-training strategies, or a moderate CHO control diet (CON = 6g/kg body mass CHO daily) for a 2-week training period. The athletes completed a 26-km race walking test protocol before and after the dietary intervention. Venous blood samples were collected pre-, post-, and 3hr postexercise and measured for serum ferritin, interleukin-6, and hepcidin-25 concentrations. Similar decreases in serum ferritin (17-23%) occurred postintervention in MAX and CON. At the baseline, CON had a greater postexercise increase in interleukin-6 levels after 26km of walking (20.1-fold, 95% CI [9.2, 35.7]) compared with MAX (10.2-fold, 95% CI [3.7, 18.7]). A similar finding was evident for hepcidin levels 3hr postexercise (CON = 10.8-fold, 95% CI [4.8, 21.2]; MAX = 8.8-fold, 95% CI [3.9, 16.4]). Postintervention, there were no substantial differences in the interleukin-6 response (CON = 13.6-fold, 95% CI [9.2, 20.5]; MAX = 11.2-fold, 95% CI [6.5, 21.3]) or hepcidin levels (CON = 7.1-fold, 95% CI [2.1, 15.4]; MAX = 6.3-fold, 95% CI [1.8, 14.6]) between the dietary groups. Higher resting serum ferritin (p = .004) and hotter trial ambient temperatures (p = .014) were associated with greater hepcidin levels 3hr postexercise. Very high CHO diets employed by endurance athletes to increase CHO oxidation have little impact on iron regulation in elite athletes. It appears that variations in serum ferritin concentration and ambient temperature, rather than dietary CHO, are associated with increased hepcidin concentrations 3hr postexercise.

High-fat versus high-carbohydrate diets for optimal higher intensity endurance exercise performance: and the winner is….

High-fat versus high-carbohydrate diets for optimal higher intensity endurance exercise performance: and the winner is….

Microstructural and carbohydrate compositional changes induced by enzymatic saccharification of green seaweed from West Africa

The use of marine macroalgae as carbon source for fermentation is gaining increasing attention due to their high carbohydrate content and availability. Three green seaweed species Chaetomorpha linum, Ulva fasciata and Caulerpa taxifolia were investigated for their amenability to enzymatic saccharification. Microstructural changes were studied in order to understand the physical changes occurring in the seaweeds during saccarification and to identify structural barriers. C. linum had highest glucan content (20%), compared to 16% in U. fasciata and 6% in C. taxifolia indicating large differences in composition. Glucose yields obtained after 24 h of enzymatic saccharification were 59, 38 and 60% for C. taxifolia, U. fasciata and C. linum, respectively, based on the glucan content. Pre-autoclaving increased the saccharification yield to 81, 99 and 71%, respectively. Morphologically, C. linum displayed unbranched filaments, U. fasciata two-cell layer large sheets and C. taxifolia featured leaf like structures. Enzymatic saccharification resulted in cell wall degradation and release of the chlorophyll content in C. linum, delamination of sheets in U. fasciata and surface erosion of leaves in C. taxifolia. C. taxifolia deviated in being very rich in β-1,3 linked xylan (46%), which was only hydrolysed at 1% xylose yield due to lack of β-1,3-xylanase. Based on the high cellulose content and no need for pre-treatment C. linum was the best source of glucose among the three types of green seaweed species. Further studies are warranted to assess fermentation. We also conclude that for C. taxifolia enzymatic saccharification with β-1,3-xylanase might enable further xylose release than obtained here with the enzymatic cellulase treatment.

Carbohydrate Restriction in Type 1 Diabetes: A Realistic Therapy for Improved Glycaemic Control and Athletic Performance?

Around 80% of individuals with Type 1 diabetes (T1D) in the United States do not achieve glycaemic targets and the prevalence of comorbidities suggests that novel therapeutic strategies, including lifestyle modification, are needed. Current nutrition guidelines suggest a flexible approach to carbohydrate intake matched with intensive insulin therapy. These guidelines are designed to facilitate greater freedom around nutritional choices but they may lead to higher caloric intakes and potentially unhealthy eating patterns that are contributing to the high prevalence of obesity and metabolic syndrome in people with T1D. Low carbohydrate diets (LCD; <130 g/day) may represent a means to improve glycaemic control and metabolic health in people with T1D. Regular recreational exercise or achieving a high level of athletic performance is important for many living with T1D. Research conducted on people without T1D suggests that training with reduced carbohydrate availability (often termed “train low”) enhances metabolic adaptation compared to training with normal or high carbohydrate availability. However, these “train low” practices have not been tested in athletes with T1D. This review aims to investigate the known pros and cons of LCDs as a potentially effective, achievable, and safe therapy to improve glycaemic control and metabolic health in people with T1D. Secondly, we discuss the potential for low, restricted, or periodised carbohydrate diets in athletes with T1D.

A Framework for Periodized Nutrition for Athletics.

Over the last decade, in support of training periodization, there has been an emergence around the concept of nutritional periodization. Within athletics (track and field), the science and art of periodization is a cornerstone concept with recent commentaries emphasizing the underappreciated complexity associated with predictable performance on demand. Nevertheless, with varying levels of evidence, sport and event specific sequencing of various training units and sessions (long [macrocycle; months], medium [mesocycle; weeks], and short [microcycle; days and within-day duration]) is a routine approach to training periodization. Indeed, implementation of strategic temporal nutrition interventions (macro, meso, and micro) can support and enhance training prescription and adaptation, as well as acute event specific performance. However, a general framework on how, why, and when nutritional periodization could be implemented has not yet been established. It is beyond the scope of this review to highlight every potential nutritional periodization application. Instead, this review will focus on a generalized framework, with specific examples of macro-, meso-, and microperiodization for the macronutrients of carbohydrates, and, by extension, fat. More specifically, the authors establish the evidence and rationale for situations of acute high carbohydrate availability, as well as the evidence for more chronic manipulation of carbohydrates coupled with training. The topic of periodized nutrition has made considerable gains over the last decade but is ripe for further scientific progress and field application.

Organization of Dietary Control for Nutrition-Training Intervention Involving Periodized Carbohydrate Availability and Ketogenic Low-Carbohydrate High-Fat Diet.

The authors describe the implementation of a 3-week dietary intervention in elite race walkers at the Australian Institute of Sport, with a focus on the resources and strategies needed to accomplish a complex study of this scale. Interventions involved: traditional guidelines of high carbohydrate (CHO) availability for all training sessions; a periodized CHO diet which integrated sessions with low and high CHO availability within the same total CHO intake; and a ketogenic low-CHO high-fat diet. Seven-day menus and recipes were constructed for a communal eating setting to meet nutritional goals as well as individualized food preferences and special needs. Menus also included nutrition support before, during, and after exercise. Daily monitoring, via observation and food checklists, showed that energy and macronutrient targets were achieved. Diets were matched for energy (∼14.8MJ/d) and protein (∼2.1g·kg-1·day-1) and achieved desired differences for fat and CHO, with high CHO availability and periodized CHO availability: CHO = 8.5g·kg-1·day-1, 60% energy, fat = 20% of energy and low-CHO high-fat diet: 0.5g·kg-1·day-1 CHO, fat = 78% energy. There were no differences in micronutrient intake or density between the high CHO availability and periodized CHO availability diets; however, the micronutrient density of the low-CHO high-fat diet was significantly lower. Daily food costs per athlete were similar for each diet (∼AU$ 27 ± 10). Successful implementation and monitoring of dietary interventions in sports nutrition research of the scale of the present study require meticulous planning and the expertise of chefs and sports dietitians. Different approaches to sports nutrition support raise practical challenges around cost, micronutrient density, accommodation of special needs, and sustainability.

A Mismatch Between Athlete Practice and Current Sports Nutrition Guidelines Among Elite Female and Male Middle- and Long-Distance Athletes.

Contemporary nutrition guidelines promote a variety of periodized and time-sensitive recommendations, but current information regarding the knowledge and practice of these strategies among world-class athletes is limited. The aim of this study was to investigate this theme by implementing a questionnaire on dietary periodization practices in national/international level female (n = 27) and male (n = 21) middle- and long-distance runners/race-walkers. The questionnaire aimed to gain information on between and within-day dietary choices, as well as timing of pre- and posttraining meals and practices of training with low or high carbohydrate (CHO) availability. Data are shown as percentage (%) of all athletes, with differences in responses between subgroups (sex or event) shown as Chi-square x2 when p < .05. Nearly two-thirds of all athletes reported that they aim to eat more food on, or after, hard training days. Most athletes said they focus on adequate fueling (96%) and adequate CHO and protein (PRO) recovery (87%) around key sessions. Twenty-six percent of athletes (11% of middle vs 42% of long-distance athletes [x2 (1, n = 46) = 4.308, p = .038, phi = 0.3])) reported to undertake training in the fasted state, while 11% said they periodically restrict CHO intake, with 30% ingesting CHO during training sessions. Our findings show that elite endurance athletes appear to execute pre- and post-key session nutrition recovery recommendations. However, very few athletes deliberately undertake some contemporary dietary periodization approaches, such as training in the fasted state or periodically restricting CHO intake. This study suggests mismatches between athlete practice and current and developing sports nutrition guidelines.

Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers.

Key points Three weeks of intensified training and mild energy deficit in elite race walkers increases peak aerobic capacity independent of dietary support.Adaptation to a ketogenic low carbohydrate, high fat (LCHF) diet markedly increases rates of whole‐body fat oxidation during exercise in race walkers over a range of exercise intensities.The increased rates of fat oxidation result in reduced economy (increased oxygen demand for a given speed) at velocities that translate to real‐life race performance in elite race walkers.In contrast to training with diets providing chronic or periodised high carbohydrate availability, adaptation to an LCHF diet impairs performance in elite endurance athletes despite a significant improvement in peak aerobic capacity. We investigated the effects of adaptation to a ketogenic low carbohydrate (CHO), high fat diet (LCHF) during 3 weeks of intensified training on metabolism and performance of world‐class endurance athletes. We controlled three isoenergetic diets in elite race walkers: high CHO availability (g kg−1 day−1: 8.6 CHO, 2.1 protein, 1.2 fat) consumed before, during and after training (HCHO, n = 9); identical macronutrient intake, periodised within or between days to alternate between low and high CHO availability (PCHO, n = 10); LCHF (< 50 g day−1 CHO; 78% energy as fat; 2.1 g kg−1 day−1 protein; LCHF, n = 10). Post‐intervention, V˙O2 peak during race walking increased in all groups (P < 0.001, 90% CI: 2.55, 5.20%). LCHF was associated with markedly increased rates of whole‐body fat oxidation, attaining peak rates of 1.57 ± 0.32 g min−1 during 2 h of walking at ∼80% V˙O2 peak . However, LCHF also increased the oxygen (O2) cost of race walking at velocities relevant to real‐life race performance: O2 uptake (expressed as a percentage of new V˙O2 peak ) at a speed approximating 20 km race pace was reduced in HCHO and PCHO (90% CI: −7.047, −2.55 and −5.18, −0.86, respectively), but was maintained at pre‐intervention levels in LCHF. HCHO and PCHO groups improved times for 10 km race walk: 6.6% (90% CI: 4.1, 9.1%) and 5.3% (3.4, 7.2%), with no improvement (−1.6% (−8.5, 5.3%)) for the LCHF group. In contrast to training with diets providing chronic or periodised high‐CHO availability, and despite a significant improvement in V˙O2 peak , adaptation to the topical LCHF diet negated performance benefits in elite endurance athletes, in part due to reduced exercise economy.

Leaf respiration in grapevine ( Vitis vinifera 'Chasselas') in relation to environmental and plant factors

The leaf respiration (R D ) of grapevine ( Vitis vinifera 'Chasselas') was measured under field conditions during the growing season in leaves of different physiological ages in relation to the temperature and plant water status. R D increased with the temperature and was particularly high in young growing leaves on primary and lateral shoots. The R D response to the temperature evolved over the season according to the type and age of the leaves and their phenology. Leaf aging (senescence) induced a decrease in R D at the end of the season. At constant temperatures (20 °C), the highest R D rates were measured during the rapid plant growth phase (the Q10 values were also the highest), and they progressively decreased to reach their lowest rates at the end of the growing season. The lowest R D values were measured on leaves that were inserted opposite the clusters of primary shoots at any period during the season. Water stress led to a reduction in R D , especially when the leaf temperature was above 20 °C. The nocturnal R D evolution showed that the R D rates were greatest at nightfall when the nocturnal temperatures were still high and leaf carbohydrate availability was at its highest; the rates gradually decreased to reach the lowest R D values just before dawn.

New strategies in sport nutrition to increase exercise performance

Despite over 50 years of research, the field of sports nutrition continues to grow at a rapid rate. Whilst the traditional research focus was one that centred on strategies to maximise competition performance, emerging data in the last decade has demonstrated how both macronutrient and micronutrient availability can play a prominent role in regulating those cell signalling pathways that modulate skeletal muscle adaptations to endurance and resistance training. Nonetheless, in the context of exercise performance, it is clear that carbohydrate (but not fat) still remains king and that carefully chosen ergogenic aids (e.g. caffeine, creatine, sodium bicarbonate, beta-alanine, nitrates) can all promote performance in the correct exercise setting. In relation to exercise training, however, it is now thought that strategic periods of reduced carbohydrate and elevated dietary protein intake may enhance training adaptations whereas high carbohydrate availability and antioxidant supplementation may actually attenuate training adaptation. Emerging evidence also suggests that vitamin D may play a regulatory role in muscle regeneration and subsequent hypertrophy following damaging forms of exercise. Finally, novel compounds (albeit largely examined in rodent models) such as epicatechins, nicotinamide riboside, resveratrol, β-hydroxy β-methylbutyrate, phosphatidic acid and ursolic acid may also promote or attenuate skeletal muscle adaptations to endurance and strength training. When taken together, it is clear that sports nutrition is very much at the heart of the Olympic motto, Citius, Altius, Fortius (faster, higher, stronger).

Involvement of Carbohydrates in Response to Preconditioning Flooding in Two Clones of Populus deltoides Marsh. × P. nigra L.

Poplar, a fast-growing species widely used outside its original area of distribution, was evaluated in the present study to verify its tolerance and hardening to waterlogging in anticipation of its implementation in rehabilitation practices for marginal lands subjected to flooding. Three water regimes were applied to the plants, grown in pots, with two clones (I-488 and D-64) with different sensitivities to flooding. These plants included a lot consisting of control plants (C), which were irrigated with good drainage, a non-preconditioned lot (NPr), and a third lot that was preconditioned to flooding (Pr). Furthermore, flooding was imposed on NPr and Pr plants by submerging pots up to 5 cm above the collar for 60 days followed by a 40-day recovery period. At the end of these two periods, shoot dry mass, foliar concentrations of certain ions, soluble sugars, starch and proline, and the relative electrolyte leakage were evaluated. The preconditioning treatment conferred different degrees of hardness on the treated plants compared with NPr plants. Our results revealed that high carbohydrate availability (soluble sugars and starch) is suggested to participate in sustaining membrane integrity which may affect the recuperative potential of Pr plants, notably those of clone I-488, from flooding damage.

Self-selecting Fluid Intake while Maintaining High Carbohydrate Availability Does not Impair Half-marathon Performance

We aimed to test the hypothesis that self-selecting fluid intake but maintaining high exogenous CHO availability (60 g/h) does not compromise half-marathon performance. 15 participants completed 3 half-marathons while drinking a 6% CHO solution to guidelines (DRINK) or a non-caloric solution in self-selected volumes when consuming 3×glucose (20 g) gels (G-GEL) or glucose-fructose (13 g glucose+7 g fructose) gels (GF-GEL) per hour. Fluid intake (DRINK: 1 557±182, G-GEL: 473±234, GF-GEL: 404±144 ml) and percent body mass loss (DRINK: - 0.8±0.9, G-GEL: - 2.0±0.6, GF-GEL: -2.3±1.1) were different (P<0.05) between conditions, though race time did not differ (DRINK: 110.6±14.4, G-GEL: 110.3±14.6, GF-GEL: 113.7±12.8 min). In G-GEL, there was a positive correlation (P<0.05) between body mass loss and race time. Plasma glucose was lower (P<0.05) in GF-GEL compared with other conditions, and total CHO oxidation (DRINK: 3.2±0.5, G-GEL: 3.0±0.4, GF-GEL: 2.6±0.4 g/min) was lower (P=0.06) in this trial. Self-selecting fluid intake but maintaining high CHO availability does not impair half-marathon performance. Additionally, consuming glucose-fructose mixtures in sub-optimal amounts reduces plasma glucose and total rates of CHO oxidation.

Nutritional recommendations for water polo.

Water polo is an aquatic team sport that requires endurance, strength, power, swimming speed, agility, tactical awareness, and specific technical skills, including ball control. Unlike other team sports, few researchers have examined the nutritional habits of water polo athletes or potential dietary strategies that improve performance in water polo match play. Water polo players are typically well muscled, taller athletes; female players display higher levels of adiposity compared with their male counterparts. Positional differences exist: Center players are heavier and have higher body fat levels compared with perimeter players. Knowledge of the physical differences that exist among water polo players offers the advantage of player identification as well as individualizing nutrition strategies to optimize desired physique goals. Individual dietary counseling is warranted to ensure dietary adequacy, and in cases of physique manipulation. Performance in games and during quality workouts is likely to improve by adopting strategies that promote high carbohydrate availability, although research specific to water polo is lacking. A planned approach incorporating strategies to facilitate muscle glycogen refueling and muscle protein synthesis should be implemented following intensified training sessions and matches, particularly when short recovery times are scheduled. Although sweat losses of water polo players are less than what is reported for land-based athletes, specific knowledge allows for appropriate planning of carbohydrate intake strategies for match play and training. Postgame strategies to manage alcohol intake should be developed with input from the senior player group to minimize the negative consequences on recovery and player welfare.

Carbohydrate availability and exercise training adaptation: Too much of a good thing?

Traditional nutritional approaches to endurance training have typically promoted high carbohydrate (CHO) availability before, during and after training sessions to ensure adequate muscle substrate to meet the demands of high daily training intensities and volumes. However, during the past decade, data from our laboratories and others have demonstrated that deliberately training in conditions of reduced CHO availability can promote training-induced adaptations of human skeletal muscle (i.e. increased maximal mitochondrial enzyme activities and/or mitochondrial content, increased rates of lipid oxidation and, in some instances, improved exercise capacity). Such data have led to the concept of ‘training low, but competing high’ whereby selected training sessions are completed in conditions of reduced CHO availability (so as to promote training adaptation), but CHO reserves are restored immediately prior to an important competition. The augmented training response observed with training-low strategies is likely regulated by enhanced activation of key cell signalling kinases (e.g. AMPK, p38MAPK), transcription factors (e.g. p53, PPARδ) and transcriptional co-activators (e.g. PGC-1α), such that a co-ordinated up-regulation of both the nuclear and mitochondrial genomes occurs. Although the optimal practical strategies to train low are not currently known, consuming additional caffeine, protein, and practising CHO mouth-rinsing before and/or during training may help to rescue the reduced training intensities that typically occur when ‘training low’, in addition to preventing protein breakdown and maintaining optimal immune function. Finally, athletes should practise ‘train-low’ workouts in conjunction with sessions undertaken with normal or high CHO availability so that their capacity to oxidise CHO is not blunted on race day.