Digestion in an ectothermic herbivore, the green iguana (<i>Iguana iguana</i>):Effect of food composition and body temperature

In laboratory experiments, the effect of food composition and body temperature on digestive efficiency was investigated in the lizard Iguana iguana on Curacao (Netherlands Antilles). In a series of experiments the animals were kept in cages with a temperature gradient and different foods were offered ad lib. Mean selected daytime body temperatures were 35.0-degrees-36.4-degrees-C (mean 24 h T(b): 31.8-degrees-33.7-degrees-C). Mean apparent dry-matter digestibility (DDM) varied from 30.0% to 84.2%, depending on the kind of food. Mean DDM and digestible energy were significantly inversely related to the cell wall components lignin and cutin, and these components could explain most of the variance in DDM (r = 0.88). The amount of digestible protein was significantly correlated with crude protein content in the food. Mean transit time of food through the digestive tract varied from 3.9 (berries) to 8.5 (leaves) d. A second series of experiments, in which body temperatures were varied (T(b)) range: 30.0-degrees-36.1-degrees-C), showed that an increase in body temperature induced a significant curvilinear decrease of the transit time from 10 d down to 3 d. Dry-matter digestibility, however, was not affected by a change in body temperature. Maximal fresh-food intake was inversely related at a significant level to the transit time. It is argued that body temperature affects the potential digestive capacity of the green iguana

Human Brown Fat and Obesity: Methodological Aspects

Much is known about brown adipose tissue (BAT) in rodents. Its function is to generate heat in response to low environmental temperatures and to diet or overfeeding. The knowledge about BAT in humans is still rather limited despite the recent rediscovery of its functionality in adults. This review highlights the information available on the contribution of BAT in increasing human energy expenditure in relation to obesity. Besides that methodological aspects will be discussed that need special attention in order to unravel the heat producing capacity of human BAT, the recruitment of the tissue, and its functionality

Brown adipose tissue and the regulation of nonshivering thermogenesis.

PURPOSE OF REVIEW: The recent rediscovery of functional cold activated brown adipose tissue (BAT) in adult humans fuelled an uprise in studies on this tissue. This review focuses on the contribution of human BAT to nonshivering thermogenesis and on factors other than cold that activate BAT. RECENT FINDINGS: Earlier studies revealed BAT activity using a glucose tracer for positron emission tomography/computed tomography (PET/CT) scanning. Several recent studies, using a mix of tracers and PET/CT dynamic scanning showed that human brown fat is metabolically active and related to the perfusion of the tissue. The actual contribution of BAT to nonshivering thermogenesis still needs to be explored.The last few years, several new factors that activate human BAT have been described. These studies also highlight the plasticity of brown and white adipose tissue. Some of these factors may have pharmacological significance. SUMMARY: New PET/CT studies provide information on oxidative human BAT metabolism in vivo. This new information in combination with the study on factors activating BAT are promising with respect to management of obesity and related disorders

Assessment of fat-mass loss during weight reduction in obese women.

Urho Kaleva Kekkonen Institute for Health Promotion Research, Tampere, Finland.Methods for assessing body fat mass (FM) loss were compared in 32 obese (body mass index [BMI], 29 to 41 kg/m2) premenopausal women before and after a weight loss of 13.0 +/- 3.4 kg (mean +/- SD). A four-component (4C) model was used as the criterion. The other methods were as follows: three-component models (body density with total body water [3W] or bone minerals [3M]), underwater weighing, dual-energy x-ray absorptiometry ([DXA] XR-26, software 2.5.2; Norland, Ft Atkinson, WI), bioelectric impedance analysis (BIA) with an obese-specific equation [Segal et al), skinfolds (Durnin and Womersley), and an equation with BMI (Deurenberg et al). The 3W model (bias +/- SD, 0.5 +/- 0.4 kg), XR-26 (0.6 +/- 2.1 kg), and BMI equation (-0.3 +/- 2.1 kg) gave practically unbiased mean estimations of fat loss. All other methods underestimated fat loss by at least 1.6 kg (range of bias, -2.7 to -1.6 kg). The small bias (0.7 +/- 1.0 kg) between underwater weighing and model 4C before weight reduction indicates that the two-component assumptions were valid in premenopausal, weight-stable obese women. However, particularly the water fraction of the fat-free body component (4C model) was increased after weight reduction (before, 72.9% +/- 1.4%; after, 75.7% +/- 2.2%), making both underwater weighing and the 3M model uncertain for assessment of body composition changes. A general tendency for overestimating FM was seen before and more clearly after weight reduction. However, most methods underestimated fat loss, apparently because of unexpected changes in hydration of the fat-free body component

Thermoregulation during Exercise in the Heat : Strategies for Maintaining Health and Performance

As a result of the inefficiency of metabolic transfer, >75% of the energy that is generated by skeletal muscle substrate oxidation is liberated as heat. During exercise, several powerful physiological mechanisms of heat loss are activated to prevent an excessive rise in body core temperature. However, a hot and humid environment can significantly add to the challenge that physical exercise imposes on the human thermoregulatory system, as heat exchange between body and environment is substantially impaired under these conditions. This can lead to serious performance decrements and an increased risk of developing heat illness. Fortunately, there are a number of strategies that athletes can use to prevent and/or reduce the dangers that are associated with exercise in the heat. In this regard, heat acclimatisation and nutritional intervention seem to be most effective. During heat acclimatisation, the temperature thresholds for both cutaneous vasodilation and the onset of sweating are lowered, which, in combination with plasma volume expansion, improve cardiovascular stability. Effective nutritional interventions include the optimisation of hydration status by the use of fluid replacement beverages. The latter should contain moderate amounts of glucose and sodium, which improve both water absorption and retention