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PURPOSE: The purpose of this study was to compare different methods of measuring physical activity (PA) in women by the doubly labeled water method (DLW). METHODS: Thirteen subjects participated in a 7-d protocol during which total daily energy expenditure (TDEE) was measured with DLW. Body composition, basal metabolic rate (BMR), and peak oxygen consumption were also measured. Physical activity-related energy expenditure (PAEE) was then calculated by subtracting measured BMR and the estimated thermic effect of food from TDEE. Simultaneously, over the 7 d, PA was assessed via a 7-d Physical Activity Recall questionnaire (PAR), and subjects wore secured at the waist, a Tritrac-R3D (Madison, WI), a Computer Science Application Inc. activity monitor (CSA; Shalimar, FL), and a Yamax Digi Walker-500 (Tokyo, Japan). Pearson-product moment correlations were calculated to determine the relationships among the different methods for estimating PAEE. Paired t-tests with appropriate adjustments were used to compare the different methods with DLW-PAEE. RESULTS: There was no significant difference between PAEE determined from PAR and DLW. The differences between the two methods ranged from -633 to 280 kcal.d(-1). Compared with DLW, PAEE determined from CSA, Tritrac, and Yamax was significantly underestimated by 59% (-495 kcal.d(-1)), 35% (-320 kcal.d(-1)) and 59% (-497 kcal.d(-1)), respectively. VO2peak explained 43% of the variation in DLW-PAEE. CONCLUSION: Although the group average for PAR-PAEE agreed with DLW-PAEE, there were differences in the methods among the subjects. PAEE determined by Tritrac, CSA, and Yamax significantly underestimate free-living PAEE in women.

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We hypothesized that there is no synthesis of butyric acid within organs or tissues not drained by the portal vein (PV). Two experiments were performed. In six piglets, the colonic vasculature was clamped (n = 4) or the entire colon resected while [1-13C]-butyric acid (99% enriched) was infused into a jejunal vein for 120 min; 13C enrichment of butyric acid was measured in the PV and carotid artery (ART) during the last 30 min of the infusion. In a second experiment, butyric acid tracer and unlabeled disaccharide were infused into the cecum for 120 min, and blood again was sampled from the PV and ART. For the four piglets studied during ligation of the colonic vasculature, the mean (+/- SD) ratio of the butyric acid enrichment in the ART to that in the PV (ART/PV) was 0.80+/-0.05 (ART vs. PV, P = 0.002) and for all six piglets in expt. 1, the ART/PV ratio was 0.74+/-0.1 (ART vs. PV, P = 0.001). The enrichment of butyric acid in the PV averaged 96.0% for the six studies, implying that splanchnic tissues other than the colon did not produce a substantial amount of butyric acid. For the second experiment, the ART/PV ratio was 0.80+/-0.15 (ART vs. PV, P = 0.03). These studies provide the first evidence for endogenous synthesis of butyric acid by piglets.

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Differences in oxidation of individual dietary fatty acids could contribute to the effect of dietary fat composition on risk factors for non-insulin-dependent diabetes mellitus and cardiovascular disease. Using a novel stable isotope technique, we compared fractional oxidation of chylomicron-derived oleate and palmitate in 10 healthy adults in a crossover study. 1-(13)C-labeled oleate or palmitate was emulsified into a eucaloric formula diet administered each 20 min for 7 h to produce a plateau in excretion of (13)C label in breath CO(2). Unlabeled oleate and palmitate each provided 16% of dietary energy, and other fatty acids provided 8% of energy. Total dietary fat was 40% of energy, carbohydrate was 46%, and protein was 14%. Diet without tracer was fed for 2 h before beginning tracer administration to establish a baseline fed state. Relative oxidation of oleate versus palmitate was defined as fractional oxidation of oleate divided by fractional oxidation of palmitate. Relative oxidation averaged 1.21 (99.5% confidence interval = 1.03;-1.39), indicating that fractional oxidation of oleate was significantly greater than that of palmitate.

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We sought to determine, in a piglet model, whether severe sugar malabsorption causes colonic injury or inflammation. Twenty-four piglets were randomized to receive either control formula (CON) or CON supplemented with lactulose (LAC) (N = 12 each group). After seven days, inflammation, apoptosis, and crypt cell proliferation were assessed in the proximal colon (cecum). Lactulose feeding caused persistent diarrhea. In both groups, breath H2 concentration was low, suggesting no increased fermentation in the LAC group. Weight gain/volume formula intake was identical in the CON and LAC groups (0.09+/-0.13 and 0.09+/-0.11 g/ml) respectively. Injury to the colon did not occur, but inflammation of the colon (scale 0-5) was greater in LAC (score of 1.5+/-1.38) than in CON (0.42+/-0.79; P<0.05). Cell proliferation at the basal 40% of the crypt was 92% increased in CON (labeling index 22.8+/-9.9 vs. 11.9+/-2.8; P<0.05). We conclude that persistent feeding during severe sugar malabsorption permits weight gain but may cause colitis.

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Interpretation of tracer studies of amino acid kinetics in the fed state is dependent on knowledge of splanchnic uptake of diet-derived amino acids. We studied five healthy control children and five children with cystic fibrosis (CF). After an overnight fast, the children ingested, hourly, a formula diet for 11 h. 5,5,5-[2H3]Leucine was added to the feedings during the last 6 h, and an i.v. infusion of 1-[13C]leucine was administered during the last 2 h of the formula feeding. The mean rate of splanchnic uptake of leucine was similar in the CF and control group, 23.8 +/- 24.0 and 21.5 +/- 21.2 mumol.kg-1.h-1, respectively. Fractional splanchnic uptake of leucine was not significantly different in the patients with CF (0.16 +/- 0.112 mean +/- SD) compared with the control children (0.244 +/- 0.256(-1)). The rate of whole body protein breakdown was not significantly different between the groups (CF versus control) with (159 +/- 18 versus 135 +/- 28 mumol.kg-1.h-1) or without (135 +/- 14 versus 114 +/- 20 mumol.kg-1.h-1) correction for splanchnic leucine uptake. However, for the 10 cases combined, protein breakdown corrected for splanchnic leucine uptake (147 +/- 26 mumol.kg-1.h-1) was 18% greater than uncorrected protein breakdown (124 +/- 20 mumol.kg-1.h-1) (p = 0.009). The data suggest that companion studies of splanchnic uptake might enhance the interpretation of leucine kinetics in the fed state.

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BACKGROUND: The authors have previously demonstrated abnormalities in glucose and insulin metabolism in nondiabetic black American (BA) adults versus white American (WA) adults. Whether similar glucoregulatory alterations extend to BA adolescents remain unknown. In addition, obesity, a known risk factor for insulin resistance and hyperinsulinemia, occurs in a greater proportion of BA adults and children when compared to WA. The objective of the present study was to examine the differential effects of obesity on glucose homeostasis in BA and WA adolescents. METHODS: We examined glucose homeostasis in BA and WA adolescents using oral glucose tolerance test (OGTT), intravenous glucose tolerance test (IVGTT), and [6,6-2H2]-glucose infusion. The study consisted of four age-, sex-, and pubertal stage-matched groups: 15 lean BA, 29 lean WA, 7 obese BA, and 9 obese WA. RESULTS: Both obese groups had significantly increased insulin and C-peptide area under the curve (AUC) during OGTT and IVGTT when compared to their same-race lean counterparts. During OGTT, obese BA demonstrated greater insulin and C-peptide when compared to obese WA. During IVGTT, first- and second-phase insulin were significantly greater in obese BA versus obese WA. CONCLUSION: In summary, BA adolescents demonstrated insulin resistance which is markedly exaggerated in the face of obesity when compared to WA adolescents, implying a differential impact for obesity on glucose homeostasis that is unique to the obese BA adolescent group. In conclusion, there is a need for early aggressive weight management in obese BA adolescents.

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The purpose of this study was to determine whether doubling the lactose concentration in formula for preterm infants lowers the fraction of lactose digested and/or increases the fraction of lactose fermented. Six preterm infants, 31 to 36 weeks' postconceptional age, were fed a standard preterm formula (carbohydrate is 50% lactose and 50% glucose polymer)(SC) and/or the same volume of formula modified to contain lactose as the sole carbohydrate (LAC). Relative lactose digestion during the LAC formula feeding compared with SC formula feeding was measured by using a stable isotope approach for quantifying the fractional contribution of formula lactose to plasma glucose enrichment. Relative lactose digestion was 0.98 +/- 0.17 (range, 0.70 to 1.19). Fractional fermentation of lactose was estimated from breath H2 excretion (0.52 +/- 0.34 during LAC feeding and 0.23 +/- 0.22 during SC feeding, P = .11). The rate of breath H2 excretion was much higher with LAC (1.34 +/- 0.98 mL/h) than with SC (0.27 +/- 0.29, P = .029). In conclusion, doubling the lactose concentration had only modest effects on fractional lactose digestion. Increased breath H2 excretion with LAC may relate to fermentation of nonlactose sugar or to ill-defined changes in colonic physiology or motility, which could enhance colonic fermentation of malabsorbed sugar by H2-producing bacteria.

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A rare patient with infantile spasms, hypsarrhythmia, cytochrome c oxidase deficiency and Leigh syndrome is reported. Although rare, infantile spasms and Leigh syndrome may occur simultaneously. Leigh syndrome should be included in the differential diagnosis of infantile spasms.

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To determine whether a 13C-bicarbonate, isotope dilution technique could be used to estimate relative changes in energy expenditure of leisure activities of short duration, we studied eight adolescents who performed the following activities: watching television (120 min); playing a stringed instrument (60 min plus 60 min of sitting); and walking plus rest during two approximately isocaloric sessions (slow walk at 40% of peak VO2 for 43 min plus 77 min of sitting; fast walk at 73% of peak VO2 for 22 min plus 98 min of sitting). The rate of appearance of CO2 (RaCO2) was determined from the ratio of the oral dose of 13C-bicarbonate and the isotopic enrichment of breath CO2. The net rates of excretion of CO2 (VCO2) and oxygen consumption were measured. VCO2 and RaCO2, were correlated (r = 0.93; P < 0.05). To adjust for the systematic difference in CO2 production between methods, determinations were expressed as a fraction of that during television viewing. For RaCO2, the ratios for instrument playing, walking at 40% peak VCO2, and walking at 73% peak VO2 were respectively 133 +/- 20%, 186 +/- 38%, and 206 +/- 34%; for VCO2, the respective ratios were 129 +/- 19, 210 +/- 50, and 232 +/- 39 (P > 0.05 for methods and interaction, two-way ANOVA). RaCO2 may be a useful method for detecting relative differences in energy expenditure associated with leisure activities of brief duration.

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We have developed a system for chronically catheterizing 10- to 25-d-old pigs that permits stable isotope tracer studies of intestinal or colonic assimilation of nutrients. This model also can be used to ensure constant enteral feeding or to assess the rate of entry into the terminal ileum of carbohydrates, fats, and amino acids. A plastic cannula with a luminal flange can be surgically placed in the stomach for tracer studies of sugar digestion or for controlled infusion of any formula diet. A similar cannula can be placed in the cecum for infusion of tracer and(or) substrates for studies of fermentation. The cannula has been machined so that a washer and nut can be threaded onto it, allowing the entire apparatus to be fixed to the abdominal wall. The distal end protruding above the skin was tapered to fit standard i.v. extension tubing. A carotid arterial catheter was used to sample substrates for isotopic enrichment measurements.

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BACKGROUND: Results of in vitro studies have documented colonic absorption of lactose in the newborn. A stable isotope model was developed for assessing the entry rate of intact lactose into the portal circulation in newborn piglets. METHODS: In experiment 1, unlabeled and [D-1-(13C)]-lactose were infused into two separate mesenteric veins, and in experiment 2, labeled lactose was infused into a mesenteric vein and unlabeled lactose was infused into the colon. The 13C-enrichment of plasma lactose was assessed by high performance liquid chromatography gas chromatography combined with mass spectrometry. RESULTS: The isotopic estimate of the mesenteric venous infusion rate of lactose was 91% of the theoretical. In the second experiment 13% of the unlabeled lactose infused into the colon reached the portal circulation. CONCLUSIONS: The current study provides the first, direct, in vivo confirmation of colon absorption of intact lactose. The tracer model could be used to evaluate intestinal or colonic absorption of other organic compounds not endogenously synthesized, including vitamins or drugs.

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Sugar reaching the colon because of intestinal maldigestion or malabsorption may be fermented to acetate and other short-chain fatty acids, resulting in stimulation of colonic water absorption and cell proliferation. To explore this phenomenon in more detail, we have developed a stable isotope model for estimating the fraction of colon-derived glucose or lactose that is fermented to acetate, propionate and butyrate. In an initial application of the model, [d3]-acetate and either [1-(13)C]-glucose or [D-1-(13)C]-lactose were infused into the cecum or colon of piglets, and plateau plasma acetate enrichment was monitored in the carotid artery. In acutely anesthetized piglets, the fractions of glucose and lactose fermented to acetate were 17.0 and 20.0%, respectively. In a chronically catheterized piglet, fermentation was higher (34.2%). When conducted in chronically catheterized animals or via a colostomy or ileostomy in infants, this model may be used to determine how age, previous surgery or antibiotic therapy affects the efficiency of colonic assimilation of carbohydrate.

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In vitro studies of intestinal lactase activity and breath-hydrogen studies have suggested that the capacity for lactose digestion in preterm infants is less than the usual intake. To explore this question using an in vivo approach, we determined the fraction of dietary lactose hydrolyzed to glucose (and galactose) in 14 preterm infants with a gestational age of 26-31 wk at the time of birth but a postconceptional age of 31-37 wk at the time of study. The percentage of lactose digested was estimated after 6-h, primed, constant gastric infusions of [1-(13)C]glucose and D-[-1-(13)C]lactose on alternate days. A coefficient of lactose fermentation was derived from the rates of pulmonary excretion of hydrogen and carbon dioxide. Mean (+/- SD) lactose digestion was 79 +/- 26%. There was a significant inverse rank (r = -0.799, P < 0.01) and linear (r = -0.587, P < 0.05) correlation between this variable and postconceptional age. The percentage of lactose fermented averaged 35 +/- 27%.

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BACKGROUND: Estimates of the rate of CO2 production may be useful in preterm infants, but assessment of the rate of respiratory excretion of CO2 (VCO2) may not always be practical in infants requiring constant care. We hypothesized that the rate of dilution of 13CO2 (RaCO2) would be a valid index of CO2 production in preterm infants. METHODS: Twelve studies of RaCO2 and VCO2 were performed in six enterally fed preterm infants. RaCO2 was measured using a 2-hour, primed, constant, orogastric infusion of NaH13CO3 with formula and an assessment of the plateau 13C enrichment of expired CO2. VCO2 was measured over two 10-minute intervals during the infusion using a flow-through system. Energy expenditure was estimated from these data and the food quotient. RESULTS: Mean (+/- SD) rate of CO2 production using RaCO2 (348 +/- 32 mumol/kg/min) was 114% of that estimated using VCO2 (304 +/- 51 mumol/kg/min). The ratio of VCO2/RaCO2 is equal to the fractional recovery of tracer CO2 in the expired air during the course of the tracer infusion. In studies of short duration, this ratio is generally less than 100% because of isotope exchange. For five pairs of studies performed on consecutive days, each individual value of RaCO2 on day 2 was multiplied by the mean of the individual ratios of VCO2/RaCO2 on day 1 (0.78); corrected RaCO2 was 306 +/- 19 mumol/kg/min compared with 307 +/- 59 mumol/kg/min for VCO2. CONCLUSIONS: Thus, RaCO2, particularly when corrected for isotope recovery, may be a useful index of group mean CO2 production and energy expenditure in preterm infants.

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We hypothesized that there is less suppression of whole-body protein breakdown with feeding in patients with cystic fibrosis (CF) who exhibit decreased insulin secretion after a single meal. Using [1-13C]leucine, we measured rates of nonoxidative leucine disappearance (whole-body protein synthesis) and protein breakdown in nine CF patients (6-11 y of age) and five healthy control subjects (8-10 y of age) during feeding and fasting. In the CF patients, synthesis and breakdown (x +/- SD) were 172 +/- 61 and 157 +/- 67 mumol.kg-1.h-1 during feeding and 140 +/- 24 and 178 +/- 26 mumol.kg-1.h-1 during fasting. The respective control values were 129 +/- 27 and 114 +/- 20 mumol.kg-1.h-1 during feeding and 136 +/- 13 and 173 +/- 18 mumol.kg-1.h-1 during fasting. Leucine balance was nearly identical in the two groups. By analysis of variance, there was a significant effect of feeding on protein breakdown but no difference between the groups. However, when each group was analyzed separately, feeding resulted in a 34% decrease in breakdown in the control subjects (P = 0.001) and a 23% increase in synthesis in the CF group (P = 0.058). Plasma insulin concentrations did not differ in the two groups. Thus, feeding may affect protein turnover differently in children with CF than in control children independently of plasma insulin concentration.

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In the newborn, sugars present in human milk and formulas are assimilated by both small intestinal digestion and, especially in the case of lactose, colonic bacterial fermentation. Colonic fermentation of carbohydrate serves three major functions: (1) conservation of a fraction of the metabolizable energy of dietary carbohydrate that is not absorbed in the small intestine; (2) prevention of osmotic diarrhea; and (3) production of short-chain fatty acids that stimulate sodium and water absorption, serve as fuel for colonocytes, and stimulate cell replication in colon and small intestine. Diarrhea produced in association with small bowel malabsorption of sugar may be caused by three, potentially overlapping mechanisms: (1) osmotic effects of unfermented sugar, which may cause secondary disruption of fermentation by purging the bacteria or diluting the bacteria mass; (2) damage to the colon mucosa from excessive fermentation leading to SCFA malabsorption and osmotic diarrhea on this basis; and (3) excessive fermentation leading to lowering of luminal pH and inhibition of bacterial enzymes. Therapy aimed at reducing diarrhea associated with sugar malabsorption might involve either slowing of motility to facilitate fermentation or stimulation of fermentative activity, but such interventions would depend on greater understanding of the mechanisms for colonic dysfunction in this condition.

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Previous studies on the piglet colon in newborns cleared of bacterial metabolic activity showed a capacity for lactose absorption. Colonic absorption occurred at a flux rate equal to the assimilation of lactose by the small intestine but by a process that did not involve either glucose-galactose sodium cotransport or simple diffusion. Surprisingly, colonic lactose transport did not require either fermentation or cleavage of the disaccharide for uptake. Experiments were designed to test the selectivity of the colonic transport process for a variety of carbohydrates. Colonic tissues from 4-7-d-old piglets were mounted in Ussing chambers and the mucosal-to-serosal flux of radiolabeled carbohydrates was compared with that of lactose. The results showed a 3-4-fold greater flux of galactose-containing sugars as compared with glucose-containing carbohydrates at concentrations up to 40 mM. Even lactulose, a synthetic disaccharide assumed to require bacterial digestion before assimilation, was transported readily. N-Acetylgalactosamine, a component of colonic mucus, inhibited the flux of lactose, whereas N-acetylglucosamine did not. Similarly, lactosylated BSA inhibited lactose flux, whereas nonlactosylated BSA did not. The capacity of the colon of the newborn to differentiate moieties as similar as glucose and galactose suggests an absorptive process for carbohydrates with a high degree of discrimination.

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We sought to determine how a stationary activity such as playing a stringed instrument may affect energy expenditure (EE) in adolescents. Using automated indirect calorimetry, we measured EE in eight adolescents (1 male, 7 females, 14.2 +/- 2.1 yr) while they each performed the following activities: watching television (TV) (60 min), playing a stringed instrument (60 min), and walking at 40% of peak oxygen uptake (43 min). Measurements were made during three, 6- to 7-min steady state periods of each activity. EE (mean +/- SD) was lower during TV (1.0 +/- 0.2 kcal.min-1) and instrument playing (1.4 +/- 0.2 kcal.min-1) than during walking (3.4 +/- 0.4 kcal.min-1) (P < 0.05). EE during instrument playing was 41% greater than during television viewing (P < 0.05). We conclude that relatively sedentary activities such as playing a stringed instrument can elevate EE. Conceivably, other stationary, leisure activities performed by adolescents may increase EE and have substantial, cumulative effects on long-term energy balance and fat accretion.

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We hypothesized that elevated hepatic glucose output (HGO) may occur in children with cystic fibrosis (CF) as an early sign of declining insulin secretion and that tolbutamide therapy would correct the defect. We studied eight glucose-tolerant CF patients (mean +/- SD, 9.1 +/- 1.9 y) and five healthy controls (9.0 +/- 1.6 y). Fasting glucose, insulin, and insulin-connecting peptide concentrations were not different in the CF and control subjects; however, meal stimulation tests in the CF patients suggested that insulin secretion was defective in the fed state. HGO (mg.kg-1 body weight.min-1) was 26% higher in the CF patients (4.2 +/- 0.7 versus 3.1 +/- 0.6 in HC) (p = 0.016). When normalized for fat-free mass (mg.kg fat-free mass-1.min-1), HGO was 27% higher in CF (4.9 +/- 0.8 versus 3.8 +/- 0.5) (p = 0.015). However, when expressed as a function of resting energy expenditure (mg.kcal-1), HGO was not significantly different in CF (121 +/- 22) versus healthy controls (116 +/- 30). In seven of the CF group, HGO was re-assessed after a 2-h glucose infusion at a rate of 0.90 +/- 0.02 mg.kg-1.min-1. HGO was suppressed (p < 0.05) by an amount equal to 103 +/- 18% of the glucose infusion rate. Finally, in five CF patients, HGO was re-measured after 2 wk of oral therapy with tolbutamide (750 mg/d). Tolbutamide did not affect HGO (fasting or during the glucose infusion). In conclusion, fasting HGO was elevated in the CF patients in proportion to energy expenditure.

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