P R Murgatroyd

Production, metabolism, and excretion of hydrogen in the large intestine

Hydrogen is produced during fermentation in the large intestine and may be excreted in breath and flatus or further metabolized by the flora. However, there is little information about total H2 excretion from different substrates or the extent to which it is metabolized in the colon. We have therefore measured total H2 and methane excretion in 10 healthy subjects using a whole body calorimeter. Breath gases were measured simultaneously with total excretion in response to lactulose, pectin, and banana starch. Metabolic activities of the predominant H2 consuming anaerobes (methanogenic, sulfate reducing, and acetogenic bacteria) were measured in fecal samples. Total H2 excretion on a starch and fiber-free diet was 35 +/- 6.1 mL/24 h +/- SEM. H2 from 7.5 g, 15 g, and 22.5 g lactulose was 88.1 +/- 22.4 mL, 227.0 +/- 60.7 mL, and 321.8 +/- 79.2 mL. Four of the subjects also excreted CH4, which was 51.3 +/- 5.5 mL, 97.3 +/- 18.4 mL, and 157.5 +/- 36.3 mL for the respective lactulose doses. H2 excretion was less in methanogenic subjects (7.9 mL/g lactulose) than in nonmethanogenic (17.3 mL/g), but total H2 excreted as, hydrogen + methane, was 34.9 mL/g. H2 from pectin (20 g) was 14.1% +/- 3.2% and from starch (22.2 g) 38.6% +/- 9.2% of an equivalent lactulose dose. Sixty-five percent of total H2 and CH4 was expired in breath at total excretion rates up to 200 mL/24 h. Over this the proportion decreased to 25% with an overall average of 58%. Only subjects with CH4 excretion in vivo showed methanogenesis in feces, whereas nonmethanogenic subjects showed high sulfate-reducing activity in feces (58.7 +/- 5.6 nmol 35SO4 reduced.h-1.g-1 wet wt vs. 7.9 +/- 2.0 nmol.h-1.g-1 in methanogens). Acetogenesis rates were very low in both groups. It was concluded that H2 excretion varies with different substrates. The proportion of H2 that is exhaled in breath is higher than currently accepted and varies with total excretion rate. Substantial amounts of H2 are consumed by methanogenic and sulfate-reducing bacteria.

ANALYSIS OF GASEOUS EXCHANGE IN OPEN-CIRCUIT INDIRECT CALORIMETRY

A method is described for determining rapid changes in gaseous exchange between a subject and the environment, while living in a whole body opencircuit calorimeter. The formulae which must be applied to standard estimates of oxygen consumption are derived the computation of rates of change of gas concentration is discussed the sensitivity of estimated heat production to errors in gas concentration is determined and heat production shown to be largely independent of CO2 measurements; and examples of veritication of the method for known rates of gas injection, and of its use with human subjects, are given. The method is of particular value in assessing the rapid changes in metabolic rate which occur as a result of changes in activity, nutritional state, environmental temperature and the administration of drugs. Such changes are monitored in an unrestrained subject living in a whole-body calorimeter rather than in a subject living with the restrictions imposed by a face-mask or ventilated hood.

A human calorimeter for the direct and indirect measurement of 24 h energy expenditure

1. A calorimeter for the continuous measurement of heat production and heat loss in the human subject, for at least 24 h, is described. The calorimeter operated on the heat-sink principle for direct calorimetry and an open-circuit system for indirect calorimetry. 2. Sensible heat loss was measured using a water-cooled heat exchanger, and the temperature of water entering the heat exchanger was controlled to maintain a mean temperature gradient of zero across the chamber walls. 3. Evaporative heat loss was determined from ingoing and outgoing wet-and-dry bulb temperatures and air flow-rates. 4. Problems associated with the calculation of evapoative heat loss and the estimation of the volume of incoming air in open-circuit systems are considered. 5. The calibration, limits of accuracy, sources of error and experiments with subjects are discussed.

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 macro-nutrient 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.

Impaired hydrogen metabolism in pneumatosis cystoides intestinalis

BACKGROUND Pneumatosis cystoides intestinalis (PCI) is characterized by high levels of breath hydrogen. Clinical features of PCI may be due to abnormal H2 metabolism. METHODS Breath levels of H2 and CH4 were measured in 3 patients and total gas in 2 patients with PCI on a polysaccharide-free (basal) diet and after administration of 15 g of lactulose. Metabolic activities and counts of methanogenic (MB) and sulfate-reducing (SRB) bacteria were measured in feces. Ten volunteers were also studied. RESULTS Total H2 levels in patients were 383-420 mL/day on the basal diet and 1430-1730 mL/day after lactulose administration compared with 35 +/- 6 mL/day and 262 +/- 65 mL/day, respectively, in controls. Basal breath H2 levels in controls were 27 +/- 6 vs. 214 +/- 27 mL/day in patients and after lactulose ingestion, 115 +/- 18 vs. 370 +/- 72 mL/day. Four controls were methanogenic and had high fecal MB counts. The other controls had high SRB counts and sulfate reduction rates. All patients were nonmethanogenic and had low sulfate reduction rates. CONCLUSIONS Patients with PCI excrete more H2 than controls. In normal subjects, H2 is consumed by MB or SRB; the activity of these bacteria is virtually absent in PCI. This may explain the gas accumulation in these patients.

Total energy expenditure in patients with small-cell lung cancer: results of a validated study using the bicarbonate-urea method.

The bicarbonate-urea method for measuring CO2 production was applied to eight free-living patients (mean age, 68 +/- 10 years; mean weight, 69 +/- 10 kg; mean height, 1.65 +/- 0.10 m) with unresectable small-cell lung cancer for a period of 1 day (n = 5) or 2 days (n = 3). The basal metabolic rate (BMR) was measured in all subjects. The technique was first validated against whole-body indirect calorimetry over an additional 24-hour period in five of these subjects. The bicarbonate-urea method predicted net CO2 production to be 102.1% +/- 3.4% of that measured by whole-body indirect calorimetry, and energy expenditure, 101.5% +/- 3.8% of the measured calorimeter value (8.1 +/- 1.6 MJ/d). The 24-hour recovery of label in CO2 excreted by the body was 95.6% +/- 0.5%. In free-living conditions, the bicarbonate-urea method predicted energy expenditure to be 9.0 +/- 2.6 MJ/d. BMR was elevated by a mean of 6% (P < .05) compared with the Schofield standards. The physical activity level ([PAL] the ratio of total energy expenditure [TEE] to BMR) was variable (1.15 to 1.87), but the mean value was only 1.36 +/- 0.22, considerably less than that of moderately active healthy subjects with estimated PAL values of 1.55 (P < .05) to 1.65 (P < .01) and the mean results obtained by doubly labeled water (previous studies) in healthy age- and sex-matched subjects. This is the first time a tracer method for measuring CO2 production and energy expenditure has been validated against whole-body 24-hour indirect calorimetry in patients with lung cancer or a systemic inflammatory reaction. The agreement between the two methods is similar to that observed in normal subjects. This is also the first time a tracer method has been used to measure energy expenditure in free-living patients with lung cancer. The results suggest that TEE and the energy requirements necessary to maintain energy balance were not increased despite basal hypermetabolism, because of the associated decrease in physical activity.

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) ⩾25 kg/m2 (mean BMI: 31.6±2.5 kg/m2, range=26.0–48.2 kg/m2) 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 (WLbias±2s.d.=0.51±3.26 kg; WRbias±2s.d.=−0.25±2.30 kg) was similar to ADP, DXA and TBW in both phases but it was better than T-BIA (WLbias±2s.d.=0.17±7.90 kg; WRbias±2s.d.=−0.29±7.59 kg) and skinfold thickness (WLbias±2s.d.=2.68±6.68 kg; WRbias±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.

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

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.

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.

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 20–140 g) in a whole-body indirect calorimeter, and were studied for 8 h. Ingested fat oxidation was estimated from the subjects 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.Sponsorship: This study was funded by the Nestle Foundation, Switzerland and the British Medical Research Council, UK.European Journal of Clinical Nutrition (2001) 55, 10–18