Glucose is the primary fuel for the brain and also important for exercising muscle. The purpose of the thesis was to investigate the effects of the glycaemic index (GI) of mixed meals on appetite, cognitive performances and metabolic responses during intermittent exercise in recreationally active adults. Study one investigated whether a low GI (LGI) breakfast (GI = 42.5) could suppress appetite and reduce energy intake (EI) of 12 recreationally active females (28.2 ± 8.0 years) more than a high GI (HGI) breakfast (GI = 73.5). Area under the curve of the appetite score (AS AUC) following LGI breakfast was significantly greater than the HGI trial during the 60-min postprandial (pp) period (2568 ± 1027 vs. 2198 ± 821 mm∙min, p = 0.025). The HGI breakfast facilitated a stronger appetite suppressing effect up to eight hours post breakfast than the LGI trial (18834 ± 3906 vs. 21278 ± 3610 mm∙min, p = 0.028). The EI on the LGI trial day was significantly higher than on the pre-trial day (2,215 ± 576 vs. 1,748 ± 464 kcal, corrected p = 0.008). Fourteen recreationally active males (34.5 ± 8.9 years) in study two consumed the LGI (GI = 41.3) and HGI (GI = 74.3) breakfasts in the laboratory and then prescribed LGI and HGI meals in the free living environment. In line with study one, the AS AUC was significantly smaller following HGI than LGI breakfast over the 60-min pp period (2,989 ± 1,390 vs. 3,758 ± 1,290 mm∙min, p = 0.027). The HGI meals (GI = 76.9) suppressed appetite more than the LGI meals (GI = 39.6) over 12 hours on the trial day (35,454 ± 9,730 vs. 41,244 ± 8,829 mm∙min, p = 0.009) although energy balance was not different between trials. Study three investigated whether following a LGI breakfast (GI = 42.2) providing 1 g CHO kg-1 BM could result in a better vigilance and attention than a HGI breakfast (GI = 72.4), and reduced lunch EI in 16 recreationally active males (24.4 ± 3.6 years). A significant trial x time effect in the interference time of the Stroop Colour Word Task (SCWT) (p = 0.039) showed that the LGI breakfast maintained the attentional performance up to 90-min pp. Both high pre-task glucose concentration ([Glucose]) at 15-min pp and low pre-task [Glucose] at 105-min pp in the HGI trial were associated with unfavourable outcomes in vigilance in the Rapid Information Processing Task (RIPT). The LGI pre-task [Glucose] returning back to fasting level at 60-min pp was associated positively with the response time. The pre-lunch AS was a significant predictor of the lunch EI per fat free mass which explained 21% and 26% of variance in the LGI and HGI trials respectively. No significant difference was found in the ad libitum lunch EI between trials. Sixteen recreationally active males (27.8 ± 7.7 years) in study four consumed a LGI (GI = 42) and a HGI breakfast (GI = 72.8) providing 1.2 g CHO kg-1 BM consumed 60 minutes prior to intermittent running on two separate mornings. Better attentional performance at 150-min pp was found following LGI than HGI breakfast. The significant trial x time interaction in the SCWT (p = 0.045) showed the shortest interference time performed after the last exercise session in the LGI trial. The amounts of CHO and fat being oxidized were comparable between trials during three sessions of 16-min intermittent running with an average intensity of 65% V̇O2max. In conclusion, the pre-meal appetite sensation is more predictive of the subsequent meal EI than the pre-meal [Glucose]. The meal strategy for weight management in recreationally active adults may focus on greater appetite suppression by selecting HGI foods whilst maintaining healthy eating guidelines. Recreationally active males performing sports requiring high levels of vigilance and selective attention with low physical activity levels can benefit up to 60–90 min pp from the LGI breakfast. Their attentional performance can benefit from the LGI breakfast with moderate to high intermittent intensities in the late exercise period at 150–min pp. Recreationally active adults should consider the timing of meal consumption in relation to performing intermittent exercise, in order to maximize the advantages from the LGI or HGI breakfasts for cognitive performance or appetite suppression. They may be more liberal in pre-exercise food choices if substrate oxidation during intermittent running is only of their concern.

Research investigating the effects of pre-exercise meals with varying glycemic indices on exercise performance in intermittent sports is scarce. This study determined whether whole foods of low glycemic index (GI) resulted in a metabolic and performance advantage, in comparison to high GI foods, when eaten prior to extended intermittent cardiovascular exercise, such as tournament soccer play. Consenting trained participants (10 males, 4 females, 25.8 ± 7.3 y) completed two simulated soccer tournaments separated by at least seven days. Each testing day included two 90-minute soccer matches separated by a three hour break. Using a randomized cross-over design, low-GI, lentil-based meals (GI~42) or high-GI, potato-based meals (GI~78) matched for caloric value were consumed two hours prior to and then within one hour after the first soccer match. Blood glucose, lactate, insulin, free fatty acids, and respiratory gases were measured throughout the post-prandial and testing periods. Ratings of perceived exertion (RPE) and gastrointestinal symptoms were also recorded. Performance was measured by the distance covered during five one-minute sprints, separated by two minute and thirty second rest intervals, at the end of each match. Peak post-prandial blood glucose was higher (p<0.05) in the high-GI trial (8.9 ± 2.2 molL-1 [SD]) compared to the low GI trial (5.9 ± 1.3 mmolL-1) as was insulin prior to the start of exercise (19.4 ± 2.0 versus 9.2 ¬± 1.3 umolL-1, p<0.05). Blood lactate levels were significantly higher (p<0.05) at the end of the second match during the high-GI trial (6.1 ± 1.2 mmolL-1) compared to the low-GI trial (2.5 ± 0.4 mmolL-1). Breath-by-breath analysis showed lower (p<0.05) carbohydrate oxidation during the low-GI trials compared to the high-GI at the start of the first soccer match (p<0.05). Subjects reported greater feelings of hunger during the high-GI trial versus greater feelings of fullness during the low-GI trial (p<0.05), but RPE during the low-GI (14.1 ± 0.3) was similar to the high-GI meal (14.2 ± 0.3). Sprint distance was not significantly different between treatments (p=0.27). Overall, these findings suggest that lentil-based, low-GI foods are a comparable alternative to traditional high-GI pre-exercise meals, as they result in similar performance outcomes but improved metabolic profiles. Over the long-term, improving metabolic conditions during exercise may be beneficial to the health of athletes.

Research investigating the effects of pre-exercise meals with varying glycemic indices on exercise performance in intermittent sports is scarce. This study determined whether whole foods of low glycemic index (GI) resulted in a metabolic and performance advantage, in comparison to high GI foods, when eaten prior to extended intermittent cardiovascular exercise, such as tournament soccer play. Consenting trained participants (10 males, 4 females, 25.8 ± 7.3 y) completed two simulated soccer tournaments separated by at least seven days. Each testing day included two 90-minute soccer matches separated by a three hour break. Using a randomized cross-over design, low-GI, lentil-based meals (GI~42) or high-GI, potato-based meals (GI~78) matched for caloric value were consumed two hours prior to and then within one hour after the first soccer match. Blood glucose, lactate, insulin, free fatty acids, and respiratory gases were measured throughout the post-prandial and testing periods. Ratings of perceived exertion (RPE) and gastrointestinal symptoms were also recorded. Performance was measured by the distance covered during five one-minute sprints, separated by two minute and thirty second rest intervals, at the end of each match. Peak post-prandial blood glucose was higher (p<0.05) in the high-GI trial (8.9 ± 2.2 molL-1 [SD]) compared to the low GI trial (5.9 ± 1.3 mmolL-1) as was insulin prior to the start of exercise (19.4 ± 2.0 versus 9.2 ¬± 1.3 umolL-1, p<0.05). Blood lactate levels were significantly higher (p<0.05) at the end of the second match during the high-GI trial (6.1 ± 1.2 mmolL-1) compared to the low-GI trial (2.5 ± 0.4 mmolL-1). Breath-by-breath analysis showed lower (p<0.05) carbohydrate oxidation during the low-GI trials compared to the high-GI at the start of the first soccer match (p<0.05). Subjects reported greater feelings of hunger during the high-GI trial versus greater feelings of fullness during the low-GI trial (p<0.05), but RPE during the low-GI (14.1 ± 0.3) was similar to the high-GI meal (14.2 ± 0.3). Sprint distance was not significantly different between treatments (p=0.27). Overall, these findings suggest that lentil-based, low-GI foods are a comparable alternative to traditional high-GI pre-exercise meals, as they result in similar performance outcomes but improved metabolic profiles. Over the long-term, improving metabolic conditions during exercise may be beneficial to the health of athletes.

These studies investigated the effect of physical inactivity (prolonged sitting) and physical activity (walking, standing, and moderate intensity exercise) on postprandial plasma triglyceride concentration (PPTG). In the first study, we evaluated the effect of low intensity intermittent walking at ~25% VO₂max (WALK) and energy-matched moderate intensity running at ~65% VO₂max (RUN) on PPTG, compared to a sitting control (SIT). RUN reduced incremental area under the curves for plasma triglyceride concentration (TG AUC[subscript I]), compared to WALK by 17.3% (p = 0.04) and SIT by 27% (p [less than] 0.001). The reduced TG AUC[subscript I] in RUN was accompanied by enhanced whole body insulin sensitivity, compared to WALK and SIT (for both, p [less than] 0.05). Whole body postprandial fat oxidation at rest following a high fat test meal intake was enhanced in RUN by 31% (P [less than] 0.001) and to a lesser extent in WALK by 8.4% (p [less than] 0.005), compared to SIT. In the second study, we evaluated 1) the effect of 2 days of prolonged sitting on PPTG, and 2) the effect of 4 days of SIT on the ability of an acute bout of exercise to reduce PPTG, compared to the same days of active walking and standing with calorically balanced diet (WALK+B). To distinguish the effect of prolonged sitting from the excess calorie effect, we had a sitting condition with calorically balanced diet (SIT+B) in addition to a sitting condition with hypercaloric diet (SIT+H). Following 2 days of respective food and activity control, WALK+B was lower in TG AUC[subscript T] by 21.3% and AUC[subscript I] by 17.4%, compared to SIT+H (for both, p [less than] 0.005). WALK+B was lower than SIT+B for TG AUC[subscript T] by 17.7% (p = 0.165) and AUC[subscript I] by 23.5% (p = 0.145) although statistical significance was not achieved. Remarkably, an acute exercise following 4 days of either SIT+H or SIT+B failed to reduce both TG AUC[subscript T] and AUC[subscript I], compared to SIT+B in HFTT1. The same exercise following 4 days of WALK+B, however, reduced both TG AUC[subscript T] by 29% and TG AUC[subscript I] by 32% in HFTT2, compared to SIT+B in HFTT1 (for both, p [less than] 0.02). Further, both SIT conditions reduced relative whole body fat oxidation in favor of increases in carbohydrate oxidation, compared to WALK+B by more than 40% in both HFTT1 and HFTT2. Taken together, our data suggest that 1) exercise intensity plays an independent role with higher intensity being more effective than lower intensity exercise in reducing PPTG, and 2) prolonged sitting with excess energy intake amplifies PPTG and prolonged sitting impairs the ability of an acute bout of moderate intensity exercise to reduce PPTG. This emphasizes the importance of regular participation in moderate-to-vigorous intensity exercise and reducing sitting time by increasing non-exercise physical activities (i.e., walking and standing) for the favorable postprandial metabolic health from the individual and public health perspectives. / text

No description available.

Background: Modifying the gut microbiota through the administration of probiotics during high fat feeding has been shown to attenuate weight gain and body fat accretion while improving insulin sensitivity in animal models. Objective: Our objective was to determine the effects of the probiotic VSL#3 on body weightand composition, skeletal muscle substrate oxidation, and insulin sensitivity and during 4 weeks of high-fat, hypercaloric feeding. We hypothesized that the probiotic would attenuate the body weight and fat gain and adverse changes in insulin sensitivity and substrate oxidation following high fat, hypercaloric feeding in young, non-obese males. Methods: Twenty non-obese males (18-30 y) volunteered to participate in the present study. Following a 2-week eucaloric control diet, subjects underwent a dual x-ray absorptiometry (DXA) to determine body composition, an intravenous glucose tolerance test (IVGTT) to determine insulin sensitivity, a skeletal muscle biopsy for measurement of substrate oxidation. Serum endotoxin was also measured. Subsequently, subjects were randomized to receive either VSL#3 (2 satchets) or placebo during 4 weeks of consuming a high fat (55% fat), hypercaloric diet (+1,000 kcal/day). Macronutrient composition of the high fat diet was 55% fat, 30% carbohydrate, and 15% protein. Results: There were no differences between the groups in subject characteristics or in the dependent variables at baseline. Body weight and fat mass increased less (P<0.045) following the high fat diet with VSL#3 compared to placebo. Insulin sensitivity (and other IVGTT variables) and both glucose and fat oxidation did not change significantly with time or VSL#3 treatment. Serum endotoxin concentration was not different between groups following the high-fat diet. Conclusions: VSL#3, a multi-strain probiotic, attenuated body weight and fat gain following a 4-week high fat, hypercaloric diet compared with a placebo. There were no differences between the VSL and control in circulating endotoxin, insulin sensitivity (and other IVGTT variables) or in skeletal muscle substrate oxidation. / Ph. D.

The objective of this study is to compare the caloric expenditure and oxidative sources of underwater treadmill running and land-based treadmill running at maximal and submaximal levels. Underwater running has emerged as a low load bearing form of supplementary training for cardiovascular fitness, as a way to promote recovery from strenuous exercise while maintaining aerobic fitness, and as a way to prevent injury. Prior studies have reported conflicting results as to whether underwater treadmill running elicits similar cardiorespiratory responses to land-based running. It is important to further investigate the similarities and differences between the two to determine if underwater running is as efficient as land-based running for maintenance of fitness and for rehabilitative purposes. Purpose: To compare the caloric expenditure and oxidative sources of underwater treadmill running and land treadmill running during both maximal treadmill trials to exhaustion and during 30 minute submaximal treadmill trials. Methods: 11 volunteer experienced male triathletes, ages 18-45 were recruited as participants. Each completed 6 trials total which included a maximal and submaximal oxygen consumption trial for each of three conditions: running on a water treadmill with AQx® water running shoes, running on a water treadmill without shoes, and running on a land-based treadmill. Data analysis: Data was analyzed using repeated measures ANOVAs, paired t-tests, pairwise comparisons with bonferroni adjustments, and descriptive statistics were reported. Results: For maximal oxygen consumption trials VO2, RPE, RER, and BP were not significantly different between modalities. Maximal HR was found to be significantly different between modalities, and was shown to be greater on land than in the water. For submaximal VO2, trials HR, RPE, RER, and post BP were not found to be significantly different between modalities. Average VO2, total calories expended, and pre systolic BP were found to be significantly different, and were shown to be greater on land than in water. Conclusions: While maximal exertion running on underwater treadmills seems to elicit similar cardiorespiratory responses to running on land-based treadmills, differences were seen at submaximal exertion levels. It remains unclear whether underwater treadmill running can elicit similar training stimuli as land running at submaximal levels.

We hypothesized that supplementation of dietary conjugated linoleic acid (CLA) and arginine singly or in combination would increase animal performance and meat quality by decreasing adiposity and increasing lean mass in growing-finishing pigs. Sixteen pigs (80 kg) were assigned to four treatments in a 2 x 2 factorial design, differing in dietary fatty acid and amino acid composition [control: 2.05% alanine (isonitrogenous control) plus 1% canola oil (lipid control); CLA: 2.05% alanine + 1% CLA; arginine: 1% arginine + 1% canola oil; arginine + CLA: 1% arginine + 1 CLA]. Preliminary tests indicated that up to 2% arginine was acceptable without interfering with lysine absorption. Pigs were allowed to feed free choice until reaching 110 kg. There were no significant differences across treatments in feed intake, weight gain, or feed efficiency. CLA tended to decrease carcass length (P = 0.06), whereas backfat thickness tended to be greater in pigs supplemented with arginine (P = 0.08). Arginine decreased muscle pH at 45 min postmortem (P = 0.001) and tended to increase lightness of muscle at 24 h postmortem (P = 0.07). CLA supplementation increased the concentrations of trans-isomers of 18:1 (P = 0.001) and SFA (P = 0.01) in s.c. and r.p. adipose tissue. CLA supplementation increased palmitate incorporation into total lipids in longissimus muscle (P = 0.01). Glucose oxidation to CO₂ in r.p. and s.c. adipose tissue were greater in pigs supplemented with CLA in the absence or presence of arginine (P = 0.03 and P = 0.04, respectively). The volume of s.c. adipocytes in s.c. and r.p. adipose tissues was greater in pigs supplemented with CLA, arginine, or CLA plus arginine than in control pigs (P = 0.001). Neither CLA nor arginine affected the expression of PGC-1[alpha],AMPK, mTOR, CPT-1A, FAS, or SCD (P > 0.05) in any tissues. We conclude that there was no significant interaction between arginine and CLA. Supplementary CLA or arginine to finishing-growing pigs did not modulate growth performance and did not reduce adiposity. CLA increased intramuscular fat content without deteriorating meat quality traits and increased saturated fatty acids and substrate oxidation in adipose tissues. In the presence of 1% of canola oil or CLA in the diet, arginine has the potential to deteriorate meat quality by reducing early postmortem pH and by increasing carcass fatness.

This thesis investigated the effects of omega-3 supplementation (2.0 g/day EPA + 1.0 g/day DHA) for 12 weeks on human skeletal muscle sarcolemmal and mitochondrial membrane fatty acid (FA) composition and whole body energy expenditure in young healthy males. Supplementation resulted in significant incorporation of EPA and DHA into sarcolemmal and mitochondrial membranes, with an increase in total unsaturation of mitochondrial membranes. The incorporation profile of the sarcolemma and mitochondria differed, with the mitochondria mimicking changes in whole muscle. There were no changes in the protein content of mitochondrial and selected proteins involved in energy metabolism, except for a significant increase in the long form of UCP3. Despite changes in membrane FA compositions, there were no changes in whole body substrate oxidation at rest or during exercise. These data demonstrate that omega-3 supplementation for 12 weeks altered the FA composition of sarcolemmal and mitochondrial membranes in human skeletal muscle.

The relationship between substrate oxidation (RER) and food intake (FI) is undefined. This study examined the effects of RER modified by a glucose pre-load (GL), exercise (EX) and GL with EX on, FI and energy balance (NEB) in normal-weight boys (9-12 y) and men (20-30 y). Subjects (15 boys, 15 men) were randomized with treatments of either water or GL followed by either EX or rest. Measures included RER, energy expenditure (EE)(kcal/kg), subjective appetite, FI(kcal/kg) measured at a pizza lunch and NEB (kcal/kg). FI(kcal/kg) was reduced by GL(p < 0.0001), and further decreased with GL ingested prior to EX(p = 0.0254). RER was increased with GL(p < 0.0001) and EX(p = 0.0043), and was higher in men compared to boys (p = 0.007). There was no association between RER and FI(kcal/kg). In conclusion, there was no relationship between RER and FI, suggesting that FI is not affected by substrate oxidation.