Massey Documents by Type
Permanent URI for this communityhttps://mro.massey.ac.nz/handle/10179/294
Browse
3 results
Search Results
Item Metabolic flexibility and endurance performance : a thesis submitted for the degree of Doctor of Philosophy, School of Sport and Exercise, College of Health, Massey University(Massey University, 2017) O'Connor, William JamesThis thesis examined the sex-specific biochemical, physiological and physical performance responses of highly-trained endurance athletes to chronic moderate and low carbohydrate (CHO) training diets. In addition, a novel exogenous ketone supplement was studied to examine its effects on participants’ physiology and performance during the two contrasting diets. STUDY ONE: This study was designed to test whether adaptation to a low CHO diet affects physical capacity during prolonged exercise. Thirteen highly-trained endurance athletes (eight males, VO₂max = 66.0 ± 9.5 mL·kg⁻¹·min⁻¹ ; five females, VO₂max = 50.6 ± 8.4 mL·kg⁻¹·min⁻¹) consumed a moderate (>5 g CHO·kg⁻¹·day⁻¹) or low (<2 g CHO·kg⁻¹·day⁻¹) CHO training diet for four weeks, in a randomised cross-over design. Performance was measured, after a 24 h moderate CHO “loading” regime, through a self-paced time trial to complete a fixed workload, equivalent to five hours at a workload calculated to elicit 55% VO₂max. Although time-to-complete was not significantly different between diets, the average absolute (watts) and relative (W/kg) power outputs were significantly better on the low CHO diet (p = 0.03 and 0.02 respectively). Both sexes responded similarly in terms of performance, whilst only women significantly improved body composition when CHO was restricted (p = 0.02). It was concluded that when CHO is restricted during training, trained endurance athletes show improved ultra-endurance performance relative to their body mass. STUDY TWO: This study was designed to test the sex specific response to a low CHO diet during fasted endurance exercise. The participants and dietary restrictions were the same as outlined in Study One. Physiological measures were collected before, during and after a two-hour ride at a fixed power output, equivalent to 60 % VO₂max. The ride was undertaken after an overnight (>12 hours) fast and completed at three points throughout each dietary intervention (baseline, week two, week four). As expected there were a significant main effect of diet and time on substrate oxidation rates during fasted exercise (p < 0.05). The low CHO diet resulted in lower CHO oxidation and higher fat oxidation (FATox) in both sexes throughout the exercise. The degree of ‘adaptation’ to low CHO intake increased from baseline to week four, with significant interactions between trial and diet (p < 0.05). There was a sex specific negative correlation between the rate of CHO oxidation and perceived exertion (RPE) at the end of the fasted exercise (p = 0.001). Women consistently had a higher RPE at the end of the exercise (p = 0.04). These data show that both men and women can increase their rates of FATox, in a time-dependent manner, when CHO is restricted in the training diet. STUDY THREE: This study was designed to examine the differences in the blood metabolome of highly-trained male endurance athletes (VO₂max = 6.0 ± 9.5 mL·kg⁻¹·min⁻¹)who each underwent two contrasting dietary interventions, in a randomised crossover design as follows: four weeks moderate (> 5 g CHO·kg⁻¹·day⁻¹) or low (< 2 g CHO·kg⁻¹·day⁻¹) CHO. Exercise training was controlled during both conditions. Fasting venous blood samples were collected before and after exercise at 60% VO₂max and the plasma metabolome was analysed using 700 Hz H1 nuclear magnetic resonance (NMR) spectroscopy. Unsupervised (PCA) and supervised (PLSA-DA & OPLS-DA) multivariate statistical analysis models failed to statistically separate the sample groups in regards to the dietary intervention. However, both methods of supervised discriminant analysis (PLS-DA and OPLS-DA) could separate groups based on time (i.e. pre–post exercise). The variable influence on projection (VIP) was used to identify the individual metabolites causing the group separation within the discriminant analysis. Metabolites were analysed using two-way ANOVA and paired t-tests, with the only significant difference being the blood glucose response to exercise at the end of each dietary intervention (p = 0.006). In conclusion, neither the resting nor exercising metabolome is significantly influenced by the CHO content of the diet. This indicates that endurance-trained individuals possess the metabolic flexibility to counter changes in dietary CHO availability and maintain a normal circulating metabolic profile. STUDY FOUR: The aim of this case study was two-fold: to test the effectiveness of a proposed study, and to explore the validity of reports which have claimed that ingesting a ketone supplement can improve endurance performance. One highly-trained male triathlete (VO₂max = 73.0 mL·kg⁻¹·min⁻¹) completed four time-to-exhaustion (TTE) cycling bouts, each preceded by two hours of cycling at 60% VO₂max (power = 213 W). The exercise bouts were completed in a crossover design as follows: ketogenic diet (< 1.5 g CHO·kg⁻¹·day⁻¹) and regular (non-ketogenic) sports drink (K), ketogenic diet with ketone-containing drink (K+KS), high CHO diet (> 5 g CHO·kg⁻¹·day⁻¹) and regular sports drink (CHO), moderate CHO diet and ketone-containing drink (CHO+KS). Ketosis was confirmed with sustained resting blood β – hydroxybutyrate (β-HB) levels of >0.2 mM. Ketone supplementation was associated with better performance following both dietary interventions, with CHO+KS being better than K+KS (12:54 minutes vs 13:32 minutes, respectively). Ketone supplementation resulted in higher [β-HB] during exercise relative to the sports drink (0.63 & 0.78 mM vs 0.20 & 0.25 mM, respectively). VO₂ and blood lactate did not noticeably differ during the fixed intensity ride, but differed greatly during the TTE, with VO₂ beginning higher on the high CHO diet. The results from this study show the potential benefits of ingesting a ketone supplement on endurance performance and suggest that the moderate CHO status of the individual may have an additive effect. Based on these results, it was suggested that a full scientific study be carried out to further test the effectiveness of ketone supplementation on endurance performance. STUDY FIVE: The aim of this study was to test the effects of ingesting a ketone supplement on endurance performance in two different metabolic states, induced by dietary interventions. Six well-trained male endurance athletes (age: 29 ± 9 yrs, mass: 74.1 ± 7.7 kg, VO₂max: 64.1 ± 5.8 mL·kg⁻¹·min⁻¹) underwent a randomised, double-blinded, placebo-controlled protocol, consisting of two dietary interventions, completed as a cross-over design. Following each dietary intervention, a performance session was carried out, during which, participants drank either a ketone-containing (KS) or placebo (PLB) drink. Thus, the performance session was carried out a total of six times; habitual diet (BASE1, BASE2), moderate-CHO diet + PLB (PLB+CHO), moderate-CHO diet + KS (KS+CHO), ketogenic diet + PLB (PLB+K), ketogenic diet + KS (KS+K). Physiological measures were taken during each performance session, which consisted of a 40-minute fixed intensity ride, followed by a self-paced time trial (TT), to complete a fixed workload equivalent to 20 minutes at 75% VO₂ max. There were no main effects or interactions between diet and KS on TT performance or body mass. The KS significantly increased the beta-hydroxybutyrate concentration [β-HB] in the blood at rest and during exercise (peak = 1.1 mM) (p = 0.001). The KS caused an attenuated blood lactate response during the TT compared to baseline and PLB. The respiratory exchange ratio (RER) was significantly lower on the ketogenic diet at rest and throughout fixed intensity exercise but did not differ during the TT. It is concluded that the circulating [β-HB] attained were not high enough to significantly contribute to muscular energy provision via oxidative phosphorylation and that future research into ketone supplements and exercise performance should ensure that a minimum of 2 mM [β-HB] is obtained. Further, the CHO status of the individual can be largely ignored as supplementation appears to be equally effective irrespective of the CHO status.Item The biosynthesis of methyl ketones with special reference to their presence in Cheddar cheese : being a thesis presented for the degree of Doctor of Philosophy of the Massey University of Manawatu(Massey University, 1964) Lawrence, R CThe similarity of the pattern of methyl ketones obtained from the steam distillates at atmospheric pressure of cheeses made under controlled aseptic conditions, despite the wide differences in bacterial flora, led to the suspicion that the methyl ketones were being formed as artifacts. This was confirmed by steam distilling cheeses from 1 day to 13 months old when the qualitative patterns and quantitative amounts differed little with the age of the cheese. Evidence was produced to show that the greater part of these methyl ketones must be formed during the heat treatment of milk fat. The maximum quantities of methyl ketones obtainable from cheese and from milk fat, determined by exhaustive steam distillation at atmospheric pressure, averaged from 14 p.p.m. for 2-undecanone to 46 p.p.m. for 2-pentadecanone. Some artifact formation of methyl ketones also occurred, although to a greatly reduced extent, when dairy products containing milk fat were steam distilled under reduced pressure at 40°. As methyl ketones in low concentrations could be extracted from mature cheese at room temperature by solvents or by flushing cheese suspension with nitrogen, milk fat appears to contain precursors which break down to methyl ketones slowly during cheese ripening, this breakdown being accelerated at higher temperatures. Two possible modes of formation of the methyl ketones with an odd number of carbon atoms, found in limiting quantity in the steam distillates of Cheddar cheese, were considered:- (a) From precursors, probably β-keto acids, bound in milk fat. (b) The β-oxidation of free fatty acids, formed by the lipolysis of milk triglycerides, and subsequent decarboxylation of the β-keto acids formed. The use of radioactive milk fat from a lactating cow which had been injected intravenously with carboxy-14C acetate allowed a direct comparison to be made between the labelling patterns of fatty acids and the corresponding methyl ketones from the same milk source. The similarity of the labelling patterns suggests that the C6 to C16 β-keto acids and the corresponding fatty acids have a common precursor (or that one is the precursor of the other) and are together incorporated into the triglycerides. Only butyric acid of the C4 to C16 fatty acids in all 3 milkings had a higher specific activity than the corresponding methyl ketone. This suggests that the acetone found in steam distillates of milk fat is formed from a compound (probably D-β-hydroxybutyrate), derived almost entirely from a precursor other than acetate. The finding that the saturated C18 acid in all 3 samples of radioactive milk fat had an extremely low activity was in agreement with the fact that no C17 methyl ketone was detected in any of the numerous steam distillates from milk fat or cheese. This supports the generally accepted view that, in the biosynthesis of milk fat, the fatty acids up to c16 acid are synthesised from an acetate pool, whereas C18 acids and above are obtained from the blood triglycerides. The possibility that methyl ketones were being formed in Cheddar cheese from the β-oxidation of free fatty acids, as well as from a slow breakdown of bound β-keto acids in milk fat, was shown to be improbable. Triglycerides of acids (undecanoic, nonanoic, and heptanoic), which occur normally only in traces in milk fat, were synthesised and incorporated in Cheddar cheeses. On steam distillation of these cheeses when mature, no methyl ketones corresponding to the acids in the added triglycerides were obtained, although the normal range of methyl ketones with an odd number of carbon atoms was found in the distillates. A detailed study of the metabolism of fatty acids and synthetic triglycerides by spores and mycelium of Penicillium roqueforti was undertaken, this fungus being chosen as a general representative of lipolytic organisms that might be of importance in producing Cheddar flavour. The effect of the growth medium, pH of solution, concentration of acid and inorganic ions on both oxygen uptake and methyl ketone formation was determined. The rate of methyl ketone formation suggested the synthesis of adaptive β-keto acid decarboxylases after a lag period of 1 to 2 hours. An hypothesis based upon the possible toxicity of the C6 to C12 β-keto acids can explain a number of the experimental results: (1) Only one methyl ketone was formed (2) The most toxic acids were those which gave the least amount of methyl ketone (3) Concentrations of the C8 to C12 fatty acids that markedly inhibited the respiration of mycelium were nevertheless oxidised to considerable quantities of the corresponding methyl ketone. The relationship between the toxic action of fatty acids and chain length was found to be dependent upon pH. The chain length of the most toxic acid increased with pH, being C10 acid at pH 2.5 and C12 at pH's 5.2 and 6.0. At pH 6.8 none of the acids from C4 to C18 inhibited oxygen uptake but C14 acid was the most toxic acid at pH 8.0. There appeared to be no sharp dividing line between the metabolic activity, with respect to fatty acids, of spores and mycelium. Mycelium oxidised fatty acids rapidly giving varying amounts of methyl ketone but considerably more CO2 than spores. In general spores formed higher amounts of methyl ketones than mycelium but showed also a slight but definite ability to form CO2 from octanoic acid. Evidence for a β-oxidation mechanism in the fungal metabolism of fatty acids was obtained by the use of 1-C14 and 2-C14 octanoic acids. A relatively slow movement of intermediates through the T.C.A. cycle was also indicated. High concentrations of triglycerides were oxidised slowly by spores to methyl ketones when equivalent concentrations of the free acid (up to 66 μmoles/ml) inhibited methyl ketone formation. It seems probable that the very slow rate of formation of methyl ketones is due to the inhibitory effect of the ketones themselves on the lipases. Methyl carbinols were not detected in significant amounts as products of the metabolism of methyl ketones, evidence being obtained on the contrary that the carbinols were possibly precursors of the ketones during the oxidation of fatty acids by spores. Cell free extracts obtained from mycelium were able to oxidise low concentrations of octanoic acid (0.5 μ-moles/ml or less) after a lag of up to 3 hours. The supplementation of the extracts with several coenzymes, known to be associated with fatty acid oxidation, or with T.C.A. cycle intermediates were unable, however, to decrease the lag before oxidation started. No methyl ketones were detected after the oxidation of fatty acids by cell-free extracts but were formed when cell debris from the Hughes Press was used. This suggests that the β-keto acid decarboxylases were tightly bound to the cell walls.Item Synthesis and analysis of libraries of potential flavour compounds : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry at Massey University, Palmerston North, New Zealand(Massey University, 2006) Bang, Kyong-AThe goal of this project was to synthesise potential flavour compounds combinatorially and identify key components for further investigation as flavourants in dairy products. This thesis describes the design and synthesis of libraries of ketones and γ-lactones that will be evaluated for flavour potential. Gas chromatography-mass spectrometry (GCMS), the Fox, and gas chromatography-olfactometry (GC-O) were used throughout this study. Ketones were synthesised individually via a two-step sequence: a Grignard reaction followed by the oxidation of the resulting alcohol in Chapter 2. Some compounds selected from the Fox analysis were assessed by GC-O. The analysis gave promising results for aromatic and cyclopropyl ketones and a library of cyclopropyl ketones was prepared. Individual racemic lactones were synthesised via a two-step sequence: the Linstead modification of the Knoevenagel reaction and subsequent lactonisation in Chapter 3. Libraries of racemic γ-lactones (C8-C12), including α-substituted γ-lactones, were produced combinatorially. Further, synthesis of a library of γ-thionolactones was achieved by treatment of a library of γ-lactones with Lawesson's reagent. The libraries were analysed by GC-O. A (R)-dodecalactone was synthesised from L-glutamic acid and the (S)-enantiomer was synthesised by the same sequence from D-glutamic acid in Chapter 4. Asymmetric syntheses of both enantiomeric series of γ-lactones utilizing the Sharpless asymmetric dihydroxylation reaction was employed to give the libraries in Chapter 5. Libraries of a-substituted and β-substituted γ-lactones were synthesised combinatorially and analysed by GC-O.