Role of substrate utilization and thermogenesis on body-weight control with particular reference to alcohol

Alcohol (ethanol; EtOH) provides fuel energy to the body (29·7 kJ (7·1 kcal)/g, 23·4 kJ (5·6 kcal)/ml), as do other macronutrients, but no associated essential nutrients. The thermogenic effect of EtOH (on average 15 % of its metabolizable value) is much greater than that of the main substrates utilized by the body, i.e. fat and carbohydrates (CHO), suggesting a lower net efficiency of energy utilization for EtOH than for fat and CHO. EtOH cannot be stored in the body and is toxic, so that there is an obligatory continuous oxidation of EtOH and it becomes the priority fuel to be metabolized. In contrast to CHO, its rate of oxidation does not depend on the dose ingested. As with CHO intake, it engenders a shift in postprandial substrate utilization (decrease in fat oxidation), but by a non-insulin-mediated mechanism. A limited amount of EtOH can be converted to fatty acids by hepatic de novo lipogenesis (as occurs with high levels of CHO feeding) from acetate production, which inhibits lipolysis in peripheral tissues. There is no evidence that EtOH consumed under normoenergetic conditions (i.e. isoenergetically replacing CHO or fat) leads to greater body fat storage than fat or CHO. However, there is still a lack of experimental studies on the influence of EtOH on the level of spontaneous physical activity in man. This effect may well depend on the dose of EtOH consumed as well as other intrinsic factor

Variability of gait patterns during unconstrained walking assessed by satellite positioning (GPS)

It is established that the ratio between step length (SL) and step frequency (SF) is constant over a large range of walking speed. However, few data are available about the spontaneous variability of this ratio during unconstrained outdoor walking, in particular over a sufficient number of steps. The purpose of the present study was to assess the inter- and intra-subject variability of spatio-temporal gait characteristics [SL, SF and walk ratio (WR=SL/SF)] while walking at different freely selected speeds. Twelve healthy subjects walked three times along a 100-m athletic track at: (1) a slower than preferred speed, (2) preferred speed and (3) a faster than preferred speed. Two professional GPS receivers providing 3D positions assessed the walking speed and SF with high precision (less than 0.5% error). Intra-subject variability was calculated as the variation among eight consecutive 5-s samples. WR was found to be constant at preferred and fast speeds [0.41 (0.04)m·s and 0.41 (0.05)m·s respectively] but was higher at slow speeds [0.44 (0.05)m·s]. In other words, between slow and preferred speed, the speed increase was mediated more by a change in SF than SL. The intra-subject variability of WR was low under preferred [CV, coefficient of variation = 1.9 (0.6)%] and fast [CV=1.8 (0.5)%] speed conditions, but higher under low speed condition [CV=4.1 (1.5)%]. On the other hand, the inter-subject variability of WR was 11%, 10% and 12% at slow, preferred and fast walking speeds respectively. It is concluded that the GPS method is able to capture basic gait parameters over a short period of time (5s). A specific gait pattern for slow walking was observed. Furthermore, it seems that the walking patterns in free-living conditions exhibit low intra-individual variability, but that there is substantial variability between subject

QGP tomography with photon tagged jets in ALICE

$\gamma +$jet events provide a tomographic measurement of the medium formed in heavy ion collisions at LHC energies. Tagging events with a well identified high $p_{T}$ direct photon and measuring the correlation distribution of hadrons emitted oppositely to the photon, allows us to determine, with a good approximation, both the jet fragmentation function and the back-to-back azimuthal misalignement of the direct photon and the jet. Comparing these two observables measured in $pp$ collisions with the ones measured in $AA$ collisions will reveal the modifications of the jet structure induced by the medium formed in $AA$ collisions and consequently will infer the medium properties.Comment: 3 pages, 3 figures, Proceedings for 5th International Conference on Quarks and Nuclear Physic

Total Energy Expenditure, Energy Intake, and Body Composition in Endurance Athletes Across the Training Season: a Systematic Review

Background: Endurance athletes perform periodized training in order to prepare for main competitions and maximize performance. However, the coupling between alterations of total energy expenditure (TEE), energy intake, and body composition during different seasonal training phases is unclear. So far, no systematic review has assessed fluctuations in TEE, energy intake, and/or body composition in endurance athletes across the training season. The purpose of this study was to (1) systematically analyze TEE, energy intake, and body composition in highly trained athletes of various endurance disciplines and of both sexes and (2) analyze fluctuations in these parameters across the training season. Methods: An electronic database search was conducted on the SPORTDiscus and MEDLINE (January 1990–31 January 2015) databases using a combination of relevant keywords. Two independent reviewers identified potentially relevant studies. Where a consensus was not reached, a third reviewer was consulted. Original research articles that examined TEE, energy intake, and/or body composition in 18–40-year-old endurance athletes and reported the seasonal training phases of data assessment were included in the review. Articles were excluded if body composition was assessed by skinfold measurements, TEE was assessed by questionnaires, or data could not be split between the sexes. Two reviewers assessed the quality of studies independently. Data on subject characteristics, TEE, energy intake, and/or body composition were extracted from the included studies. Subjects were categorized according to their sex and endurance discipline and each study allocated a weight within categories based on the number of subjects assessed. Extracted data were used to calculate weighted means and standard deviations for parameters of TEE, energy intake, and/or body composition. Results: From 3589 citations, 321 articles were identified as potentially relevant, with 82 meeting all of the inclusion criteria. TEE of endurance athletes was significantly higher during the competition phase than during the preparation phase (p < 0.001). During the competition phase, both body mass and fat-free mass were significantly higher compared to other seasonal training phases (p < 0.05). Conclusions: Limitations of the present study included insufficient data being available for all seasonal training phases and thus low explanatory power of single parameters. Additionally, the classification of the different seasonal training phases has to be discussed. Male and female endurance athletes show important training seasonal fluctuations in TEE, energy intake, and body composition. Therefore, dietary intake recommendations should take into consideration other factors including the actual training load, TEE, and body composition goals of the athlete

Dieting and weight cycling as risk factors for cardiometabolic diseases: who is really at risk?

Despite the poor prognosis of dieting in obesity management, which often results in repeated attempts at weight loss and hence weight cycling, the prevalence of dieting has increased continuously in the past decades in parallel to the steadily increasing prevalence of obesity. However, dieting and weight cycling are not limited to those who are obese or overweight as substantial proportions of the various population groups with normal body weight also attempt to lose weight. These include young and older adults as well as children and adolescents who perceive themselves as too fat (due to media, parental and social pressures), athletes in weight-sensitive competitive sports (i.e. mandatory weight categories, gravitational and aesthetic sports) or among performers for whom a slim image is professionally an advantage. Of particular concern is the emergence of evidence that some of the potentially negative health consequences of repeated dieting and weight cycling are more readily seen in people of normal body weight rather than in those who are overweight or obese. In particular, several metabolic and cardiovascular risk factors associated with weight cycling in normal-weight individuals have been identified from cross-sectional and prospective studies as well as from studies of experimentally induced weight cycling. In addition, findings from studies of experimental weight cycling have reinforced the notion that fluctuations of cardiovascular risk variables (such as blood pressure, heart rate, sympathetic activity, blood glucose, lipids and insulin) with probable repeated overshoots above normal values during periods of weight regain put an additional stress on the cardiovascular system. As the prevalence of diet-induced weight cycling is increasing due to the opposing forces of an ‘obesigenic’ environment and the media pressure for a slim figure (that even targets children), dieting and weight cycling is likely to become an increasingly serious public health issue

Fasting substrate oxidation at rest assessed by indirect calorimetry: is prior dietary macronutrient level and composition a confounder?

Indirect calorimetry, the measurement of O₂ consumption and CO₂ production, constitutes an invaluable tool as the most common method for analyzing whole-body energy expenditure, and also provides an index of the nature of macronutrient substrate oxidation—namely, carbohydrate (CHO) versus fat oxidation. The latter constitutes a key etiological factor in obesity as this condition can only develop when total fat oxidation is chronically lower than total exogenous fat intake. The standardization of indirect calorimetry measurements is essential for accurately tracking the relative proportion of energy expenditure derived from CHO and fat oxidation. Here we analyze literature data to show that the average fasting respiratory quotient typically shifts from approximately 0.80 to 0.90 (indicating a doubling of resting CHO oxidation) in response to a switch in dietary CHO intake (as % energy) from 30 to 60%. This underscores the importance of taking into account dietary macronutrient composition prior to indirect calorimetry studies in the interpretation of data on substrate utilization and oxidation

How dieting makes the lean fatter: from a perspective of body composition autoregulation through adipostats and proteinstats awaiting discovery

Whether dieting makes people fatter has been a subject of considerable controversy over the past 30 years. More recent analysis of several prospective studies suggest, however, that it is dieting to lose weight in people who are in the healthy normal range of body weight, rather than in those who are overweight or obese, that most strongly and consistently predict future weight gain. This paper analyses the ongoing arguments in the debate about whether repeated dieting to lose weight in normal-weight people represents unsuccessful attempts to counter genetic and familial predispositions to obesity, a psychosocial reaction to the fear of fatness or that dieting per se confers risks for fatness and hence a contributing factor to the obesity epidemic. In addressing the biological plausibility that dieting predisposes the lean (rather than the overweight or obese) to regaining more body fat than what had been lost (i.e. fat overshooting), it integrates the results derived from the re-analysis of body composition data on fat mass and fat-free mass (FFM) losses and recoveries from human studies of experimental energy restriction and refeeding. These suggest that feedback signals from the depletion of both fat mass (i.e. adipostats) and FFM (i.e. proteinstats) contribute to weight regain through the modulation of energy intake and adaptive thermogenesis, and that a faster rate of fat recovery relative to FFM recovery (i.e. preferential catch-up fat) is a central outcome of body composition autoregulation in lean individuals. Such a temporal desynchronization in the restoration of the body's fat vs. FFM results in a state of hyperphagia that persists beyond complete recovery of fat mass and interestingly until FFM is fully recovered. However, as this completion of FFM recovery is also accompanied by fat deposition, excess fat accumulates. In other words, fat overshooting is a prerequisite to allow complete recovery of FFM. This confers biological plausibility for post-dieting fat overshooting – which through repeated dieting and weight cycling would increase the risks for trajectories from leanness to fatness. Given the increasing prevalence of dieting in normal-weight female and male among young adults, adolescents and even children who perceive themselves as too fat (due to media, family and societal pressures), together with the high prevalence of dieting for optimizing performance among athletes in weight-sensitive sports, the notion that dieting and weight cycling may be predisposing a substantial proportion of the population to weight gain and obesity deserves greater scientific scrutiny