Breath carbon stable isotope ratios identify changes in energy balance and substrate utilization in humans.

Rapid detection of shifts in substrate utilization and energy balance would provide a compelling biofeedback tool for individuals attempting weight loss. As a proof of concept, we tested whether the natural abundance of exhaled carbon stable isotope ratios (breath δ(13)C) reflects shifts between negative and positive energy balance. Volunteers (n=5) consumed a 40% energy-restricted diet for 6 days followed by 50% excess on day 7. Breath was sampled immediately before and 1 h and 2 h after breakfast, lunch and dinner. Exhaled breath δ(13)C values were measured by cavity ring-down spectroscopy. Using repeated measures analysis of variance (ANOVA) followed by Dunnett's contrasts, pre-breakfast breath values on days 2-6 were compared with day 1, and postprandial day 7 time points were compared with pre-breakfast day 7. Energy restriction diminished pre-breakfast breath δ(13)C by day 3 (P<0.05). On day 7, increased energy intake was first detected immediately before dinner (-23.8±0.6 vs -21.9±0.7‰, P=0.002 (means±s.d.)), and breath δ(13)C remained elevated at least 2 h post dinner. In conclusion, when shifting between negative and positive energy balance, breath δ(13)C showed anticipated isotopic changes. Although additional research is needed to determine specificity and repeatability, this method may provide a biomarker for marked increases in caloric intake.

Effect of clothing weight on body weight.

BACKGROUND: In clinical settings, it is common to measure weight of clothed patients and estimate a correction for the weight of clothing, but we can find no papers in the medical literature regarding the variability in clothing weight of adults with weather, season and gender. METHODS: Fifty adults (35 women) were weighed four times during a 12-month period with and without clothing. Clothing weights were determined and regressed against minimum, maximum and average daily outdoor temperature. RESULTS: The average clothing weight (±s.d.) throughout the year was significantly greater in men than in women (1.2±0.3 vs 0.8±0.3 kg, P<0.0001). The average within-person minimum and the average within-person maximum clothing weights across the year were 0.9±0.2 and 1.5±0.4 kg for men, and 0.5±0.2 and 1.1±0.4 kg for women, respectively. The within-person s.d. in clothing weight was 0.3 kg for both men and women. Over the 55 °C range in the lowest to the highest outdoor temperatures, the regressions predicted a maximal change in clothing weight of only 0.4 kg in women and 0.6 kg in men. CONCLUSION: The clothing weight of men is significantly greater than that of women, but there is little variability throughout the year. Therefore, a clothing adjustment of approximately 0.8 kg for women and 1.2 kg for men is appropriate regardless of outdoor temperature.

Effect of exercise on the diurnal variation in energy substrate use during a high-fat diet.

Aerobic exercise increases 24-h fat oxidation following initiation of a high-fat diet. The objective of this study is to examine the time course of increased fat oxidation under exercise and sedentary conditions. Eighteen healthy subjects completed a randomized crossover design (sedentary and exercise visits) staying for five consecutive days in a metabolic chamber each visit. On day 1, 30% of energy intake was from fat; days 2-5 had 50% of energy as fat. During exercise, subjects rode on a stationary cycle at 45% of VO2max for 1 h in the mornings and evenings. Respiratory gases and urinary nitrogen were collected to calculate macronutrient oxidation and non-protein respiratory exchange ratio (NPRER). This data, collected continuously (24-h periods), were subsequently divided into three time segments: (1) exercise + recovery (1000-1200 hours, 2100-2200 hours), (2) sleep (2300-0645 hours), and (3) wake (all remaining hours). NPRER on exercise versus sedentary visits was lower for the sleep segment (0.77 ± 0.01 01 vs. 0.81 ± 0.01, p < 0.001), higher for the exercise + recovery segment (0.88 ± 0.01 vs. 0.86 ± 0.01, p < 0.001), and was not different for the wake segment. Fat oxidation was significantly higher for exercise versus sedentary treatments during sleep (41 ± 2 vs. 31 ± 2 g), wake (62 ± 3 vs. 51 ± 3 g), and exercise + recovery segments (33 ± 3 vs.16 ± 1 g), but so was fat intake by design (171 ± 8 vs. 128 ± 7 g/d). Although exercise showed greater fat oxidation during all segments, dietary fat intake was also higher. Therefore, based on NPRER, the time of day during which the exercise treatment increased the ratio of fat to carbohydrate oxidation was during sleep.

Impact of exercise and dietary fatty acid composition from a high-fat diet on markers of hunger and satiety.

To compare the effects of both dietary fatty acid composition and exercise vs. sedentary conditions on circulating levels of hunger and satiety hormones. Eight healthy males were randomized in a 2 × 2 crossover design. The four treatments were 3 days of HF diets (50% of energy) containing high saturated fat (22% of energy) with exercise (SE) or sedentary (SS) conditions, and high monounsaturated fat (30% of energy) with exercise (UE) or sedentary (US) conditions. Cycling exercise was completed at 45% of VO(2)max for 2h daily. On the third HF day, 20 blood samples were drawn over a 24h period for each hormone (leptin, insulin, ghrelin, and peptide YY (PYY)). A visual analog scale (VAS) was completed hourly between 0800 and 2200. Average 24h leptin and insulin levels were lower while 24h PYY was higher during exercise vs. sedentary conditions. FA composition did not differentially affect 24h hormone values. VAS scores for hunger and fullness did not differ between any treatment but did correlate with ghrelin, leptin, and insulin. High saturated or unsaturated fat diets did not differ with respect to markers of hunger or satiety. Exercise decreased 24h leptin and insulin while increasing PYY regardless of FA composition.

Insights into energy balance from doubly labeled water.

Obesity is defined as the excess storage of energy in the form of fat that results from imbalances between energy intake and expenditure. The study of the components of energy balance has undergone a significant advancement with the application of the doubly labeled water (DLW) method to the measurement of human energy expenditure. This manuscript includes a selective review of the studies that have utilized the doubly labeled method as it applies to the study of human obesity. Although generally now accepted, one of the major surprises from the early applications of DLW was that obese individuals have higher energy expenditures than lean controls. Moreover, weight gain, even in the already obese, is associated with an increase in energy expenditure as weight is one of the strongest predictors of total energy expenditure. Similarly, studies of weight loss treatment show a decrease in energy expenditure due to weight loss and due to adaptive changes in energetic efficiency, but these changes do not account for the common cessation of weight loss observed after 12-26 weeks of restriction. The accumulating data from the application of the DLW method suggest a need to place greater emphasis on mechanisms that lead to a mismatch between energy intake and expenditure rather than a continuing emphasis on energy intake or energy expenditure alone.

Circannual variation in relative weight of children 5 to 16 years of age.

BACKGROUND: Summer weight gain in children has been reported; however, this is usually based on two time points. Our objective was to investigate monthly variation in weight status. METHODS: Cross-sectional, de-identified health records including height, weight and demographics, collected between 2007 and 2012 from South Central Wisconsin in 70 531 children age 5-16 years were analysed. The monthly averages in body mass index (BMI) z-score were analysed cross-sectionally followed by a paired analysis for a subset with one visit each during school and summer months. RESULTS: BMI z-scores during the summer months (June-August) were lower than values during the school year (September-May). Of note, there was a rapid decrease in BMI z-scores from May to June, with June BMI z-score values being 0.065 units less (95% CI 0.046-0.085) than those in May, little change from June to August and a rapid increase between the August and September BMI z-scores. CONCLUSION: The monthly pattern does not fully agree with previous two-point school-based studies. Results raise concern that the use of two time point measures of BMIs (early fall and late spring) is suboptimal for evaluation of circannual variation. We suggest that future evaluation of the effect of school-based or summer interventions utilizes additional measures in those periods so that a seasonal analysis can be performed.

Entrainment of the diurnal rhythm of plasma leptin to meal timing.

To identify the physiologic factor(s) that entrain the diurnal rhythm of plasma leptin, leptin levels were measured hourly after changes in light/dark cycle, sleep/wake cycle, and meal timing. Four young male subjects were studied during each of two protocols, those being a simulated 12-h time zone shift and a 6.5-h meal shift. During the baseline day, plasma leptin demonstrated a strong diurnal rhythm with an amplitude of 21%, zenith at 2400 h, and nadir between 0900 and 1200 h. Acute sleep deprivation did not alter plasma leptin, but day/night reversal (time zone shift) caused a 12+/-2 h shift (P < 0.01) in the timing of the zenith and nadir. When meals were shifted 6.5 h without changing the light or sleep cycles, the plasma leptin rhythm was shifted by 5-7 h (P < 0.01). The phase change occurred rapidly when compared with changes in the diurnal rhythm of cortisol, suggesting that leptin levels are not acutely entrained to the circadian clock. The leptin rhythm was altered by meal timing in a manner very similar to the rhythm of de novo cholesterol synthesis. We conclude that the diurnal rhythm of plasma leptin in young males is entrained to meal timing.

Activity, adiposity and weight change in Jamaican adults.

OBJECTIVE: Populations in developing countries are particularly vulnerable to the development of obesity in the period of rapid transition to a more modernized lifestyle. We sought to determine the relationship between activity energy expenditure (AEE), adiposity and weight change in an adult population undergoing rapid socio-economic transition. METHODS: Total daily energy expenditure (TDEE) was measured using the doubly labelled water method, resting energy expenditure (REE) using indirect calorimetry and AEE calculated as the difference between TDEE and REE, in adults from a working class community in Spanish Town, Jamaica. During six years of follow-up, weight was measured between one and four times. Mixed effects regression modelling was used to test for association between components of the energy budget and weight change. RESULTS: Men (n = 17) weighed more but women (n = 18), had significantly more body fat, 38.5% vs 24.5%, respectively (p < 0.01). Men had higher levels of EE, particularly AEE after adjustment for body weight, 66.3 versus 46.4 kJ/kg.d for men and women, respectively (p < 0.001). At baseline, adjusted AEE was inversely associated with body fat in men and women, r = -0.46 and r = -0.48, respectively (p < 0.05). Mean rate of weight change was + 1.1 and + 1.2 kg/year for men and women, respectively. No component of EE, ie TDEE, REE or AEE, significantly predicted weight change in this small sample. CONCLUSIONS: These results suggest an important role for AEE in maintaining low levels of adiposity. The lack of association between EE and weight change, however, suggests populations in transition are at risk of obesity from environmental factors (eg dietary) other than simply declining physical activity levels.

High energy expenditure is not protective against increased adiposity in children.

BACKGROUND: Low levels of energy expenditure (TEE) may contribute to excess weight during childhood, but limited longitudinal data exist. OBJECTIVES: This is to test whether low TEE during the first 6 years of life could predict excess weight status at 8 years. METHODS: Total energy expenditure from doubly labelled water, weight, stature, waist circumference and fat mass and fat-free mass (FFM) in children at 0.25, 2, 4 and 6 years of age. This cohort includes individuals at high (n = 27) and low risk (n = 26) for childhood obesity, based upon whether pre-pregnant maternal obesity. A linear mixed effects model was fit to TEE. Individual variation was accounted for as a random effect. Residual TEE was calculated for age and individually averaged across time. RESULTS: Fat-free mass (kg) was highly correlated (R2 = 0.91) with TEE (kcal/day), and waist circumference and sex were also significant predictors of TEE. TEE residual tracked within individuals. TEE residuals did not correlate with either BMI or %fat at age 8 years. CONCLUSION: Using the residual TEE approach to identify high and low TEE during the first 6 years of life did not explain excess weight at 8 years of life in this cohort of children at high and low risk of obesity based upon maternal obesity status.

Familial and individual predictors of obesity and insulin resistance in urban Hispanic children.

BACKGROUND: High intake of sugar-sweetened beverages (SSB) has been suggested to contribute to the pediatric obesity epidemic, however, how the home food environment influence children's intake of SSB among Hispanic families is still poorly understood. OBJECTIVES: To evaluate the relationships between the home food environment and Hispanic children's diet in relation to weight status and insulin resistance (IR). METHODS: A food frequency questionnaire was administered to 187 Hispanic children (ages 10 to 14 years) and anthropometrics were measured. IR was estimated from fasting insulin and glucose levels using the homeostasis model assessment of insulin resistance (HOMAIR ). Parents reported on family demographics and the home food environment. A structural equation modelling approach was applied to examine the hypothesized relationships among variables. RESULTS: The prevalence of childhood overweight and obesity was 52.8% and it was positively associated with HOMAIR (ß = 0.687, P < .0001). Children's SSB consumption was positively associated with children's body mass index z-score (ß = 0.151, P < 0.05) and subsequently to HOMAIR . Children's SSB consumption was predicted by home availability (ß = 0.191) and parental intake of SSB (ß = 0.419) (P < 0.05). The model fit indices [χ(2) = 45.821 (d.f. = 30, P > 0.01 and < 0.05), χ(2) /d.f. = 1.53, root mean square error of approximation = 0.053 (90% confidence interval = 0.016, 0.082), comparative fit index = 0.904] suggested a satisfactory goodness-of-fit. CONCLUSIONS: The home food environment and parental diet seem to play an important role in the children's access to and intake of SSB, which in turn predicted children's weight status.

Association between apolipoprotein E phenotype and endogenous cholesterol synthesis as measured by deuterium uptake.

STUDY OBJECTIVE: The aim was to determine if central pool cholesterol formation rate is related to apo E phenotype in healthy normolipidaemic males. DESIGN: Subjects consumed a fixed composition diet for 5 d and at 07:00 hours on d 5 drank 0.7 g deuterium oxide (D2O).kg-1 body water. Over d 5 body water deuterium enrichment was maintained by ingestion of labelled drinking water. The fractional synthetic rate of the central pool free cholesterol was determined over two consecutive 12 h intervals by the incorporation of deuterium from body water into plasma unesterified cholesterol. SUBJECTS: Participants were healthy male volunteers, mean age 26.4 years. They were divided into E2/(2 or 3) and E4/(4 or 3) alleles, n = 9 in each group. MEASUREMENTS AND MAIN RESULTS: Subjects with E2/- showed lower fractional synthetic rates than E4/- subjects, at 0.070(SEM 0.007) v 0.097(0.009) d-1 over the 24 h period (p less than 0.05). Cholesterol fractional synthetic rate was higher during the night than during the day (p less than 0.05). CONCLUSIONS: These findings suggest an increased central pool free cholesterol synthesis in individuals possessing the apo epsilon-4 versus epsilon-2 allele. Apo E related regulation of whole body de novo cholesterol synthesis may therefore contribute to observed variations in plasma cholesterol levels.

Twenty-four-hour leptin levels respond to cumulative short-term energy imbalance and predict subsequent intake.

Leptin plays a vital role in the regulation of energy balance in rodent models of obesity. However, less information is available about its homeostatic role in humans. The aim of this study was to determine whether leptin serves as an indicator of short-term energy balance by measuring acute effects of small manipulations in energy intake on leptin levels in normal individuals. The 12-day study was composed of four consecutive dietary-treatment periods of 3 days each. Baseline (BASE) [100% total energy expenditure (TEE)] feeding, followed by random crossover periods of overfeeding (130% TEE) or underfeeding (70% TEE) separated by a eucaloric (100% TEE) washout (WASH) period. The study participants were six healthy, nonobese subjects. Leptin levels serially measured throughout the study period allowed a daily profile for each treatment period to be constructed and a 24-h average to be calculated; ad libitum intake during breakfast "buffet" following each treatment period was also measured. Average changes in mesor leptin levels during WASH, which were sensitive to energy balance effected during the prior period, were observed. After underfeeding, leptin levels during WASH were 88 +/- 16% of those during BASE compared with 135 +/- 22% following overfeeding (P = 0.03). Leptin levels did not return to BASE during WASH when intake returned to 100% TEE, but instead were restored (104 +/- 21% and 106 +/- 16%; not significant) only after subjects crossed-over to complementary dietary treatment that restored cumulative energy balance. Changes in ad libitum intake from BASE correlated with changes in leptin levels (r2 = 0.40; P = 0.01). Leptin levels are acutely responsive to modest changes in energy balance. Because leptin levels returned to BASE only after completion of a complementary feeding period and restoration of cumulative energy balance, leptin levels reflect short-term cumulative energy balance. Leptin seems to maintain cumulative energy balance by modulating energy intake.

Effects of dietary protein on theophylline pharmacokinetics and caffeine and aminopyrine breath tests.

The effects of low- and high-protein diets on theophylline kinetics and the time course of changes in 13C-labeled caffeine and aminopyrine CO2 breath tests were examined in six young men. With a low-protein diet, mean theophylline clearance fell 21% (P less than 0.04) and the t1/2 rose from 8.0 to 10.6 hours (P less than 0.02). With a high-protein diet, mean theophylline clearance rose 26% (P less than 0.004) and the t1/2 shortened to 7.4 hours (P less than 0.03). Theophylline volume of distribution and protein binding did not change. Renal clearance of theophylline was lowered during the low-protein diet. Theophylline clearance correlated with caffeine breath test values during the low- (r = 0.73) and high- (r = 0.70) protein diets. Theophylline clearance correlated less well with the aminopyrine breath test values during the low- (r = 0.47) and high- (r = 0.55) protein diets. Thus dietary protein significantly influenced theophylline clearance, but the caffeine and aminopyrine breath tests showed a differential response to this important environmental factor.

The caffeine CO2 breath test: dose response and route of N-demethylation in smokers and nonsmokers.

The optimal conditions for performing the caffeine CO2 breath test (CBT) were investigated in smokers and nonsmokers. Caffeine labeled with 13C or 14C in all three (1, 3, and 7) methyl groups or specifically in the 1-, 3-, or 7-methyl groups were orally administered to healthy adults and the expiration of labeled CO2 was measured for 8 or 24 hr. The absolute rate of labeled CO2 excretion from trilabeled caffeine was proportional to the dose up to 3 mg/kg in all subjects. In smokers, the rate of labeled CO2 excretion averaged twice that in nonsmokers at all doses. A correlation was observed between the 2-hr cumulative CO2 excretion from trilabeled caffeine and the apparent oral metabolic clearance rate (MCR) of caffeine (R = 0.90). Monolabeled CBTs in smokers and nonsmokers demonstrated that 80% +/- 4% of labeled CO2 expired in the breath during the first 2 hr of a trilabeled CBT was derived from the 3 position; at 6 to 8 hr equal amounts were derived from the 3 and 7 positions. Little N-demethylation was observed from the 1 position at any time during the 8-hr test. The results indicate that the 2-hr cumulative excretion of labeled CO2 could be used to accurately predict the metabolic clearance rate of caffeine is the best CBT parameter for detecting the effect of smoking on caffeine N-demethylation. The data suggest that the primary routes of caffeine metabolism are 3-N-demethylation and ring hydroxylation and confirm that caffeine metabolites are N-demethylated primarily in the 3 and 7 positions.

Changes in total body water with age.

Extensive cross-sectional studies demonstrate a diminution of total body water in elderly and very old subjects. These findings are supported by less extensive longitudinal studies. Cross-sectional studies indicate that the decrease in total body water is mainly due to decreased intracellular water, but this is not supported by the findings of longitudinal studies. Despite the observed changes in total body water, both animal and human studies indicate little or no change in the relationship between total body water and fat-free mass with aging.

Energy expenditure from doubly labeled water: some fundamental considerations in humans.

The isotopic loading dose and metabolic period for the measurement of energy expenditure in humans by the doubly labeled water method were predicted by a propagation of error analysis. Factors considered for sources of error were analytical errors in the mass spectrometric determination of isotopic enrichments, biological variation in the isotopic enrichments, uncertainties in total body water (TBW), evaporative water loss, and metabolic fuel. The predicted optimal isotopic loading doses were 0.3 g H2 18O/kg TBW and 0.12 g 2H2O/kg TBW for all subjects except neonates in which they were 0.4 g H2 18O/kg TBW and 0.16 g 2H2O/kg TBW. The optimal metabolic periods were 3 to 14 days in neonates and children, and 5 to 28 days in adults. The theoretical coefficient of variation of the doubly labeled water method for the measurement of energy expenditure is between 4 and 8%.

Balancing energy expenditure and body weight.

It has been nearly 50 y since Mayer and coworkers hypothesized that the mechanisms controlling energy balance are accurate in persons with high levels of physical activity, but that in sedentary persons there is a threshold of physical activity below which these mechanisms become imprecise and that this leads to obesity. This hypothesis, however, was relatively untested in humans because of the difficulty of measuring total energy expenditure (TEE). The development of the doubly labeled water method has obviated this problem and we have now begun to test the Mayer hypothesis in humans. A review of cross-sectional data from doubly labeled water studies in adults provided support for the Mayer hypothesis in men but not in women. Men with TEE > approximately 1.75 times the resting metabolic rate (RMR) had lower body mass indexes than did those with lower expenditures. Further support for the hypothesis was obtained from a longitudinal study of previously obese women. Women with ratios of TEE to RMR > approximately 1.75 gained less weight than did those with lower energy expenditures. When a subset of the less active women was placed in an exercise program that increased TEE:RMR to 1.75, weight gain was arrested. Weight gain resumed when the exercise program ended. The doubly labeled water method now makes it possible to quantitatively and objectively test a hypothesis proposed almost 50 y ago. Results generally support the Mayer hypothesis of a threshold of physical activity that protects against weight gain.

The importance of clinical research: the role of thermogenesis in human obesity.

The hypothesis that human obesity is caused by deficient thermogenesis has been proposed by many investigators throughout the 20th century. Supporting evidence was obtained from epidemiologic studies of dietary intake, animal models with aberrant brown adipose tissue (BAT) function, and genetic studies of human polymorphisms of genes involved in BAT function. Supporting evidence was also obtained from clinical studies of the thermogenic effect of meals, but these measures capture only a short portion of the day and may miss some of the thermogenic effect. To capture the effects throughout the day and to move the studies out of the metabolic ward, investigators have used the doubly labeled water (DLW) method to measure total daily energy expenditure. DLW studies have not supported the above hypothesis. Increases in total energy expenditure (TEE) during overfeeding have been small (0.9 +/- 0.8 MJ/d) and account for an average of only 18 +/- 18% of the excess energy intake. Most of this increase is in the resting metabolic rate. Moreover, these studies showed little variation in the changes in resting metabolic rate or in thermogenesis from meals during overfeeding. Instead, the component that is most variable and that accounts for the variability in weight gain during overfeeding is the energy expended in physical activity. This component of TEE deserves greater attention in future studies. These studies of thermogenesis have shown the importance of clinical research as part of a comprehensive approach to understanding the etiology of human obesity.

A compilation of total daily energy expenditures and body weights in healthy adults.

Measurements of total energy expenditure (TEE) by the doubly labeled water method were compiled from 22 studies to identify the range of variation and significant determinants of energy requirements in healthy adults. The 126 male and 173 female subjects (aged 18-78 y) were separated into four groups: athletes, Pima Indians, people in developing countries, and others. The groups differed significantly (P < 0.001) with respect to TEE, TEE/BMR, TEE-BMR divided by weight, and TEE-BMR. Stepwise multiple regression demonstrated that fat-free mass (FFM) and age are significant variables that can explain 65% of the variation in TEE. These data demonstrate that total daily energy expenditure varies dramatically among healthy, free-living adults. The relationship between body fatness and nonbasal energy expenditure was negative at high energy outputs but considerable variation in body fatness was present among sedentary individuals, suggesting that a low rate of nonbasal energy expenditure is a permissive factor for obesity.