Reliability of the measurement of postprandial thermogenesis in men of three levels of body fatness

Calculating Diet-Induced Thermogenesis in Mice

Diet-induced thermogenesis (DIT) is the increase in energy expenditure (EE) associated with food intake. Increasing DIT may lead to weight loss, so it is expected that increasing DIT will decrease body mass index and body fat mass. DIT in humans has been measured in various ways, but there is no way to calculate absolute DIT values in mice. Therefore, we developed a method to measure DIT in mice by applying a method more commonly used in humans. First, we measure the energy metabolism of mice under fasting conditions. EE is then plotted against the square root of activity, and a linear regression equation is fitted to the data. Next, we measure the energy metabolism of mice fed ad libitum and plotted EE in the same way. DIT is calculated by subtracting the predicted EE value from the EE value of mice fed at the same activity count. This method not only allows observation of the time course of the absolute value of DIT but also allows calculation of the ratio of DIT to caloric intake and the ratio of DIT to EE.

The Role and Regulatory Mechanism of Brown Adipose Tissue Activation in Diet-Induced Thermogenesis in Health and Diseases

Brown adipose tissue (BAT) has been considered a vital organ in response to non-shivering adaptive thermogenesis, which could be activated during cold exposure through the sympathetic nervous system (SNS) or under postprandial conditions contributing to diet-induced thermogenesis (DIT). Humans prefer to live within their thermal comfort or neutral zone with minimal energy expenditure created by wearing clothing, making shelters, or using an air conditioner to regulate their ambient temperature; thereby, DIT would become an important mechanism to counter-regulate energy intake and lipid accumulation. In addition, there has been a long interest in the intriguing possibility that a defect in DIT predisposes one to obesity and other metabolic diseases. Due to the recent advances in methodology to evaluate the functional activity of BAT and DIT, this updated review will focus on the role and regulatory mechanism of BAT biology in DIT in health and diseases and whether these mechanisms are applicable to humans.

A novel method for measuring diet-induced thermogenesis in mice

Diet-induced thermogenesis (DIT) refers to energy expenditure (EE) related to food consumption. Enhancing DIT can lead to weight loss. Factors that increase DIT are expected to lower body mass index and body fat mass. Although various methods have been developed for measuring DIT in humans, there is currently no method available for calculating absolute DIT values in mice. Therefore, we attempted to measure DIT in mice by applying the method more commonly used for humans. Mouse energy metabolism was first measured under fasting conditions; EE was plotted against the square root of the activity count, and a linear regression equation was fit to the data. Then, energy metabolism was measured in mice that were allowed to feed ad libitum, and EE was plotted in the same way. We calculated the DIT by subtracting the predicted EE value from the fed EE value for the same activity count. The methodology for measuring DIT in mice may be helpful for researching ways of combatting obesity by increasing DIT.

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The methodology for measuring absolute DIT values in mice is developed.

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For mice, the proportion of DIT compared with calorie intake and EE are 12.3% and 21.7%, respectively.

Successful and unsuccessful weight-loss maintainers: strategies to counteract metabolic compensation following weight loss

Adaptive thermogenesis and reduced fat oxidative capacity may accompany weight loss, continuing in weight maintenance. The present study aimed (1) to determine whether weight-reduced and weight-loss relapsed women are at greater metabolic risk for weight gain compared with BMI-matched controls with no weight-loss history, and (2) to identify protective strategies that might attenuate weight loss-associated adaptive thermogenesis and support successful weight-loss maintenance. Four groups of women were recruited: reduced-overweight/obese (RED, n 15), controls (low-weight stable weight; LSW, n 19) BMI <27 kg/m²; relapsed-overweight/obese (REL, n 11), controls (overweight/obese stable weight; OSW, n 11) BMI >27 kg/m². Body composition (bioelectrical impedance), 75 g oral glucose tolerance test, fasting and postprandial metabolic rate (MR) and substrate utilisation (RER) and physical activity (accelerometer (7 d)) were measured. Sociobehavioural questionnaires and 3 × 24 h diet recalls were completed. Fasting and postprandial MR, RER and total daily energy intake (TDEI) were not different between RED and REL v. controls (P > 0·05). RED consumed less carbohydrate (44·8 (sd 10·3) v. 53·4 (sd 10·0) % TDEI, P = 0·020), more protein (19·2 (sd 6·0) v. 15·6 (sd 4·2) % TDEI, P = 0·049) and increased physical activity, but behaviourally reported greater dietary restraint (P = 0·002) compared with controls. TDEI, macronutrient intake and physical activity were similar between OSW and REL. REL reported higher subjective fasting and lower postprandial ratings of prospective food consumption compared with OSW. Weight-reduced women had similar RMR (adjusted for fat-free mass) compared with controls with no weight-loss history. Increased physical activity, higher protein intake and greater lean muscle mass may have counteracted weight loss-associated metabolic compensation and highlights their importance in weight-maintenance programmes.

Validity and reproducibility of a novel method for time-course evaluation of diet-induced thermogenesis in a respiratory chamber

We developed a novel method for computing diet-induced thermogenesis (DIT) in a respiratory chamber and evaluated the validity and reproducibility of the method. We hypothesized that DIT may be calculated as the difference between postprandial energy expenditure (EE) and estimated EE (sum of basal metabolic rate and physical activity (PA)-related EE). The estimated EE was derived from the regression equation between EE from respiration and PA intensity in the fasting state. It may be possible to evaluate the time course of DIT using this novel technique. In a validity study, we examined whether DIT became zero (theoretical value) for 6 h of fasting in 11 subjects. The mean value of DIT calculated by the novel and traditional methods was 22.4 ± 13.4 and 3.4 ± 31.8 kcal/6 h, respectively. In the reproducibility study, 15 adult subjects lived in the respiratory chamber for over 24 h on two occasions. The DIT over 15 h of postprandial wake time was calculated. There were no significant differences in the mean values of DIT between the two test days. The within-subject day-to-day coefficient of variation for calculated DIT with the novel and traditional methods was approximately 35% and 25%, respectively. The novel method did not have superior reproducibility compared with that of the traditional method. However when comparing the smaller variation in the fasting state than the theoretical value (zero), the novel method may be better for evaluating interindividual differences in DIT than the traditional method and also has the ability to evaluate the time-course.

Methodological considerations for meal-induced thermogenesis: measurement duration and reproducibility

Meal-induced thermogenesis (MIT) research findings have been highly inconsistent, in part, due to the variety of durations and protocols used to measure MIT. In the present study, we aimed to determine the following: (1) the proportion of a 6 h MIT response completed at 3, 4 and 5 h; (2) the associations between the shorter durations and the 6 h measures; (3) whether shorter durations improved the reproducibility of the measurement. MIT was measured in response to a 2410 kJ mixed composition meal in ten individuals (five males and five females) on two occasions. Energy expenditure was measured continuously for 6 h post-meal using indirect calorimetry, and MIT was calculated as the increase in energy expenditure above the pre-meal RMR. On average, 76, 89 and 96 % of the 6 h MIT response was completed within 3, 4 and 5 h, respectively, and MIT at each of these time points was strongly correlated with the 6 h MIT response (range for correlations, r 0·990-0·998; P< 0·01). The between-day CV for the 6 h measurement was 33 %, but it was significantly lower after 3 h of measurement (CV 26 %; P= 0·02). Despite variability in the total MIT between days, the proportion of MIT that was completed at 3, 4 and 5 h was reproducible (mean CV: 5 %). While 6 h are typically required to measure the complete MIT response, the 3 h measures provide sufficient information about the magnitude of the MIT response and may be applicable for testing individuals on repeated occasions.

Inconspicuous assessment of diet-induced thermogenesis using whole-body indirect calorimetry

We report a novel technique for computing diet-induced thermogenesis using data from 24-h respiration chamber measurements of 76 subjects. Physical activity (PA) was determined using a radar system to assess its duration and an accelerometer to evaluate its intensity. The regression line relating PA and energy expenditure facilitated calculation of the integrated thermogenic response to the total energy ingested (11.4% ± 3.8%), which is consistent with the values classically reported in the literature (10%) at the group level.

Validation of three predictive equations for basal metabolic rate in adults

Objective

To cross-validate three predictive set of equations for basal metabolic rate (BMR) developed by Schofield (Schofield database), Henry (Oxford database) and Cole (Oxford database) using mean values for age, weight, height and BMR of published studies.

Design

Literature review of studies published from 1985 to March 2002.

Setting

All studies selected used appropriate methods and followed conditions that met the criteria established for basal metabolism, were performed in healthy adults, and were not part of the Schofield or Oxford database.

Subjects

A total of 261 groups of men and women from 175 studies were selected and categorised in three age groups (18.5–29.9, 30.0–59.9, ≥60 years old) and three body mass index (BMI) groups (normal weight, overweight and obese).

Results

Linear regression and concordance correlation analysis showed that the three sets of equations had the same association and agreement with measured BMR, across gender, age, and BMI groups. The agreement of all equations was moderate for men and poor for women. The lowest mean squared prediction errors (MSPRs) were given by Henry equations in men and Cole equations in women. Henry and Cole equations gave lower values than Schofield equations, except for men over 60 years of age. Henry equations were the most accurate in men. None of the three equations performed consistently better in women.

Conclusion

These results support the use of Henry equations in men with a wide range of age and BMI. None of the proposed predictive equations seem to be appropriate to estimate BMR in women.

Best Practice Methods to Apply to Measurement of Resting Metabolic Rate in Adults: A Systematic Review

Several factors may alter apparent resting metabolic rate (RMR) during measurement with indirect calorimetry. Likewise, numerous indirect calorimetry measurement protocols have been developed over the years, and the methodology employed could influence test results. As part of a larger project to determine the role of indirect calorimetry in clinical practice, a systematic review of the literature was undertaken to determine the ideal subject condition and test methodology for obtaining reliable measurement of RMR with indirect calorimetry. Food, ethanol, caffeine, and nicotine affect RMR for a variable number of hours after consumption; therefore, intake of these items must be controlled before measurement. Activities of daily living increase metabolic rate, but a short rest (< or =20 minutes) before testing is sufficient for the effect to dissipate. Moderate or vigorous physical activity has a longer carryover effect and therefore must be controlled in the hours before a measurement of RMR is attempted. Limited data were found regarding ideal ambient conditions for RMR testing. Measurement duration of 10 minutes with the first 5 minutes deleted and the remaining 5 minutes having a coefficient of variation <10% gave accurate readings of RMR. Individuals preparing for RMR measurement via indirect calorimetry should refrain from eating, consuming ethanol and nicotine, smoking, and engaging in physical activity for varying times before measurement. The test site should be physically comfortable and the individual should have 10 to 20 minutes to rest before measurement commences. A 10-minute test duration with the first 5 minutes discarded and the remaining 5 minutes having a coefficient of variation of <10% will give an accurate measure of RMR.

Diet induced thermogenesis

Objective

Daily energy expenditure consists of three components: basal metabolic rate, diet-induced thermogenesis and the energy cost of physical activity. Here, data on diet-induced thermogenesis are reviewed in relation to measuring conditions and characteristics of the diet.

Methods

Measuring conditions include nutritional status of the subject, physical activity and duration of the observation. Diet characteristics are energy content and macronutrient composition.

Results

Most studies measure diet-induced thermogenesis as the increase in energy expenditure above basal metabolic rate. Generally, the hierarchy in macronutrient oxidation in the postprandial state is reflected similarly in diet-induced thermogenesis, with the sequence alcohol, protein, carbohydrate, and fat. A mixed diet consumed at energy balance results in a diet induced energy expenditure of 5 to 15 % of daily energy expenditure. Values are higher at a relatively high protein and alcohol consumption and lower at a high fat consumption. Protein induced thermogenesis has an important effect on satiety.

In conclusion, the main determinants of diet-induced thermogenesis are the energy content and the protein- and alcohol fraction of the diet. Protein plays a key role in body weight regulation through satiety related to diet-induced thermogenesis.

Metabolic and cardiovascular responses to liquid and solid test meals

There is indirect evidence from previous studies that the physiological responses to a liquid test meal may differ from those seen after consumption of a solid meal. The aim of the present study was to determine the metabolic and cardiovascular responses to isoenergetic high-carbohydrate mixed nutrient liquid or solid test meals, providing 2.1 MJ (approximately 70% of which was from carbohydrate), in eight healthy men following an overnight fast. Metabolic rate increased significantly after both meals (P < 0.0001, time effect), but the increase was significantly greater after the solid than after the liquid test meal (0.40 (SE 0.14), 0.26 (SE 0.10) kJ/min respectively, P = 0.001). The respiratory exchange ratio increased significantly after both the liquid and solid test meals, with no significant differences between them. Forearm blood flow increased significantly after the liquid test meal (0.70 (SE 0.33) ml/100 ml per min, P < 0.0001), whilst it decreased after the solid meal (-0.28 (SE 0.16) ml/100 ml per min, P < 0.0001). Heart rate increased on both occasions, but the response was significantly greater after the solid meal (P = 0.02). There were no significant plasma noradrenaline responses, but there were significantly higher increases in serum insulin and blood glucose following the solid meal. Thus, the physical form of a test meal affects the physiological responses to nutrient ingestion.

Energy expenditure

Although human energy expenditure has been studied for over 100 years, many unanswered questions remain regarding the role that individual components of energy expenditure have in the etiology of obesity. Most techniques for measuring physical activity, the most variable component of TDEE, are less than adequate, and differences in energy metabolism are difficult to detect in a static comparison. When energy expenditure is examined in obese and lean subjects at one point in time, there frequently are no differences in energy expenditure when appropriately normalized. However, when subjects are studied longitudinally or when the system is perturbed (such as overfeeding or exercising), differences can be observed. Using a combination of the techniques available today, each component can be reliably studied, and the role that each has in the development of obesity can be ascertained.

Decrease in fat oxidation following a meal in weight-reduced individuals: a possible mechanism for weight recidivism

This study examined the effect that dietary-induced weight loss has on body composition, energy metabolism, and substrate oxidation at rest and during the 5-hour period following a meal. Twenty older (age:mean +/- SE, 61 +/- 1 years; range, 56 to 70 y) obese (body mass index > 32 kg/m2) subjects (12 women, eight men) completed an 11-week dietary restriction program in which they lost 9 +/- l kg. Fat and fat-free mass were reduced (P < .05) by 15% and 5%, respectively. Resting metabolic rate decreased by 15% (P < .05). Overall, weight loss did not alter the percentage of energy derived from fat sources (approximately 47% of energy) under resting conditions. In contrast, the percentage of calories derived from fat during the 5-hour postmeal period decreased from baseline to post-weight loss from 38% +/- 3% to 26% +/- 4% (P < .05) of total calories expended. The reduction in fat oxidation subsequent to a meal may facilitate fat storage, and may be one mechanism by which one regains weight following weight loss.

The thermic effect of food in normal-weight and overweight pregnant women

A defective thermic response to food may be an energy-sparing adaptation in both obesity and pregnancy. To evaluate the combined effect of obesity and pregnancy on postprandial thermogenesis, the thermic effect of food was assessed for a 240 min period following a high-carbohydrate meal and a typical mixed meal in nine normal-weight non-pregnant, eight overweight non-pregnant, eight normal-weight pregnant and six overweight pregnant women using indirect calorimetry. A test meal that provided 60% of each subject's measured daily requirement for basal metabolism was used. Pregnant women were studied during weeks 30-35 of gestation. Neither obesity nor pregnancy altered the thermic effect of food, although the response to the mixed meal was greater (P < 0.01) than that to the high-carbohydrate meal in all cases. The mean responses for the high-carbohydrate and mixed meals were 26.9 (SD 6.0) and 30.1 (SD 6.2) % baseline energy expenditure respectively, and 7.4 (SD 1.6) and 8.3 (SD 1.6) % of the meal energy load respectively. Obesity and pregnancy were associated with hyperinsulinaemia (P < 0.005) following both test meals, suggesting that postprandial thermogenesis was not altered by insulin resistance in this group. The incremental glucose response was elevated (P < 0.001) in the pregnant women following both test meals; overweight women tended to have a greater incremental glucose response following the high-carbohydrate meal, but it was not significant (P = 0.065). These results do not provide evidence of an impaired thermic response to food in either overweight or third trimester pregnant women.

Influence of aerobic fitness, activity level, and smoking history on the acute thermic effect of nicotine

Individual variability in sensitivity to the acute thermic effects of nicotine has been difficult to study because of methodological limitations in the use of smoking to manipulate nicotine dose. This study examined the influence of smoking history, body composition, and, in a subset of subjects, aerobic fitness and physical activity on the thermic effect of nicotine using a measured-dose nasal spray procedure. Following overnight fasting and smoking abstinence, 38 healthy male smokers were intermittently administered a nicotine dose corrected for body weight (15 micrograms/kg, approx. 1.1 mg for average subject) or placebo on separate occasions in a within-subjects study. Indirect calorimetry was used to assess resting energy expenditure (REE) before and after dosing. Acute thermic response to nicotine ranged from -4.3 to +10.8 kcal/h (-5.4% to +12.6% of REE). Thermic response to nicotine was correlated significantly with aerobic fitness (r = 0.58, p < 0.005), physical activity (r = 0.44, p < 0.05), and number of pack-years of smoking (r = 0.43, p < 0.01). Thermic response was marginally correlated with percent body fat (r = -0.23, p < 0.10), but not with body weight (r = 0.04), percent of ideal weight for height (r = -0.10), or lean body mass (r = 0.05). These results indicate that male smokers higher in fitness and activity and with greater smoking exposure histories may experience greater increases in energy expenditure as a result of nicotine intake via smoking. Consequently, variability in these characteristics could help account for some of the variability in weight gain after stopping smoking.

Weight loss and weight cycling in amateur wrestlers: implications for performance and resting metabolic rate

Amateur wrestlers practice weight loss for ergogenic reasons. The effects of rapid weight loss on aerobic performance are adverse and profound, but the effects of anaerobic performance are equivocal. Anaerobic performance--strength and power--may be the most relevant type of performance to the wrestler. Maintenance of or even small decrements in anaerobic performance may translate into improvements in performance relative to the weight class, the factor by which wrestlers are matched for competition. During the recovery period between the official weigh-in and competition, wrestlers achieve at least partial nutritional recovery, which appears to benefit performance. Successive bouts of (a) weight loss to make weight and (b) recovery for performance lead to weight cycling. There is speculation that weight cycling may contribute to chronic glycogen depletion, reductions in fat-free weight, a decrease in resting metabolic rate, and an increase in body fat. The latter two would augment the difficulty of losing weight for subsequent weigh-ins. Most research indicates that the suppressed resting metabolic rate with weight loss in wrestlers appears to be transient, but subsequent research is needed for confirmation.