Laure Gabert

Visceral Fat Accumulation During Lipid Overfeeding Is Related to Subcutaneous Adipose Tissue Characteristics in Healthy Men

CONTEXT The hypothesis of a limited expansion of sc adipose tissue during weight gain provides an attractive explanation for the reorientation of excess lipids toward ectopic sites, contributing to visceral adipose depots and metabolic syndrome. OBJECTIVE Our objective was to define whether the characteristics of sc adipose tissue influence the partition of lipids toward abdominal fat depots during weight gain in healthy men. RESEARCH DESIGN AND METHODS Forty-one healthy nonobese volunteers performed a 56-day overfeeding protocol (+760 kcal/d). Insulin sensitivity was estimated by euglycemic hyperinsulinemic clamp. Changes in abdominal visceral and sc adipose tissue depots were measured by magnetic resonance imaging. The fate of ingested lipids before and after overfeeding was investigated using a [d31]palmitate test meal, and gene expression was measured by real-time PCR in sc fat biopsies. RESULTS Overfeeding led to a 2.5-kg body weight increase with large interindividual variations in abdominal sc and visceral adipose tissues. There was no relationship between the relative expansions of these 2 depots, but the increase in visceral depot was positively associated with the magnitude of the postprandial exogenous fatty acid release in the circulation during the test meal. The regulation of lipid storage-related genes (DGAT2, SREBP1c, and CIDEA) was defective in the sc fat of the subjects exhibiting the largest accumulation in visceral depot. CONCLUSIONS Characteristics of sc adipose tissue appear therefore to contribute to the development of visceral fat depot, supporting the adipose tissue expandability theory and extending it to early stages of weight gain in nonobese subjects.

Activity energy expenditure is a major determinant of dietary fat oxidation and trafficking, but the deleterious effect of detraining is more marked than the beneficial effect of training at current recommendations

BACKGROUND Previous studies suggested that physical activity energy expenditure (AEE) is a major determinant of dietary fat oxidation, which is a central component of fat metabolism and body weight regulation. OBJECTIVE We tested this hypothesis by investigating the effect of contrasted physical activity levels on dietary saturated and monounsaturated fatty acid oxidation in relation to insulin sensitivity while controlling energy balance. DESIGN Sedentary lean men (n = 10) trained for 2 mo according to the current guidelines on physical activity, and active lean men (n = 9) detrained for 1 mo by reducing structured and spontaneous activity. Dietary [d31]palmitate and [1-¹³C]oleate oxidation and incorporation into triglyceride-rich lipoproteins and nonesterified fatty acid, AEE, and muscle markers were studied before and after interventions. RESULTS Training increased palmitate and oleate oxidation by 27% and 20%, respectively, whereas detraining reduced them by 31% and 13%, respectively (P < 0.05 for all). Changes in AEE were positively correlated with changes in oleate (R² = 0.62, P < 0.001) and palmitate (R² = 0.66, P < 0.0001) oxidation. The d31-palmitate appearance in nonesterified fatty acid and very-low-density lipoprotein pools was negatively associated with changes in fatty acid translocase CD36 (R² = 0.30), fatty acid transport protein 1 (R² = 0.24), and AcylCoA synthetase long chain family member 1 (ACSL1) (R² = 0.25) expressions and with changes in fatty acid binding protein expression (R² = 0.33). The d31-palmitate oxidation correlated with changes in ACSL1 (R² = 0.39) and carnitine palmitoyltransferase 1 (R² = 0.30) expressions (P < 0.05 for all). Similar relations were observed with oleate. Insulin response was associated with AEE (R² = 0.34, P = 0.02) and oleate (R² = 0.52, P < 0.01) and palmitate (R² = 0.62, P < 001) oxidation. CONCLUSION Training and detraining modified the oxidation of the 2 most common dietary fats, likely through a better trafficking and uptake by the muscle, which was negatively associated with whole-body insulin sensitivity.

13C tracer recovery in human stools after digestion of a fat-rich meal labelled with [1,1,1-13C3]tripalmitin and [1,1,1-13C3]triolein.

Lipid metabolism studies focus mainly on oxidation and storage but rarely on faecal elimination, which is needed to assess total lipid distribution during the postprandial period. The purpose of the present work was to set up and validate the analysis of lipid tracers in stools, with an aim of later using this methodology in studies of postprandial lipid tracer metabolism. Eight subjects received a mixture of [1,1,1-(13)C3]tripalmitin and [1,1,1-(13)C3]triolein with a fat-rich meal. The nature and amounts of (13)C lipids excreted in stools during 3 days post-dose were determined by gas chromatography/mass spectrometry (GC/MS) and gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) analysis of fatty acid methyl esters (FAMEs) from total fatty acid (TFA), free fatty acid (FFA) and triacylglycerol (TAG) fractions. The results were expressed as the Cumulative Tracer Recovery of the administered dose (CTR%). The quantities and labelling of FAMEs were higher in FFA than in TAG, indicating that label loss was not due to a lack of digestive lipase activity. The labelling was higher for C16:0 than for C18:1. The CTRs were 7.03 ± 0.77% and 6.87 ± 0.91%, respectively, in TFA and FFA for [1-(13)C] C16:0, while they were 0.60 ± 0.15% and 0.51 ± 0.11% for [1-(13)C] C18:1 (mean ± sem). By studying the kinetics of lipid excretion from subjects, two groups emerged. The first one showed rapid excretion in stool #1, whereas the second showed slower excretion in stools #2-#3. A significant difference was found in the FFA in stool #1 for C16:0 (p < 0.01) and C18:1 (p < 0.05). Individual excretion kinetics showed marked variability. Nevertheless, the CTR over the 3-day study period was substantial and homogenous for all subjects. These results confirm that the assessment of faecal elimination is of great importance when establishing total lipid distribution during the postprandial period and validate the analysis of cumulative tracer loss during 72 h post-tracer ingestion.

Exercise performed immediately after fructose ingestion enhances fructose oxidation and suppresses fructose storage

BACKGROUND Exercise prevents the adverse effects of a high-fructose diet through mechanisms that remain unknown. OBJECTIVE We assessed the hypothesis that exercise prevents fructose-induced increases in very-low-density lipoprotein (VLDL) triglycerides by decreasing the fructose conversion into glucose and VLDL-triglyceride and fructose carbon storage into hepatic glycogen and lipids. DESIGN Eight healthy men were studied on 3 occasions after 4 d consuming a weight-maintenance, high-fructose diet. On the fifth day, the men ingested an oral (13)C-labeled fructose load (0.75 g/kg), and their total fructose oxidation ((13)CO2 production), fructose storage (fructose ingestion minus (13)C-fructose oxidation), fructose conversion into blood (13)C glucose (gluconeogenesis from fructose), blood VLDL-(13)C palmitate (a marker of hepatic de novo lipogenesis), and lactate concentrations were monitored over 7 postprandial h. On one occasion, participants remained lying down throughout the experiment [fructose treatment alone with no exercise condition (NoEx)], and on the other 2 occasions, they performed a 60-min exercise either 75 min before fructose ingestion [exercise, then fructose condition (ExFru)] or 90 min after fructose ingestion [fructose, then exercise condition (FruEx)]. RESULTS Fructose oxidation was significantly (P < 0.001) higher in the FruEx (80% ± 3% of ingested fructose) than in the ExFru (46% ± 1%) and NoEx (49% ± 1%). Consequently, fructose storage was lower in the FruEx than in the other 2 conditions (P < 0.001). Fructose conversion into blood (13)C glucose, VLDL-(13)C palmitate, and postprandial plasma lactate concentrations was not significantly different between conditions. CONCLUSIONS Compared with sedentary conditions, exercise performed immediately after fructose ingestion increases fructose oxidation and decreases fructose storage. In contrast, exercise performed before fructose ingestion does not significantly alter fructose oxidation and storage. In both conditions, exercise did not abolish fructose conversion into glucose or its incorporation into VLDL triglycerides. This trial was registered at clinicaltrials.gov as NCT01866215.

Salivary composition in obese vs normal-weight subjects: towards a role in postprandial lipid metabolism?

In the pathophysiological context of obesity, oral exposure to dietary fat can modulate lipid digestion and absorption, but underlying in-mouth mechanisms have not been clearly identified. Therefore, we tested the hypothesis that salivary components related to dietary fat sensitivity would differ according to body mass index (BMI) and postprandial lipid metabolism in young men. Saliva was collected from nine normal-weight (BMI=22.3±0.5 kg m−2) and nine non-morbid obese (BMI=31.7±0.3 kg m−2) men before an 8-h postprandial metabolic exploration test involving the consumption of a 40-g fat meal, in which obese subjects revealed a delayed postprandial lipid metabolism. Nine salivary characteristics (flow, protein content, lipolysis, amylase, proteolysis, total antioxidant status, lysozyme, lipocalin 1 and carbonic anhydrase-VI) were investigated. We show that, under fasting conditions, salivary lipolysis was lower in obese vs normal-weight subjects, whereas proteolysis and carbonic anhydrase VI were higher. We reveal through multivariate and Mann–Whitney analysis that differences in fasting salivary lipolysis and proteolysis between both groups are related to differences in postprandial lipid metabolism including exogenous fatty-acid absorption and β-oxidation. These results suggest a potential role of salivary composition on postprandial lipid metabolism and bring novel causal hypotheses on the links between salivary composition, sensitivity to dietary fat oral income and postprandial lipid metabolism according to BMI.

Validation of pentaacetylaldononitrile derivative for dual 2H gas chromatography/mass spectrometry and 13C gas chromatography/combustion/isotope ratio mass spectrometry analysis of glucose

A reference method to accurately define kinetics in response to the ingestion of glucose in terms of total, exogenous and endogenous glucose is to use stable-isotope-labelled compounds such as 2H and 13C glucose followed by gas chromatography/mass spectrometry (GC/MS) and gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) analysis. The use of the usual pentaacetyl (5Ac) derivative generates difficulties in obtaining accurate and reproducible results due to the two chromatographic peaks for the syn and anti isomers, and to the isotopic effect occurring during acetylation. Therefore, the pentaacetylaldononitrile derivative (Aldo) was validated for both isotopes, and compared with the 5Ac derivative. A correction factor including carbon atom dilution (stoichiometric equation) and the kinetic isotopic effect (KIE) was determined. Analytical validation results for the 2H GC/MS and 13C GC/C/IRMS measurements produced acceptable results with both derivatives. When 2H enrichments of plasma samples were < or = 1 mol % excess (MPE), the repeatability (RSD(Aldo Intra assay and Intra day) <0.94%, RSD(5Ac Intra assay and Intra day) <3.29%), accuracy (Aldo <3.4%, 5Ac <29.0%), and stability of the derivatized samples were significantly better when the Aldo derivatives of the plasma samples were used (p < 0.05). When the glucose kinetics were assessed in nine human subjects, after glucose ingestion, the plasma glucose 2H enrichments were identical with both derivatives, whereas the 13C enrichments needed a correction factor to fit together. Due to KIE variation, this correction factor was not constant and had to be calculated for each batch of analyses, to obtain satisfactory results. Mean quantities of exogenous glucose exhibit marked difference (20.9 +/- 1.3g (5Ac) vs. 26.7 +/- 2.5g (Aldo)) when calculated with stoichiometric correction, but fit perfectly when calculated after application of the correction factor (22.1 +/- 1.3g (5Ac) vs. 22.9 +/- 1.9g (Aldo)). Finally, the pentaacetylaldononitrile derivative, used here in GC/C/IRMS for the first time, enables measurement of 2H and 13C enrichments in plasma glucose with a single sample preparation.

Effects of roux-en-Y gastric bypass surgery on postprandial fructose metabolism.

Fructose is partly metabolized in small bowel enterocytes, where it can be converted into glucose or fatty acids. It was therefore hypothesized that Roux‐en‐Y gastric bypass (RYGB) may significantly alter fructose metabolism.

Exercise training improves fat metabolism independent of total energy expenditure in sedentary overweight men, but does not restore lean metabolic phenotype

Background:Obesity is a dietary fat storage disease. Although exercise prevents weight gain, effects of chronic training on dietary fat oxidation remains understudied in overweight adults.Objective:We tested whether 2 months of training at current guidelines increase dietary fat oxidation in sedentary overweight adults like in sedentary lean adults.Design:Sedentary lean (n=10) and overweight (n=9) men trained on a cycle ergometer at 50% VO2peak, 1 h day−1, four times per week, for 2 months while energy balance was clamped. Metabolic fate of [d31]palmitate and [1-13C]oleate mixed in standard meals, total substrate use, total energy expenditure (TEE), activity energy expenditure (AEE) and key muscle proteins/enzymes were measured before and at the end of the intervention.Results:Conversely to lean subjects, TEE and AEE did not increase in overweight participants due to a spontaneous decrease in non-training AEE. Despite this compensatory behavior, aerobic fitness, insulin sensitivity and fat oxidation were improved by exercise training. The latter was not explained by changes in dietary fat trafficking but more likely by a coordinated response at the muscle level enhancing fat uptake, acylation and oxidation (FABPpm, CD36, FATP1, ACSL1, CPT1, mtGPAT). ACSL1 fold change positively correlated with total fasting (R2=0.59, P<0.0001) and post-prandial (R2=0.49, P=0.0006) fat oxidation whereas mtGPAT fold change negatively correlated with dietary palmitate oxidation (R2=0.40, P=0.009), suggesting modified fat trafficking between oxidation and storage within the muscle. However, for most of the measured parameters the post-training values observed in overweight adults remained lower than the pre-training values observed in the lean subjects.Conclusion:Independent of energy balance and TEE, exercise training at current recommendations improved fitness and fat oxidation in overweight adults. However the improved metabolic phenotype of overweight adults was not as healthy as the one of their lean counterparts before the 2-month training, likely due to the spontaneous reduction in non-training AEE.

Comparison of high-temperature conversion and equilibration methods for the determination of d31-palmitic acid oxidation in man using continuous-flow isotope ratio mass spectrometry.

During nutritional interventions, the ingestion of d(31)-palmitic acid and H(2)(18)O allows the assessment of dietary fatty acid oxidation from cumulative (2)H recovery in urine and the estimation of the total body water pool (TBW) from (18)O dilution. Continuous-flow isotope ratio mass spectrometry (CF-IRMS) coupled to either equilibration or high-temperature conversion (HTC) techniques permits (2)H- and (18)O-enrichment measurements in biological fluids. Thus it was of great interest to compare these methods applied to the determination of dietary fatty acid oxidation. The linearity, accuracy and correlation between CF-equilibration and CF-HTC were first checked using (2)H- and (18)O-enriched water and urine samples. Urine samples from 14 subjects were then measured with both methods. The (2)H and (18)O raw data were normalised against calibration lines. The final aim was to study the impact of the normalised raw results on physiological data (i.e. TBW and d(31)-palmitate recovery). No significant difference was observed between the (18)O- and (2)H-enrichment measurements depending on the analytical method used. The TBW volumes calculated from the (18)O enrichments measured either with CF-equilibration or CF-HTC were not significantly different: respectively, 45.1 ± 1.0 L or 45.7 ± 1.0 L (mean ± sem, p = 0.09). The palmitic acid oxidation results obtained from the (2)H-enrichment measurements and the TBW from CF-equilibration vs. CF-HTC were not significantly different (p ≥ 0.26): with δ(2)H values of, respectively, 16.2 ± 1.6% vs. 16.2 ± 1.1% at 8 h, 18.7 ± 2.0% vs. 17.6 ± 1.3% at 12 h and 21.7 ± 1.9% vs. 21.5 ± 1.3% at 3 days post-dose (mean ± sem). Thus, even if CF-HTC was preferred because it was more practical to carry out, both methods allow the study of dietary lipid oxidation in man and generate similar results.