Cold-induced heat production preceding shivering

Individual changes in heat production and body temperature were studied in response to cold exposure, prior to shivering. The subjects ten women (seven men) were of normal weight, had a mean age of 23 (SD 3) years and average BMI 22.2 (SD 1.6) Kg/m2. They were lying supine under thermoneutral conditions for 30 min and were subsequently exposed to air of 15 degrees C until shivering occurred. Heat production was measured with a ventilated hood. Body composition was measured with underwater weighing and 2H dilution. Body temperatures were measured with thermistors. Heat production during cold exposure prior to shivering increased and reached a plateau. Skin temperature decreased and did not reach a plateau during the test period. The non-shivering interval (NSI) ranged from 20 to 148 min, was not related to body composition and was not significantly different between women (81 (sd 15) min) and men (84 (sd 34) min). NSI was negatively related to skin temperature (r2 0.44, P=0.004), and skin temperature was related to heat production (r2 0.39, P=0.007). In conclusion, subjects with a relatively large heat production during cold exposure maintained a relatively high skin temperature but showed a short NSI, independent of differences in body composition

Human thermoregulation : individual differences in cold induced thermogenesis

This thesis reports on the variation in human metabolic and insulative responses to mild cold. Whether a significant amount of cold-induced non-shivering thermogenesis exists in adult humans, is still under debate. The existence and variation of cold-induced nonshivering thermogenesis was shown by exposing healthy volunteers to mild cold (Chapter 2). Measurements were performed in summer and repeated in winter (Chapter 3) to investigate seasonal changes in cold response. The magnitude of the cold response was a function of cold acclimatization. On average, non-shivering thermogenesis was higher in winter compared to summer. Interestingly, the relative contribution of metabolic and temperature response was subject specific and consistent throughout the seasons. This means that a person with a relatively large response in summer does so again in winter although the size of the response is not necessarily the same. In addition, subjects that show a metabolic response, i.e. a high metabolism during cold, show a small insulative response, i.e. a decreased skin temperature during cold, and vice versa. Once this was established, the magnitude of the metabolic increase prior to the initiation of shivering was studied (Chapter 4). Subjects with a comparatively large heat production during cold exposure maintained a relatively high skin temperature but started shivering earlier, independent of differences in body composition. This combination of responses is in line with a metabolic defense mechanism of the body to a mild cold stimulus. In the previous experiments, the relation between thermogenesis during cold and body composition was studied in lean subjects. Subsequently, lean and overweight subjects were compared with respect to thermogenesis and insulation in response to mild cold and rewarming (Chapter 5). The increase in heat production corrected for body surface area was relatively low in overweight subjects during cold exposure and rewarming. It is argued that not body temperature triggers heat production, but that differences in heat balance may explain the differences between lean and overweight subjects. The energy efficient response of the overweight subjects can have consequences for energy balance in the long term. If heat balance leans towards an insulative response, the body conserves energy instead of expending it, possibly resulting in a positive energy balance that causes weigh gain. In search of factors related to cold-induced non-shivering thermogenesis, sympathetic nervous system activity was studied (Chapter 6). Both whole body and local cooling showed that both groups respond very different to the same environmental temperature change. During both conditions the overweight subjects seemed to conserve more heat and showed lower cold-induced thermogenesis compared to their lean controls. The observed larger increase in cold-induced norepinephrine levels in overweight subjects indicates a blunted response of the sympathetic nervous system that can contribute to body weight gain and resistance to weight loss. Thus, the sympathetic nervous system plays a role in cold-induced thermogenesis differences between lean and overweight subjects. Differences in thermoregulation between individuals may lead to inaccuracies in body temperature predictions from thermal models. The data that was collected during the research for this thesis was used to validate a model for the predictions of body temperature (Chapter 7). The successful incorporation of individual data in this model showed that research is needed to define subject-specific characteristics that predict the metabolic response or to identify tests for characterization of individuals. In conclusion, the considerable variation in cold-induced non-shivering thermogenesis has potential implications for energy balance. Weight status and the sympathetic nervous system are determinants. Future research should focus on further explanation of variation in cold-induced thermogenesis, relation to diet-induced energy expenditure and skin perfusion, implications for energy balance and the potential of pharmacological interventions

Individual differences in body temperature and the relation to energy expenditure: the influence of mild cold

Inter-individual differences in body temperature and resting metabolic rate (RMR), during comfortable temperature and mild cold were studied. Sleeping metabolic rate (SMR) was measured overnight at 22°C and RMR the following morning at 22°C and at 16°C. Intestinal, rectal and skin temperatures were measured as well as the electromyography (EMG). The SMR and the RMR corrected for body composition were significantly related (

Seasonal changes in metabolic and temperature responses to cold air in humans

The metabolic and temperature response to mild cold were investigated in summer and winter in a moderate oceanic climate. Subjects were 10 women and 10 men, aged 19–36 years and BMI 17–32 kg/m2. Metabolic rate (MR) and body temperatures were measured continuously in a climate chamber with an ambient temperature of 22 °C for 1 h and subsequently 3 h of 15 °C. The average metabolic response during cold exposure, measured as the increase in kJ/min over time, was significantly higher in winter (11.5%) compared to summer (7.0%,

High protein intake sustains weight maintenance after body weight loss in humans.

BACKGROUND: A relatively high percentage of energy intake as protein has been shown to increase satiety and decrease energy efficiency during overfeeding. AIM: To investigate whether addition of protein may improve weight maintenance by preventing or limiting weight regain after weight loss of 5-10% in moderately obese subjects. DESIGN OF THE STUDY: In a randomized parallel design, 148 male and female subjects (age 44.2 +/- 10.1 y; body mass index (BMI) 29.5 +/- 2.5 kg/m2; body fat 37.2 +/- 5.0%) followed a very low-energy diet (2.1 MJ/day) during 4 weeks. For subsequent 3 months weight-maintenance assessment, they were stratified according to age, BMI, body weight, restrained eating, and resting energy expenditure (REE), and randomized over two groups. Both groups visited the University with the same frequency, receiving the same counseling on demand by the dietitian. One group (n=73) received 48.2 g/day additional protein to their diet. Measurements at baseline, after weight loss, and after 3 months weight maintenance were body weight, body composition, metabolic measurements, appetite profile, eating attitude, and relevant blood parameters. RESULTS: Changes in body mass, waist circumference, REE, respiratory quotient (RQ), total energy expenditure (TEE), dietary restraint, fasting blood-glucose, insulin, triacylglycerol, leptin, beta-hydroxybutyrate, glycerol, and free fatty acids were significant during weight loss and did not differ between groups. During weight maintenance, the 'additional-protein group' showed in comparison to the nonadditional-protein group 18 vs 15 en% protein intake, a 50% lower body weight regain only consisting of fat-free mass, a 50% decreased energy efficiency, increased satiety while energy intake did not differ, and a lower increase in triacylglycerol and in leptin; REE, RQ, TEE, and increases in other blood parameters measured did not differ. CONCLUSION: A 20% higher protein intake, that is, 18% of energy vs 15% of energy during weight maintenance after weight loss, resulted in a 50% lower body weight regain, only consisting of fat-free mass, and related to increased satiety and decreased energy efficiency

Validation of an individualized model of human thermoregulation for predicting responses to cold air

Most computer models of human thermoregulation are population based. Here, we individualised the Fiala model [Fiala et al. (2001) Int J Biometeorol 45:143–159] with respect to anthropometrics, body fat, and metabolic rate. The predictions of the adapted multisegmental thermoregulatory model were compared with measured skin temperatures of individuals. Data from two experiments, in which reclining subjects were suddenly exposed to mild to moderate cold environmental conditions, were used to study the effect on dynamic skin temperature responses. Body fat was measured by the three-compartment method combining underwater weighing and deuterium dilution. Metabolic rate was determined by indirect calorimetry. In experiment 1, the bias (mean difference) between predicted and measured mean skin temperature decreased from 1.8°C to -0.15°C during cold exposure. The standard deviation of the mean difference remained of the same magnitude (from 0.7°C to 0.9°C). In experiment 2 the bias of the skin temperature changed from 2.0±1.09°C using the standard model to 1.3±0.93°C using individual characteristics in the model. The inclusion of individual characteristics thus improved the predictions for an individual and led to a significantly smaller systematic error. However, a large part of the discrepancies in individual response to cold remained unexplained. Possible further improvements to the model accomplished by inclusion of more subject characteristics (i.e. body fat distribution, body shape) and model refinements on the level of (skin) blood perfusion, and control functions, are discussed

Validation of an individualised model of human thermoregulation for predicting responses to cold air

Most computer models of human thermoregulation are population based. Here, we individualised the Fiala model [Fiala et al. (2001) Int J Biometeorol 45:143–159] with respect to anthropometrics, body fat, and metabolic rate. The predictions of the adapted multisegmental thermoregulatory model were compared with measured skin temperatures of individuals. Data from two experiments, in which reclining subjects were suddenly exposed to mild to moderate cold environmental conditions, were used to study the effect on dynamic skin temperature responses. Body fat was measured by the three-compartment method combining underwater weighing and deuterium dilution. Metabolic rate was determined by indirect calorimetry. In experiment 1, the bias (mean difference) between predicted and measured mean skin temperature decreased from 1.8°C to -0.15°C during cold exposure. The standard deviation of the mean difference remained of the same magnitude (from 0.7°C to 0.9°C). In experiment 2 the bias of the skin temperature changed from 2.0±1.09°C using the standard model to 1.3±0.93°C using individual characteristics in the model. The inclusion of individual characteristics thus improved the predictions for an individual and led to a significantly smaller systematic error. However, a large part of the discrepancies in individual response to cold remained unexplained. Possible further improvements to the model accomplished by inclusion of more subject characteristics (i.e. body fat distribution, body shape) and model refinements on the level of (skin) blood perfusion, and control functions, are discussed