Dietary sulfur amino acid restriction in humans with overweight and obesity: a translational randomized controlled trial

BACKGROUND

Dietary sulfur amino acid restriction (SAAR) improves metabolic health in animals. In this study, we investigated the effect of dietary SAAR on body weight, body composition, resting metabolic rate, gene expression profiles in white adipose tissue (WAT), and an extensive blood biomarker profile in humans with overweight or obesity.

METHODS

N = 59 participants with overweight or obesity (73% women) were randomized stratified by sex to an 8-week plant-based dietary intervention low (~ 2 g/day, SAAR) or high (~ 5.6 g/day, control group) in sulfur amino acids. The diets were provided in full to the participants, and both investigators and participants were blinded to the intervention. Outcome analyses were performed using linear mixed model regression adjusted for baseline values of the outcome and sex.

RESULTS

SAAR led to a ~ 20% greater weight loss compared to controls (β 95% CI - 1.14 (- 2.04, - 0.25) kg, p = 0.013). Despite greater weight loss, resting metabolic rate remained similar between groups. Furthermore, SAAR decreased serum leptin, and increased ketone bodies compared to controls. In WAT, 20 genes were upregulated whereas 24 genes were downregulated (FDR < 5%) in the SAAR group compared to controls. Generally applicable gene set enrichment analyses revealed that processes associated with ribosomes were upregulated, whereas processes related to structural components were downregulated.

CONCLUSION

Our study shows that SAAR leads to greater weight loss, decreased leptin and increased ketone bodies compared to controls. Further research on SAAR is needed to investigate the therapeutic potential for metabolic conditions in humans.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT04701346, registered Jan 8th 2021, https://www.

CLINICALTRIALS

gov/study/NCT04701346.

Validity and reproducibility of a whole-room indirect calorimeter for the estimation of VO2 , VCO2 , and resting metabolic rate

Whole-room indirect calorimeters (WRICs) provide accurate instruments for the measurement of respiratory exchange, energy expenditure, and macronutrient oxidation. Here, we aimed to determine the validity and reproducibility of a 7500 L WRIC for the measurement of ventilation rates and resting metabolic rate (RMR). Technical validation was performed with propane combustion tests (n = 10) whereas biological reproducibility was tested in healthy subjects (13 women, 6 men, mean ± SD age 39.6 ± 15.3) in two 60 min measurements separated by 24 h. Subjects followed a run-in protocol prior to measurements. The coefficient of variation (CV) and intraclass correlation coefficient (ICC) were calculated for ventilation rates of O2 (VO2), CO2 (VCO2), the respiratory quotient (RQ; VCO2/VO2), and RMR. Technical validation showed good validity with CVs ranging from 0.67% for VO₂ to 1.00% for energy expenditure. For biological reproducibility, CVs were 2.89% for VO₂ ; 2.67% for VCO₂ ; 1.95% for RQ; and 2.68% for RMR. With the exception of RQ (74%), ICCs were excellent for VO₂ (94%), VCO₂ (96%) and RMR (95%). Excluding participants that deviated from the run-in protocol did not alter results. In conclusion, the 7500 L WRIC is technically valid and reproducible for ventilation rates and RMR.

Validation of energy expenditure and macronutrient oxidation measured by two new whole-room indirect calorimeters

OBJECTIVE

The aim of this study was to validate two new whole-room indirfect calorimeters according to Room Indirect Calorimetry Operating and Reporting Standards (RICORS 1.0).

METHODS

For technical validation, 16 propane combustion tests were performed to determine accuracy and precision of energy expenditure (EE) and ventilation rates of oxygen (VO₂ ), carbon dioxide (VCO₂ ), and respiratory exchange ratio (VCO₂ /VO₂ ). For biological validation, eight participants (mean [SD], age 24.1 [2.5] years; BMI 24.3 [3.1] kg/m² ) underwent four 24-hour protocols under highly standardized conditions: (1) isocaloric sedentary, (2) fasting sedentary, (3) isocaloric active, and (4) fasting active. Reliability (coefficients of variation [CV]) and minimal detectable changes (MDC) were calculated for 24-hour EE, sleeping metabolic rate (SMR), physical activity energy expenditure (PAEE), thermic effect of food (TEF), and macronutrient oxidation rates.

RESULTS

Technical validation showed high reliability and recovery rates for VO₂ (0.75% and 100.8%, respectively), VCO₂ (0.49% and 100.6%), and EE (0.54% and 98.2%). Biological validation revealed CV and MDC for active conditions of 1.4% and 4.3% for 24-hour EE, 1.7% and 5.9% for SMR, and 30.2% and 38.4% for TEF, as well as 5.8% and 10.5% for PAEE, respectively. Mean CV and MDC for macronutrient oxidation rates were 9.9% and 22.9%, respectively.

CONCLUSIONS

The precision of 24-hour EE and SMR was high, whereas it was lower for PAEE and poor for TEF.

Validation of whole room indirect calorimeters: refinement of current methodologies

Whole room indirect calorimeter (WRIC) validation techniques consist of propane combustion (PC) or infusion of mixed carbon dioxide (CO₂) and nitrogen (N₂) by a precision blender (PB). To determine the best method, PC of 6, 10, 22‐h and PB infusions of 6, 10, and 14‐h, were conducted. The 14‐h infusion consisted of two metabolic settings. Energy expenditure (EE; kJ), ventilation (V; liters/min) of oxygen (VO₂), VCO₂, and respiratory quotient (VCO₂/VO₂) obtained from the WRIC were extrapolated to the respective test durations and compared to similarly calculated values. Moreover, accurate equations (AE) were derived to correct infusions for additional N₂. As a final evaluation of a PC validated WRIC, weight maintenance (WM), energy balance (EB), respiratory quotient (RQ), and food quotients (FQ) were determined in 22 subjects who had repeat 24‐h EE measurements. Statistical analyses (P < 0.05) were conducted (SPSS, version 23). Significant differences in RQ existed between PC and stoichiometry after 6‐h. Errors for the rest of the PC tests ranged from −1.5 ± 2.4 (VCO₂) to 2.8 ± 4.6% (EE). When compared with the WRIC, all uncorrected metabolic parameters for six and 10‐h PB infusions were significantly different with errors from −12.8 ± 1.6 (VO₂) to 6.0 ± 2.8% (RQ). The AE reduced the magnitude of errors to −12.4 ± 1.5 (RQ) to 2.2 ± 3.0% (RQ). The PB infusion with two settings showed similar performance. No differences in WM, EB, RQ, or FQ existed in the subjects. In conclusion, 10‐h PC tests are sufficient for validating WRICs.

Impact of breakfast skipping compared with dinner skipping on regulation of energy balance and metabolic risk

Background: Meal skipping has become an increasing trend of the modern lifestyle that may lead to obesity and type 2 diabetes.Objective: We investigated whether the timing of meal skipping impacts these risks by affecting circadian regulation of energy balance, glucose metabolism, and postprandial inflammatory responses.Design: In a randomized controlled crossover trial, 17 participants [body mass index (in kg/m²): 23.7 ± 4.6] underwent 3 isocaloric 24-h interventions (55%, 30%, and 15% carbohydrate, fat, and protein, respectively): a breakfast skipping day (BSD) and a dinner skipping day (DSD) separated by a conventional 3-meal-structure day (control). Energy and macronutrient balance was measured in a respiration chamber. Postprandial glucose, insulin, and inflammatory responses in leukocytes as well as 24-h glycemia and insulin secretion were analyzed.Results: When compared with the 3-meal control, 24-h energy expenditure was higher on both skipping days (BSD: +41 kcal/d; DSD: +91 kcal/d; both P < 0.01), whereas fat oxidation increased on the BSD only (+16 g/d; P < 0.001). Spontaneous physical activity, 24-h glycemia, and 24-h insulin secretion did not differ between intervention days. The postprandial homeostasis model assessment index (+54%) and glucose concentrations after lunch (+46%) were, however, higher on the BSD than on the DSD (both P < 0.05). Concomitantly, a longer fasting period with breakfast skipping also increased the inflammatory potential of peripheral blood cells after lunch.Conclusions: Compared with 3 meals/d, meal skipping increased energy expenditure. In contrast, higher postprandial insulin concentrations and increased fat oxidation with breakfast skipping suggest the development of metabolic inflexibility in response to prolonged fasting that may in the long term lead to low-grade inflammation and impaired glucose homeostasis. This trial was registered at clinicaltrials.gov as NCT02635139.

A New Whole Room Indirect Calorimeter for Measurement of the Energetics of Exercise

The purpose of this study was to compare the accuracy of exercise energy expenditure (EXEE) measurements from a metabolic cart (HG_MC) to that obtained with a new exercise whole room indirect calorimeter (EX_WRIC). First, the HG_MC and the EX_WRIC were subjected to 10, 30-min ethanol (99.8% purity) and propane (99.5% purity) combustion validations, respectively, for EE, ventilation rates (liters) of oxygen (VO₂), carbon dioxide (VCO₂), and the respiratory quotient (RQ; VCO₂/VO₂). Then, 15 healthy adults (13 men and 2 women) cycled at 65% age predicted heart rate max for random determination of their EXEE, VO₂, VCO₂ and RQ after a 12-hr fast with both the HG-MC and EX_WRIC. Comparing stoichiometry to combustion, the HG_MC underestimated EE (P<0.05), VO₂ (P<0.05), VCO₂ (P<0.05), and RQ (P<0.05) while no differences were found for the EX_WRIC. The EXEE and VO₂ were lower (P<0.05) while RQ was greater (P<0.05) when measured with the HG_MC versus the EX_WRIC. The EX_WRIC was more accurate than the HG_MC without the related tethered connections.

Evaluation of a new whole room indirect calorimeter specific for measurement of resting metabolic rate

BACKGROUND

The most common methods for obtaining human resting metabolic rate (RMR) use either a ventilated hood connected to a metabolic cart (VH_MC) or calculation by many prediction equations utilizing the person's height and weight. These methods may be inherently inaccurate. The objective of this study is to compare the accuracy for the measurement of RMR by three methods: a new whole room indirect calorimeter specific for this purpose (RMR_WRIC), VH_MC and calculation by the Mifflin equation (ME). First, the VH_MC (Vmax Encore 2900, Carefusion Inc, San Diego, CA) and RMR_WRIC (Promethion GA-6/FG-1, Sable Systems Intl, Las Vegas, NV) were subjected to 10, one-hour ethanol (99.8 % purity) and propane (99.5 % purity) combustion tests, respectively, for simulated metabolic measurements. Thereafter, 40 healthy adults (22 M/18 F, 78.0 ± 24.5 kg, BMI = 25.6 ± 4.8, age 36.6 ± 13.4 years) had one-hour RMR (kcal), ventilation (liters) rates of oxygen (VO2), carbon dioxide (VCO2) and RQ (VCO2/VO2) measured after a 12-h fast with both the VH_ MC and the RMR_WRIC in a randomized fashion. The resting state was documented by heart rate. The RMR was also calculated using the ME, which was compared to both the RMR_WRIC and the VH_MC. All simulated and human metabolic data were extrapolated to 24-h and analyzed (SPSS, Ver. 22).

RESULTS

Comparing stoichiometry to actual combustion, the VH_MC underestimated simulated RMR (p < 0.05), VO2 (p < 0.05), VCO2 (p < 0.05) and the RQ. Similarly the RMR_WRIC underestimated simulated RMR (p < 0.05) and VO2 while overestimating VCO2 and the RQ. There was much greater variability in the simulated metabolic data between combustion and the VH_MC as compared to that of the RMR_WRIC. With regards to the volunteers, the RMR, RQ, VO2 and VCO2 determined by the VH_MC tended to be lower in comparison to these measurements determined by the RMR_WRIC. Finally, RMR calculated utilizing the ME was significantly (p < 0.05) less than the RMR_WRIC but similar to that obtained by the VH_MC.

CONCLUSION

The RMR_WRIC was more accurate and precise than either the VH_MC or ME, which has implications for determining energy requirements for individuals participating in weight loss or nutrition rehabilitation programs.

Effects of CPAP on energy expenditure in obese obstructive sleep apnoea patients: A pilot study

We conducted a placebo-controlled crossover pilot study investigating the effects of 2 mo of active and sham continuous positive airway pressure (CPAP) on energy expenditure (EE) via whole-room indirect calorimetry in three obese obstructive sleep apnoea (OSA) patients. Total 24-h (active: 2970 ± 254 kcal/d, sham: 2705 ± 217 kcal/d; p = 0.015) and mean sleeping (active: 1.60 ± 0.20 kcal/min; sham: 1.47 ± 0.17 kcal/min; p = 0.038) EE were significantly increased after active vs. sham CPAP. Findings suggest that CPAP may correct a hypoxia-related adaptive decrease in thermogenesis.

Postprandial thermogenesis and substrate oxidation are unaffected by sleep restriction

Background/Objectives

The extent to which alterations in energy expenditure (EE) in response to sleep restriction contribute to the short sleep-obesity relationship is not clearly defined. Short sleep may induce changes in resting metabolic rate (RMR), thermic effect of food (TEF), and postprandial substrate oxidation.

Subjects/Methods

Ten females (age and BMI: 22-43 y and 23.4-28 kg/m²) completed a randomized, crossover study assessing the effects of short (4 h/night) and habitual (8 h/night) sleep duration on fasting and postprandial RMR and respiratory quotient (RQ). Measurements were taken after 3 nights using whole-room indirect calorimetry. The TEF was assessed over a 6-h period following consumption of a high-fat liquid meal.

Results

Short vs. habitual sleep did not affect RMR (1.01 ± 0.05 and 0.97 ± 0.04 kcal/min; p=0.23). Fasting RQ was significantly lower after short vs. habitual sleep (0.84 ± 0.01 and 0.88 ± 0.01; p=0.028). Postprandial EE (short: 1.13 ± 0.04 and habitual: 1.10 ± 0.04, p=0.09) and RQ (short: 0.88 ± 0.01 and habitual: 0.88 ± 0.01, p=0.50) after the high-fat meal were not different between conditions. TEF was similar between conditions (0.24 ± 0.02 kcal/min in both; p=0.98), as was the ~6-h incremental area under the curve (1.16 ± 0.10 and 1.17 ± 0.09 kcal/min x 356 min after short and habitual sleep, respectively; p=0.92).

Conclusions

Current findings observed in non-obese healthy premenopausal women do not support the hypothesis that alterations in TEF and postprandial substrate oxidation are major contributors to the higher rate of obesity observed in short sleepers. In exploring a role of sleep duration on EE, research should focus on potential alterations in physical activity to explain the increased obesity risk in short sleepers.

Experimental sleep curtailment causes wake-dependent increases in 24-h energy expenditure as measured by whole-room indirect calorimetry

BACKGROUND

Epidemiologic evidence has shown a link between short sleep and obesity. Clinical studies suggest a role of increased energy intake in this relation, whereas the contributions of energy expenditure (EE) and substrate utilization are less clearly defined.

OBJECTIVE

Our aim was to investigate the effects of sleep curtailment on 24-h EE and respiratory quotient (RQ) by using whole-room indirect calorimetry under fixed-meal conditions.

DESIGN

Ten females aged 22-43 y with a BMI (in kg/m²) of 23.4-27.5 completed a randomized, crossover study. Participants were studied under short- (4 h/night) and habitual- (8 h/night) sleep conditions for 3 d, with a 4-wk washout period between visits. Standardized weight-maintenance meals were served at 0800, 1200, and 1900 with a snack at 1600. Measures included EE and RQ during the sleep episode on day 2 and continuously over 23 h on day 3.

RESULTS

Short compared with habitual sleep resulted in significantly higher (± SEM) 24-h EE (1914.0 ± 62.4 compared with 1822.1 ± 43.8 kcal; P = 0.012). EE during the scheduled sleep episode (0100-0500 and 2300-0700 in short- and habitual-sleep conditions, respectively) and across the waking episode (0800-2300) were unaffected by sleep restriction. RQ was unaffected by sleep restriction.

CONCLUSIONS

Short compared with habitual sleep is associated with an increased 24-h EE of ~92 kcal (~5%)--lower than the increased energy intake observed in prior sleep-curtailment studies. This finding supports the hypothesis that short sleep may predispose to weight gain as a result of an increase in energy intake that is beyond the modest energy costs associated with prolonged nocturnal wakefulness.

Do Obese Eat Faster Than Lean Subjects? Food Intake Studies in Pima Indian Men

Food intake rate has previously been derived from observation of eating behavior in laboratory settings or in public eating establishments. Although it has been suggested that obese individuals eat faster than lean individuals, observations of such an "obese eating style" have yielded mixed results. In the present study, the relationship between ad-libitum food intake rate and obesity was evaluated over 4 days on a metabolic ward in 28 healthy Pima Indian men (Mean +/- SD; 29 +/- 7 y, 100.4 +/- 27.1 kg, 33 +/- 10% body fat) using an automated food selection system containing a large variety of foods. Total energy intake averaged 18829 +/- 3299 kJ/d consisting of 47 +/- 4, 40 +/- 3, and 13 +/- 1 percent of carbohydrate, fat and protein, respectively. The average meal duration was 25 +/- 7 min. Food intake rate was 68 +/- 21 g/min while carbohydrate, fat and protein intake rates were 23 +/- 6, 9 +/- 3 and 6 +/- 2 g/min, respectively. Food intake rate correlated negatively with % body fat (r = -0.61, P < 0.01). Similar relationships were found between the intake rates of carbohydrate, fat and protein and body fatness. Only prospective studies will indicate whether a slow food intake rate may contribute to the etiology of obesity by possibly reducing satiety.

Twenty-four hour metabolic rate measurements utilized as a reference to evaluate several prediction equations for calculating energy requirements in healthy infants

Background

To date, only short-duration metabolic rate measurements of less than four hours have been used to evaluate prediction equations for calculating energy requirements in healthy infants. Therefore, the objective of this analysis was to utilize direct 24-hour metabolic rate measurements from a prior study to evaluate the accuracy of several currently used prediction equations for calculating energy expenditure (EE) in healthy infants.

Methods

Data from 24-hour EE, resting (RMR) and sleeping (SMR) metabolic rates obtained from 10 healthy infants, served as a reference to evaluate 11 length-weight (LWT) and weight (WT) based prediction equations. Six prediction equations have been previously derived from 50 short-term EE measurements in the Enhanced Metabolic Testing Activity Chamber (EMTAC) for assessing 24-hour EE, (EMTACEE-LWT and EMTACEE-WT), RMR (EMTACRMR-LWT and EMTACRMR-WT) and SMR (EMTACSMR-LWT and EMTACSMR-WT). The last five additional prediction equations for calculating RMR consisted of the World Health Organization (WHO), the Schofield (SCH-LWT and SCH-WT) and the Oxford (OXFORD-LWT and OXFORD-WT). Paired t-tests and the Bland & Altman limit analysis were both applied to evaluate the performance of each equation in comparison to the reference data.

Results

24-hour EE, RMR and SMR calculated with the EMTACEE-WT, EMTACRMR-WT and both the EMTACSMR-LWT and EMTACSMR-WT prediction equations were similar, p = NS, to that obtained from the reference measurements. However, RMR calculated using the WHO, SCH-LWT, SCH-WT, OXFORD-LWT and OXFORD-WT prediction equations were not comparable to the direct 24-hour metabolic measurements (p < 0.05) obtained in the 10 reference infants. Moreover, the EMTACEE-LWT and EMTACRMR-LWT were also not similar (p < 0.05) to direct 24-hour metabolic measurements.

Conclusions

Weight based prediction equations, derived from short-duration EE measurements in the EMTAC, were accurate for calculating EE, RMR and SMR in healthy infants.

Energy expenditure in chow-fed female non-human primates of various weights

BACKGROUND

Until now no technology has been available to study energy metabolism in monkeys. The objective of this study was to determine daily energy expenditures (EE) and respiratory quotients (RQ) in female monkeys of various body weights and ages.

METHODS

16 socially reared Bonnet Macaque female monkeys [5.5 +/- 1.4 kg body weight, modified BMI (length measurement from head to base of the tail) = 28.8 +/- 6.7 kg/crown-rump length, m2 and 11.7 +/- 4.6 years] were placed in the primate Enhanced Metabolic Testing Activity Chamber (Model 3000a, EMTAC Inc. Santa Barbara, CA) for 22-hour measurements of EE (kcal/kg) and RQ (VCO2/VO2). All were fed monkey chow (4.03 kcal/g) ad-libitum under a 12/12 hour light/dark cycle. Metabolic data were corrected for differences in body weight. Results were divided into day (8-hours), dark (12 hours) and morning (2-hours) periods. Data analysis was conducted utilizing SPSS (Version 13).

RESULTS

Modified BMI negatively correlated with 22-hour energy expenditure in all monkeys (r = -0.80, p < 0.01). The large variability of daily energy intake (4.5 to 102.0 kcal/kg) necessitated division into two groups, non-eaters (< 13 kcal/kg) and eaters (> 23 kcal/kg). There were reductions (p < 0.05) in both 22-hour and dark period RQs in the "non-eaters" in comparison to those who were "eaters". Monkeys were also classified as "lean" (modified BMI < 25) or "obese" (modified BMI > 30). The obese group had lower EE (p < 0.05) during each time period and over the entire 22-hours (p < 0.05), in comparison to their lean counterparts.

CONCLUSION

The EMTAC proved to be a valuable tool for metabolic measurements in monkeys. The accuracy and sensitivity of the instrument allowed detection of subtle metabolic changes in relation to energy intake. Moreover, there is an association between a reduction of energy expenditure and a gain in body weight.

Lower energy expenditures in infants from obese biological mothers

Background

Previous studies in adults have found that a lower resting metabolic rate is a predictor of future body weight gain.

Methods

To determine if energy expenditures are reduced in infants born to obese mothers, 21 healthy infants (3.9 ± 1.9 months) born to lean (n = 7, BMI < 25 kg/m²), overweight (n = 7, BMI between 25–30) and obese (n = 7, BMI>30) mothers, respectively, participated in this study. Measurements of infant weight, length and skin-fold thicknesses, and mother's weight and height were obtained. Infant energy expenditure was measured for 4-hours using the Enhanced Metabolic Testing Activity Chamber. Metabolic data were extrapolated to 24-hours and adjusted for differences in age and body composition using linear regression analysis (SPSS, version 13) and expressed as kcal/day. Differences between the three groups were determined by one way ANOVA with the Bonferroni Post Hoc test procedure (p < 0.05).

Results

Infants born to obese mothers had a greater BMI (16.7 ± 1.2) than those from both the overweight (15.3 ± 1.4, p < 0.05) and lean groups (15.1 ± 1.3; p < 0.05). The infants of obese mothers had greater body fat (26.8 ± 2.1) than those from the overweight group (22.4 ± 5.0, p < 0.06). Infant BMI correlated (r = 0.53; p < 0.01) with that of their mothers. Extrapolated 24-h EE (kcal/d) correlated with fat-free mass (r = 0.94; p < 0.01). Infants extrapolated 24-h EE from both obese (472.1 ± 30.7 kcal/d; p < 0.05) and overweight groups (471.8 ± 39.5; p < 0.05) were lower than those of the lean group (532.4 ± 30.7).

Conclusion

Lower extrapolated 24-h energy expenditure was present in infants of overweight and obese biological mothers during the first three to six months of life. Furthermore, these infants showed increased BMI and body fat. If these changes are unchecked future childhood obesity may result.

Energy expenditures & physical activity in rats with chronic suboptimal nutrition

BACKGROUND

Sub-optimally nourished rats show reduced growth, biochemical and physiological changes. However, no one has assessed metabolic rate adaptations in rats subjected to chronic suboptimal nutrition (CSN). In this study energy expenditure (EE; kcal/100 g body weight) and physical activity (PA; oscillations in weight/min/kg body weight) were assessed in rats subjected to three levels of CSN.

RESULTS

Body weight gain was diminished (76.7 +/- 12.0 and 61.6 +/- 11.0 g) in rats fed 70 and 60% of the ad-libitum fed controls which gained more weight (148.5 +/- 32.3 g). The rats fed 80% gained weight similarly to controls (136.3 +/- 10.5 g). Percent Fat-free body mass was reduced (143.8 +/- 8.7 and 142.0 +/- 7.6 g) in rats fed 70 and 60% of ad-libitum, but not in those fed 80% (200.8 +/- 17.5 g) as compared with controls (201.6 +/- 33.4 g). Body fat (g) decreased in rats fed 80% (19.7 +/- 5.3), 70% (15.3 +/- 3.5) and 60% (9.6 +/- 2.7) of ad-libitum in comparison to controls (26.0 +/- 6.7). EE and PA were also altered by CSN. The control rats increased their EE and PA during the dark periods by 1.4 +/- 0.8 and 1.7 +/- 1.1 respectively, as compared with light the period; whereas CSN rats fed 80 and 70% of ad-libitum energy intake had reduced EE and PA during the dark periods as compared with the light period EE(7.5 +/- 1.4 and 7.8 +/- 0.6 vs. 9.0 +/- 1.2 and 9.7 +/- 0.8; p < 0.05, respectively), PA(3.1 +/- 0.8 and 1.6 +/- 0.4 vs. 4.1 +/- 0.9 and 2.4 +/- 0.4; p < 0.05) and RQ (0.87 +/- 0.04 and 0.85 +/- 0.5; vs. 0.95 +/- 0.03 and 0.91 +/- 0.05 p < 0.05). In contrast, both light (7.1 +/- 1.4) and dark period (6.2 +/- 1.0) EE and PA (3.4 +/- 0.9 and 2.5 +/- 0.5 respectively) were reduced in rats fed 60% of ad-libitum energy intake.

CONCLUSION

CSN rats adapt to mild energy restriction by reducing body fat, EE and PA mainly during the dark period while growth proceeds and lean body mass is preserved. At higher levels of energy restrictions there is decreased growth, body fat and lean mass. Moreover EE and PA are also reduced during both light and dark periods.

Relationship between maternal obesity and infant feeding-interactions

Background

There are no data regarding the relationship between maternal adiposity and interaction and feeding of infants and possible contribution to childhood obesity. In this study we determined the relationship between maternal body weight and composition and infant feeding patterns and maternal-infant interaction during 24-hour metabolic rate measurements in the Enhanced Metabolic Testing Activity Chamber (EMTAC).

Methods

The amount of time four obese (BMI = 33.5 ± 5.3 kg/m²) and three normal weight (BMI = 23.1 ± 0.6 kg/m²) biological mothers, spent feeding and interacting with their infants, along with what they ingested, was recorded during 24-hour metabolic rate measurements in the EMTAC. The seven infants were 4.9 ± 0.7 months, 69 ± 3 cm, 7.5 ± 0.8 kg, 26 ± 3 % fat and 29 ± 25 percentile for weight for length. Energy and macronutrient intake (kcal/kg) were assessed. Maternal body composition was determined by air displacement plethysmorgraphy and that of the infants by skin-fold thicknesses. Pearson correlations and independent t-tests were utilized for statistical analysis (p < 0.05).

Results

Infants born to obese biological mothers consumed more energy (87.6 ± 18.9 vs. 68.1 ± 17.3) and energy as carbohydrate (25 ± 6 vs.16 ± 3; p < 0.05) than their normal weight counterparts. Most of the increased intake was due to complementary feedings. Twenty-four hour infant energy intake increased with both greater maternal body weight (r = 0.73;p < 0.06) and percent body fat. Furthermore, obese biological mothers spent less total time interacting (570 ± 13 vs. 381 ± 30 minutes) and feeding (298 ± 32 vs.176 ± 22 minutes) (p < 0.05) their infants than their normal weight counterparts. Twenty-four hour interaction time negatively correlated with both maternal body weight (r = -0.98; p < 0.01) and percent body fat (r = -0.92; p < 0.01). Moreover, infants of obese mothers slept more (783 ± 38 vs. 682 ± 32 minutes; p < 0.05) than their normal weight counterparts. However, there were no differences in total 24-hour energy expenditure, resting and sleeping metabolic rates (kcal/kg) for infants born to obese and normal weight biological mothers.

Conclusion

Greater maternal body weight and percent body fat were associated with greater infant energy intakes. These infants were fed less frequently and consumed more carbohydrates in a shorter period of time as compared to infants from normal weight biological mothers. These variations in feeding patterns may predispose certain infants to obesity.

Exogenous recombinant human growth hormone effects during suboptimal energy and zinc intake

Background

Energy and Zinc (Zn) deficiencies have been associated with nutritional related growth retardation as well as growth hormone (GH) resistance. In this study, the relationship between suboptimal energy and/or Zn intake and growth in rats and their response to immunoreactive exogenous recombinant human GH (GHi), was determined.

Results

Rats treated with GHi and fed ad-libitum energy and Zn (100/100) had increased IGFBP-3 (p < 0.05) as compared with NSS (215 ± 23 vs. 185 ± 17 ng/ml) along with similar body weight gain. Rats treated with GHi and fed suboptimal energy and full Zn (70/100) had significantly increased weight gain (109.0 ± 18.2 vs. 73.8 ± 11.0 g) and serum IGF-I levels (568 ± 90 vs. 420 ± 85 ng/ml), along with decreased total body water (TBW; 61.0 ± 1.6 vs. 65.7 ± 2.1%) as compared to NSS controls. However, body weight gain was reduced (p < 0.05) as compared with rats fed ad-libitum energy. Growth hormone treated rats fed only suboptimal Zn (100/70), had increased weight gain (217.5 ± 13.2 vs. 191.6 ± 17.9 g; p < 0.05) compared to those given NSS. These rats gained weight in similar amounts to those fed full Zn. Rats treated with GHi and fed both suboptimal energy and Zn (70/70) showed similar results to those fed suboptimal energy with appropriate Zn (70/100), along with significant increases in IGFBP-3 levels (322 ± 28 vs. 93 ± 28 ng/ml). All restricted rats had reduced 24-h EE (kcal/100 g BW) and physical activity index (oscillations/min/kg BW) and GHi did not overcome these effects.

Conclusion

These results suggest that GHi enhances weight gain in rats with suboptimal energy and Zn intake but does not modify energy expenditure or physical activity index. Suboptimal Zn intake did not exacerbate the reduced growth or decrease in energy expenditure observed with energy restriction.

Carbohydrate malabsorption may increase daily energy requirements in infants

OBJECTIVE

Carbohydrate malabsorption in infants has been found to increase nutrient losses. However, the effect of this alteration on daily metabolic rate is unknown. We assessed daily metabolic rates in infants with asymptomatic carbohydrate malabsorption (ACM) after a single fruit juice load.

METHODS

Sixteen healthy infants with ACM (63.3 +/- 5.6 cm, 7.5 +/- 1.0 kg, 5.6 +/- 0.8 mo, peak breath hydrogen [BH2] = 39.1 +/- 22.4 ppm) and 16 without ACM (64.3 +/- 3.9 cm, 7.8 +/- 1.0 kg, 5.0 +/- 0.8 mo, BH2 = 9.4 +/- 4.7 ppm), after a single fruit juice load, had 24-h energy expenditure (24-h EE; kcal x kg(-1) x d(-1)), resting (RMR; kcal x kg(-1) x d(-1)) and sleeping (SMR; kcal x kg(-1) x d(-1)) metabolic rates extrapolated from 3.5-h assessments in the Enhanced Metabolic Testing Activity Chamber. Furthermore, RMR was calculated with the World Health Organization (WHO), Schofield weight-based and weight- and height-based equations. Carbohydrate absorption was determined by BH2. Differences (P < 0.05) were determined by t test.

RESULTS

All infants with ACM had greater (P < 0.05) extrapolated 24-h EE (91.2 +/- 24.8 versus 78.0 +/- 6.8) and RMR (71.8 +/- 15.2 versus 59.5 +/- 5.9). This represented an increase of 15-18.5%, respectively, in energy expenditures. Carbohydrate malabsorption was a significant determinant of EE, RMR, and SMR. However, the WHO (53.8 +/- 1.0 versus 54.1 +/- 0.9) and both Schofield equations (54.7 +/- 0.9 versus 54.9 +/- 1.0 and 50.6 +/- 7.5 versus 47.3 +/- 6.7) failed to detect any differences in RMR. There was a 20 percentile reduction in growth performance in infants with carbohydrate malabsorption.

CONCLUSIONS

Infants with ACM following fruit juice ingestion may have increased daily energy expenditure leading to increased metabolic requirements.

Daily metabolic rate in healthy infants

BACKGROUND

Previous estimates of daily metabolic rate in infants were based on short-term unstandardized measurements of energy expenditure (EE).

OBJECTIVE

Determine 24-hour metabolic profiles in infants.

METHODS

Energy expenditure (kcal/min by indirect calorimetry) and physical activity (oscillations in weight/min/kg body weight) were measured in 10 healthy infants (5.0+/-0.8 months, 68+/-3 cm, 7.3+/-0.8 kg) for 24 hours in the Enhanced Metabolic Testing Activity Chamber while allowing parental interaction. Energy intake, 24-hour EE, resting metabolic rate (RMR), and sleeping metabolic rate (SMR) (kcal/kg/day) were determined. In addition, extrapolated 24-hour EE, RMR, and SMR from the first 4 and 6 hours of data were compared with 24-hour measurements.

RESULTS

Twenty-four-hour energy intake, EE, RMR, and SMR (mean+/-SD) were 78.2+/-17.6, 74.7+/-3.8, 65.1+/-3.5, and 60.3+/-3.9, respectively. EE and physical activity showed a decrease at 11:30 pm and a return to daytime levels by 5:30 am, suggesting a metabolic circadian rhythm. Extrapolated 24-hour EE, RMR, and SMR from the first 4 hours (72.2+/-6.6, 65.9+/-8.7, and 64.9+/-6.4) and 6 hours (74.8+/-6.7, 65.8+/-6.6, and 64.8+/-5.6) were similar to 24-hour measurements.

CONCLUSIONS

An apparent circadian rhythm in metabolic rate and physical activity was detected by 24-hour measurements. Furthermore, shorter-term measurements of the variables were comparable with 24-hour values.

New equations for calculating the components of energy expenditure in infants

OBJECTIVES

To derive new equations for 24-hour energy expenditure (24-h EE; kcal/d) and resting (RMR; kcal/d) and sleeping metabolic rates (SMR; kcal/d) in young infants by using the Enhanced Metabolic Testing Activity Chamber (EMTAC).

METHODS

Data from 50 (25 male/25 female) healthy normally growing infants (4.9 +/- 1.6 months, 7.1 +/- 1.4 kg, 65 +/- 5 cm) who had 24-h EE, RMR, and SMR extrapolated from 4- to 6-hour metabolic measurements in the EMTAC were used to derive new equations for 24-h EE, RMR, and SMR. Equations were derived by means of multiple regression analysis (SPSS 8.0), with weight alone or with length and weight entered as independent variables. Similar data from 10 additional test infants (4 male/6 female, 5.1 +/- 0.6 months, 7.5 +/- 1.0 kg, 65 +/- 5 cm) were used to cross-validate the new equations.

RESULTS

Twenty-four-hour EE, RMR, and SMR were 79.6 +/- 19.2, 66.8 +/- 15.1, and 62.3 +/- 10.3 kcal/kg per day, respectively. No differences existed in RMR (kcal/kg per day) from the 10 test infants between the weight (68.6 +/- 1.9) and height-weight based equations (68.4 +/- 6.1) or that measured by the EMTAC (67.6 +/- 10.2). Weight was the major predictor of 24-h EE, RMR, and SMR. The WHO, Schofield-weight and weight-height equations underestimated (P <.05) by 19%, whereas the new equations were within 4% of RMR obtained from the EMTAC.

CONCLUSIONS

The new equations for assessing energy requirements in healthy infants are more accurate than those previously published that underestimated 24-h EE by 15 kcal/kg per day.

Association between infantile colic and carbohydrate malabsorption from fruit juices in infancy

OBJECTIVE

To determine whether infantile colic (IC) is associated with malabsorption of carbohydrates present in fruit juices.

METHODS

In this double-blind study, parents of 30 healthy infants (5.1 +/- 0.7 months, 7.4 +/- 1.0 kg, 64 +/- 4 cm) were administered a questionnaire to quantitatively assess IC. Thereafter, they were divided into 2 groups, 16 infants with and 14 without IC. Within each treatment group infants were fed 120 mL (16.3 +/- 2.0 mL/kg) of either white grape (sorbitol-free; 1:1 fructose-to-glucose ratio) or apple (sorbitol 0.5 g/dL; 2.6:1 fructose-to-glucose ratio) juice. Physical activity (PA), energy expenditure (EE), crying, and sleeping times were measured for 0.5 and 3.0 hours before and after juice feeding, respectively, using the Enhanced Metabolic Testing Activity Chamber. Carbohydrate malabsorption was determined by breath hydrogen (BH(2)) gas analysis after juice feedings. Statistical differences between groups were determined by 2-way analysis of variance with the Tukey procedure.

RESULTS

Infants with IC fed apple juice exhibited carbohydrate malabsorption as shown by increased BH(2) excretion, whereas those without IC absorbed carbohydrates normally when fed this juice. Infants fed apple juice with carbohydrate malabsorption cried more and consequently slept less during the last 1.5 hours of the study. This was associated with increased PA and EE as compared with infants without IC fed apple juice. In contrast, infants fed white grape juice, regardless of IC, showed no increase in BH(2) excretion, PA, and EE. Furthermore, crying and sleeping times were unchanged in infants fed white grape juice regardless of the presence or absence of IC.

CONCLUSIONS

IC was associated with carbohydrate malabsorption from fruit juices containing sorbitol and a high fructose-to-glucose ratio.

Low dosages of exogenous growth hormone and its effect on growth in an animal model of suboptimal nutrition

In a previous study, weight gain, insulin growth factor-1 (IGF-1) and insulin growth factor binding protein-3 (IGFBP-3) were increased in rats fed suboptimal levels of energy and administered 0.1 mg/100 g of body weight of recombinant human growth hormone (rhGH). Our objective was to determine whether these anabolic effects were still obtained with lower dosages of rhGH in similarly fed rats. Three groups of male, prepubertal Sprague-Dawley rats were administered rhGH and three groups of similar rats were given normal saline solution daily (0.05 mg/100 g of body weight subcutaneously). All rats were fed a balanced 1:1 carbohydrate:fat ratio diet for 4 wk. Restricted rats within each treatment were pair fed 80% and 60% ad libitum. Daily body weight, food intake, and efficiency were recorded. After 4 wk, serum IGF-1 and IGFBP-3, body fat, fat-free mass, and total body water were determined. Total weight gain and serum IGFBP-3 were significantly higher, with a tendency for increased body fat, in rats treated with rhGH and fed at 60% ad libitum. However, within each treatment, energy restriction caused decreased body fat and total body water. These results suggest that lower dosages of rhGH provide anabolic effects during suboptimal energy intake.

Consequences of incomplete carbohydrate absorption from fruit juice consumption in infants

BACKGROUND

Most infants consume fruit juices by 6 months of age. However, fruit juices containing sorbitol may be associated with carbohydrate malabsorption without clinical symptoms. We hypothesized that increased physical activity and metabolic rate may be associated with carbohydrate malabsorption.

METHODS

Physical activity and metabolic rate were determined in 14 healthy infants ([mean +/- SD] age, 5.1 +/- 0.8 months; weight, 7.8 +/- 1.1 kg; length, 67 +/- 4.2 cm; and body fat, 26% +/- 5%) for 3 hours in a respiratory chamber. Seven were fed pear juice, and the other 7 were fed white grape juice (120 mL) after a 2-hour fast. Pear juice contains sorbitol and a high fructose-glucose ratio, whereas white grape juice is sorbitol free and has a low fructose-glucose ratio. Carbohydrate absorption was determined by breath hydrogen gas analysis. The study was double-blinded.

RESULTS

When compared with the infants without carbohydrate malabsorption (peak breath hydrogen level < 20 ppm above baseline), 5 of the 7 infants fed pear juice and 2 of the 7 infants fed white grape juice exhibited carbohydrate malabsorption (peak breath hydrogen level > or = 20 ppm above baseline; P < .01). These infants also exhibited both increased physical activity (P < .001) and metabolic rate (P < .05) after juice consumption in comparison with infants with normal carbohydrate absorption. When grouped according to the type of juice consumed, only infants fed pear juice exhibited increases in physical activity (P < .01).

CONCLUSIONS

Carbohydrate malabsorption is associated with increased physical activity and metabolic rate in infants. Most of the infants who had carbohydrate malabsorption consumed pear juice. Therefore, fruit juices containing sorbitol and high levels of fructose may not be optimal for young infants.

Determinants of energy expenditure and fuel utilization in man: effects of body composition, age, sex, ethnicity and glucose tolerance in 916 subjects

BACKGROUND

24-h energy expenditure (24-EE) and 24-h respiratory quotient (24-RQ) are important measurements in obesity research, but their accurate assessment is limited to few specialized laboratories.

OBJECTIVES

1) To provide comprehensive prediction equations for 24-EE, sleeping metabolic rate (SMR) and 24-RQ, based on a large number of Caucasian and Pima Indian subjects, covering a wide range of body weight and composition, body fat distribution, and age and 2) to test whether Pima Indians have lower metabolic rate and/or higher 24-RQ than Caucasians.

SUBJECTS AND METHODS

916 non-diabetic subjects, aged 31.5 +/- 11.9 y, body weight 90.5 +/- 26.1 kg (mean +/- s.d.), (561 males, 355 females; 416 Caucasians, 500 Pima Indians; 720 with normal (NGT) and 196 with impaired (IGT) glucose tolerance) spent 24 h in a respiratory chamber for measurements of 24-EE, SMR and 24-RQ. Fat-free mass (FFM) and fat mass (FM) were assessed by either hydrodensitometry or DEXA. Waist circumference and waist-to-thigh ratio (WTR) were determined as measures of body fat distribution.

RESULTS

In a stepwise multiple regression analysis, FFM, FM, sex, age, WTR, and ethnicity were significant independent determinants of 24-EE (2258 +/- 422 kcal/d), explaining 85% of its variability (24-EE (kcal/d)=696 + 18.9 FFM (kg) + 10.O FM (kg) + 180 male -1.9 age (y) + 7.1 WTR (per decimal) + 44 Pima Indian). SMR (1623 +/- 315kcal/d) was determined (78% of variability) by FFM, FM, sex, age, WTR, and glucose tolerance (SMR (kcal/d) = 443 +/- 14.6 FFM (kg) + 6.9 FM (kg) + 79 male - 1.0 age (y) + 5.8 WTR (per decimal) + 38 IGT), but not by ethnicity. Adjustment for the respective variables reduced the variance in 24-EE from 422 to 162 kcal/d and in SMR from 315 to 146kcal/d. 24-RQ (0.854 +/- 0.026) was determined by waist circumference and energy balance (24-RQ = 0.88429-0.00175 waist circumference (cm) + 0.00004 energy balance (%)), but not by sex, ethnicity or glucose tolerance. With this equation only 13% of the variability in 24-RQ could be explained (residual variance 0.024). Compared to Caucasians, Pima Indians had higher 24-EE, but similar SMR and 24-RQ.

CONCLUSIONS

This analysis provides comprehensive prediction equations for 24-EE, SMR and 24-RQ from their major known determinants. It confirms the previous findings that, even after adjustment for body composition, age, sex, ethnicity, and glucose tolerance, there is still considerable variability in energy expenditure and substrate oxidation that may, in part, be genetically determined. In adult Pima Indians, we found no evidence for lower metabolic rate or impaired fat oxidation that could explain the propensity towards obesity in this ethnic group.

Comprehensive assessment of the components of energy expenditure in infants using a new infant respiratory chamber

BACKGROUND

Current methods for energy expenditure (EE) measurements in term infants do not include simultaneous measurements of basal and sleeping metabolic rates (BMR and SMR) or a measure of physical activity (PA). Furthermore, prediction equations for calculating EE are not appropriate for use in infants with metabolic disorders.

OBJECTIVE

To develop and utilize a new infant respiratory chamber for simultaneous measurements of EE (kJ/d), preprandial BMR (kJ/d), SMR (kJ/d) and an index of PA (oscillations/min/kg body weight) in infants with a variety of metabolic disorders, for up to four hours in a hospital setting, while allowing parental interaction in a comfortable environment.

METHODS

We obtained simultaneous measurements of EE, BMR, SMR and PA in 21 infants (66+/-73 days of age, 4.5+/-1.7 kg body weight, 55+/-8 cm in length and 16+/-7% body fat) using our new infant respiratory chamber. Six of these infants were healthy, seven had thyroid dysfunction, five were HIV-exposed, one had AIDS, one had intrauterine and postnatal growth retardation and one was a hypothermic preterm infant. Energy expenditure, BMR and SMR were extrapolated for 24 hours. Body composition was estimated by skin-fold thickness, using age-appropriate formulae. Basal metabolic rate obtained with the infant respiratory chamber was compared to BMR that was calculated using the appropriate World Health Organization (WHO) equations.

RESULTS

In all infants both extrapolated 24-hour EE and BMR correlated with fat-free mass (r = 0.89, p<0.01 and r = 0.88, p<0.01 respectively). Twenty-four hour EE also correlated with PA (r = 0.52, p<0.05). The HIV-exposed infants had higher BMR (p<0.05) than that calculated by the appropriate WHO equation. We found that the caloric requirements for the infant with growth retardation were underestimated based on the infant's weight and age.

CONCLUSIONS

The infant respiratory chamber can measure all of the main components of EE. Some of the results obtained differed significantly from those obtained by the WHO equations; therefore, the new infant respiratory chamber is necessary for estimating EE in infants with metabolic and growth disorders.

Comparison of several equations and derivation of a new equation for calculating basal metabolic rate in obese children

OBJECTIVES

To compare basal metabolic rate (BMR) calculated by the Harris-Benedict, Ravussin, Cunningham, World Health Organization (WHO) and Schofield equations to BMR determined in an obese pediatric population. The second objective is to derive a new equation, based on measured BMR in obese children, for calculating BMR in obese pediatric patients.

METHODS

The study included 110 (50 male/60 female) healthy obese subjects (BMI > 28) (11.7 +/- 2.8 years, 73 +/- 27 kg, 152 +/- 14 cm and 38 +/- 6% fat) who had preprandial BMR determined by indirect calorimetry. These results were compared to BMR calculated with the five above mentioned equations. Fat-free mass was determined by bioelectrical impedance and body composition was calculated using the appropriate equation. The age groups analyzed were as follows: males 3 to 10 and 11 to 18 years old; females 3 to 10 and 11 to 18 years old. A new equation was derived by stepwise multiple regression analysis using 100 randomly selected subjects from our test group and tested using the remaining 10 subjects.

RESULTS

Basal metabolic rate calculated by the Ravussin and Cunningham equations in all subgroups was lower (p < 0.05) than measured BMR. Basal metabolic rate calculated by the Harris-Benedict equation was lower (p < 0.05) than measured BMR in male populations ages 3 to 10, 11 to 18, and in the entire cohort. Measured BMR was overestimated by the Harris-Benedict equation (p < 0.05) in females 11 to 18 years old; by the WHO equation (p < 0.05) in both male and females 3 to 10 years old and by the Schofield equation (p < 0.05) in males 11 to 18 years old. In comparison to measured BMR, the WHO equation appeared to be the most accurate for estimating BMR in males and females 11 to 18 years old. However, BMR calculating using our new equation in the 10 test subjects was similar to measured BMR.

CONCLUSIONS

The WHO equation was the most accurate of the prediction equations studied. However, our new prediction equation may be more appropriate for calculating BMR in an obese pediatric population.

Effects of exogenous recombinant human growth hormone on an animal model of suboptimal nutrition

BACKGROUND

Nutritional dwarfing, a form of suboptimal nutrition, has been identified as a frequent cause of short stature and delayed sexual development in children. Retarded growth is an adaptive response to suboptimal nutrition.

OBJECTIVE

To assess whether recombinant human growth hormone (rhGH) may promote growth during various levels of suboptimal nutrition.

METHODS

Using a previously developed rat model of suboptimal nutrition, six groups of rats (six rats/group) were fed a balanced 1:1 carbohydrate:fat ratio diet for 4 weeks. Three of the groups were administered daily injections of rhGH (0.1 mg/100 g BW) subcutaneously in the back while the other three groups were kept as controls and were given similar dosages of normal saline solution (NSS). Restricted rats within each treatment group were pair fed 80 and 60% of the ad-libitum rats intake. Daily intake of the 80 and 60% fed groups were determined based on the intake of the ad-libitum fed groups. Serum IGF-I and insulin were determined after 4 weeks of dietary treatment by radioimmunoassay while IGFBP-3 was determined by an immunoradiometric assay. Body composition was assessed in all rats by carcass analysis.

RESULTS

After 4 weeks, total weight gain and tail growth were higher (p < 0.05) in the rhGH treated group at 80 and 60% of-libitum energy intake. Serum levels of IGF-I and IGFBP-3 were higher (p < 0.05) in rhGH treated rats fed at 60% of ad-libitum. In comparison to the NSS groups, administration of rhGH in rats fed ad-libitum increased total body water. Energy restriction caused decreased fat percentage (p < 0.05) in both rhGH and NSS groups without differences among treated groups.

CONCLUSION

These results suggest that the anabolic effects of rhGH may overcome mild to moderate energy restriction.

Evaluation of differential effects of carbohydrate and fat intake on weight gain, serum IGF-1 and erythrocyte Na+K+ATPase activity in suboptimal nutrition in rats

OBJECTIVE

Suboptimal nutrition leads to growth delay, frequently without over clinical or biochemical signs. We hypothesize that changes in serum IFG-1 and erythrocyte sodium-potassium ATPase activity (ENKA) may be indices of suboptimal nutrition.

METHODS

Male Sprague-Dawley rats were pair-fed for 4 weeks with balanced diets of different carbohydrate (CHO) to fat (FAT) ratios (3:1, 2:1, and 1:1) and three levels of energy intake (ad-libitum, 80%, and 60%), corrected for actual body weight). Daily weight gain and weekly tail growth were monitored while ENKA, serum total protein, T3, insulin and IGF-1 were measured after four weeks. Refeeding experiments were also performed with the 3:1 and 1:1 CHO:FAT diets, including 4 weeks of dietary restriction and one week of ad-libitum feeding.

RESULTS

Weight gain, tail growth, and IGF-1 decreased (p < 0.05) in all groups after 1 week of dietary restriction. A decrease in ENKA (p < 0.05) was found in rats that consumed 60% of ad-libitum energy intake only after 4 weeks. At the end of dietary treatment, weight gain was higher (p < 0.05) in rats fed the 3:1 CHO:FAT diet. In contrast, when energy was restricted to 80% or 60% of ad-libitum intake, rats fed the 1:1 CHO:FAT diet gained more weight (p < 0.05) compared to the 3:1 and 2:1 CHO:FAT diets. After 1 week of refeeding body weight, tail growth and ENKA returned to control values while serum IGF-1 levels remained depressed.

CONCLUSIONS

Acute nutritional changes are clearly detected by a reduction of serum IGF-1 while ENKA may be a useful index for assessing chronic suboptimal nutrition.

Decreased ratio of fat to carbohydrate oxidation with increasing age in Pima Indians

BACKGROUND

Some metabolic changes related to age may increase the prevalence of obesity. Previous studies have shown that a low relative metabolic rate and a low ratio of fat to carbohydrate utilization are predictors of body weight gain. However, a possible relationship between age and energy substrate utilization (respiratory quotient; RQ = VCO2/VO2) has not been reported.

OBJECTIVE

To determine whether RQ increases and therefore fat oxidation decreases with age in Pima Indian men, independent of body fat and energy balance.

METHODS

We analyzed longitudinal data collected in seven non-diabetic Pima Indian men (31 +/- 6 years, 167 +/- 8 cm, 111.0 +/- 23.7 kg and 41 +/- 9% fat at baseline) who had repeated measurements of 24-hour RQ 7 years apart. On both admissions, subjects were fed a weight maintenance diet (50% carbohydrate, 30% fat and 20% protein) for 3 days before spending 1 day within a respiratory chamber for measurements of 24-hour energy expenditure, basal metabolic rate, sleeping metabolic rate and 24-hour RQ. Paired t-test was used to determine differences between the first and last measurement of 24-hour RQ. Cross-sectional data in 131 Pima Indian men (28 +/- 9 years, 171 +/- 6 cm, 94.5 +/- 24.4 kg, and 32 +/- 9% fat) were also analyzed to determine the relationship between 24-hour RQ and age. Multiple regression analysis was used to adjust 24-hour RQ for differences in energy balance (intake/expenditure in %) and percent body fat and metabolic rate for differences in body size and composition.

RESULTS

Over a 7-year period, mean unadjusted and adjusted 24-hour RQ increased (p < 0.01). Cross-sectional data analysis showed that both the unadjusted (r = 0.19, p < 0.03) and adjusted (r = 0.19, p < 0.03) 24-hour RQ correlated with increasing age while adjusted BMR (r = -0.21, p < 0.02) correlated inversely with age.

CONCLUSIONS

Despite a higher body fat content, older individuals utilize less fat than their younger counterparts. Reduced fat utilization and decreased BMR with age may both contribute to increasing obesity in older individuals.

Spontaneous overfeeding with a 'cafeteria diet' in men: effects on 24-hour energy expenditure and substrate oxidation

OBJECTIVE

To investigate the relationship between obesity and ad libitum food intake (quantity and composition) and to assess the impact of ad libitum food intake on energy expenditure and macronutrient oxidation.

DESIGN

Male volunteers were first fed a weight maintaining diet for at least 4 days before selecting their food for the next 5 days from two computerized vending machines offering a variety of familiar, palatable foods. 24-h energy expenditure (24EE) and substrate oxidation were measured in a respiratory chamber on the last day of each weight maintenance and ad libitum intake periods.

SETTING

Ten day admission on a metabolic research ward.

SUBJECTS

Thirty-four non-diabetic Pima Indian males covering a wide range of body weight and body composition (30 +/- 8 y, 102.1 +/- 30.2 kg, 34 +/- 9% body fat, mean +/- s.d.).

RESULTS

Weight maintenance requirements averaged 2913 +/- 342 kcal/d. Energy intake during the ad libitum period increased to 4550 +/- 921 kcal/d (12 +/- 1% protein, 40 +/- 4% fat, 48 +/- 4% carbohydrate) i.e., a spontaneous overeating by 54 +/- 32% above weight maintenance requirement, resulting in a 0.9 +/- 1.0 kg body weight gain. Neither the composition of the selected diet nor the degree of overeating was associated with physical characteristics, such as body weight and body composition. When compared with baseline, spontaneous overeating on day 5 was associated with a 396 +/- 233 kcal/d increase in 24EE, a 607 +/- 503 kcal/d increase in carbohydrate oxidation, a 214 +/- 392 kcal/d decreased in lipid oxidation (P < 0.01), and no change in protein oxidation. Increased carbohydrate oxidation correlated with the excess carbohydrate intake (r = 0.69, P = 0.0001) accounting for 68 +/- 13% (mean +/- s.e.e.) of the excess, whereas excess fat intake was not oxidized.

CONCLUSION

In response to spontaneous overfeeding on a mixed 'cafeteria diet', excess carbohydrate intake is oxidized, suggesting a physiological control of carbohydrate stores, whereas excess fat intake is channeled toward fat stores. None of the observed changes were related to indices of obesity.

Racial difference in body core temperature between Pima Indian and Caucasian men

A low body temperature is associated with a low metabolic rate for a given body size and body composition. These two traits might have been assets in the history of a population subjected to cycles of feast and famine, but became part of an obesity-prone syndrome in our westernized society characterized by plenty of food and a sedentary lifestyle. We tested whether Pima Indians have lower body temperatures than Caucasians, a trait which might partly explain the high prevalence of obesity in this population. Twenty-five Pima Indian (28 +/- 6 yrs, 87.8 +/- 22.8 kg, 29 +/- 9% body fat) and 25 Caucasian (30 +/- 5 yrs, 80.7 +/- 18.4 kg, 22 +/- 11% body fat) men had body core temperatures measured by telemetry for 24 h while in a respiratory chamber. Mean daily body core temperature was 36.93 +/- 0.12 and 36.90 +/- 0.22 degrees C in Pima Indians and Caucasians, respectively. Since body core temperature during sleep (SLBCT) correlated with percentage body fat, a subset of 10 Pima Indians and 10 Caucasians were pair-matched for body weight and percentage body fat. In this group, SLBCT was lower in Pima Indians than in Caucasians (36.45 +/- 0.10 vs 36.65 +/- 0.27 degrees C; P < 0.01) and, ethnic group accounted for 20% of the variance in SLBCT (P < 0.01). Surprisingly, the lower SLBCT was not associated with a low metabolic rate and therefore does not seem to play a role in the etiology of obesity in Pima Indians.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between sleep stages and metabolic rate in humans

Differences in sleeping metabolic rate (SMR) among subjects may be related to different levels of energy expenditure associated with sleep stages. The relationship between energy expenditure and sleep stages was investigated overnight in 29 subjects (14 Caucasians and 15 Pima Indians, 18 males and 11 females; mean +/- SD, 31 +/- 7 yr, 83 +/- 26 kg, 27 +/- 11% fat). Sleep stages were determined by electroencephalogram recording, whereas energy expenditure was measured in a 1,000-liter Plexiglas sleep box constructed around a bed as a fast-response open-circuit indirect calorimeter. Eighty-five percent of the interindividual variability in SMR was explained by differences in fat-free mass, fat mass, age, sex, and race (r2 = 0.85). The intra-individual variance in SMR over time was related to sleep stages and to clock time. Within subjects, SMR in stage 3 was significantly lower than in stage 2 (-39 +/- 18 kcal/day; P < 0.05) and rapid eye movement sleep (-51 +/- 23 kcal/day; P < 0.05). Also, sleep stages were associated with different respiratory quotients. Because sleep stages are associated with only small differences in energy metabolism, our results suggest that sleep stages play a minor role in the variance of SMR among subjects. However, the duration of sleep may contribute to the variability of 24-h energy expenditure.

Determinants of total daily energy expenditure: variability in physical activity

Excessive energy intake and/or reduced total daily energy expenditure (TEE) causes obesity. To determine the relationship between obesity and TEE in an obesity-prone population, we measured TEE, 24-h sedentary energy expenditure (SEDEE), and basal metabolic rate (BMR) in 30 Pima Indian men (83.6 +/- 20.0 kg and 31 +/- 9% fat) by the doubly labeled water method and a respiratory chamber. The energy expenditure for physical activity (EEACT) was calculated as TEE - (BMR + 0.1 TEE), where 10% of TEE is an estimate of the thermic effect of food. Fat-free mass was the best single determinant (P < 0.01) of TEE, explaining 48% of its variance. TEE, SEDEE, BMR, and EEACT were 12,010 +/- 2292, 9945 +/- 1559, 7677 +/- 1901, and 3297 +/- 1732 kJ/d, respectively. Because EEACT is dependent on body weight, EEACT/kg body wt (41.7 +/- 23.2 kJ.d-1.kg-1) and TEE/(BMR + 0.1 TEE) (1.39 +/- 0.22) were used as indexes of the level of physical activity. Both indexes correlated negatively with percent body fat (r = -0.56, P < 0.01 and r = -0.42, P < 0.03, respectively). These results suggest that obesity is associated with lower levels of physical activity.

Energy cost of arousal: effect of sex, race and obesity

The basal (BMR) to sleeping metabolic rate (SMR) ratio might represent an estimate of the activation of the nervous system (central/sympathetic) from sleeping to basal state. Since this activation might be influenced by the degree of obesity, and might be different between sexes, we retrospectively analysed energy expenditure data collected for a large number of subjects. Twenty-four hour energy expenditure (24EE), BMR and SMR were measured in a respiratory chamber in 122 Caucasians (63 males/59 females, 32 +/- 10 years, 94 +/- 33 kg, 29 +/- 11% fat) (means +/- s.d.) and in 123 Pima Indians (68 males/55 females, 29 +/- 7 years, 100 +/- 25 kg, 34 +/- 9% fat). The BMR/SMR ratio varied greatly between individuals (1.05 +/- 0.08; range 0.87-1.34). In Pima Indians, BMR/SMR was inversely correlated to both fat mass (r = -0.26; P < 0.01) and BMI (r = -0.22; P < 0.05), whereas, in Caucasians, BMR/SMR was inversely correlated to waist/thigh circumference ratio (r = -0.28; P < 0.01). On average, the BMR/SMR was higher in Pima Indians than in Caucasians (1.06 +/- 0.08 vs. 1.03 +/- 0.07, P < 0.01) and higher in Pima Indian males than in Pima Indian females (1.08 +/- 0.09 vs. 1.04 +/- 0.06, P < 0.05). Studies are needed to investigate whether these differences in the increase in energy expenditure from the sleeping to the basal state are related to differences in the activation of the nervous system and/or to other metabolic factors.

Reduced sympathetic nervous activity. A potential mechanism predisposing to body weight gain

The sympathetic nervous system is recognized to play a role in the etiology of animal and possibly human obesity through its impact on energy expenditure and/or food intake. We, therefore, measured fasting muscle sympathetic nerve activity (MSNA) in the peroneal nerve and its relationship with energy expenditure and body composition in 25 relatively lean Pima Indian males (means +/- SD; 26 +/- 6 yr, 82 +/- 19 kg, 28 +/- 10% body fat) and 19 Caucasian males (29 +/- 5 yr, 81 +/- 13 kg, 24 +/- 9% body fat). 24-h energy expenditure, sleeping metabolic rate, and resting metabolic rate were measured in a respiratory chamber, whereas body composition was estimated by hydrodensitometry. Pima Indians had lower MSNA than Caucasians (23 +/- 6 vs 33 +/- 10 bursts/min, P = 0.0007). MSNA was significantly related to percent body fat in Caucasians (r = 0.55, P = 0.01) but not in Pimas. MSNA also correlated with energy expenditure adjusted for fat-free mass, fat mass, and age in Caucasians (r = 0.51, P = 0.03; r = 0.54, P = 0.02; and r = 0.53, P = 0.02 for adjusted 24-h energy expenditure, sleeping metabolic rate, and resting metabolic rate, respectively) but not in Pima Indians. In conclusion, the activity of the sympathetic nervous system is a determinant of energy expenditure in Caucasians. Individuals with low resting MSNA may be at risk for body weight gain resulting from a lower metabolic rate. A low resting MSNA and the lack of impact of MSNA on metabolic rate might play a role in the etiology of obesity in Pima Indians.

Relationship between skeletal muscle lipoprotein lipase activity and 24-hour macronutrient oxidation

A low ratio of whole-body 24-h fat/carbohydrate (CHO) oxidation has been shown to be a predictor of subsequent body weight gain. We tested the hypothesis that the variability of this ratio may be related to differences in skeletal muscle metabolism. Since lipoprotein lipase (LPL) plays a pivotal role in partitioning lipoprotein-borne triglycerides to adipose (storage) and skeletal muscle (mostly oxidation), we postulated that a low ratio of fat/CHO oxidation was associated with a low skeletal muscle LPL (SMLPL) activity. As an index of substrate oxidation, 24-h RQ was measured under sedentary and eucaloric conditions in 16 healthy nondiabetic Pima males. During a 6-h euglycemic, hyperinsulinemic clamp, muscle biopsies were obtained at baseline, 3, and 6 h. Heparin-elutable SMLPL activity was 2.92 +/- 0.56 nmol free fatty acids/g.min (mean +/- SD) at baseline, was unchanged (2.91 +/- 0.51) at the third hour, and increased significantly (P < 0.05) to 3.13 +/- 0.57 at the sixth hour of the clamp. The mean (of baseline and 3-h) SMLPL activity correlated inversely with 24-h RQ (r = 0.57, P < 0.03) but not with body size, body composition, or insulin-mediated glucose uptake. Since SMLPL activity is related to the ratio of whole body fat/CHO oxidation rate, a decreased muscle LPL activity may, therefore, predispose to obesity.

Effect of phenylpropanolamine on energy expenditure and weight loss in overweight women

The effect of phenylpropanolamine (PPA), a noncatecholamine sympathomimetic weight-loss agent, on energy expenditure (EE) and substrate oxidation was measured in a respiratory chamber in 24 overweight women after 4 d of treatment (PPA or placebo) during weight maintenance and after 7 wk of treatment on a hypoenergetic diet (70% of measured baseline 24-h EE). Twelve women (37 +/- 2 y, 74 +/- 6 kg, 33 +/- 1% body fat) were randomly assigned to the PPA group [75 mg osmotic release oral system (OROS)-PPA/d] and 12 (mean +/- SEM: 38 +/- 2 y, 79 +/- 1 kg, 37 +/- 1% body fat) to the placebo group. Baseline measurements of 24-h EE (7849 +/- 226 vs 7834 +/- 142 kJ/d), basal metabolic rate (BMR) and 24-h respiratory quotient (RQ) were comparable between PPA and placebo groups. After 4 d of treatment, there was no significant effect of PPA on 24-h EE, BMR, and 24-h RQ compared with placebo. Over the 7-wk diet period, however, the PPA group (n = 8) had greater weight loss than the placebo group (n = 10): -5.0 +/- 0.5 vs -3.0 +/- 0.4 kg (P < 0.05). The changes in 24-h EE and 24-h RQ over the 7 wk were not different between the groups. We conclude that weight loss is enhanced by OROS-PPA, but this change was not explained by changes in 24-h EE or 24-h RQ. The small number of subjects may have hindered detection of subtle differences in energy metabolism.

Concomitant interindividual variation in body temperature and metabolic rate

There is significant variation in metabolic rate in humans, independent of differences in body size, body composition, age, and gender. Although it has been generally held that the normal human "set-point" body temperature is 37 degrees C, these interindividual variations in metabolic rate also suggest possible variations in body temperature. To examine the possibility of correlations between metabolic rate and body temperature, triplicate measurements of oral temperatures were made before and after measurement of 24-h energy expenditure in a respiratory chamber in 23 Pima Indian men. Fasting oral temperatures varied more between individuals than can be attributed to methodological errors or intraindividual variation. Oral temperatures correlated with sleeping (r = 0.80, P < 0.0001), and 24-h (r = 0.48, P < 0.02) metabolic rates adjusted for differences in body size, body composition, and age. Similarly, in the 32 Caucasian men of the Minnesota Semi-Starvation Study, oral temperature correlated with adjusted metabolic rate, and the interindividual differences in body temperature were maintained throughout semistarvation and refeeding. These results suggest that a low body temperature and a low metabolic rate might be two signs of an obesity-prone syndrome in humans.

Lower sedentary metabolic rate in women compared with men

Since females have a greater prevalence of obesity compared with males, the question arises whether females have lower metabolic rate than males after adjusting for differences in body weight and composition. 24-h energy expenditure (24EE), basal metabolic rate (BMR), and sleeping metabolic rate (SMR) were measured in a respiratory chamber in 235 healthy, nondiabetic Caucasian subjects (114 males, 121 females). Body composition was determined by hydrodensitometry. 24EE was 124 +/- 38 kcal/d (P less than 0.002) higher in males than females after adjusting for differences in fat-free mass, fat mass, and age. Spontaneous physical activity was not significantly different between males and females. Since adjusted 24EE was 106 +/- 39 kcal/d (P less than 0.01) higher in females during the luteal phase of the menstrual cycle compared with females during the follicular phase, energy expenditure was analyzed in a subset (greater than 50 yr) to minimize the confounding effect of menstrual status. 24EE (160 +/- 66 kcal/d; P less than 0.03), BMR (116 +/- 45; P less than 0.02), and SMR (208 +/- 68 kcal/d; P less than 0.005) were higher in males compared with females of the older subset after adjusting for differences in body composition, age, and activity. In summary, sedentary 24EE is approximately 5-10% lower in females compared with males after adjusting for differences in body composition, age, and activity.

Spontaneous physical activity and obesity: cross-sectional and longitudinal studies in Pima Indians

Healthy, nondiabetic Pima Indians [103 males, 77 females; 27 +/- 6 (SD) yr, 97 +/- 25 kg, 33 +/- 9% body fat] were studied in a respiratory chamber in which spontaneous physical activity (SPA) was measured by two microwave sensors. SPA, defined as the percentage of time the subjects were active, varied widely from 4.4 to 17.5%. It was higher in males (9.3 +/- 2.0%) than in females (8.6 +/- 2.3%; P less than 0.05) and was not related to body fatness in either sex. However, SPA accounted for a significant portion of the daily energy expenditure (24-h EE) in males (1,389 +/- 423 kJ/day) and females (1,163 +/- 351 kJ/day) and correlated positively with 24-h EE adjusted for differences in fat-free mass, fat mass, age, and sex (r = 0.42, P less than 0.0001). In 88 siblings, family membership accounted for 57% of the variance in SPA (r(i) = 0.57, P less than 0.02). Body composition was reassessed in a subgroup of 123 subjects (65 males, 58 females) 33 +/- 14 mo later. In males only, SPA correlated inversely to the rate of subsequent body weight change (r = -0.25, P less than 0.05) and the rate of fat-mass change (r = -0.35, P less than 0.005). We conclude that spontaneous physical activity is a familial trait that may play a role in the pathogenesis of obesity.

Twenty-four-hour energy expenditure in Pima Indians with type 2 (non-insulin-dependent) diabetes mellitus

To assess the impact of Type 2 (non-insulin-dependent) diabetes mellitus on energy metabolism, 24-h energy expenditure, basal metabolic rate and sleeping metabolic rate were measured in a respiratory chamber in 151 Pima Indians, 102 with normal glucose tolerance (67 male/35 female, (mean +/- SD) 28 +/- 7 years, 99 +/- 24 kg, 32 +/- 9% body fat) and in 49 with Type 2 diabetes (22 male/27 female, 35 +/- 11 years, 107 +/- 33 kg, 39 +/- 7% body fat), after at least 3 days on a weight maintaining diet. After adjustment for differences in fat-free mass, fat mass, age and sex, 24-h energy expenditure, basal metabolic rate and sleeping metabolic rate were significantly higher in diabetic patients than in control subjects (72 kcal/day, p less than 0.05; 99 kcal/day, p less than 0.005; 99 kcal/day, p less than 0.001 respectively). Spontaneous physical activity was similar in both groups whereas the thermic effect of food, calculated as the mean energy expenditure corrected for activity throughout the day above sleeping metabolic rate and expressed as a percentage of energy intake, was significantly lower in Type 2 diabetic patients (17.1 +/- 7.1 vs 19.8 +/- 5.6%, p less than 0.05). Adjusted values of 24-h energy expenditure, basal metabolic rate and sleeping metabolic rate were correlated with hepatic endogenous glucose production (r = 0.22, p less than 0.05; r = 0.22, p less than 0.05; r = 0.31, p less than 0.01 respectively). Therefore, increased basal and sleeping metabolic rates, resulting in increased 24-h sedentary energy expenditure may play a role in the weight loss so often observed in Type 2 diabetic subjects in addition to the energy loss from glycosuria.

Food intake measured by an automated food-selection system: relationship to energy expenditure

Measuring food intake in a laboratory usually involves limited food choices. An automated food-selection system with two vending machines containing a large variety of foods was used to measure food intake in 10 male volunteers (31 +/- 6 y, 69.2 +/- 7.1 kg, 18 +/- 7% fat, mean +/- SD) on a metabolic ward. The effect of carbohydrate, fat, and protein intakes on 24-h energy expenditure (24EE) and substrate oxidations was measured in a respiratory chamber during day 4 of weight maintenance and day 7 of ad libitum intake. Ad libitum intake resulted in a 7-d overfeeding of 6468 +/- 3824 kJ/d above weight-maintenance requirements, leading to a 2.3 +/- 1.2-kg gain. The 10,975 +/- 3774 kJ excess energy intake on day 7 of ad libitum intake caused a 1205 +/- 920 kJ/d increase in 24EE (delta 24EE = 0.17 x delta intake - 695; r = 0.71, P less than 0.02). Of the excess carbohydrate intake, 74% was oxidized (r = 0.86, P less than 0.001), whereas excess fat intake was not. Carbohydrate and protein stores are regulated whereas excess fat intake is channeled to fat stores.

Energy expenditure by doubly labeled water: validation in lean and obese subjects

The doubly labeled water (2H2(18)O) method to assess energy expenditure in free-living conditions has been successfully validated against gas exchange measurements in lean healthy volunteers in both sedentary conditions and during sustained heavy exercise. However, no data are available on obese subjects. We therefore compared the 2H2(18)O method with indirect calorimetry (respiratory chamber) in 12 male subjects covering a wide range of body weight and composition (61-190 kg, 7-41% fat). Isotope pool sizes and elimination rates were calculated from 18O and 2H enrichments in baseline urine samples and in 7-h, 11.5-h, and daily postdose urine samples using the multipoint slope/intercept method. Results were corrected for isotopic fractionation. Mean 7-day energy expenditure in the respiratory chamber varied from 1,851 to 4,105 kcal/day. The doubly labeled water method tended to underestimate energy expenditure (-2.5 +/- 5.8%, not equal to 0, range -14 to +4%), with the larger underestimate observed in heavier and fatter subjects (r = -0.82 and -0.68, P less than 0.02, respectively). The underestimation in heavier subjects might be related to larger sequestration of deuterium during fat synthesis. In conclusion, the doubly labeled water method is a suitable and accurate method to measure energy expenditure in free-living conditions but might provide a slightly underestimated figure in fatter subjects.