Quantifying energy expenditure in childhood: utility in managing pediatric metabolic disorders

BACKGROUND

Energy expenditure prediction equations are used to estimate energy intake based on general population measures. However, when using equations to compare with a disease cohort with known metabolic abnormalities, it is important to derive one's own equations based on measurement conditions matching the disease cohort.

OBJECTIVE

We aimed to use newly developed prediction equations based on a healthy pediatric population to describe and predict resting energy expenditure (REE) in a cohort of pediatric patients with thyroid disorders.

METHODS

Body composition was measured by DXA and REE was assessed by indirect calorimetry in 201 healthy participants. A prediction equation for REE was derived in 100 healthy participants using multiple linear regression and z scores were calculated. The equation was validated in 101 healthy participants. This method was applied to participants with resistance to thyroid hormone (RTH) disorders, due to mutations in either thyroid hormone receptor β or α (β: female n = 17, male n = 9; α: female n = 1, male n = 1), with deviation of REE in patients compared with the healthy population presented by the difference in z scores.

RESULTS

The prediction equation for REE = 0.061 * Lean soft tissue (kg) - 0.138 * Sex (0 male, 1 female) + 2.41 (R2 = 0.816). The mean ± SD of the residuals is -0.02 ± 0.44 kJ/min. Mean ± SD REE z scores for RTHβ patients are -0.02 ± 1.26. z Scores of -1.69 and -2.05 were recorded in male (n = 1) and female ( n = 1) RTHα patients.

CONCLUSIONS

We have described methodology whereby differences in REE between patients with a metabolic disorder and healthy participants can be expressed as a z score. This approach also enables change in REE after a clinical intervention (e.g., thyroxine treatment of RTHα) to be monitored.

Surplus fat rapidly increases fat oxidation and insulin resistance in lipodystrophic mice

Objective

Surplus dietary fat cannot be converted into other macronutrient forms or excreted, so has to be stored or oxidized. Healthy mammals store excess energy in the form of triacylgycerol (TAG) in lipid droplets within adipocytes rather than oxidizing it, and thus ultimately gain weight. The ‘overflow hypothesis’ posits that the capacity to increase the size and number of adipocytes is finite and that when this limit is exceeded, fat accumulates in ectopic sites and leads to metabolic disease.

Methods

Here we studied the energetic and biochemical consequences of short-term (2-day) excess fat ingestion in a lipodystrophic (A-ZIP/F-1) mouse model in which adipose capacity is severely restricted.

Results

In wildtype littermates, this acute exposure to high fat diets resulted in excess energy intake and weight gain without any significant changes in macronutrient oxidation rates, glucose, TAG, or insulin levels. In contrast, hyperphagic lipodystrophic mice failed to gain weight; rather, they significantly increased hepatic steatosis and fat oxidation. This response was associated with a significant increase in hyperglycemia, hyperinsulinemia, glucosuria, hypertriglyceridemia, and worsening insulin tolerance.

Conclusions

These data suggest that when adipose storage reserves are saturated, excess fat intake necessarily increases fat oxidation and induces oxidative substrate competition which exacerbates insulin resistance resolving any residual energy surplus through excretion of glucose.

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In contrast to wild type mice, lipodystrophic Azip mice manifest striking metabolic inflexibility.

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Wild type mice respond to excess dietary fat by storing the surplus energy and thus gain weight.

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In contrast, Azip mice increase fat oxidation and energy expenditure in response to surplus energy intake.

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Unfortunately this apparently ‘helpful’ adaptation also results in substrate competition and worsening insulin resistance.

No metabolic effects of mustard allyl-isothiocyanate compared with placebo in men

Background: Induction of nonshivering thermogenesis can be used to influence energy balance to prevent or even treat obesity. The pungent component of mustard, allyl-isothiocyanate (AITC), activates the extreme cold receptor transient receptor potential channel, subfamily A, member 1 and may thus induce energy expenditure and metabolic changes.Objective: The objective of our study was to evaluate the potential of mustard AITC to induce thermogenesis (primary outcome) and alter body temperature, cold and hunger sensations, plasma metabolic parameters, and energy intake (secondary outcomes).Design: Energy expenditure in mice was measured after subcutaneous injection with vehicle, 1 mg norepinephrine/kg, or 5 mg AITC/kg. In our human crossover study, 11 healthy subjects were studied under temperature-controlled conditions after an overnight fast. After ingestion of 10 g of capsulated mustard or uncapsulated mustard or a capsulated placebo mixture, measurements of energy expenditure, substrate oxidation, core temperature, cold and hunger scores, and plasma parameters were repeated every 30 min during a 150-min period. Subjects were randomly selected for the placebo and capsulated mustard intervention; 9 of 11 subjects received the uncapsulated mustard as the final intervention because this could not be blinded. After the experiments, energy intake was measured with the universal eating monitor in a test meal.Results: In mice, AITC administration induced a 32% increase in energy expenditure compared with vehicle (17.5 ± 4.9 J · min^-1 · mouse^-1 compared with 12.5 ± 1.2 J · min^-1 · mouse^-1, P = 0.03). Of the 11 randomly selected participants, 1 was excluded because of intercurrent illness after the first visit and 1 withdrew after the second visit. Energy expenditure did not increase after ingestion of capsulated or uncapsulated mustard compared with placebo. No differences in substrate oxidation, core temperature, cold and hunger scores, or plasma parameters were found, nor was the energy intake at the end of the experiment different between the 3 conditions.Conclusion: The highest tolerable dose of mustard we were able to use did not elicit a relevant thermogenic response in humans. This trial was registered at www.controlled-trials.com as ISRCTN19147515.

An Investigation Into the Differences in Bone Density and Body Composition Measurements Between 2 GE Lunar Densitometers and Their Comparison to a 4-Component Model

We describe a study to assess the precision of the GE Lunar iDXA and the agreement between the iDXA and GE Lunar Prodigy densitometers for the measurement of regional- and total-body bone and body composition in normal to obese healthy adults. We compare the whole-body fat mass by dual-energy X-ray absorptiometry (DXA) to measurements by a 4-component (4-C) model. Sixty-nine participants, aged 37 ± 12 yr, with a body mass index of 26.2 ± 5.1 kg/cm², were measured once on the Prodigy and twice on the iDXA. The 4-C model estimated fat mass from body mass, total body water by deuterium dilution, body volume by air displacement plethysmography, and bone mass by DXA. Agreements between measurements made on the 2 instruments and by the 4-C model were analyzed by Bland-Altman and linear regression analyses. Where appropriate, translational cross-calibration equations were derived. Differences between DXA software versions were investigated. iDXA precision was less than 2% of the measured value for all regional- and whole-body bone and body composition measurements with the exception of arm fat mass (2.28%). We found significant differences between iDXA and Prodigy (p < 0.05) whole-body and regional bone, fat mass (FM), and lean mass, with the exception of hip bone mass, area and density, and spine area. Compared to iDXA, Prodigy overestimated FM and underestimated lean mass. However, compared to 4-C, iDXA showed a smaller bias and narrower limits of agreement than Prodigy. No significant differences between software versions in FM estimations existed. Our results demonstrate excellent iDXA precision. However, significant differences exist between the 2 GE Lunar instruments, Prodigy and iDXA measurement values. A divergence from the reference 4-C observations remains in FM estimations made by DXA even following the recent advances in technology. Further studies are particularly warranted in individuals with large FM contents.

Assessment of plasma acylcarnitines before and after weight loss in obese subjects

Acylcarnitines, fatty acid oxidation (FAO) intermediates, have been implicated in diet-induced insulin resistance and type 2 diabetes mellitus, as increased levels are found in obese insulin resistant humans. Moreover plasma acylcarnitines have been associated with clinical parameters related to glucose metabolism, such as fasting glucose levels and HbA1c. We hypothesized that plasma acylcarnitines would correlate with energy expenditure, insulin sensitivity and other clinical parameters before and during a weight loss intervention. We measured plasma acylcarnitines in 60 obese subjects before and after a 12 week weight loss intervention. These samples originated from three different interventions (diet alone (n = 20); diet and exercise (n = 21); diet and drug treatment (n = 19)). Acylcarnitine profiles were analysed in relation to clinical parameters of glucose metabolism, insulin sensitivity and energy expenditure. Conclusions were drawn from all 60 subjects together. Despite amelioration of HOMA-IR, plasma acylcarnitines levels increased during weight loss. HOMA-IR, energy expenditure and respiratory exchange ratio were not related to plasma acylcarnitines. However non-esterified fatty acids correlated strongly with several acylcarnitines at baseline and during the weight loss intervention (p < 0.001). Acylcarnitines did not correlate with clinical parameters of glucose metabolism during weight loss, questioning their role in insulin resistance and type 2 diabetes mellitus.

Mild cold effects on hunger, food intake, satiety and skin temperature in humans

BACKGROUND

Mild cold exposure increases energy expenditure and can influence energy balance, but at the same time it does not increase appetite and energy intake.

OBJECTIVE

To quantify dermal insulative cold response, we assessed thermal comfort and skin temperatures changes by infrared thermography.

METHODS

We exposed healthy volunteers to either a single episode of environmental mild cold or thermoneutrality. We measured hunger sensation and actual free food intake. After a thermoneutral overnight stay, five males and five females were exposed to either 18°C (mild cold) or 24°C (thermoneutrality) for 2.5 h. Metabolic rate, vital signs, skin temperature, blood biochemistry, cold and hunger scores were measured at baseline and for every 30 min during the temperature intervention. This was followed by an ad libitum meal to obtain the actual desired energy intake after cold exposure.

RESULTS

We could replicate the cold-induced increase in REE. But no differences were detected in hunger, food intake, or satiety after mild cold exposure compared with thermoneutrality. After long-term cold exposure, high cold sensation scores were reported, which were negatively correlated with thermogenesis. Skin temperature in the sternal area was tightly correlated with the increase in energy expenditure.

CONCLUSIONS

It is concluded that short-term mild cold exposure increases energy expenditure without changes in food intake. Mild cold exposure resulted in significant thermal discomfort, which was negatively correlated with the increase in energy expenditure. Moreover, there is a great between-subject variability in cold response. These data provide further insights on cold exposure as an anti-obesity measure.

Sleep deficits but no metabolic deficits in premanifest Huntington's disease

Objective

Huntington disease (HD) is a fatal autosomal dominant, neurodegenerative condition characterized by progressively worsening motor and nonmotor problems including cognitive and neuropsychiatric disturbances, along with sleep abnormalities and weight loss. However, it is not known whether sleep disturbances and metabolic abnormalities underlying the weight loss are present at a premanifest stage.

Methods

We performed a comprehensive sleep and metabolic study in 38 premanifest gene carrier individuals and 36 age‐ and sex‐matched controls. The study consisted of 2 weeks of actigraphy at home, 2 nights of polysomnography and multiple sleep latency tests in the laboratory, and body composition assessment using dual energy x‐ray absorptiometry scanning with energy expenditure measured over 10 days at home by doubly labeled water and for 36 hours in the laboratory by indirect calorimetry along with detailed cognitive and clinical assessments. We performed a principal component analyses across all measures within each studied domain.

Results

Compared to controls, premanifest gene carriers had more disrupted sleep, which was best characterized by a fragmented sleep profile. These abnormalities, as well as a theta power (4–7Hz) decrease in rapid eye movement sleep, were associated with disease burden score. Objectively measured sleep problems coincided with the development of cognitive, affective, and subtle motor deficits and were not associated with any metabolic alterations.

Interpretation

The results show that among the earliest abnormalities in premanifest HD is sleep disturbances. This raises questions as to where the pathology in HD begins and also whether it could drive some of the early features and even possibly the pathology. Ann Neurol 2015;78:630–648

Exploring glycosuria as a mechanism for weight and fat mass reduction. A pilot study with remogliflozin etabonate and sergliflozin etabonate in healthy obese subjects

Inhibitors of sodium-dependent glucose co-transporter 2 (SGLT2) increase glucose excretion in the urine and improve blood glucose in Type 2 diabetes mellitus. Glycosuria provides an energy and osmotic drain that could alter body composition. We therefore conducted a pilot study comparing the effects on body composition of two SGLT2 inhibitors, remogliflozin etabonate (RE) 250 mg TID (n = 9) and sergliflozin etabonate (SE) (1000 mg TID) (n = 9), with placebo (n = 12) in obese non-diabetic subjects. Both drugs were well tolerated during 8 weeks of dosing, and the most common adverse event was headache. No urinary tract infections were observed, but there was one case of vaginal candidiasis in the RE group. As expected, RE and SE increased urine glucose excretion, with no change in the placebo group. All the subjects lost weight over 8 weeks, irrespective of treatment assignment. There was a reduction in TBW measured by D₂O dilution in the RE group that was significantly greater than placebo (1.4 kg, p = 0.029). This was corroborated by calculation of fat-free mass using a quantitative magnetic resonance technique. All but one subject had a measurable decrease in fat mass. There was significant between-subject variability of weight and fat loss, and no statistically significant differences were observed between groups. Despite a lack of a difference in weight and fat mass loss, the leptin/adiponectin ratio, a measure of insulin resistance, was significantly decreased in the RE group when compared to placebo and SE, suggesting that this SGTL-2 inhibitor may improve metabolic health independent of a change in fat mass.

An approach to quantifying abnormalities in energy expenditure and lean mass in metabolic disease

Background/objectives:

The objective of this study was to develop approaches to expressing resting energy expenditure (REE) and lean body mass (LM) phenotypes of metabolic disorders in terms of Z-scores relative to their predicted healthy values.

Subjects/methods:

Body composition and REE were measured in 135 healthy participants. Prediction equations for LM and REE were obtained from linear regression and the range of normality by the standard deviation of residuals. Application is demonstrated in patients from three metabolic disorder groups (lipodystrophy, n=7; thyrotoxicosis, n=16; and resistance to thyroid hormone (RTH), n=46) in which altered REE and/or LM were characterised by departure from the predicted healthy values, expressed as a Z-score.

Results:

REE (kJ/min)=−0.010 × age (years)+0.016 × FM (kg)+0.054 × fat-free mass (kg)+1.736 (R²=0.732, RSD=0.36 kJ/min).

LM (kg)=5.30 × bone mineral content (kg)+10.66 × height² (m)+6.40 (male).

LM (kg)=0.20 × fat (kg)+14.08 × height² (m)−2.93 (female).

(male R²=0.55, RSD=3.90 kg; female R²=0.59, RSD=3.85 kg).

We found average Z-scores for REE and LM of 1.77 kJ/min and −0.17 kg in the RTH group, 5.82 kJ/min and −1.23 kg in the thyrotoxic group and 2.97 kJ/min and 4.20 kg in the LD group.

Conclusion:

This approach enables comparison of data from individuals with metabolic disorders with those of healthy individuals, describing their departure from the healthy mean by a Z-score.

Prediction of weight loss and regain following dietary, lifestyle, and pharmacologic intervention

To develop statistical models for predicting weight loss and regain, we analyzed the phenotypic responses in an outpatient study of 60 obese subjects randomized to one of three 12-week interventions, diet (-600 kcal) alone, diet with exercise, and diet with sibutramine. This was followed by 12 weeks of observation. The best of the "baseline covariates" models was one that incorporated intervention group and baseline homeostasis model assessment-estimated insulin resistance (HOMA(IR)). It predicted week 12 weight change with R(2) of 0.38 and root mean square error (√MSE) of 2.92 kg. An alternative model incorporating baseline fat mass plus change in weight and HOMA(IR) at week 4 improved the prediction (R(2), 0.67, √MSE, 2.19 kg). We could not identify a satisfactory model to predict weight regain. We conclude that prediction of weight loss over 12 weeks is significantly improved when short-term weight change is incorporated into the model. This information could be utilized to forecast the success of a weight-loss program and to motivate and contribute to innovative designing of obesity trials.

Mitochondrial oxidative phosphorylation is impaired in patients with congenital lipodystrophy

OBJECTIVE

Lipid accumulation in skeletal muscle and the liver is strongly implicated in the development of insulin resistance and type 2 diabetes, but the mechanisms underpinning fat accrual in these sites remain incompletely understood. Accumulating evidence of muscle mitochondrial dysfunction in insulin-resistant states has fuelled the notion that primary defects in mitochondrial fat oxidation may be a contributory mechanism. The purpose of our study was to determine whether patients with congenital lipodystrophy, a disorder primarily affecting white adipose tissue, manifest impaired mitochondrial oxidative phosphorylation in skeletal muscle.

RESEARCH DESIGN AND METHODS

Mitochondrial oxidative phosphorylation was assessed in quadriceps muscle using 31P-magnetic resonance spectroscopy measurements of phosphocreatine recovery kinetics after a standardized exercise bout in nondiabetic patients with congenital lipodystrophy and in age-, gender-, body mass index-, and fitness-matched controls.

RESULTS

The phosphocreatine recovery rate constant (k) was significantly lower in patients with congenital lipodystrophy than in healthy controls (P<0.001). This substantial (∼35%) defect in mitochondrial oxidative phosphorylation was not associated with significant changes in basal or sleeping metabolic rates.

CONCLUSIONS

Muscle mitochondrial oxidative phosphorylation is impaired in patients with congenital lipodystrophy, a paradigmatic example of primary adipose tissue dysfunction. This finding suggests that changes in mitochondrial oxidative phosphorylation in skeletal muscle could, at least in some circumstances, be a secondary consequence of adipose tissue failure. These data corroborate accumulating evidence that mitochondrial dysfunction can be a consequence of insulin-resistant states rather than a primary defect. Nevertheless, impaired mitochondrial fat oxidation is likely to accelerate ectopic fat accumulation and worsen insulin resistance.

Mitochondrial dysfunction in patients with primary congenital insulin resistance

Mitochondrial dysfunction is associated with insulin resistance and type 2 diabetes. It has thus been suggested that primary and/or genetic abnormalities in mitochondrial function may lead to accumulation of toxic lipid species in muscle and elsewhere, impairing insulin action on glucose metabolism. Alternatively, however, defects in insulin signaling may be primary events that result in mitochondrial dysfunction, or there may be a bidirectional relationship between these phenomena. To investigate this, we examined mitochondrial function in patients with genetic defects in insulin receptor (INSR) signaling. We found that phosphocreatine recovery after exercise, a measure of skeletal muscle mitochondrial function in vivo, was significantly slowed in patients with INSR mutations compared with that in healthy age-, fitness-, and BMI-matched controls. These findings suggest that defective insulin signaling may promote mitochondrial dysfunction. Furthermore, consistent with previous studies of mouse models of mitochondrial dysfunction, basal and sleeping metabolic rates were both significantly increased in genetically insulin-resistant patients, perhaps because mitochondrial dysfunction necessitates increased nutrient oxidation in order to maintain cellular energy levels.

Assessment of acute and chronic pharmacological effects on energy expenditure and macronutrient oxidation in humans: responses to ephedrine

Evidence of active brown adipose tissue in human adults suggests that this may become a pharmacological target to induce negative energy balance. We have explored whole-body indirect calorimetry to detect the metabolic effects of thermogenic drugs through administration of ephedrine hydrochloride and have assessed ephedrine's merits as a comparator compound in the evaluation of novel thermogenic agents. Volunteers randomly given ephedrine hydrochloride 15 mg QID (n = 8) or placebo (n = 6) were studied at baseline and after 1-2 and 14-15 days of treatment. We demonstrate that overnight or 23-hour, 2% energy expenditure (EE) and 5% fat (FO) or CHO oxidation effects are detectable both acutely and over 14 days. Compared to placebo, ephedrine increased EE and FO rates overnight (EE 63 kJ day 2, EE 105 kJ, FO 190 kJ, day 14), but not over 23 h. We conclude that modest energy expenditure and fat oxidation responses to pharmacological interventions can be confidently detected by calorimetry in small groups. Ephedrine should provide reliable data against which to compare novel thermogenic compounds.

Quantitative magnetic resonance (QMR) for longitudinal evaluation of body composition changes with two dietary regimens

We have recently reported a validation study of a prototype low-field strength quantitative magnetic resonance (QMR) instrument for measurement of human body composition (EchoMRI-AH). QMR was very precise, but underreported fat mass (FM) by 2-4 kg when compared to a 4-compartment (4C) model in this cross-sectional study. Here, we report the performance of an updated instrument in two longitudinal studies where FM was decreasing. Healthy obese volunteers were given a modest energy deficit diet for 8 weeks (study A) and obese patients with heart failure and/or at high cardiovascular risk were prescribed a low energy liquid diet for 6 weeks (study B). FM was measured at the start and end of these periods by QMR, dual-energy X-ray absorptiometry (DXA) and 4C. A higher proportion of the weight lost came from fat in study A compared with study B, where loss of total body water (TBW) played a greater part. The intraclass correlation between QMR and 4C estimates of FM loss (DeltaFat) was 0.95, but 20 of 22 estimates of DeltaFat by QMR were lower than the corresponding estimate by the 4C model. Bland-Altman analysis demonstrated that estimates of FM loss by QMR were ~1.0 and 0.7 kg lower than those obtained with 4C (P = 0.0008) and DXA (P = 0.049), respectively. Measurement precision remained high. QMR measurement should prove valuable for quantifying modest changes of FM in small trials.

Insulin sensitivity and body composition in children with classical and nonclassical congenital adrenal hyperplasia

BACKGROUND

Reduced insulin sensitivity and increased fat mass have been reported in children and adults with congenital adrenal hyperplasia (CAH). To understand the potential mechanisms underlying these differences, we assessed insulin sensitivity and body composition in children with classical or nonclassical (late-presenting) CAH compared with normal controls.

SUBJECTS AND METHODS

Thirty-seven children with CAH (26 classical and 11 nonclassical) median (range) age 9.4 year (0.5-15.8) were compared with 41 healthy control children age 11.0 year (3.2-17.1). All children had an overnight fasting blood sample and body composition assessed by DEXA. Pubertal children (14 CAH and 19 controls) also had an oral glucose tolerance test. Classical and nonclassical CAH groups were each compared with controls, adjusting for age, gender and pubertal status. Results Classical CAH children had more fat mass than controls (P = 0.03), while nonclassical CAH children had more lean mass (P = 0.006) and higher systolic blood pressure (P = 0.003) than control children. Among pubertal children, nonclassical CAH children had higher mean insulin (0-120 min; P = 0.04), stimulated insulin (0-30 min; P = 0.02), 120 min insulin (P = 0.004) and 120 min glucose levels (P = 0.03) than controls, but no difference in disposition index.

DISCUSSION

Greater body fat in classical (early-presenting) CAH children could reflect the effects of lifetime glucocorticoid therapy. In contrast, the greater lean mass and parameters of insulin resistance in nonclassical (late-presenting) CAH children likely indicate the adverse metabolic effects of prolonged postnatal androgen excess.

Partial lipodystrophy and insulin resistant diabetes in a patient with a homozygous nonsense mutation in CIDEC

Lipodystrophic syndromes are characterized by adipose tissue deficiency. Although rare, they are of considerable interest as they, like obesity, typically lead to ectopic lipid accumulation, dyslipidaemia and insulin resistant diabetes. In this paper we describe a female patient with partial lipodystrophy (affecting limb, femorogluteal and subcutaneous abdominal fat), white adipocytes with multiloculated lipid droplets and insulin-resistant diabetes, who was found to be homozygous for a premature truncation mutation in the lipid droplet protein cell death-inducing Dffa-like effector C (CIDEC) (E186X). The truncation disrupts the highly conserved CIDE-C domain and the mutant protein is mistargeted and fails to increase the lipid droplet size in transfected cells. In mice, Cidec deficiency also reduces fat mass and induces the formation of white adipocytes with multilocular lipid droplets, but in contrast to our patient, Cidec null mice are protected against diet-induced obesity and insulin resistance. In addition to describing a novel autosomal recessive form of familial partial lipodystrophy, these observations also suggest that CIDEC is required for unilocular lipid droplet formation and optimal energy storage in human fat.

Intramyocellular lipid levels are associated with peripheral, but not hepatic, insulin sensitivity in normal healthy subjects

Increased levels of IMCL (intramyocellular lipid) have been shown to be associated with reduced steady-state glucose infusion rates during a hyperinsulinaemic-euglycaemic clamp (M-value). The aim of the present study was to explore how IMCL levels relate to the insulin-mediated suppression of endogenous glucose production [hepatic SI (insulin sensitivity)] and increase in glucose disposal (peripheral SI). In the present study, 11 healthy young adults (7 male, 4 female; aged 21-31 years) undertook, in random order, an hyperinsulinaemic-euglycaemic clamp combined with stable glucose isotope enrichment to measure peripheral and hepatic SI, a 1H-MRS (proton-magnetic resonance spectroscopy) scan to determine IMCL levels and a DXA (dual-energy X-ray absorptiometry) scan to assess body composition. IMCL levels (range, 3.2-10.7) were associated with whole-body fat mass (r=0.787, P=0.004), fat mass corrected for height (r=0.822, P=0.002) and percentage of central fat mass (r=0.694, P=0.02), but were not related to whole-body FFM (fat-free mass; r=-0.472, P=0.1). IMCL levels correlated closely with the M-value (r=-0.727, P=0.01) and FFM-corrected peripheral SI (r=-0.675, P=0.02), but were not related to hepatic SI adjusted for body weight (r=0.08, P=0.8). The results of the present study suggest that IMCL accumulation may be a sensitive marker for attenuations in peripheral, but not hepatic, SI in normal populations. Given the close relationship of IMCL levels to whole-body and central abdominal fat mass, relative increases in the flux of lipids from adipose tissue to the intramyocellular compartment may be an integral part of the mechanisms underlying reductions in SI.

Early diet and peak bone mass: 20 year follow-up of a randomized trial of early diet in infants born preterm

BACKGROUND

Preterm infants are at risk of metabolic bone disease due to inadequate mineral intake with unknown consequences for later bone health.

OBJECTIVE

To test the hypotheses that (1) early diet programs peak bone mass and bone turnover; (2) human milk has a beneficial effect on these outcomes; (3) preterm subjects have reduced peak bone mass compared to population reference data.

DESIGN

20 year follow-up of 202 subjects (43% male; 24% of survivors) who were born preterm and randomized to: (i) preterm formula versus banked breast milk or (ii) preterm versus term formula; as sole diet or supplement to maternal milk. Outcome measures were (i) anthropometry; (ii) hip, lumbar spine (LS) and whole body (WB) bone mineral content (BMC) and bone area (BA) measured using DXA; (iii) bone turnover markers.

RESULTS

Infant dietary randomization group did not influence peak bone mass or turnover. The proportion of human milk in the diet was significantly positively associated with WBBA and BMC. Subjects receiving >90% human milk had significantly higher WBBA (by 3.5%, p=0.01) and BMC (by 4.8%, p=0.03) than those receiving <10%. Compared to population data, subjects had significantly lower height SDS (-0.41 (SD 1.05)), higher BMI SDS (0.31 (1.33)) and lower LSBMD SDS (-0.29 (1.16)); height and bone mass deficits were greatest in those born SGA with birthweight <1250 g (height SDS -0.81 (0.95), LSBMD SDS -0.61 (1.3)).

CONCLUSION

Infant dietary randomization group did not affect peak bone mass or turnover suggesting the observed reduced final height and LS bone mass, most marked in growth restricted subjects with the lowest birthweight, may not be related to sub-optimal early nutrition. The higher WB bone mass associated with human milk intake, despite its low nutrient content, may reflect non-nutritive factors in breast milk. These findings may have implications for later osteoporosis risk and require further investigation.

Postreceptor insulin resistance contributes to human dyslipidemia and hepatic steatosis

Metabolic dyslipidemia is characterized by high circulating triglyceride (TG) and low HDL cholesterol levels and is frequently accompanied by hepatic steatosis. Increased hepatic lipogenesis contributes to both of these problems. Because insulin fails to suppress gluconeogenesis but continues to stimulate lipogenesis in both obese and lipodystrophic insulin-resistant mice, it has been proposed that a selective postreceptor defect in hepatic insulin action is central to the pathogenesis of fatty liver and hypertriglyceridemia in these mice. Here we show that humans with generalized insulin resistance caused by either mutations in the insulin receptor gene or inhibitory antibodies specific for the insulin receptor uniformly exhibited low serum TG and normal HDL cholesterol levels. This was due at least in part to surprisingly low rates of de novo lipogenesis and was associated with low liver fat content and the production of TG-depleted VLDL cholesterol particles. In contrast, humans with a selective postreceptor defect in AKT2 manifest increased lipogenesis, elevated liver fat content, TG-enriched VLDL, hypertriglyceridemia, and low HDL cholesterol levels. People with lipodystrophy, a disorder characterized by particularly severe insulin resistance and dyslipidemia, demonstrated similar abnormalities. Collectively these data from humans with molecularly characterized forms of insulin resistance suggest that partial postreceptor hepatic insulin resistance is a key element in the development of metabolic dyslipidemia and hepatic steatosis.

Complement abnormalities in acquired lipodystrophy revisited

CONTEXT

Lipodystrophy is a heterogeneous condition characterized by an inherited or acquired deficiency in the number of adipocytes required for the storage of energy as triglycerides. Acquired lipodystrophy is frequently associated with other autoimmune disorders. One well-studied form is characterized by the selective loss of upper body fat in association with activation of the alternative complement pathway by C3 nephritic factor, low complement factor C3, and mesangiocapillary glomerulonephritis.

OBJECTIVE

We now describe an immunologically distinct form of acquired generalized lipodystrophy, with evidence of activation of the classical complement pathway (low C4) and autoimmune hepatitis. Patients and Research Design: Three unrelated patients with acquired lipodystrophy and low complement C4 levels are described. In vitro analysis of the complement pathway was undertaken to determine the reason for the low C4 complement levels. Biopsies were obtained from liver, bone marrow, and adipose tissue for histological analysis.

RESULTS

All three patients manifested near-total lipodystrophy, chronic hepatitis with autoimmune features, and low C4 complement levels. Additional autoimmune diseases, including severe hemolytic anemia, autoimmune thyroid disease, and polyneuropathy, were variably present. Detailed studies of complement pathways suggested constitutive classical pathway activation.

CONCLUSIONS

Although the previously described syndrome, which typically results in a cephalad pattern of partial lipodystrophy, results from activation of the alternative complement pathway, this form, in which lipodystrophy is generalized, is associated with activation of the classical pathway. Future therapeutic approaches to these disorders may benefit from being tailored to their distinct immunopathogenesis.

Efficiency of autoregulatory homeostatic responses to imposed caloric excess in lean men

Obesity implies a failure of autoregulatory homeostatic responses to caloric excess. We studied the mechanisms, effectiveness, and limits of such responses in six lean (21.9 +/- 1.3 kg/m(2)), healthy men based in a metabolic suite for 17 wk of progressive intermittent overfeeding (OF) (3 wk, baseline; 3 wk, 20% OF; 1 wk, ad libitum; 3 wk, 40% OF; 1 wk, ad libitum; 3 wk, 60% OF; 3 wk, ad libitum). Body composition was assessed by a four-compartment model using dual X-ray absorptiometry, deuterium dilution, and plethysmography. Magnetic resonance imaging assessed subcutaneous/visceral fat at abdominal level at baseline and at the end of 60% OF. Energy intake was assessed throughout, energy expenditure (EE) and substrate oxidation rates were measured repeatedly by whole body calorimetry (calEE), and free-living EE (TEE) was measured by doubly labeled water at baseline and after 60% OF. At the end of 60% OF, calEE and TEE had increased by just 11.4% (P = 0.001) and 16.2% (P = 0.001), respectively. Weight and body fat (fat mass) had increased by 5.98 kg (8.8%, P = 0.001) and 3.31 kg (22.6%, P = 0.01), respectively. The relative increase in visceral fat (32.6%, P = 0.02) exceeded that of subcutaneous fat (13.3%, P = 0.002) in the abdominal region. The computed energy cost of tissue accretion differed from the excess ingested by only 13.1% (using calEE) and 11.6% (using TEE), indicating an absence of effective dissipative mechanisms. We conclude that elevations in EE provide very limited autoregulatory capacity in body weight regulation, and that regulation must be dominated by hypothalamic modulation of energy intake. This result supports present conclusions from genetic studies in which all known causes of human obesity are related to defects in the regulation of appetite.

Validation of a quantitative magnetic resonance method for measuring human body composition

OBJECTIVE

To evaluate a novel quantitative magnetic resonance (QMR) methodology (EchoMRI-AH, Echo Medical Systems) for measurement of whole-body fat and lean mass in humans.

METHODS AND PROCEDURES

We have studied (i) the in vitro accuracy and precision by measuring 18 kg Canola oil with and without 9 kg water (ii) the accuracy and precision of measures of simulated fat mass changes in human subjects (n = 10) and (iii) QMR fat and lean mass measurements compared to those obtained using the established 4-compartment (4-C) model method (n = 30).

RESULTS

(i) QMR represented 18 kg of oil at 40 degrees C as 17.1 kg fat and 1 kg lean while at 30 degrees C 15.8 kg fat and 4.7 kg lean were reported. The s.d. of repeated estimates was 0.13 kg for fat and 0.23 kg for lean mass. Adding 9 kg of water reduced the fat estimates, increased misrepresentation of fat as lean, and degraded the precision. (ii) the simulated change in the fat mass of human volunteers was accurately represented, independently of added water. (iii) compared to the 4-C model, QMR underestimated fat and over-estimated lean mass. The extent of difference increased with body mass. The s.d. of repeated measurements increased with adiposity, from 0.25 kg (fat) and 0.51 kg (lean) with BMI <25 kg/m(2) to 0.43 kg and 0.81 kg respectively with BMI >30 kg/m(2).

DISCUSSION

EchoMRI-AH prototype showed shortcomings in absolute accuracy and specificity of fat mass measures, but detected simulated body composition change accurately and with precision roughly three times better than current best measures. This methodology should reduce the study duration and cohort number needed to evaluate anti-obesity interventions.

Validity of the leg-to-leg bioimpedance to estimate changes in body fat during weight loss and regain in overweight women: a comparison with multi-compartment models

OBJECTIVES

To investigate changes in body composition and the validity of the leg-to-leg bioimpedance (LTL) method to measure body fat during active weight loss (WL) and weight regain (WR).

DESIGN

Longitudinal, 12-week weight loss intervention (3.3-3.8 MJ/day) and subsequent follow-up at 1 year.

SUBJECTS

Fifty-eight adult women aged between 24 and 65 years (mean age: 46.8+/-8.9 years) and with a body mass index (BMI) > or =25 kg/m(2) (mean BMI: 31.6+/-2.5 kg/m(2), range=26.0-48.2 kg/m(2)) participated in the study.

MEASUREMENTS

Fat mass (FM) was measured at baseline, 12 weeks, 24 weeks and 52 weeks using three- and four-compartment (4-C) models, air displacement plethysmography (ADP), deuterium dilution - total body water (TBW), dual-energy X-ray absorptiometry (DXA), skinfold thickness (SFT), tetrapolar bioelectrical impedance analysis (T-BIA) and LTL.

RESULTS

At the end of the weight loss programme, subjects lost 9.9+/-3.5 kg weight (P<0.001) and 7.6+/-0.5 kg fat (P<0.001) but after 1 year they had regained 4.9+/-3.7 kg of weight and 3.7+/-2.9 kg of fat. The 4-C model showed that FM and TBW accounted for 76.2 and 23.6% of the loss in body mass and 81.8 and 17.7% of the tissue accrued during weight regain, respectively. The estimate of body fat change by LTL relative to multi-compartment models (WL(bias+/-2s.d.)=0.51+/-3.26 kg; WR(bias+/-2s.d.)=-0.25+/-2.30 kg) was similar to ADP, DXA and TBW in both phases but it was better than T-BIA (WL(bias+/-2s.d.)=0.17+/-7.90 kg; WR(bias+/-2s.d.)=-0.29+/-7.59 kg) and skinfold thickness (WL(bias+/-2s.d.)=2.68+/-6.68 kg; WR(bias+/-2s.d.)=-0.84+/-3.80 kg).

CONCLUSIONS

Weight loss and regain were associated with minimal changes in lean tissue as measured using multi-compartment models. The LTL system is a useful method to measure body composition changes during clinical weight management programmes.

Variability of appetite control mechanisms in response to 9 weeks of progressive overfeeding in humans

BACKGROUND

The current epidemic of obesity demonstrates that mechanisms for maintaining human energy balance are readily subverted by adverse environmental conditions. The critical elements of this dysregulation are poorly understood. Most previous research into what regulates the intake side of the energy balance equation has been handicapped by the use of short-term within-day experimental tests.

OBJECTIVE

We enrolled six non-obese men to a 17-week protocol involving three 21 days periods of progressive overfeeding (+20, +40 and +60%) separated by free diet periods to test for compensatory satiety.

RESULTS

Responses to overfeeding differed markedly with evidence of 'compensators' and 'non-compensators', but on average, subsequent food intake was stimulated rather than suppressed after overfeeding in spite of markedly elevated body fat (+13%) and fasting leptin (+116%).

DISCUSSION

The inefficient response of in-built appetite control mechanisms emphasizes the need to adopt intentional cognitive restraint in the modern environment when food is plentiful.

Improvement in insulin sensitivity without concomitant changes in body composition and cardiovascular risk markers following fixed administration of a very low growth hormone (GH) dose in adults with severe GH deficiency

OBJECTIVE

Untreated GH-deficient adults are predisposed to insulin resistance and excess cardiovascular mortality. We showed previously that short-term treatment with a very low GH dose (LGH) enhanced insulin sensitivity in young healthy adults. The present study was therefore designed to explore the hypothesis that LGH, in contrast to the standard GH dose titrated to normalize serum IGF-I levels (SGH), may have differing effects on insulin sensitivity, body composition, and cardiovascular risk markers [lipid profile, C-reactive protein (CRP), interleukin-6 (IL-6), tumour necrosis factor-alpha (TNF-alpha) and adiponectin] in adults with severe GH deficiency.

PATIENTS AND METHODS

In this 12-month open, prospective study, 25 GH-deficient adults were randomized to receive either a fixed LGH (0.10 mg/day, n = 13) or SGH (mean dose 0.48 mg/day, n = 12), and eight age- and body mass index (BMI)-matched GH-deficient adults acted as untreated controls. Fasting blood samples were collected at baseline and at months 1, 3, 6, 9 and 12. Assessments of insulin sensitivity, using the hyperinsulinaemic euglycaemic clamp technique, and body composition, using dual-energy X-ray absorptiometry, were performed at baseline and at month 12.

RESULTS

The LGH decreased fasting glucose levels (P < 0.01) and enhanced insulin sensitivity (P < 0.02), but body composition, nonesterified fatty acid (NEFA) levels and cardiovascular risk markers were unchanged. The SGH did not modify insulin sensitivity, decreased truncal fat mass (P < 0.05), CRP (P < 0.05) and IL-6 (P < 0.05) levels, and increased NEFA levels (P < 0.05). No changes were observed with the untreated controls.

CONCLUSION

Our data indicate that, in contrast to the SGH, fixed administration of the LGH enhances insulin sensitivity with no apparent effects on body composition, lipolysis and other surrogate cardiovascular risk markers in adults with severe GH deficiency. Thus, the LGH may potentially be a beneficial replacement dose in reducing type 2 diabetes risk in adults with severe GH deficiency.

Energy expenditure and adaptive responses to an acute hypercaloric fat load in humans with lipodystrophy

Humans respond to an acute excess of ingested energy by storing the surplus energy as triglyceride in white adipose tissue. To study the energetic response to acute overfeeding in human subjects with limited adipose tissue capacity, we recruited seven subjects with lipodystrophy and seven lean healthy controls. Total fat mass was approximately 70% lower in lipodystrophic subjects (mean, 6.1 kg) than in body mass index-matched lean controls (mean, 22.0 kg). Energy expenditure and macronutrient oxidation rates were assessed in chamber calorimeters on two separate occasions for 40 h, during which time subjects consumed either an energy-balanced diet or a diet incorporating 30% excess energy as fat. On the energy-balanced diet, total daily energy expenditure and basal metabolic rate were linearly associated with lean mass in both groups (r(2) = 0.83) and were not significantly different between groups when corrected for lean mass. In response to the fat challenge, total energy expenditure did not increase significantly in healthy controls (9,472 +/- 1,069 to 9,724 +/- 1,114 kJ/d; P = 0.189). Substrate oxidation results confirm that excess fat was predominantly stored. In contrast, lipodystrophic subjects significantly increased total daily energy expenditure (11,081 +/- 1,226 to 11,730 +/- 1,374 kJ/d; P < 0.005). This was largely attributable to a 29% increase in fat oxidation. Thus, subjects with lipodystrophy uniquely respond to an acute hypercaloric load with a higher energy expenditure increment and by increasing fat oxidation. Insight into the molecular mechanisms responsible for this phenomenon may yield novel therapeutic approaches for obesity.

A family with severe insulin resistance and diabetes due to a mutation in AKT2

Inherited defects in signaling pathways downstream of the insulin receptor have long been suggested to contribute to human type 2 diabetes mellitus. Here we describe a mutation in the gene encoding the protein kinase AKT2/PKBbeta in a family that shows autosomal dominant inheritance of severe insulin resistance and diabetes mellitus. Expression of the mutant kinase in cultured cells disrupted insulin signaling to metabolic end points and inhibited the function of coexpressed, wild-type AKT. These findings demonstrate the central importance of AKT signaling to insulin sensitivity in humans.

Comparison of narrow-angle fan-beam and pencil-beam densitometers: in vivo and phantom study of the effect of bone density, scan mode, and tissue depth on spine measurements

This study compared the in vivo and in vitro performances of the Lunar MD and Prodigy dual-energy X-ray absorptiometers (DXAs). Ten volunteers and three different spine phantoms were studied to determine the effect of scan mode, tissue depth, and bone density on measures of spine bone area (BA), bone mineral content (BMC), and areal bone mineral density (BMD). These studies demonstrated that the choice of scan mode was most important for the Prodigy and for subjects who were thin, obese, or had low BMD. Increase in tissue depth caused an increase in measured BMC and BMD for the MD but had a small effect on Prodigy results if the appropriate scan mode was selected. BA was dependent on the BMD for both DXA systems. Results using a hydroxyapatite phantom demonstrated that after correcting for the calibration of Lunar systems, the BMC measured by the MD and Prodigy was similar to the calculated hydroxyapatite content of the phantom. In vivo studies confirmed the in vitro findings and demonstrated that even when the appropriate scan mode was selected, the BMC, BMD, and T-scores were significantly higher on the Prodigy than MD.

Leptin does not respond to 48 h fat deposition or mobilization in women

OBJECTIVE

To test the hypothesis that acute responses of plasma leptin concentration to energy balance manipulation are mediated by fat flux.

DESIGN

Ten healthy women aged 31-63 y, mass 48-113.5 kg, fat mass 8.5-62.5 kg, were studied for 3 days in a whole-body calorimeter on two occasions. After a control day (D1) during which energy balance was maintained, diet was manipulated to induce fat deposition (FD) or mobilization (FM) of 50 g/day for 2 days (D2 & D3). A difference totalling of 194+/-18.6 g fat was achieved between manipulations without significant effects on carbohydrate or protein balance. Fasting plasma leptin was measured on D2 and D4.

RESULTS

After the control day plasma leptin concentration averaged 19.01+/-9.8 ng/ml, and was found to be linearly related to body fat mass. After 2 days manipulation of fat balance, leptin concentrations were 21.4+/-10.3 ng/ml (FD) and 21.2+/-11.3 ng/ml (FM). There was no significant difference between treatments in either control day or postmanipulation leptin concentrations, nor did the treatments induce any differences in glucose or insulin concentration responses.

CONCLUSION

Although in states of energy balance leptin concentration is linearly related to fat mass, acute modulation of leptin concentration during energy imbalance is not mediated by fat flux.

Net protein oxidation is adapted to dietary protein intake in domestic cats (Felis silvestris catus)

Cats have a requirement for dietary protein two to three times that of omnivores and herbivores. This was reported to be due to the hepatic catabolic enzymes of this species being set to a permanently high level and, therefore, showing little adaptation to low dietary protein. A major mechanism for adapting to dietary protein in other species is amino acid oxidation (hereafter referred to as protein oxidation), and the objective of this study was to determine whether protein oxidation in cats was correlated with protein intake. Net protein and net fat oxidation in six adult cats were studied directly from gas exchanges using indirect calorimetry, after feeding moderate protein (MP; 35% energy) and high protein (HP; 52% energy) diets. Protein oxidation was significantly higher (P < 0.05) when cats were fed the HP diet (28.4 plus minus 0.7 mg/min) rather than the MP diet (20.4 plus minus 0.8 mg/min). Fat oxidation was significantly higher (P < 0.05) when cats consumed the MP diet (9.0 plus minus 0.7 mg/min) rather than the HP diet (4.7 plus minus 0.5 mg/min). Protein oxidation was significantly correlated (linear regression, R(2) = 46.0, P < 0.05) with protein intake such that the mean ratio of 18-h oxidation: 18-h intake was 1.2 on both diets. Fat oxidation was significantly correlated (linear regression, R(2) = 18.9, P < 0.05) with fat intake such that the mean ratio of 18-h fat oxidation: 18-h fat intake was 1.1 (MP) and 0.9 (HP). This study demonstrated that cats adapt net protein oxidation at these levels of protein intake, and the reason for the high dietary protein requirement of this species is, therefore, unclear.

Dose-response relationship between fat ingestion and oxidation: quantitative estimation using whole-body calorimetry and 13C isotope ratio mass spectrometry

OBJECTIVE

To determine dose-dependent relationship between ingested fat and its oxidation in the immediate post-prandial period in humans.

DESIGN

Subjects were randomly selected for the study at the Dunn Clinical Nutrition Centre, Cambridge, UK. Subjects ingested naturally enriched 13C corn-oil doses (range 20-140g) in a whole-body indirect calorimeter, and were studied for 8 h. Ingested fat oxidation was estimated from the subject's breath 13C enrichment and total carbon dioxide production. Total fat and carbohydrate oxidation were estimated from non-protein oxygen and carbon dioxide exchanges. Endogenous fat oxidation was estimated as the difference between total fat and ingested fat oxidation.

RESULTS

The amount of fat dose oxidized was nonlinearly related to the amount ingested. On average, 25.6+/-2.7% of the mean fat dose was oxidized. A significant (r = - 0.72, P < 0.001) inverse correlation was found between the amount of fat dose and the proportion oxidized. Endogenous carbohydrate oxidation was negatively and significantly correlated to fat dose oxidized (r= -0.61, P < 0.01), but it was not correlated to endogenous fat oxidation.

CONCLUSIONS

There was a nonlinear relationship between amount of fat dose and its quantity that was oxidized in the immediate post-prandial period. The inverse relationship between the size of the fat load and the proportion that was oxidized post-prandially implies increased dietary fat storage beyond about 50 g in a normal resting adult. This has important implications for 13CO2-based studies.

Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index

BACKGROUND

Although international interest in classifying subject health status according to adiposity is increasing, no accepted published ranges of percentage body fat currently exist. Empirically identified limits, population percentiles, and z scores have all been suggested as means of setting percentage body fat guidelines, although each has major limitations.

OBJECTIVE

The aim of this study was to examine a potential new approach for developing percentage body fat ranges. The approach taken was to link healthy body mass index (BMI; in kg/m(2)) guidelines established by the National Institutes of Health and the World Health Organization with predicted percentage body fat.

DESIGN

Body fat was measured in subjects from 3 ethnic groups (white, African American, and Asian) who were screened and evaluated at 3 universities [Cambridge (United Kingdom), Columbia (United States), and Jikei (Japan)] with use of reference body-composition methods [4-compartment model (4C) at 2 laboratories and dual-energy X-ray absorptiometry (DXA) at all 3 laboratories]. Percentage body fat prediction equations were developed based on BMI and other independent variables.

RESULTS

A convenient sample of 1626 adults with BMIs < or =35 was evaluated. Independent percentage body fat predictor variables in multiple regression models included 1/BMI, sex, age, and ethnic group (R: values from 0.74 to 0.92 and SEEs from 2.8 to 5.4% fat). The prediction formulas were then used to prepare provisional healthy percentage body fat ranges based on published BMI limits for underweight (<18.5), overweight (> or =25), and obesity (> or =30).

CONCLUSION

This proposed approach and initial findings provide the groundwork and stimulus for establishing international healthy body fat ranges.

Macronutrient disposal during controlled overfeeding with glucose, fructose, sucrose, or fat in lean and obese women

BACKGROUND

Previous short-term studies (< or =6 h) showed differences in energy expenditure (EE) and macronutrient oxidation in response to overfeeding with different types of dietary carbohydrate. This finding could have implications for obesity.

OBJECTIVE

We used 96-h continuous whole-body calorimetry in 8 lean and 5 obese women to assess metabolic disposal (energy dissipation and glycogen or fat storage) of a controlled excess of dietary energy supplied as different carbohydrate sources or as fat.

DESIGN

Five dietary treatments were applied in random order: energy balance (control) and overfeeding by 50% of energy requirements with fat (O(fat)) or predominantly with glucose, fructose, or sucrose (O(cho)). Macronutrient oxidation rates were assessed from nonprotein gaseous exchanges. Net macronutrient balances were calculated as cumulative differences between intake and oxidation.

RESULTS

Increased EE in response to overfeeding dissipated 7.9% of the energy excess with a variation in EE of <1.7% across overfeeding treatments (NS). EE during the O(fat) treatment significantly exceeded that during the control treatment in the lean but not in the obese women. There were no significant differences between lean and obese women in macronutrient oxidation or balances, so data were pooled. O(cho) induced glycogen storage on day 1 ( approximately 100 g) but thereafter progressively stimulated carbohydrate oxidation so that balance was reached on days 3 and 4. Fat oxidation was proportionately suppressed. Of the excess carbohydrate, 74% was oxidized; there were no significant differences between the various O(cho) treatments. O(fat) stimulated fat oxidation by 18% and suppressed carbohydrate oxidation. On average, 12% of the excess energy was stored as glycogen and 88% as fat; there was no significant difference between overfeeding treatments.

CONCLUSION

There was no significant difference in fat balance during controlled overfeeding with fat, fructose, glucose, or sucrose.

Evaluation of the novel Tanita body-fat analyser to measure body composition by comparison with a four-compartment model

The Tanita body-fat analyser is a novel device to estimate body fat, based on the principles of bioelectrical impedance. It differs from other impedance systems which use surface electrodes in that the subjects stand bare-footed on a metal sole-plate which incorporates the electrodes, hence impedance is measured through the legs and lower trunk. In 104 men and 101 women (16-78 years and BMI 16-41 kg/m2) the mean bias in body-fat mass measured using the Tanita body-fat analyser was 0.8 (2SD 7.9) kg relative to a four-compartment model. This is comparable to the other prediction techniques tested (conventional tetrapolar impedance -1.3 (2SD 6.9) kg, skinfold thicknesses 0.3 (2SD 7.4) kg, and BMI-based formulas -0.2 (2SD 9.0) kg and -0.6 (2SD 8.5) kg), but the agreement was poorer than for 'reference' methods to measure body fat (density 0.2 (2SD 3.7) kg, total body water -0.9 (2SD 3.4) kg and dual-energy X-ray absorptiometry 0.1 (2SD 5.0) kg). The present paper also describes the derivation of a new prediction equation for the calculation of body composition from the Tanita body-fat analyser. The equation incorporates sex, age, and a log-transformation of height, weight and the measured impedance to predict body fat measured by a four-compartment model. This approach is recommended in the derivation of other prediction equations in body composition analysis. Using this novel prediction equation the residual standard deviations were 4.8% for men and 3.3% for women. A similar analysis using data collected with a conventional tetrapolar system yielded residual standard deviations of 4.3% for men and 3.1% for women. This demonstrates that the practical simplicity of the novel Tanita method is not associated with a clinically significant decrement in performance relative to a traditional impedance device.

Effects of inactivity and diet composition on human energy balance

OBJECTIVES

To investigate the influences of inactivity and dietary macronutrient composition on energy and fat balance and to look for interactions between them.

DESIGN

Two-day measurements of energy expenditure and substrate oxidation on five occasions; ad libitum food intake from diets of 35% and 60% energy as fat, with and without imposed activity, and a fixed overfeeding at 35% fat with free activity.

SUBJECTS

Eight normal-weight male volunteers.

MEASUREMENTS

Energy expenditure and substrate oxidation by indirect whole-body calorimetry, and macronutrient intakes from food consumption on ad libitum regimens.

RESULTS

Subjects consumed the same energy, mean 11.6 MJ/d, regardless of activity level, on the 35% diet. Subjects consumed more energy on the 60% than the 35% diet, mean 14 vs. 11.6 MJ/d. Inactivity induced a strong positive energy balance: 5.1 (60% diet), and 2.6 MJ/d (35% diet). Energy balance with activity was not significantly different between diets, nor significantly different from zero: 1.1 MJ/d (60% diet), and -0.2 MJ/d (35% diet). When intentionally overfed, subjects failed to compensate by raising voluntary activity.

CONCLUSION

Energy intake was not regulated over a 2-day period in response to either imposition of inactivity or a high-fat diet. Activity proved essential to the avoidance of significant positive energy balance.

Effect of dietary manipulation on substrate flux and energy balance in obese women taking the appetite suppressant dexfenfluramine

BACKGROUND

Studies in lean men show poor regulation of energy (EB) and fat balance (FB) during manipulation of dietary ratios of fat to carbohydrate. High-fat (HF), high-energy diets cause hyperphagia and a positive EB and FB.

OBJECTIVE

The protocol was designed to measure substrate flux and EB in obese women taking dexfenfluramine (DF) or placebo (PL) during an HF (50% of energy) or low-fat (25% of energy; LF) diet. We hypothesized that alterations in dietary fat would not be regulated and would lead to a positive EB and FB.

DESIGN

The study was double-blind, randomized, and placebo-controlled, with 4 treatments (LF/DF, HF/DF, LF/PL, and HF/PL) and a crossover. Five days of continuous, whole-body calorimetry measurements were made in 6 subjects after 8 d of home DF/PL treatment. Macronutrient balance and EB were measured within the chamber as the cumulative difference between ad libitum intake and oxidation.

RESULTS

The HF diet increased energy (HF, 10.50 MJ/d; LF, 8.13 MJ/d; P < 0.0001) and fat intakes (HF, 5.34 MJ/d; LF, 2.06 MJ/d; P < 0.0001), leading to a positive EB (delta = 2.37 MJ/d) and FB (delta = 2.31 MJ/d). DF reduced energy (DF, 8.96 MJ/d; PL, 9.66 MJ/d; P < 0.01) and macronutrient intakes, but did not increase energy expenditure (delta = -0.31 MJ/d; P < 0.01), or 24-h fat oxidation (delta = 0.03 MJ/d; P = 0.46).

CONCLUSIONS

EB and FB are poorly regulated with HF, energy-dense diets in obese women, which leads to fat deposition and weight gain.

Dietary compensation in response to covert imposition of negative energy balance by removal of fat or carbohydrate

Compensatory changes in energy intake (EI) and macronutrient metabolism in response to modest covert underfeeding were tested by whole-body calorimetry in eight lean men. Each was studied on three occasions comprising a controlled stabilization day followed by manipulation and outcome days in a whole-body calorimeter. On the manipulation day EI was fixed, and calculated to maintain energy balance (CONTROL) or to provide 85% of CONTROL BY removing energy as carbohydrate (CHOred) or as fat (FATred). On the outcome day, ad libitum EI was allowed at fixed mealtimes. CHOred and FATred manipulations generated significantly different energy balances (-1.10 (SE 0.13) MJ, P = 0.000; -1.10 (SE 0.12) MJ, P = 0.000) and fat balances (-0.61 (SE 0.23) MJ, P = 0.03; -1.09 (SE 0.20) MJ, P = 0.000), but not carbohydrate balances (-0.39 (SE 0.22) MJ, NS; 0.11 (SE 0.23) MJ, NS) by the end of the manipulation day compared with CONTROL. On the outcome day, EI was significantly higher than CONTROL after CHOred (+1.58 (SE 0.33) MJ, P = 0.004) and FATred (+1.21 (SE 0.49) MJ, P = 0.022) with no differences between treatments. Overall 48 h energy balances averaged close to zero at -0.14, +0.34, +0.04 MJ on CONTROL, CHOred and FATred respectively. Total 48 h energy intakes on CHOred and FATred averaged 101 (SE 1.7)% and 99 (SE 2.5)% of CONTROL, thus demonstrating accurate detection of a mild energy deficit and efficient next-day compensation. Despite significant differences in macronutrient oxidation rates, the energy homeostatic mechanism appeared to be independent of specific macronutrient deficits.

Short-term effects of alcohol consumption on appetite and energy intake

The relationship between alcohol intake and obesity remains uncertain. Evidence suggesting that alcohol-derived energy may be unregulated points to an inability to maintain appetite, energy balance and, hence, body weight when alcohol is introduced to the diet. This study investigated the short-term effects of alcohol on hunger and energy intake in 20 lean women. On 4 occasions, subjects were given a randomised preload drink ('alcohol', 'no alcohol', 'carbohydrate', 'water') followed by visual analogue scales (VAS) rating hunger and an ad lib test meal. There was no difference in hunger ratings (p > 0.05) nor in the amount of energy consumed during the test meal (F = 1.66, p > 0.05) following any of the 4 preloads. Consumption of the 2 high energy preload drinks ('alcohol', 0.91 MJ; 'CHO', 0.72 MJ) did not result in a compensatory decrease in the amount of energy subsequently eaten (ad lib intake: 'alcohol' = 2.62 MJ, 0.32 SEM; 'no alcohol' = 2.98 MJ, 0.28 SEM; 'CHO' = 2.93 MJ, 0.21 SEM; 'water' = 2.82 MJ, 0.25 SEM), suggesting either no physiological recognition or no regulation of energy consumed within a drink in quantities of less than 1 MJ. The addition of either alcoholic or CHO-containing carbonated beverages into the diet will result, in the short-term, to an overall increase in energy intake.

Changes in macronutrient balance during over- and underfeeding assessed by 12-d continuous whole-body calorimetry

Alterations in energy balance must be accommodated by adjustments in the net storage of the major energy-yielding macronutrients: carbohydrate, protein, and fat. This study used continuous whole-body calorimetry to measure changes in energy expenditure and substrate oxidation during a 12-d imposed energy imbalance in six lean men on mixed diets (overfeeding: 16.5 MJ/d, +33%, n = 3; underfeeding: 3.5 MJ/d, -67%, n = 3). Changes in total energy expenditure (TEE) and its components were modest; TEE changed by +6.2% (overfeeding) and -10.5% (underfeeding). In consequence, body weight changed by +2.90 and -3.18 kg. Marked changes in metabolic fuel selection occurred over the course of the study. Carbohydrate intake (540 and 83 g/d for overfeeding and underfeeding, respectively) exerted direct autoregulatory feedback on carbohydrate oxidation (551 and 106 g/d at day 12 for overfeeding and underfeeding, respectively). Subjects were close to balance by day 5. Changes in protein oxidation were small and not sufficient to prevent the oxidation of body protein mass, or its accretion, in response to energy deficit or surplus. Fat oxidation (59 and 177 g/d for overfeeding and underfeeding, respectively) was not sensitive to dietary fat intake (150 and 20 g/d, for overfeeding and underfeeding, respectively), rather, its oxidation was inversely related to the oxidation of other substrates. Changes in fat balance accounted for 74.1% and 84.0% of the energy imbalance during overfeeding and underfeeding, respectively. This study shows a clear oxidative hierarchy for the macronutrients. Metabolic fuel selection is dominated by the need to maintain carbohydrate balance. This induces inappropriate counterregulatory alterations in fat oxidation during energy surplus.

Physical activity and obesity: problems in correcting expenditure for body size

OBJECTIVE

To explore the best method of adjusting energy expended on physical activity (AEE) for differences in body size. Many publications have expressed AEE per kg body weight (i.e. using weight 1.0 as denominator). This makes the unjustified assumption that all activities are weight-dependent.

DESIGN

Retrospective analysis of data from ninety-two 24-h whole-body calorimetry measurements in women, and 574 doubly-labelled water measurements in men and women to calculate the optimal exponents of body weight for adjusting AEE.

RESULTS

The analysis proved that weight 1.0 over-corrects for size differences and yields invalid conclusions about relationships between physical activity and obesity. An exponent close to 0.5 is more appropriate for sedentary lifestyles. However the correct exponent is itself dependent on the relative mix of weight-dependent and non-weight-dependent activities undertaken.

CONCLUSION

We conclude that it is impossible to recommend a generalizable coefficient for adjusting AEE, and that great caution must be exercised when interpreting AEE data from individuals of markedly different body sizes.

Metabolic fuel utilisation in obese women before and after weight loss

OBJECTIVE

To test the hypothesis that weight rebound following slimming diets may be caused by an adaptive alteration in fuel utilisation involving a suppression of fat oxidation thus favouring fat storage in adipose tissue.

DESIGN

Repeat measurements before and after two 14 d cycles of controlled weight loss using a very low energy diet (1.9MJ/d).

SUBJECTS

Eight moderately obese women (body weight: 85.6 +/- 10.1 kg, BMI: 31 +/- 2 kg/m2, age: 42.6 +/- 10.1 years).

MEASUREMENTS

Energy expenditure and substrate balances using 24-h whole-body indirect calorimetry and naturally labelled 13C-glucose.

RESULTS

Aggregate weight loss was 5.1 +/- 0.8 kg. Twenty-four hour energy expenditure declined by 12% (8359 +/- 282 to 7366 +/- 191 kJ/d, p < 0.001). Net fat utilisation was not significantly depressed (4009 +/- 366) to 3613 +/- 191 kJ/d, NS), and the proportion of energy derived from fat was unchanged at 48.0% before weight loss and 49.0% after weight loss.

CONCLUSION

The well-recognised phenomenon of reduced energy expenditure is unlikely to be a major cause of weight regain. The results do not support the theory that altered fuel selection in post-obese subjects may be the cause of difficulty in maintaining weight loss.

Alcohol and the regulation of energy balance: overnight effects on diet-induced thermogenesis and fuel storage

The effect of alcohol on overnight energy expenditure and substrate disposal was studied in eleven subjects (five men, six women) using whole-body indirect calorimetry for 15.5 h after test meals. Three test meals were studied in random order with at least 48 h between treatments: control, 50% of maintenance energy needs provided as 14, 40 and 46% energy from protein, fat and carbohydrate respectively; alcohol addition, control plus 23% energy as alcohol; alcohol substitution, control with alcohol replacing 23% of carbohydrate energy. ANOVA revealed no significant sex effects. Alcohol-induced thermogenesis dissipated only 15 (SD 14)% of the alcohol energy. Alcohol addition had no significant effect on protein or carbohydrate oxidation but fat oxidation was suppressed (P < 0.0005) to an extent equivalent to storing 74 (SD 51)% of the alcohol energy as fat. Alcohol substitution reduced carbohydrate oxidation (P < 0.009) to an equivalent of 42 (SD 41)% and also spared fat (P < 0.005) to an equivalent of 59 (SD 37)% of the alcohol energy. It is concluded that alcohol has no special thermogenic capacity, and that its energy can be accounted for in a similar way to carbohydrate.

Effects on metabolic rate and fuel selection of a selective beta-3 agonist (ICI D7114) in healthy lean men

METHOD

ICI D7114 is a selective beta-3 agonist which in some animals increases metabolic rate, promotes weight loss and improves glucose tolerance. To investigate its potential usefulness in humans, 16 healthy young men (mean age 28.9 +/- 8.0 years; body mass index 22.5 +/- 1.6 kg/m2) were given ICI D7114 (150 mg/day, 2.08 +/- 0.24 mg/kg body weight) or placebo for 14 days in a double-blind randomised parallel group trial. Energy expenditure (EE) and substrate oxidation were assessed by continuous whole-body indirect calorimetry on Day 0 (before dosing), on day 1 (acute effect) and on Day 14 (chronic effect).

RESULTS

Analysis of covariance indicated no significant effects on EE 4 h post-dose (Day 1, +2.4%, NS; Day 14, +1.0%, NS). There was no chronic effect on either the lowest 1 h of sleeping EE (+2.2%, NS) or 24 h EE (+0.7%, NS). There was a marginally significant chronic stimulation of basal metabolic rate (+3.6%, P = 0.042). ICI D7114 had no significant influence on protein, fat or carbohydrate oxidation. Tolerability and safety data showed that there were no increases in resting heart rate or blood pressure; no change in plasma potassium or reports of tremor; no haematological or biochemical abnormalities and no adverse events.

CONCLUSION

We conclude that over 14 days ICI D7114 at a dose level of 150 mg/day has no biologically significant effect on EE in healthy, lean men.

Covert manipulation of dietary fat and energy density: effect on substrate flux and food intake in men eating ad libitum

This study assessed whether human food intake is regulated by negative feedback, directly or indirectly, from carbohydrate stores (glycogenostatic model). Six men were studied on three occasions during 7 d of whole-body indirect calorimetry, throughout which they had ad libitum access to one of three covertly manipulated diets: low fat (20% of energy as fat, 67% of energy as carbohydrate, and 13% of energy as protein; 4.80 kJ/g; LF), medium fat (40% of energy as fat, 47% of energy as carbohydrate, and 13% of energy as protein; 5.59 kJ/g; MF), or high fat (60% of energy as fat, 27% of energy as carbohydrate, and 13% of energy as protein; 7.04 kJ/g; HF). Energy intakes increased with percent fat (F[92,60] = 36.7; P < 0.001), producing average daily balances of -0.27, 0.77, and 2.58 MJ/d during the LF, MF, and HF diets, respectively. Changes in carbohydrate stores were attenuated by autoregulatory changes in carbohydrate oxidation. Carbohydrate balance showed a negative relation to the subsequent day's energy balance (t = 2.696; P = 0.0082) but explained only 5.5% of the variance. The relation for fat was positive (t = 5.245; P < 0.0001), accounting for 19.9% of the variance (stepwise regression). LF, lower-energy diets are more satiating than are HF-higher-energy diets, but carbohydrate stores per se did not entirely account for the change that diet composition had on energy intake. This study suggests that protein and carbohydrate have potential to reduce subsequent energy intake whereas there was no apparent reductive effect due to fat.

Estimating energy expenditure from specific activity of urine urea during lengthy subcutaneous NaH14CO3 infusion

Five healthy male subjects were continuously infused subcutaneously with [14C]bicarbonate (12.3 microCi/day) using a mini pump for 5 days while in a whole body calorimeter. Energy expenditure was varied over a range of 1.35-1.75 times basal metabolic rate. Urine collections were obtained throughout the study and used to measure the specific activity of urea, from which CO2 production was estimated. It was assumed that the recovery of label in gaseous CO2 was 95% of that infused and that the specific activity of urea was 85% that of expired CO2. Continuous daily collections of calorimeter air revealed that 95.6 +/- 1.3% (SD) of infused label was recovered as gaseous CO2, with little daily variation. Another 1.5 +/- 0.4% was recovered as urinary urea. The estimated CO2 production, calculated from the specific activity of urea in 24-h urine samples corrected for the small effects due to changes in the size and specific activity of the urea pool, was found to be 100 +/- 5% of the calorimeter estimate for 1-day periods (20.80 +/- 1.44 mol CO2/day) and 100 +/- 2% for 4-day periods. This study suggests that, in healthy subjects, the labeled [14C]bicarbonate-urea method can provide reasonable estimates of net CO2 production over the range examined.

Alterations in fuel selection and voluntary food intake in response to isoenergetic manipulation of glycogen stores in humans

This study investigated the relative importance of alterations in carbohydrate intake or oxidation as mechanisms for rectifying extreme perturbations of glycogen stores. Six lean men were studied on three occasions in which a stabilization period (days 1 and 2) was immediately followed by whole-body indirect calorimetry (days 3-5). Glycogen stores were manipulated on days 3 and 4 by using isoenergetic diets providing carbohydrate at 79% (HC), 48% (MC), or 9% (LC) of energy. Free access to MC meals and snacks was allowed on days 5 and 6 outside the calorimeter. The manipulations caused large alterations in glycogen stores (HC, +206 g; MC, +132 g; LC, -121 g; HC vs LC, 327 g), but subsequent voluntary food intake was very similar across treatments (HC, 18.2 MJ/36 h; MC, 17.7 MJ/36 h; LC, 18.1 MJ/36 h, NS). Over days 3-5 the average difference in carbohydrate intake (HC vs LC) was 16.1 MJ (1010 g), but balances differed by only 1.7 MJ (110 g) because of autoregulatory changes in carbohydrate oxidation. These were the only significant mechanisms for reestablishing carbohydrate balance.

Fatness in relation to substrate oxidation during exercise

The aim of this study was to test the hypothesis that differences in fuel utilisation during exercise, determined by muscle fibre-type profile, are an aetiological factor for obesity as proposed by Wade et al. (Lancet 1990, 335, 805-8). An investigation was carried out of relationships between body fatness (assessed by skinfolds, densitometry and dual X-ray absorptiometry) and fuel utilisation represented by the respiratory exchange ratio (RER, assessed by indirect calorimetry) during three cycle ergometer exercises. Exercise 1 was an exact replication of the Wade protocol (fixed 100 Watt load and unstandardised with respect to antecedent diet and activity). Exercises 2 (fasted) and 3 (fed) were highly standardised and adjusted to represent the same relative workload for each subject (45% VO2max). The subjects were 37 randomly-selected untrained men. None of the exercises yielded significant correlations between fatness and RER. The results refute the initial hypothesis linking substrate oxidation and body fatness. Inspection of the body composition data for Wade's subjects reveals that they were abnormally lean. This suggests that their findings may have been confounded by coincident correlations between fitness and fatness, and may not represent a true causal relationship.

Effect of alcohol on postmeal fat storage

Energy expenditure and macronutrient balances were assessed in normal healthy men by whole-body indirect calorimetry after meals consumed with and without ethanol to test the theory that alcohol energy is not fully available because of futile cycling. Alcohol addition (A) or isoenergetic substitution (S) caused fat retention by significantly suppressing its oxidation when the alcohol was actively metabolized (0-6h). However, on protocol S, fat balance was later reestablished due to raised fat oxidation (6-20.5 h) secondary to a relative carbohydrate deficiency. On protocol A, fat balance remained significantly raised. The thermogenic effect of alcohol was similar to that of carbohydrate, providing no evidence for futile cycling. Short-term studies that fail to account for later readjustments of macronutrient balance can be misleading. We conclude that alcohol has a fat-sparing effect similar to that of carbohydrate and will only cause fat gain when consumed in excess of normal energy needs.