ORCID Profile
0000-0001-6726-9328
Current Organisation
University of South Australia
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Publisher: Wiley
Date: 14-02-2017
DOI: 10.1113/JP273230
Publisher: Wiley
Date: 19-08-2021
DOI: 10.1113/JP280221
Abstract: Brief (5–6 days) adaptation to a low carbohydrate high fat diet in elite athletes increased exercise fat oxidation to rates previously observed with medium (3–4 weeks) or chronic ( months) adherence to this diet, with metabolic changes being washed out in a similar time frame. Increased fat utilisation during exercise was associated with a 5–8% increase in oxygen cost at speeds related to Olympic Programme races. Acute restoration of endogenous carbohydrate (CHO) availability (24 h high CHO diet, pre‐race CHO) only partially restored substrate utilisation during a race warm‐up. Fat oxidation continued to be elevated above baseline values although it was lower than achieved by 5–6 days’ keto adaptation CHO oxidation only reached 61% and 78% of values previously seen at exercise intensities related to race events. Acute restoration of CHO availability failed to overturn the impairment of high‐intensity endurance performance previously associated with low carbohydrate high fat adaptation, potentially due to the blunted capacity for CHO oxidation. We investigated substrate utilisation during exercise after brief (5–6 days) adaptation to a ketogenic low‐carbohydrate (CHO), high‐fat (LCHF) diet and similar washout period. Thirteen world‐class male race walkers completed economy testing, 25 km training and a 10,000 m race (Baseline), with high CHO availability (HCHO), repeating this (Adaptation) after 5–6 days’ LCHF ( n = 7 CHO: g day −1 , protein: 2.2 g kg −1 day −1 80% fat) or HCHO ( n = 6 CHO: 9.7 g kg −1 day −1 protein: 2.2 g kg −1 day −1 ) diet. An Adaptation race was undertaken after 24 h HCHO and pre‐race CHO (2 g kg −1 ) diet, identical to the Baseline race. Substantial ( %) increases in exercise fat oxidation occurred in the LCHF Adaptation economy and 25 km tests, reaching mean rates of ∼1.43 g min −1 . However, relative (ml min −1 kg −1 ) was higher ( P 0.0001), by ∼8% and 5% at speeds related to 50 km and 20 km events. During Adaptation race warm‐up in the LCHF group, rates of fat and CHO oxidation at these speeds were decreased and increased, respectively ( P 0.001), compared with the previous day, but were not restored to Baseline values. Performance changes differed between groups ( P = 0.009), with all HCHO athletes improving in the Adaptation race (5.7 (5.6)%), while 6/7 LCHF athletes were slower (2.2 (3.4)%). Substrate utilisation returned to Baseline values after 5–6 days of HCHO diet. In summary, robust changes in exercise substrate use occurred in 5–6 days of extreme changes in CHO intake. However, adaptation to a LCHF diet plus acute restoration of endogenous CHO availability failed to restore high‐intensity endurance performance, with CHO oxidation rates remaining blunted.
Publisher: Springer Science and Business Media LLC
Date: 08-10-2021
DOI: 10.1007/S13668-021-00374-0
Abstract: The 2013 Australian Dietary Guidelines (ADG) have been criticised for making only brief reference to sustainability considerations. With the ADG currently under review, the purpose of this rapid review was to determine the environmental impacts associated with food consumption in Australia and New Zealand. Of the 20 articles included, greenhouse gas emissions (GHGe) were the most common environmental indicator (n = 12), followed by water use and water footprint (n = 7), and carbon footprint (n = 3). Whilst there are commonalities between different environmental indicators such as the large impact of discretionary food consumption on GHGe, cropland scarcity footprint, and water scarcity footprint, there is wide variation in these indicators for other food groups. Furthermore, modelling of current food consumption data to the recommended diet does not necessarily result in improvement of all indicators. The next iteration of the ADG should promote consumption of foods and dietary patterns that are associated with positive health and environmental outcomes.
Publisher: Public Library of Science (PLoS)
Date: 26-06-2020
Publisher: Human Kinetics
Date: 09-2018
Abstract: 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 in idualized 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 (∼14.8 MJ/d) and protein (∼2.1 g·kg −1 ·day −1 ) and achieved desired differences for fat and CHO, with high CHO availability and periodized CHO availability: CHO = 8.5 g·kg −1 ·day −1 , 60% energy, fat = 20% of energy and low-CHO high-fat diet: 0.5 g·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.
Publisher: Wiley
Date: 29-08-2013
Publisher: MDPI AG
Date: 05-05-2022
DOI: 10.3390/NU14091929
Abstract: We implemented a multi-pronged strategy (MAX) involving chronic (2 weeks high carbohydrate [CHO] diet + gut-training) and acute (CHO loading + 90 g·h−1 CHO during exercise) strategies to promote endogenous and exogenous CHO availability, compared with strategies reflecting lower ranges of current guidelines (CON) in two groups of athletes. Nineteen elite male race walkers (MAX: 9 CON:10) undertook a 26 km race-walking session before and after the respective interventions to investigate gastrointestinal function (absorption capacity), integrity (epithelial injury), and symptoms (GIS). We observed considerable in idual variability in responses, resulting in a statistically significant (p 0.001) yet likely clinically insignificant increase (Δ 736 pg·mL−1) in I-FABP after exercise across all trials, with no significant differences in breath H2 across exercise (p = 0.970). MAX was associated with increased GIS in the second half of the exercise, especially in upper GIS (p 0.01). Eighteen highly trained male and female distance runners (MAX: 10 CON: 8) then completed a 35 km run (28 km steady-state + 7 km time-trial) supported by either a slightly modified MAX or CON strategy. Inter-in idual variability was observed, without major differences in epithelial cell intestinal fatty acid binding protein (I-FABP) or GIS, due to exercise, trial, or group, despite the 3-fold increase in exercise CHO intake in MAX post-intervention. The tight-junction (claudin-3) response decreased in both groups from pre- to post-intervention. Groups achieved a similar performance improvement from pre- to post-intervention (CON = 39 s [95 CI 15–63 s] MAX = 36 s [13–59 s] p = 0.002). Although this suggests that further increases in CHO availability above current guidelines do not confer additional advantages, limitations in our study execution (e.g., confounding loss of BM in several in iduals despite a live-in training c environment and significant increases in aerobic capacity due to intensified training) may have masked small differences. Therefore, athletes should meet the minimum CHO guidelines for training and competition goals, noting that, with practice, increased CHO intake can be tolerated, and may contribute to performance outcomes.
Publisher: MDPI AG
Date: 12-08-2021
DOI: 10.3390/NU13082767
Abstract: Given the importance of exercise economy to endurance performance, we implemented two strategies purported to reduce the oxygen cost of exercise within a 4 week training c in 21 elite male race walkers. Fourteen athletes undertook a crossover investigation with beetroot juice (BRJ) or placebo (PLA) [2 d preload, 2 h pre-exercise + 35 min during exercise] during a 26 km race walking at speeds simulating competitive events. Separately, 19 athletes undertook a parallel group investigation of a multi-pronged strategy (MAX n = 9) involving chronic (2 w high carbohydrate [CHO] diet + gut training) and acute (CHO loading + 90 g/h CHO during exercise) strategies to promote endogenous and exogenous CHO availability, compared with strategies reflecting lower ranges of current guidelines (CON n = 10). There were no differences between BRJ and PLA trials for rates of CHO (p = 0.203) or fat (p = 0.818) oxidation or oxygen consumption (p = 0.090). Compared with CON, MAX was associated with higher rates of CHO oxidation during exercise, with increased exogenous CHO use (CON peak = ~0.45 g/min MAX: peak = ~1.45 g/min, p 0.001). High rates of exogenous CHO use were achieved prior to gut training, without further improvement, suggesting that elite athletes already optimise intestinal CHO absorption via habitual practices. No differences in exercise economy were detected despite small differences in substrate use. Future studies should investigate the impact of these strategies on sub-elite athletes’ economy as well as the performance effects in elite groups.
Publisher: Public Library of Science (PLoS)
Date: 04-06-2020
No related grants have been discovered for Sara Forbes.