Endurance training with constant energy intake in identical twins: changes over time in energy expenditure and related hormones

The effects of exercise training and of its interaction with the genotype on components of energy expenditure and related hormones were examined in young male monozygotic twins. Energy intake was maintained at the pretraining level for a 93-day training period. The estimated net energy deficit induced by training was 244 MJ and was associated with a 5-kg body weight loss that was almost entirely explained by body fat loss. Resting metabolic rate (RMR) was significantly decreased by 8% after training despite the preservation of fat-free mass (FFM). Accordingly, plasma norepinephrine (NE) concentrations, NE appearance rate, and plasma levels of triiodothyronine (T3), free T3, and total thyroxine (T4) were lower after training. The energy cost of standardized exercise was also reduced after the training program. A modest to significant within-twin-pair resemblance was observed for absolute changes in the RMR, thermic effect of food, energy cost of exercise, NE clearance, and plasma concentrations of thyroid hormones. These results suggest that when exercise training is associated with a substantial negative energy balance, energy expenditure and levels of related hormones are decreased, and this effect is partly accounted for by heredity.

Genetic influences on the response of body fat and fat distribution to positive and negative energy balances in human identical twins

This article summarizes a series of intervention studies conducted with pairs of young adult male identical twins and designed to determine whether there is any evidence for genotype x overfeeding or genotype x negative energy balance interaction effects in the changes in body weight, body composition, fat distribution, computerized tomography-assessed abdominal visceral fat, resting metabolic rate and thermic response to a standardized meal of mixed composition brought about by chronic exposure to appropriate experimental treatments. These studies demonstrated that individual differences in response to chronic alterations in energy balance are common. The comparison of the heterogeneity in response between the pairs of twins in contrast to the variance within pairs revealed that members of the same twin pair are significantly more alike than individuals who are not genetically related by descent. The intrapair resemblance in response was particularly strong for the changes in body mass, body composition, subcutaneous fat distribution and abdominal visceral fat. In contrast, the results of two long-term intervention studies showed that variations in resting metabolic rate following exposure to chronic overfeeding or negative energy balance induced by exercise were accounted for primarily by the changes in body mass. Finally, the thermic response to food was not modified by any of the experimental treatments. On the basis of these observations, we conclude that there are individuals at risk of gaining weight and body fat or who are resistant to weight loss. These differences in susceptibility to chronic overfeeding or in sensitivity to negative energy balance seem to be largely explained by genetic factors whose exact nature remains to be determined.

Acute effect of exercise and low-fat diet on energy balance in heavy men

OBJECTIVE

To quantify the acute effect of the exercise-low-fat diet combination on energy balance compared with sedentarity and a high fat diet in overweight individuals.

DESIGN AND MEASUREMENTS

We assessed the acute effect of exercise and ad libitum intake of low-fat foods on daily energy balance. Six heavy men participated in two randomly assigned sessions which required a 24 h stay in a whole body indirect calorimeter. Sessions were preceded by either a 60 min aerobic exercise at 50% VO2 max or a 60 min rest. Subjects were fed a low-fat diet (mean FO = 0.89) after exercise and a mixed diet (mean FQ = 0.85) after the resting period.

RESULTS

The difference in energy balance between the two conditions was 7.3 MJ. About half of the effect was attributable to the energy surplus expended during exercise whereas the remaining fraction was explained by the difference in post-exercise energy balance.

CONCLUSION

In heavy men, the combination of a low-fat diet and exercise has a strong acute effect on energy balance compared to a rest-mixed diet condition.

Androstane-3alpha,17beta-diol glucuronide as a steroid correlate of visceral obesity in men

Plasma levels of androstane-3alpha,17beta-diol glucuronide (3alpha-DIOL-G) and androsterone glucuronide (ADT-G) as well as testosterone and adrenal C19 steroid concentrations were measured in a sample of 80 men in whom visceral adipose tissue (AT) accumulation was also determined by computed tomography. Plasma 3alpha-DIOL-G concentrations showed significant positive correlations with total body fat mass (r = 0.31; P < 0.05) and percent body fat (r = 0.28; P < 0.05). Furthermore, plasma 3alpha-DIOL-G levels were significantly associated with visceral adipose tissue accumulation (r = 0.41; P < 0.0005) as well as fasting plasma insulin (r = 0.35; P < 0.005) and glycemic and insulinemic responses to an oral glucose load (r = 0.39; P < 0.0005 and r = 0.32; P < 0.005, respectively). However, associations between 3alpha-DIOL-G and plasma glucose-insulin homeostasis indexes were no longer significant after adjustment for visceral AT area. ADT-G levels were not significantly associated with any of the adiposity variables. Subjects matched for abdominal sc AT area but with either low or high levels of visceral AT area showed significant differences in 3alpha-DIOL-G concentrations (P < 0.05), whereas subjects with low or high levels of abdominal sc AT but similar levels of visceral AT had similar 3alpha-DIOL-G concentrations. Among men with high testosterone levels, subjects with reduced 3alpha-DIOL-G concentrations had lower visceral adipose tissue accumulation than subjects with increased 3alpha-DIOL-G levels. The present results indicate that plasma 3alpha-DIOL-G, but not ADT-G, is a steroid correlate of visceral obesity. Excess visceral adipose tissue and/or concomitant alterations in insulin levels or in vivo insulin action could be responsible for the increased 3alpha-DIOL-G formation observed in this condition.

Abdominal visceral fat is associated with a BclI restriction fragment length polymorphism at the glucocorticoid receptor gene locus

Several investigations have suggested that body fat distribution is influenced by nonpathologic variations in the responsiveness to cortisol. Genetic variations in the glucocorticoid receptor (GRL) could therefore potentially have an impact on the level of abdominal fat. A restriction fragment length polymorphism (RFLP) has previously been detected with the BclI restriction enzyme in the GRL gene identifying two alleles with fragment lengths of 4.5 and 2.3 kb. This study investigates whether abdominal fat areas measured by computerized tomography (CT) are associated with this polymorphism in 152 middle-aged men and women. The less frequent 4.5-kb allele was found to be associated with a higher abdominal visceral fat (AVF) area independently of total body fat mass (4.5/4.5 vs. 2.3/2.3 kb genotype; men: 190.7 +/- 30.1 vs. 150.7 +/- 33.3 cm2, p = 0.04; women: 132.7 +/- 37.3 vs. 101.3 +/- 34.5 cm2, p = 0.06). However, the association with AVF was seen only in subjects of the lower tertile of the percent body fat level. In these subjects, the polymorphism was found to account for 41% (p = 0.003) and 35% (p = 0.007), in men and women, respectively, of the total variance in AVF area. The consistent association between the GRL polymorphism detected with BclI and AVF area suggests that this gene or a locus in linkage disequilibrium with the BclI restriction site may contribute to the accumulation of AVF.

Acute effects of exercise on energy intake and feeding behaviour

The main objective of the present study was to evaluate the short-term effects of exercise of different intensities on energy intake. Eleven young men were submitted to three randomly assigned sessions (one control and two exercise sessions) in which they ate, ad libitum, foods from a buffet-type meal. The energy cost of exercise was the same in the two exercise sessions. Results showed that there was no significant change in post-exercise subjective levels of hunger and fullness as well as total energy and macronutrient intakes in comparison with the control session. However, when energy intake relative to expenditure was considered by subtracting the surplus of energy expended during exercise from total energy intake, high-intensity exercise exerted a greater reducing effect on this variable compared with the control and low-intensity exercise sessions. These results suggest that for a given level of energy expenditure, high-intensity exercise favours negative energy balance to a greater extent than low-intensity exercise.

Association between median episiotomy and severe perineal lacerations in primiparous women

OBJECTIVE

To evaluate the association between median episiotomy and severe (third- and fourth-degree) perineal lacerations in primiparous women.

DESIGN

Retrospective cohort study.

SETTING

University-affiliated hospital providing secondary obstetric care in Quebec City.

PATIENTS

A total of 6522 primiparous women who gave birth vaginally to a single live baby in cephalic position between 1985 and 1993.

OUTCOME MEASURE

Incidence of third- and fourth-degree perineal lacerations.

RESULTS

Median episiotomy was performed in 4390 women (67.3%). A total of 1002 women (15.4%) had a third- or fourth-degree laceration. The frequency of severe perineal lacerations was 20.6% with episiotomy and 4.5% without episiotomy (relative risk [RR] 4.58, 95% confidence interval [CI] 3.74-5.62). This association persisted after adjustment by stratified analysis for type of delivery and birth weight (RR 3.03, 95% CI 2.52-3.63) and by logistic regression for type of delivery, birth weight, epidural analgesia, shoulder dystocia, baby's head circumference, experience of the physician and year of delivery (odds ratio 3.58, 95% CI 2.84-4.50).

CONCLUSION

Median episiotomy is strongly associated with third- and fourth-degree perineal lacerations in primiparous women. Reducing the use of this procedure could decrease the occurrence of severe perineal tears.

Cloning, chromosomal localization, and functional analysis of the murine estrogen receptor beta

Estrogen receptor beta (ER beta) is a novel steroid receptor that is expressed in rat prostate and ovary. We have cloned the mouse homolog of ER beta and mapped the gene, designated Estrb, to the central region of chromosome 12. The cDNA encodes a protein of 485 amino acids that shares, respectively, 97% and 60% identity with the DNA- and ligand-binding domains of mouse (m) ER alpha. Mouse ER beta bind to an inverted repeat spaced by three nucleotides in a gel mobility shift assay and transactivates promoters containing synthetic or natural estrogen response elements in an estradiol (E2)-dependent manner. Scatchard analysis indicates that mER beta has slightly lower affinity for E2 [dissociation constant (Kd) = 0.5 nM] when compared with mER alpha (Kd = 0.2 nM). Antiestrogens, including 4-hydroxytamoxifen (OHT), ICI 182,780, and a novel compound, EM-800, inhibit E2-dependent transactivation efficiently. However, while OHT displays partial agonistic activity with ER alpha on a basal promoter linked to estrogen response elements in Cos-1 cells, this effect is not observed with mER beta. Cotransfection of mER beta and H-RasV12 causes enhanced activation in the presence of E2. Mutagenesis of a serine residue (position 60), located within a mitogen-activated protein kinase consensus phosphorylation site abolishes the stimulatory effect of Ras, suggesting that the activity of mER beta is also regulated by the mitogen-activated protein kinase pathway. Surprisingly, the coactivator SRC-1 up-regulates mER beta transactivation both in the absence and presence of E2, and in vitro interaction between SRC-1 and the ER beta ligand-binding domain is enhanced by E2. Moreover, the ligand-independent stimulatory effect of SRC-1 on ER beta transcriptional activity is abolished by ICI 182,780, but not by OHT. Our results demonstrate that while ER beta shares many of the functional characteristics of ER alpha, the molecular mechanisms regulating the transcriptional activity of mER beta may be distinct from those of ER alpha.

The MspI polymorphism of the apolipoprotein A-II gene as a modulator of the dyslipidemic state found in visceral obesity

The aim of the present study was to examine the effect of variation at the apolipoprotein (apo) A-II gene locus on lipoprotein levels in visceral obesity. A total of 145 sedentary men, free from metabolic disorders requiring pharmacotherapy, were classified into two groups on the basis of their apo A-II-MspI genotype determined by the polymerase chain reaction: 1) 43 M1 carriers or M1M2, including two M1M1 homozygotes and 41 M1M2 heterozygotes, and 2) 102 M2M2 homozygotes for the presence of a MspI restriction site. The two genotypic groups did not differ for body mass index (BMI, expressed in kg/m2), body fat mass, visceral adipose tissue (AT) accumulation, as well as for insulin, glucose and free fatty acids levels measured in the fasting state and in response to an oral glucose tolerance test. In addition, 65 and 63% of M1 carriers had plasma HDL2 cholesterol levels and a HDL2/HDL3 cholesterol ratio below the 50th percentile of their distributions compared with 45%(P < 0.05) and 46%(P = 0.06), respectively, in M2M2 homozygotes. When subjects were further divided on the basis of visceral AT accumulation (below and above a value of 130 cm2), M1 carriers with low levels of visceral AT were characterized by high plasma HDL cholesterol and HDL2 cholesterol concentrations as well as by a higher HDL2/HDL3 ratio, compared with M1 carriers with high levels of visceral AT (> 130 cm2), or with M2M2 homozygotes with either a high or a low accumulation of visceral AT. Furthermore, M1 carriers with high levels of visceral AT showed a trend for lower plasma HDL2 cholesterol levels and were characterized by a significantly lower HDL2/HDL3 cholesterol ratio compared with the other three groups. No difference in HDL and HDL2 cholesterol levels and in the HDL2/HDL3 cholesterol ratio was noted when M2 homozygotes with lower versus higher levels of visceral AT were compared. The contribution of hyperinsulinemia was also examined by dividing subjects on the basis of the 50th percentile of the integrated insulin response to an oral glucose challenge. Significantly lower plasma HDL2 cholesterol levels and a reduced HDL2/HDL3 cholesterol ratio were noted among M1 carriers with high plasma insulin responses compared with M1 carriers with low insulin responses. Among M2M2 homozygotes, no difference was noted in plasma HDL cholesterol and in HDL2 cholesterol concentrations between men with low versus high insulin responses to the oral glucose load. These results suggest that the apo A-II-MspI polymorphism could modulate plasma HDL cholesterol levels among visceral obese, insulin-resistant men.

Negative energy balance with exercise in identical twins: plasma glucose and insulin responses

The effects of long-term (93 days) negative energy balance on plasma glucose and insulin were investigated by means of exercise with constant energy intake in seven pairs of young sedentary male identical twins. Results showed a significant decrease in fasting (-24%, P < 0.02) and postprandial insulin (-16%, P < 0.05). Fasting and postprandial plasma glucose and glucagon were not modified. Mean glucose disposal rate measured during a euglycemic-hyperinsulinemic clamp performed in five twin pairs was increased by 34% (P = 0.13). No significant intrapair similarity was found for the responses of fasting and postprandial insulin levels and of glucose disposal rate. Changes in glucose disposal rate were significantly greater in high compared with low losers for computerized tomography-measured abdominal visceral fat (3.0 +/- 1.1 vs. 0.3 +/- 0.5 mg x kg(-1) x min(-1), P < 0.05) despite similar losses in total body fat. We conclude that 1) a long-term negative energy balance generated by exercise training significantly reduces plasma insulin levels, whereas insulin sensitivity tends to be improved; 2) training-induced changes in insulin sensitivity are associated with changes in abdominal visceral fat; and 3) data from this experiment conducted with a small number of twin pairs suggest that the genotype does not seem to be a major determinant of the changes in insulin levels and sensitivity brought about by negative energy balance with exercise.

Energy and macronutrient balances for humans in a whole body metabolic chamber without control of preceding diet and activity level

OBJECTIVE

To examine the relationships between 24 h energy and macronutrient balances in a whole body metabolic chamber subsequent to periods when subjects maintained their normal food intake and physical activity levels.

SUBJECTS

Thirteen males and 17 females were studied for two 24 h sessions while consuming an estimated isocaloric diet with a food quotient of 0.85.

MEASUREMENTS

Energy expenditure and macronutrient oxidation rates were measured twice for 24 h in whole body indirect calorimeter.

RESULTS

Positive and significant correlations were evident between energy and lipid balances (r = 0.38, P < 0.05 and r = 0.54, P < 0.01, respectively) and differences between the two sessions for energy and lipid balances were also significantly correlated (r = 0.40, P < 0.05). Accounting for carbohydrate or protein balances improved the strength of each of these associations.

CONCLUSION

These results indicate that for subjects in a small but significant positive energy balance, with uncontrolled diet and activity preceding their metabolic chamber sessions, that 24 h energy balance is positively correlated with lipid balance. Accounting for associations between lipid, carbohydrate, protein and energy balances, improved the strength of the association between 24 h lipid and energy balances. The implications of these results are that in these conditions modifications to lipid balance are important for weight maintenance.

RNA-labelled Ro and La ribonucleoprotein complexes reassembled in vitro; characterization by gel shift analysis

Ro and La RNP complexes were reassembled from in vitro labelled hY5 RNA and HeLa cell extracts. These complexes were then visualized through retardation of migration of labelled hY5 RNA in non-denaturing polyacrylamide gels. Three major complexes (named A, B, and C) were formed when crude cellular extracts (S100 fraction) were used. Using monospecific anti-60-kD Ro (Ro60) and anti-La antibodies to retard RNPs containing these antigens during migration in the gels, the three major complexes were shown to contain Ro60 (C), La (B), or both proteins (A). The specificity of RNA-protein interactions in the reassembled complexes was further demonstrated using two 3'-shortened hY5 RNA transcripts lacking the La-binding site (hY5-Alu I RNA) and both the Ro60 and La-binding sites (hY5-Hha I RNA). hY5-Hha I RNA still formed a single, minor complex when incubated with S100 extract, suggesting interaction with a yet undefined protein. In addition, we used the capacity of specific antibodies to retard the migration of the reassembled complexes to design a detection assay for anti-Ro and anti-La autoantibodies. Using 84 human sera, our assay was shown to approximate the specificity and sensitivity of an immunoprecipitation assay where 32P-labelled cell extracts are used as source of antigens. Our assay may be used to detect low levels of antibodies to conformational determinants on Ro60 and La proteins in human sera and antibody preparations.

Associations between 12 year changes in body fatness and lipoprotein-lipid levels in men and women of the Québec Family Study

OBJECTIVE

To investigate the associations between 12 year changes in body composition, subcutaneous fat distribution vs changes in plasma lipoprotein-lipid levels.

DESIGN

12 year prospective study.

SUBJECTS

A sample of 95 women and 93 men of the Québec Family Study initially tested in 1980.

MEASUREMENTS

Various body fatness variables as well as fasting plasma lipoprotein-lipid concentrations performed both in 1980 and 1992.

RESULTS

In both 1980 and 1992, a high body fat mass and an elevated accumulation of subcutaneous trunk fat were associated with a significant deterioration in the plasma lipoprotein-lipid profile. Furthermore, correlation analysis performed on differences noted during the 12 years follow-up revealed significant associations between changes in body fat mass and in plasma cholesterol [r = 0.52, P < 0.0005] in women. In both men and women, an increased body fat mass was associated with an increased CHOL/HDL-cholesterol ratio [r = 0.37, P < 0.01 (men) and r = 0.54, P < 0.0005 (women)]. Correlations between changes in fat mass and plasma lipids were generally of higher magnitude in women than in men. Changes in subcutaneous trunk fat were associated with changes in plasma HDL-chol levels (r = -0.22, P < 0.05) in men whereas in women, changes in trunk adiposity were related to changes in both plasma CHOL (r = 0.25, P < 0.05) and TG (r = 0.32, P < 0.005) levels.

CONCLUSION

These results support the notion that the increased adiposity observed among aging adult men and women is a significant component of the deterioration in the plasma lipoprotein-lipid profile noted over a 12 year follow-up period.

A single threshold value of waist girth identifies normal-weight and overweight subjects with excess visceral adipose tissue

Our objective was to determine threshold values of waist girth, waist-to-hip ratio (WHR), and sagittal diameter corresponding to an accumulation of visceral adipose tissue of 130 cm2 and to verify whether these threshold values could be influenced by sex, age, menopausal status, and the degree of obesity. From the regression equations computed in the total sample of 213 men [aged (mean+/- SD) 37.8 +/- 12.2 y] and 190 women (aged 37.3 +/- 12.1 y), a waist girth of approximately 95 cm in both sexes, WHR values of 0.94 in men and of 0.88 in women, and sagittal diameters of 22.8 cm in men and 25.2 cm in women corresponded to a visceral adipose tissue area of 130 cm2. In both sexes, threshold values of waist girth corresponding to critical amounts of visceral adipose tissue were generally lower in subjects who were > or = 40 y old (approximately 90 cm) than in younger individuals (approximately 100 cm). Similar differences were found for WHR and sagittal diameter threshold values. Finally, threshold values of waist girth corresponding to critical amounts of visceral adipose tissue were essentially similar in normal-weight and overweight men and women, whereas threshold values of WHR were in general higher in normal-weight than in overweight subjects. In conclusion, our results suggest that the relations of anthropometric variables to visceral adipose tissue accumulation are age-specific. However, waist girth is likely to be a more convenient anthropometric correlate of visceral adipose tissue than the WHR because threshold values of waist girth corresponding to critical amounts of visceral adipose tissue do not appear to be influenced by sex or by the degree of obesity.

Role of body fat loss in the exercise-induced improvement of the plasma lipid profile in non-insulin-dependent diabetes mellitus

The study was designed to examine the impact of exercise training on the plasma lipid profile in non-insulin-dependent diabetes mellitus (NIDDM) and, more particularly, to determine the relationship between changes in body fat mass and changes in the lipid profile. Eleven men with NIDDM exercised for 1 hour thrice per week on an ergocycle over a 6-month period at 60% maximal oxygen uptake (Vo2max). Diet and hypoglycemic agents were kept constant throughout this period. Vo2max, body composition, fasting plasma glucose and insulin levels, glycosylated hemoglobin, and the lipid profile were determined at baseline, in the middle (3 months), and at the end (6 months) of the training program. When the subjects were considered as a group, the only significant effect of training was on Vo2max, which increased from 32.2 +/- 1.2 mL/kg/min at baseline to 38.0 +/- 1.7 mL/kg/min at 6 months (P < .001). When the data were analyzed on an individual basis, significant associations were observed between changes in body fat mass and changes in the low-density lipoprotein (LDL) cholesterol/high-density lipoprotein (HDL) cholesterol ratio (r = .62,P = .04) or triglyceride (TG) levels (r = .64,P = .03). These data indicate that fat loss, not training per se, favorably alters the lipid profile of subjects with NIDDM who participate in an aerobic physical-conditioning program.

Autoantigenic epitopes on hY5 Ro RNA are distinct from regions bound by the 60-kDa Ro and La proteins

We recently reported the identification in human anti-Ro serum of Abs specifically immunoprecipitating deproteinized hY5 RNA. In the present report, we characterized the epitopes recognized by anti-hY5 RNA Abs. Using deletion and site-directed mutagenesis of hY5 cDNA and in vitro transcribed RNAs with intact and 3'-shortened ends, we have defined two conformational antigenic determinants distinct from the regions known to bind Ro and La proteins. One of these epitopes (epitope A) is present in the middle portion of hY5 RNA and is dependent on the presence of a four-nucleotide sequence (AACC at position 58-61) that may form a single-stranded loop. Deleting these four nucleotides or modifying the stem structures proximal or distal to this loop abolishes recognition of the mutated RNAs by Abs. The second epitope (epitope B) requires the presence of another four-nucleotide sequence (CUUG at position 74-77) in between the Ro and La binding sites. Deleting this CUUG sequence or modifying nucleotides on the 5' side of the stem structure below the Ro60 binding site severely compromises the interaction with Abs. Since Abs to deproteinized hY RNAs are restricted to anti-hY5 RNA and target determinants not involved in interactions with known hY5 RNA-binding proteins, human RohY5 particles may play a direct role in the immunization process, leading to the production of anti-hY5 RNA autoantibodies.

Seven-year changes in body fat and visceral adipose tissue in women. Association with indexes of plasma glucose-insulin homeostasis

OBJECTIVE

To study the associations between changes in body fatness, visceral adipose tissue (AT), and indexes of plasma glucose-insulin homeostasis over a 7-year follow-up period.

RESEARCH DESIGN AND METHODS

A sample of 30 nondiabetic women aged 35.2 +/- 5.6 (SD) years at baseline was studied.

RESULTS

Changes in visceral AT and in subcutaneous AT (measured by computed tomography) as well as changes in body fat mass (obtained by hydrostatic weighting) were significantly related to changes in fasting plasma insulin levels and in plasma insulin area measured after a 75-g oral glucose load (0.47 < or = r < or = 0.62; P < 0.01). Changes in visceral AT but not in body fat mass or in subcutaneous AT area were significantly associated with changes in plasma glucose area (r = 0.37; P < 0.05). When two subgroups of women with similar mean increases in body fat mass but with either small or large increases in visceral AT were compared, the subgroup with the largest gain in visceral AT showed the greatest deterioration in indexes of plasma glucose-insulin homeostasis. On the other hand, when two subgroups with similar mean increases in visceral AT but with different changes in body fat mass were compared, both subgroups showed similar changes in plasma glucose and insulin concentrations.

CONCLUSIONS

Results of this 7-year follow-up study in women suggest that changes in indexes of plasma glucose-insulin homeostasis are significantly associated with changes in visceral AT, even after control for changes in body fat mass.

Autoantigenic epitopes on hY5 Ro RNA are distinct from regions bound by the 60-kDa Ro and La proteins

We recently reported the identification in human anti-Ro serum of Abs specifically immunoprecipitating deproteinized hY5 RNA. In the present report, we characterized the epitopes recognized by anti-hY5 RNA Abs. Using deletion and site-directed mutagenesis of hY5 cDNA and in vitro transcribed RNAs with intact and 3'-shortened ends, we have defined two conformational antigenic determinants distinct from the regions known to bind Ro and La proteins. One of these epitopes (epitope A) is present in the middle portion of hY5 RNA and is dependent on the presence of a four-nucleotide sequence (AACC at position 58-61) that may form a single-stranded loop. Deleting these four nucleotides or modifying the stem structures proximal or distal to this loop abolishes recognition of the mutated RNAs by Abs. The second epitope (epitope B) requires the presence of another four-nucleotide sequence (CUUG at position 74-77) in between the Ro and La binding sites. Deleting this CUUG sequence or modifying nucleotides on the 5' side of the stem structure below the Ro60 binding site severely compromises the interaction with Abs. Since Abs to deproteinized hY RNAs are restricted to anti-hY5 RNA and target determinants not involved in interactions with known hY5 RNA-binding proteins, human RohY5 particles may play a direct role in the immunization process, leading to the production of anti-hY5 RNA autoantibodies.

A major gene for resting metabolic rate unassociated with body composition: results from the Québec Family Study

A major gene hypothesis for resting metabolic rate (RMR) was investigated using segregation analysis (POINTER) of data on families participating in Phase 2 of the Québec Family Study. Complete analyses were conducted on RMR adjusted for age, and also on RMR adjusted for age and other covariates, primarily fat mass (FM) and fat-free mass (FFM). Prior to adjustment for covariates, support for a major gene hypothesis was equivocal-i.e., there was evidence for either a major gene or a multifactorial component (i.e., polygenic and/or familial environment). The multifactorial model was preferred over the major gene model, although the latter did segregate according to Mendelian expectations. However, after the effects of FM and FFM were accounted for, a major gene effect was unambiguous and compelling. The putative locus accounted for 57% of the variance, affected 7% of the sample, and led to high values of RMR. The lack of a significant multifactorial effect suggested that the familial etiology of RMR adjusted for FM and FFM was likely to be entirely a function of the major locus. Comparing the RMR results from pre- and post-adjustment for FM and FFM suggests a plausible hypothesis. We know from earlier studies in this sample that there is a putative major gene for FM and a major non-Mendelian effect for FFM. The current study leads us to speculate that: (1) the gene(s) affecting body size and body composition also may have an effect on RMR, and further (2) removal of the effect of the major gene(s) for body size and composition allowed for detection of an additional major gene affecting only the RMR. Thus, RMR appears to be an oligogenic trait.

Overfeeding in identical twins: 5-year postoverfeeding results

From a total of 12 pairs of young male identical twins who were overfed by an estimated 84,000 kcal over a period of 100 days, several pairs (eight to 11, depending on variables) were remeasured for body weight, body composition with the underwater weighing technique, regional fat distribution from skinfolds, girths, computed tomography (CT) fat areas in the abdominal region, and fasting plasma glucose, insulin, total cholesterol, high-density lipoprotein (HDL) cholesterol, and triglycerides 4 months and 5 years after completion of the overfeeding protocol. At 4 months, the twins had lost approximately 7 of 8 kg that they had gained with overfeeding. However, 5 years later, body weight had increased by 5 kg over the preoverfeeding level. Fluctuations in fat mass were greater than those in fat-free mass. The younger twins gained approximately twice as much as the older twins in the late recovery period, a difference attributed to the late phase of growth in body mass in the former. Upper-body fat was reduced at 4 months of follow-up study, but was increased in the late recovery phase. All blood values were normalized in the postoverfeeding periods. A within-pair resemblance was generally observed for the changes noted in the recovery periods, but it was more striking when variations between preoverfeeding and 4-month or 5-year values were considered. We conclude from these observations that there were no persistent effects of exposure to the overfeeding protocol over the expected age-associated increases in body mass, body fat, upper-body fat, abdominal visceral fat (AVF), and metabolic variables predictive of risk for common diseases in individuals of normal body weight and with no family history of obesity. The intrapair resemblance suggests that the genotype contributes to the alterations observed in the recovery from overfeeding and in the age-associated changes.

Plasma high-density lipoprotein cholesterol but not apolipoprotein A-I is a good correlate of the visceral obesity-insulin resistance dyslipidemic syndrome

Apolipoprotein (apo) A-I is a major component of high-density lipoproteins (HDLs), and it has been suggested that measurement of apo A-I may provide additional information in the assessment of coronary heart disease (CHD) risk. In the present study in a sample of 111 men (age [mean +/- SD], 35.3 +/- 6.6 years), we determined whether a low apo A-I concentration is associated with the cluster of metabolic abnormalities that characterize the visceral obesity-insulin resistance dyslipidemic syndrome. For this purpose, the first and fourth quartiles of apo A-I and HDL cholesterol (HDL-C) concentrations were compared in relation to body fat distribution, glucose tolerance, and plasma insulin and lipoprotein levels. Men in the first quartile (< the 25th percentile) of HDL-C, as compared with men in the fourth quartile (> the 75th percentile), were characterized by an elevated visceral adipose tissue (AT) accumulation (P < .05), as well as by increased plasma levels of triglycerides ([TGs] P < .0001), apo B (P < .0005), and insulin (P < .01). These differences were not found when the first and fourth quartiles of plasma apo A-I concentrations were compared. These results suggest that plasma levels of HDL-C are more closely associated with the various features of the visceral obesity-insulin resistance syndrome than plasma apo A-I.

Anthropometric correlates to changes in visceral adipose tissue over 7 years in women

OBJECTIVE

To investigate the association between either increases or decreases in visceral adipose tissue and changes in anthropometric indices in a group of 32 women studied over a 7-y period.

SUBJECTS

32 women aged 35.1 +/- 5.4 (SD) years at baseline.

MEASUREMENTS

Waist and hip circumferences, body fat mass (hydrostatic weighing) and viscera adipose tissue (computed tomography) were measured at baseline and at follow-up.

RESULTS

Waist girth, waist-to-hip ratio, sagittal diameter and visceral adipose tissue area were all significantly higher at follow-up than at baseline (p < 0.05). Changes in visceral adipose tissue area were strongly correlated to changes in waist girth, hip girth, sagittal diameter and body fat mass (0.80 < or = r < or = 0.91 p < 0.0001). However, the association between changes in waist-to-hip ratio and those in visceral adipose tissue area was of low magnitude (r = 0.35; p = 0.05). Partial correlation analyses showed that the association between changes in visceral adipose tissue area and changes in either waist girth (p < 0.01) or sagittal diameter (p < 0.0001) remained significant even after control for 7-y variation in total body fatness.

CONCLUSION

Results of the present study suggest that changes in visceral adipose tissue accumulation that occur with age in women are better predicted by changes in waist girth or sagittal diameter than by changes in waist-to-hip ratio.

Insulin and glucagon responses to adrenaline infusion in abdominal obese men

OBJECTIVE

To investigate the hormonal, cardiovascular and metabolic responses of visceral vs subcutaneous obese men to infused adrenaline.

DESIGN

Intervention study of an hour adrenaline infusion (0.01 micrograms/kg fat-free mass/min).

SUBJECTS

Eighteen moderately obese men (age: 30-40 y, BMI: 28-34 kg/m2) divided according to their degree (low vs high) of visceral adipose tissue (AT) accumulation.

MEASUREMENTS

Various fatness and fat distribution variables (computed tomography and anthropometry), heart rate and blood pressure, plasma concentrations of gluco-regulatory hormones, glucose, glycerol and free fatty acids (FFA).

RESULTS

Similar increases were noted in heart rate, plasma adrenaline, FFA and glycerol levels in both low and high visceral AT groups after hormonal infusion. There was a tendency for plasma glucagon responses to be higher in men with high amounts of visceral fat (p = 0.07). Plasma glucose levels increased in both groups, but significantly more in men with low levels of visceral AT (p < 0.05), whereas plasma insulin concentrations increased significantly only in men with high amounts of visceral AT in response to adrenaline infusion (p < 0.01). In the overall sample of obese men, visceral AT accumulation (but not the fat mass) was positively correlated with plasma insulin (r = 0.70) and glucagon responses (r = 0.63) to the hormone infusion (p < 0.01). These metabolic responses were not related to the achieved catecholamine concentration.

CONCLUSION

These results suggest that some of the impairments in plasma glucose-insulin homeostasis noted in visceral obesity may be related to an abnormal metabolic response to an adrenaline challenge.

A case study on energy balance during an expedition through Greenland

A 59-year-old man who had always been lean was submitted to overfeeding for two months in preparation for a 3-week expedition through Greenland, during which a considerable negative energy balance was expected. The overfeeding protocol consisted of an estimated energy surplus of 2000 kJ per day and this induced body weight and fat gains of 4.7 and 3.6 kg, respectively. Whole-body indirect calorimetry measurements following 4 and 8 weeks of overfeeding showed that there was no change in the subject's daily energy expenditure. Ad libitum energy intake measured during a buffet-type meal was substantially increased during overfeeding. As expected, the expedition induced a negative energy balance which reduced body weight below the pre-overfeeding level. Daily energy expenditure measured 12 days after the expedition, when the subject had recovered his initial body weight, was decreased by 1.4 MJ/day. The increase in ad libitum energy intake observed during the pre-expedition overfeeding persisted after the expedition. These adaptations tended to persist three weeks and four months after the end of the expedition. These results suggest that both energy expenditure and intake were modified after the expedition to prevent a subsequent body energy deficit.

The hyperphagic effect of a high-fat diet and alcohol intake persists after control for energy density

This study was performed to investigate the effect of a high-fat diet and alcohol (high-fat, alcohol) intake on subsequent spontaneous energy intake when controlling for food energy density. Twelve adults males participated in two 1-d randomly assigned sessions that only differed by the macronutrient composition of the appetizer served at lunchtime. Dietary energy was mainly provided by lipid and alcohol in one appetizer whereas carbohydrate was the main source of energy in the other appetizer. The energy density, content, and weight of the foods were comparable in the two appetizers. Ad libitum energy intake measured at lunchtime after ingestion of the high-fat, alcohol appetizer exceeded that observed after the high-carbohydrate appetizer by >812kJ (P<0.01). This overfeeding had no detectable effect on postprandial hunger and was not compensated by changes in energy intake at dinnertime. In conclusion, this study demonstrates that a high-fat diet and alcohol favor subsequent overfeeding, which is not due to their higher energy density.

Effects of exercise training on abdominal obesity and related metabolic complications

Excessive deposition of visceral adipose tissue is known to predispose to cardiovascular diseases. Considerable epidemiological and experimental evidence suggests that many physiological factors are involved in the aetiology of premature atherosclerosis associated with visceral obesity. Insulin resistance is frequently associated with abdominal obesity, and probably plays an important role in the pathophysiology of hypertriglyceridaemia, low levels of plasma high-density lipoprotein (HDL)-cholesterol, hypertension and reduced fibrinolytic activity. Exercise training may counteract the aberrant metabolic profile associated with abdominal obesity both directly and as a consequence of body fat loss. Exercise may increase insulin sensitivity, favourably alter the plasma lipoprotein profile and improve fibrinolytic activity. Changes in the activity of insulin-sensitive glucose transporters and of skeletal muscle lipoprotein lipase are some of the possible explanations for the increased insulin sensitivity and improved blood lipid profile associated with regular exercise. This review presents physical training as a relevant nonpharmacological tool in the treatment of abdominal obesity and associated metabolic disorders. The impact of regular exercise on the different aspects of the insulin resistance syndrome is discussed. The roles of gender, age and the state of insulin resistance on the metabolic effect of physical training are also considered.

Genetic pleiotropy for resting metabolic rate with fat-free mass and fat mass: the Québec Family Study

Shared genetic and familial environmental causes for the associations among resting metabolic rate (RMR), fat-free mass (FFM), and fat mass (FM) were investigated in families participating in phase 2 of the Québec Family Study. A multivariate familial correlation model assessing the pattern of significant cross-trait correlations between family members (e.g., RMR in parents with FFM in offspring) was used to infer the etiology of the associations. For each of FM and FFM with RMR, significant sibling, parent-offspring, and intraindividual cross-trait correlations suggests the associations are familial. Furthermore, the lack of significant spouse cross-trait correlations suggests that the familial aggregation is primarily genetic. Bivariate heritability estimates suggest that as much as 45% to 50% of the shared variance between FFM and RMR may be genetic, and as much as 28% to 34% for FM and RMR. This study supports the notion that the gene(s) affecting each of FFM and FM also influence the RMR. Moreover, the lack of any familial associations between FFM and FM suggests that the effects of each body size component on RMR are independent, i.e., more than one genetic source on the RMR-body size association. The possibility that RMR is an oligogenic trait (i.e., more than one underlying genetic etiology) should be further investigated using more complex multivariate segregation methods until specific genes can be tested.

Reproducibility of 24-h energy expenditure and macronutrient oxidation rates in an indirect calorimeter

The maintenance of weight and adipose tissue mass in humans appears to be related to a balance between the rates of oxidation and consumption of macronutrients; yet, little evidence is available on the reproducibility of 24-h macronutrient oxidation rates and how this relates to diet in the days preceding a chamber session. This study examined the reproducibility of 24-h macronutrient oxidation rates, 24-h energy expenditure (EE), and respiratory quotient (RQ) in 30 adults who ate their habitual diets before two 24-h whole body indirect calorimeter sessions. Results showed that the within-subject coefficients of variation (CVws) for 24-h EE and RQ were 2.8 and 2.6%, respectively. CVws for macronutrient oxidations ranged from approximately 15 to 25%. Means comparisons of 24-h EE, RQ, and macronutrient oxidation rates between sessions showed no significant differences, and all variables had significant positive intraclass correlation coefficients (P < 0.05). In conclusion, macronutrient oxidations all showed significant reproducibility for the group and a significant but lower reproducibility for individuals when habitual diet and activity preceded the experimental sessions.

Differences in fat balance underlying obesity

Energy balance occurs under free-living conditions when macronutrient balance is achieved (i.e., the intake of each macronutrient corresponds to its use). Among the components of macronutrient balance, fat balance is the one which is at greater risk of large deviations because of a reduced potential of fat to decrease food intake acutely and to promote its oxidation. This may represent a problem for individuals predisposed to obesity who are characterized by an increased taste preference for fat and a reduced capacity to oxidize fat when their body weight is normal. When these individuals are exposed to a lifestyle favouring a positive fat balance, a greater demand is imposed on sympathetic nervous system activity which is stimulated by hyperinsulinaemia. Accordingly, muscle sympathetic nerve activity (MSNA) is greater in obese hyperinsulinaemic individuals in the basal state, whereas they display a blunted response in MSNA to the acute administration of insulin. In this context, where the ability to further stimulate sympathetic activity is low, fat gain and its related increased lipid mobilization and oxidation remain the ultimate means to restore fat balance.

Body fatness in active individuals reporting low lipid and alcohol intake

OBJECTIVES

To evaluate body fatness in subjects complying with common public health guidelines for lipid and alcohol intake as well as physical activity participation.

SUBJECTS

A sample of 358 male subjects who participated in phase 1 of the Quebec Family Study.

DESIGN

The association between adiposity, lipid and alcohol intake and physical activity participation was analyzed in the overall sample. A comparison of body fatness in individuals adhering or not to public health recommendations was also performed.

RESULTS

Significant positive correlations were observed between the percentage of dietary energy as lipid and adiposity indicators. Accordingly, subjects classified as low-fat consumers displayed significantly lower levels of fat mass and subcutaneous adiposity compared to high-fat consumers. When subjects reporting low lipid and alcohol intake and regular participation in vigorous physical activities were compared to those exhibiting opposite behaviors, the between-group difference in subcutaneous adiposity was doubled and this was essentially explained by an increase in the difference for truncal subcutaneous adiposity.

CONCLUSION

These results indicate that the adherence to a lifestyle characterized by high-fat and alcohol intake as well as sedentariness promotes fat gain, particularly in the trunk area.

Social class interacts with the association between macronutrient intake and subcutaneous fat

BACKGROUND

A large amount of evidence shows that adiposity is associated both with macronutrient composition of the habitual diet and socio-economic variables. Since dietary habits may covariate with social status, these two groups of factors may act as mutual confounders when studying their independent impact on adiposity.

OBJECTIVE

To investigate the independent relationship between educational level and dietary habits with adiposity. To study interactive effects of educational level on the association between macronutrient intake and adiposity.

DESIGN

This cross-sectional study was based on dietary records, interviews and anthropometry of 358 men and 368 women of the Québec Family Study.

STATISTICS

Partial correlation analyses were applied to clarify independent correlations of body fatness with educational level, dietary habits and other behavioural factors. ANCOVA was used to detect interactive effects of educational level on macronutrient versus adiposity relationships.

RESULTS

Inverse associations between educational level and BMI, percent body fat, truncal skinfolds were found in women but not in men. Both protein and lipid intake correlated or tended to correlate positively with some of the adiposity measures in women. Protein intake correlated positively with truncal skinfolds in men of lower but not higher educational level.

CONCLUSIONS

The results emphasize the importance of including demographic variables like social status in surveys dealing with the relationships between adiposity and dietary habits.

Do elevated levels of abdominal visceral adipose tissue contribute to age-related differences in plasma lipoprotein concentrations in men?

Age-related differences in body fat and more specifically in the accumulation of abdominal visceral adipose tissue were examined as a potential covariate for the alteration in the plasma lipoprotein profile found with aging. For that purpose, results from 79 young adults (aged 24.5 +/- 4.0 years) were compared to 61 middle-aged men (54.7 +/- 6.4 years). Younger men had significantly lower body fat mass and abdominal visceral adipose tissue area measured by computed tomography than middle-aged men (P < 0.0001). Plasma cholesterol, triglyceride, apolipoprotein (apo) B, low density lipoprotein (LDL)-cholesterol and LDL apo B levels, as well as the ratio of plasma cholesterol to high density lipoprotein (HDL)-cholesterol were all significantly lower in younger men as compared to middle-aged men (P < 0.0001). The comparison of younger men to middle-aged men with comparable levels of abdominal visceral fat and total body fat eliminated the age-related differences in plasma triglyceride and in the ratio of plasma cholesterol to HDL-cholesterol, whereas the difference in plasma apolipoprotein B levels, although still significant, was largely reduced. Age-related differences in plasma cholesterol and in LDL-cholesterol levels were still observed after this matching procedure and the differences between age-groups were essentially of similar magnitude than before pairing. In summary, these results suggest that the deterioration of plasma lipoprotein profile observed in middle-aged men as compared to young adult men is partly mediated by concomitant increases in total body fat and abdominal visceral adipose tissue. However, other factors related to the aging process appear to be involved, particularly for the age-related increase in plasma LDL-cholesterol.

Exercise, macronutrient preferences and food intake

The impact of physical training on body weight and fat depends on the ability of exercise to promote a negative fat balance. This effect is more likely to occur in individuals who are good responders in fat oxidation to exercise and who adhere to a dietary regimen containing a low to moderate amount of fat. Experimental evidence suggests that exercise per se may also increase the preference for carbohydrates, i.e. reduce the relative fat content of the diet, and this might be related to the composition of the substrate mix oxidized during exercise. The body fat loss resulting from a long-term negative fat balance is associated with a progressive decrease in fat oxidation which is likely involved in the occurrence of resistance to lose fat in reduced obese individuals. This suggests that fat loss related factors represent signals for neurosystems controlling feeding behavior. Further research pertaining to exercise and the control of food intake should focus on the mechanisms by which exercise may influence neurosystems which are known to affect food intake.

Alcohol and a high-fat diet: a combination favoring overfeeding

The effects of alcohol and dietary fat on spontaneous energy and macronutrient intakes were investigated in eight male subjects who participated in a protocol including four randomly assigned 2-d sessions during which they ate ad libitum. In each session they had free access to either high- or low-fat foods, with alcohol or a placebo. The high-fat diet was associated with a substantial increase in daily energy intake. Alcohol had no inhibitory effect on food intake and its energy content was thus associated with an additional increase in energy intake. The enhancing effects of alcohol and dietary fat on daily energy intake were additive so that overfeeding was maximal (2.8 MJ/d) under the high-fat diet+alcohol condition. To further examine the effects of alcohol on energy and macronutrient intakes, reported food intake was studied in 351 men and 360 women who had been tested in the Québec Family Study. The results showed that a high alcohol intake was associated with a high daily energy intake and had no inhibitory effect on lipid intake. In conclusion, a dietary regimen providing a high fraction of energy as alcohol and fat increases the risk for positive energy balance under free-living conditions.

Regional differences in adipose tissue lipolysis from lean and obese women: existence of postreceptor alterations

Lipolysis studies were performed on isolated adipose cells obtained from two subcutaneous regions (abdominal and femoral) in 26 premenopausal women (16 obese and 10 lean subjects). Because obese adipocytes from both sites were significantly larger than lean fat cells, glycerol release measured by an ultrasensitive bioluminescent method was corrected for variation in cell surface area. Epinephrine induced antilipolysis at low concentrations and a net lipolytic response at higher doses, regardless of the subjects' fatness and the anatomic location of fat. However, the catecholamine and the selective alpha 2-adrenergic agonist, UK-14304, promoted a greater maximal antilipolytic response in both femoral and subcutaneous abdominal adipose cells from obese individuals that from lean individuals. Epinephrine- and UK-14304-induced maximal antilipolysis of femoral adipocytes was also positively associated with indicators of total adiposity. On the other hand, the maximal lipolytic responses to postadrenoceptor agents such as dibutyryl adenosine 3',5'-cyclic monophosphate, forskolin, and theophylline were lower in both adipose regions in obese than in lean women. Femoral fat cell lipolysis in the presence of these agents was negatively correlated with body fatness indexes. These results suggest that, in women covering a wide range of adiposity, variations in the lipolytic response of femoral fat cells to epinephrine may involve changes in the functional balance between alpha 2- and beta-adrenoceptors and also alterations located at different postreceptor levels.

Sleep and psychological characteristics of children on a psychiatric inpatient unit

OBJECTIVE

To assess the association of objective measures of sleep-wake patterns and psychological status and abuse history of children hospitalized in a psychiatric inpatient unit.

METHOD

Thirty-nine inpatient children participated in the study. They were monitored for one to three consecutive nights with miniature wrist activity monitors for objective assessment of sleep-wake patterns. In addition, a thorough psychiatric and psychosocial assessment was completed with each child and the parents.

RESULTS

Children's self-ratings of depression, hopelessness, and low self-esteem were significantly correlated with objective sleep measures indicating poorer sleep quality. No significant correlations between intelligence scores and sleep measures were found. Nonabused and sexually abused children had better sleep quality than physically abused children.

CONCLUSIONS

Sleep quality during hospitalization is strongly associated with self experiences of depression, hopelessness, and low self-esteem in children with severe behavior disorders.

Exercise and energy intake: effect of substrate oxidation

The main objective of this study was to evaluate the short-term effect of exercise-induced alteration in fat oxidation on postexercise spontaneous energy and macronutrient intakes. Eleven young males were submitted to two randomly assigned sessions of 48 h each, during which they were requested to eat in the laboratory. One of these sessions was preceded by a 90-min exercise bout at an intensity of 60% VO2max. During both sessions, subjects ate ad lib food with a fat content conforming to the recommendations of nutrition agencies with a food quotient (FQ) > or = 0.85. Results showed that there was no significant change in postexercise energy and macronutrient intakes in comparison with the sedentary session. However, when subjects were subdivided into two groups on the basis of the respiratory quotient (RQ) measured during exercise, men with a low RQ (high fat oxidation) were characterized by a reduced postexercise increase in energy intake relative to the energy cost of exercise (ECE), i.e., they were more predisposed to be in negative postexercise energy balance compared to those exhibiting a high RQ. Accordingly, exercise RQ was positively associated with postexercise energy and lipid balance. These results show that postexercise energy balance partly depends on the composition of the substrate mix oxidized during exercise.

Nutritional determinants of the insulin resistance syndrome

Recent data show that fat balance is the only component of macronutrient balance which is not precisely regulated. The adherence to a lifestyle characterized by high fat food habits and sedentariness thus favor a positive fat balance which may persist for a long period of time. The resulting body fat gain contributes to the restoration of fat and energy balance because of the enhancing effect of fat gain on fat oxidation. Individuals predisposed to obesity seem to be particularly vulnerable to a positive lipid balance because they are characterized by a reduced fat oxidation when their body weight is normal and by a reduced capacity to increase fat oxidation when exposed to a high fat diet. Body fat gain, particularly in the deep abdominal area, is also associated with an increase in insulinemia which is known to acutely inhibit fat mobilization and oxidation. Beyond these peripheral metabolic effects, hyperinsulinemia with euglycemia can influence neuronal regulation of energy balance which ultimately results in an increase in sympathetic nervous system activity. An increased sympathetic tonus exerts an enhancing effect on fat oxidation and energy expenditure and a reducing effect on food intake. As discussed in this report, hyperinsulinemia thus appears to be an adaptation which is part of a regulatory system aimed at restoring fat and energy balance under conditions favoring body fat accumulation.

Hyperinsulinemia and regulation of energy balance

Recent data suggest that hyperinsulinemia with euglycemia may favor the restoration of energy balance when one gains body weight. To test the validity of this concept in humans, the data of 24 young men who had been exposed to a 353-MJ overfeeding protocol for 100 d and who were remeasured after a 4-mo follow-up were analyzed. The sample was subdivided in two groups on the basis of the overfeeding-induced change in postprandial plasma insulin. The increase in postprandial energy expenditure induced by overfeeding was significantly greater in high than in low postprandial insulin responders (P < 0.05) but not after body fat gain was controlled for. After the overfeeding protocol, the loss of subcutaneous adiposity was greater in high than in low postprandial insulin responders. However, this difference was no more significant after the gain in fat mass was controlled for. There was no difference between the two groups in post-overfeeding loss of body weight, fat mass, or fat-free mass. These results partly agree with the idea that hyperinsulinemia resulting from a long-term positive energy balance and its associated fat gain exert a regulatory role promoting the restoration of energy balance.

Exercise-training, macronutrient balance and body weight control

It is well established that exercise-training can induce body weight and fat losses provided that mean daily energy expenditure exceeds mean energy intake. Recent experimental data show that under free living conditions, the composition of macronutrient intake tends to differ from the composition of macronutrient utilization when the body is in energy imbalance, even over a short period of time. Since protein and carbohydrate balances are precisely regulated under unrestricted food intake conditions, a body energy deficit is necessarily equivalent to a lipid deficit. In the context of an aerobic training program, a body lipid deficit should be spontaneously reached by performing prolonged vigorous exercise on a regular basis and by preventing a diet with a high fat content. However, as body fat decreases with exercise there is an associated decrease in the lipid content of the fuel mix oxidized and this acts to progressively decrease the lipid deficit. Ultimately, a new lipid balance will be reached at a reduced level of body fatness when the proportion of lipid in the substrate mix will become similar to the proportion of lipid in the diet. Recent research observations show that such a program has the potential to induce a substantial fat loss, particularly in the abdominal area, and a significant improvement of the metabolic profile of obese individuals. These beneficial effects cannot be maintained on a long-term basis if the new exercise and food habits are not incorporated in the lifestyle of these individuals.

Plasma glucose, insulin, and glucagon before and after long-term overfeeding in identical twins

Plasma glucose, insulin, and glucagon levels were measured before and after long-term overfeeding (4.2 MJ/d during a 100-day period) in 24 lean adults (12 pairs of monozygotic twins). Fasting plasma glucose, insulin, and glucagon were significantly increased by overfeeding. During a 75-g oral glucose tolerance test (OGTT), no major alteration in glucose tolerance was observed and insulin area under the curve was increased. During a meal test, insulin and glucagon areas under the curve were increased. The pre-overfeeding values for glucose, insulin, and glucagon (fasting and areas) were not correlated with the gains in body weight and in fat mass. However, fasting glucagon before overfeeding was positively correlated with the gains in abdominal visceral fat and in femoral fat. The changes with overfeeding in insulin area during the OGTT were positively correlated with the changes in total subcutaneous fat, even after adjustment for total body fat gain. Significant twin intrapair similarity was observed for fasting plasma glucagon before overfeeding and for the changes in fasting insulin and glucagon with overfeeding. These results indicate that (1) in response to long-term overfeeding, both fasting insulin and glucagon are increased; (2) initial levels of glucose, insulin, and glucagon do not predict the gains in body weight and total body fat during overfeeding, but are related to changes in indicators of fat topography; (3) the changes in total subcutaneous fat represent an important correlate of insulin changes with overfeeding; and (4) the genotype could be an important determinant of insulin and glucagon responses to a prolonged positive-energy-balance period.

Transgenic glutathione peroxidase mouse models for neuroprotection studies

Seleno-glutathione peroxidase (GSHPx) is considered to be the major enzymatic activity in charge of removing excess cytosolic and mitochondrial H2O2 in most tissues including brain. Intracellular GSHPx activity is therefore hypothesized to be one important factor that contributes to minimize hydroxyl radical formation via Fenton-type reactions. An animal model was developed to challenge this hypothesis in vivo and evaluate the role of GSHPx in hydroperoxide metabolism and oxidative stress homeostasis. Three lines of transgenic mice, homozygous for the integration of 1 to 3 GSHPx transgene copies, have been generated. The transgene was placed under transcriptional control of a metallothionein promoter (hMT-IIA). This promoter was chosen because metallothionein expression, normally low in most tissues, can be induced by several inflammatory cytokines, protein kinase C activators, and stress agents including heavy metals. The data reported here provide information on the constitutive expression of GSHPx mRNA and enzyme in various brain regions of healthy untreated adult tg-MT-GPx mice. Northern and/or Western analysis indicated that transgenic GSHPx was expressed constitutively in all brain regions investigated in tg-MT-GPx-6 mice, including the cerebral cortex, brainstem, hippothalamus, cerebellum, substantia nigra, and striatum. Similar results were obtained with the two other transgenic lines, tg-MT-GPx-11 and -13. Depending on the brain region, the GSHPx immunoreactivity detected in tissue extracts with an immunoaffinity-purified polyclonal antibody was about 2- to 5-fold stronger in transgenic extracts than in their non-tg counterparts (western blots). In contrast, the corresponding increase in GSHPx activity measured in these extracts was smaller, for example, about 1.5-fold in transgenic mesencephalon. Immunocytochemical data indicated that GSHPx-like staining was distinctly more intense in transgenic midbrain brain sections than in corresponding non-tg sections. Interestingly, only a subset of the cells displayed higher density staining that most likely reflects increased amounts of GSHPx protein. This observation suggests that the stained cells, not yet identified, may have larger GSHPx activity increments than the cell-average increments measured in tissue extracts. Current work is in progress to determine whether transgenic GSHPx expression may be induced by inflammatory processes or perturbations of heavy metal metabolism.