Exercise and Obesity

This paper reviews succinctly the evidence for a role of regular exercise in the prevention and the treatment of obesity and of its metabolic complications. Seventeen propositions relevant to an understanding of the topic are considered. The evidence suggests that regular exercise can be an important factor in the development of sustained negative energy balance conditions provided the volume of activity is high. This implies a program of low to moderate intensity exercise performed on an almost daily basis for at least one hour per session. To induce significant weight and fat losses and to treat overweight and obese patients, compliance to the program for several years becomes a necessity. Exercise increases lipid substrate oxidation and may favor carbohydrate intake for the same amount of energy intake. The acute effects of exercise on resting metabolic rate are well documented, but the long-term influences of exercise training seem to be small and are rapidly suppressed with the cessation of training. The obese benefits also from a regular exercise regimen in terms of improved insulin sensitivity, lipid and lipoprotein profile, and blood pressure, as well as reduced risk of death. Regular exercise, such as walking, is a healthy course of action for the overweight or the obese patients.

Segregation Analysis of Body Mass Index in an Unselected French-Canadian Sample: The Québec Family Study

Interest in a single gene etiology for obesity, as assessed by the body mass index (BMI), has been spurred recently by reports of a putative recessive major gene for extreme values, which accounts for as much as 40% of the variance. The major gene hypothesis was evaluated here in the Québec Family Study, a random sample of 375 French-Canadian volunteer families. This report represents one component in a more complete investigation of obesity in these families. In contrast to the recent studies, a major gene hypothesis for BMI was not verified here. Although there was a major effect, it did not conform to a Mendelian pattern of transmission. A multifactorial component (i.e., polygenic and/or common environmental factors) accounted for 42% of the phenotypic variance. In addition, evidence of heterogeneity between the generations was found. The heterogeneity was traced to the major non-Mendelian component (which accounted for 0.01% of the variance in parents and over 40% in offspring) rather than to the multifactorial one. These results would suggest that a simple recessive gene mixed model may not be sufficient to explain the familial distribution of the BMI. Several factors which may have contributed to these results include temporal trends and surrogate effects such as those related to variation in body composition and energy balance components.

Abdominal obesity and mortality: The Pennington Center Longitudinal Study

The purpose of this study was to determine the association between visceral adipose tissue (VAT) and all-cause mortality. The sample included 1089 white men and women 18–84 years of age from the Pennington Center Longitudinal Study, a prospective cohort of participants assessed between 1995 and 2008, and followed for mortality until 31 December 2009. Abdominal VAT was measured at the L4–L5 vertebral level using computed tomography. There were 27 deaths during an average of 9.1 years of follow-up. Abdominal VAT was significantly associated with mortality after adjustment for age, sex and year of examination (hazards ratio (HR) 1.46; 95% confidence interval 1.05–2.05). The association was stronger after the inclusion of abdominal subcutaneous adipose tissue (SAT), smoking status, alcohol consumption and leisure-time physical activity as additional covariates (HR 1.74; 1.17–2.59). Limiting the sample to participants who were free of stroke, heart disease and cancer at baseline reduced the strength of the relationship slightly (HR 1.62; 1.07–2.47). Abdominal SAT was not associated with mortality, either alone or in combination with VAT and other covariates. The results support the assertion that abdominal VAT is an important therapeutic target for obesity reduction efforts.

Net environmental benefit: introducing a new LCA approach on wastewater treatment systems

Life cycle assessment (LCA) allows evaluating the potential environmental impacts of a product or a service in relation to its function and over its life cycle. In past LCAs applied to wastewater treatment plants (WWTPs), the system function definition has received little attention despite its great importance. This has led to some limitations in LCA results interpretation. A new methodology to perform LCA on WWTPs is proposed to avoid those limitations. It is based on net environmental benefit (NEB) evaluation and requires assessing the potential impact of releasing wastewater without and with treatment besides assessing the impact of the WWTP's life cycle. The NEB allows showing the environmental trade-offs between avoided impact due to wastewater treatment and induced impact by the WWTP's life cycle. NEB is compared with a standard LCA through the case study of a small municipal WWTP consisting of facultative aerated lagoons. The NEB and standard LCA show similar results for impact categories solely related to the WWTP's life cycle but differ in categories where wastewater treatment environmental benefit is accounted for as NEB considers influent wastewater quality whereas standard LCA does not.

Osteomark: a surgical navigation system for oral and maxillofacial surgery

The purpose of this project was to test a surgical navigation tool designed to help execute a surgical treatment plan. It consists of an electromagnetically tracked pencil that is used to mark bone intraoperatively. The device was tested on a precision block, an ex vivo pig mandible and during performance of six endoscopic vertical ramus osteotomies on pig cadavers. The difference between actual pencil position and that displayed by the computer was measured three times each at ten 2mm holes on the block (n=30 observations) and on the ex vivo mandible (n=11 measurements). Errors between planned and actual osteotomy locations for the cadaver procedures were measured. The mean distance between known and displayed locations was 1.55 ± 0.72 mm on the precision block and 2.10 ± 0.88 mm on the pig mandible. The error measured marking the same point on the block multiple (n=5) times was 0.58 ± 0.37 mm. The mean error on the simulated osteotomies was 2.35 ± 1.35 mm. Osteomark was simple to use and permitted localisation of holes and osteotomies with acceptable accuracy. In the future, the device and algorithms will be revised to further decrease error and the system will be tested on live animals.

Associations between Ixodes scapularis ticks and small mammal hosts in a newly endemic zone in southeastern Canada: implications for Borrelia burgdorferi transmission

Immature Ixodes scapularis infestation and Borrelia burgdorferi infection of wild small mammals were studied from June to October in 2007 and from May to October in 2008 at 71 study sites in a zone where I. scapularis populations and environmental Lyme disease risk are emerging in southwestern Quebec. Seasonal host-seeking activity of immature I. scapularis was similar to patterns reported previously in Canada and the USA: nymphal activity peaked in spring while larval activity peaked in late summer. Synchronous activity of nymphs with some larvae was observed in late spring, which could favour establishment of B. burgdorferi strains that cause short-lived infections in their hosts. White-footed mice (Peromyscus leucopus), deer mice (P. maniculatus), chipmunks (Tamias striatus), and red squirrels (Tamiasciurus hudsonicus) carried 92.0% of the larvae and 94.2% of the nymphs collected. Adult male white-footed mice carried significantly larger numbers of both larval and nymphal I. scapularis than other species and classes of small mammals (different demographic groups or physiological status: age, sex, sexual activity). We conclude that seasonality and host association were comparable to previous studies in North America, even in the context of a newly endemic pattern of low infection prevalence and low densities of host-seeking and feeding I. scapularis in southwestern Quebec. Our studies suggest that B. burgdorferi transmission cycles are focused on adult male mice (which carried 35% of all feeding ticks collected in the study), so control methods targeting this class of hosts may be particularly effective. However, our study also suggested that habitats containing a diverse host structure may dilute transmission cycles by partitioning of nymphal and larval ticks on different host species.

Short sleep duration preferentially increases abdominal adiposity in adults: preliminary evidence

What is already known about this subject •  The evidence that short sleep duration is another determinant of obesity is accumulating. •  Lack of sleep has been reported to constitute a metabolic stressor, with increased cortisol concentrations as the end product. What this study adds •  This is the first study to show that short sleep duration is associated with a preferential increase in abdominal adiposity in adults.

SUMMARY

The aim of this 6-year longitudinal study was to verify whether short sleep duration preferentially increases abdominal adiposity in adults. A total of 276 adults, aged 18-64 years, from the Quebec Family Study were available for this study. Anthropometric measurements (body mass index and waist circumference), self-reported sleep duration and several covariates were assessed. A regression equation derived from the changes in body mass index and waist circumference of normal- and long-duration sleepers (reference category, ≥ 7 h of sleep per night, n = 233) was used to predict the change in waist circumference of short-duration sleepers (≤6 h of sleep per night, n = 43). Additionally, the influence of sleep duration on waist circumference changes was modelled by using linear regression in both sleep duration groups, adjusting for changes in body mass index and other covariates. We observed that measured (actual) changes in waist circumference were significantly greater than predicted changes (mean ± SEM: 3.41 ± 0.53 vs. 2.69 ± 0.51 cm, respectively, P < 0.05), implying that short-duration sleepers had an excess of abdominal fat accumulation over the 6-year follow-up period. After controlling for the changes in total adiposity as measured by body mass index, only short-duration sleepers gained more abdominal adiposity over 6 years. The present study provides evidence that short sleep duration is associated with preferential increases in abdominal adiposity in adults. This finding is of particular concern because abdominal adiposity is correlated with a number of metabolic anomalies.

Script Generation Following Frontal and Parietal Lesions

The purpose of this investigation was to distinguish putative effects of parietal lobe lesions on script generation, in distinction from the better known and established effects of frontal lobe lesions. Nine patients, most with excised parietal lesions, were compared to nine age, gender and education matched normal participants. Eleven patients with excised tumors of the frontal lobe were compared to twelve age, gender and education matched normal subjects. Participants were requested to generate, out loud, scripts corresponding to everyday activities. Half the scripts were relatively more demanding with respect to temporal representation (understanding the time line of events) and the other half with respect to spatial representation (understanding the layout of the actions in space). These two conditions were further broken down into conditions of high and low demands on working memory (reciting the scripts backwards versus forward). The frontal lobe patients enunciated significantly fewer actions overall. They were also significantly more impaired than the normal participants on all tasks with high demands on working memory, and more often, high temporal demands (sequencing and perseverative errors). The parietal lobe patients had significant difficulty in sequencing in all conditions, and manifested no perseveration. Though script generation tasks have been primarily associated with frontal lobe function until now, consideration should be given to the type of activity being scripted as a function of relative demands on spatial or temporal representation, as well as working memory, and the contributions of other lobes ought to be taken into consideration.

Template to improve glycemic control without reducing adiposity or dietary fat

Drugs that improve chronic hyperglycemia independently of insulin signaling or reduction of adiposity or dietary fat intake may be highly desirable. Ad36, a human adenovirus, promotes glucose uptake in vitro independently of adiposity or proximal insulin signaling. We tested the ability of Ad36 to improve glycemic control in vivo and determined if the natural Ad36 infection in humans is associated with better glycemic control. C57BL/6J mice fed a chow diet or made diabetic with a high-fat (HF) diet were mock infected or infected with Ad36 or adenovirus Ad2 as a control for infection. Postinfection (pi), systemic glycemic control, hepatic lipid content, and cell signaling in tissues pertinent to glucose metabolism were determined. Next, sera of 1,507 adults and children were screened for Ad36 antibodies as an indicator of past natural infection. In chow-fed mice, Ad36 significantly improved glycemic control for 12 wk pi. In HF-fed mice, Ad36 improved glycemic control and hepatic steatosis up to 20 wk pi. In adipose tissue (AT), skeletal muscle (SM), and liver, Ad36 upregulated distal insulin signaling without recruiting the proximal insulin signaling. Cell signaling suggested that Ad36 increases AT and SM glucose uptake and reduces hepatic glucose release. In humans, Ad36 infection predicted better glycemic control and lower hepatic lipid content independently of age, sex, or adiposity. We conclude that Ad36 offers a novel tool to understand the pathways to improve hyperglycemia and hepatic steatosis independently of proximal insulin signaling, and despite a HF diet. This metabolic engineering by Ad36 appears relevant to humans for developing more practical and effective antidiabetic approaches.

Investigation of LRP8 gene in 1p31 QTL linked to LDL peak particle diameter in the Quebec family study

The small, dense LDL phenotype is associated with an increased cardiovascular disease risk. A genome-wide scan performed on 236 nuclear families of the Quebec Family Study (QFS) revealed a quantitative trait locus affecting LDL peak particle diameter (LDL-PPD) and density on the 1p31 region. This region contains the low-density lipoprotein receptor-related protein 8 (LRP8) gene. LRP8, a receptor for apolipoprotein (apo) E, modulates apoE levels, thus contributing to plasma cholesterol and triglyceride (TG) concentrations. We investigate the effects of LRP8 polymorphisms on LDL-PPD, on the relative proportion of small LDL (<255Å) and the absolute concentration of cholesterol among the small LDL particles. LRP8 rs5174 was associated with LDL-PPD and estimated cholesterol concentrations in the small LDL particles adjusted for the effects of age and sex (p=0.008, p=0.04, respectively). LRP8 rs3820198 was associated with total and LDL-cholesterol levels as well as with apoB concentrations adjusted for the effects of age and sex (p=0.005, p=0.004 and p=0.01, respectively) but not with LDL size-related variables. These results suggest that LRP8 gene polymorphisms influence plasma cholesterol levels as well as size and composition of LDL particles.

Improvements in glucose homeostasis in response to regular exercise are influenced by the PPARG Pro12Ala variant: results from the HERITAGE Family Study

AIMS/HYPOTHESIS

Exercise training improves glucose homeostasis, but large inter-individual differences are reported, suggesting a role of genetic factors. We investigated whether variants either confirmed or newly identified as diabetes susceptibility variants through genome-wide association studies (GWAS) modulate changes in phenotypes derived from an IVGTT in response to an endurance training programme.

METHODS

We analysed eight polymorphisms in seven type 2 diabetes genes (CDKAL1 rs7756992; CDKN2A and CDKN2B rs10811661 and rs564398; HHEX rs7923837; IGF2BP2 rs4402960; KCNJ11 rs5215; PPARG rs1801282; and TCF7L2 rs7903146) in a maximum of 481 sedentary, non-diabetic white individuals, who participated in a 20-week endurance training programme. Associations were tested between the variants and changes in IVGTT-derived phenotypes.

RESULTS

The only evidence of association with training response was found with PPARG rs1801282 (Pro12Ala). We observed that Ala carriers experienced greater increase in overall glucose tolerance (Deltaglucose disappearance index Ala/Ala 0.22 +/- 0.22, Pro/Ala 0.14 +/- 0.06, Pro/Pro 0.004 +/- 0.03; p = 0.0008), glucose effectiveness (Ala/Ala 0.28 +/- 0.41, Pro/Ala 0.44 +/- 0.14, Pro/Pro 0.09 +/- 0.06; p = 0.004), acute insulin response to glucose (Ala/Ala 64.21 +/- 37.73, Pro/Ala -11.92 +/- 40.30, Pro/Pro -46.30 +/- 14.70; p = 0.03) and disposition index (Ala/Ala 551.8 +/- 448.5, Pro/Ala 534.6 +/- 218.3, Pro/Pro -7.44 +/- 88.18; p = 0.003).

CONCLUSIONS/INTERPRETATION

Compared with Pro/Pro individuals, PPARG Ala carriers experienced greater improvements in glucose and insulin metabolism in response to regular endurance training. However, we did not find evidence of association between type 2 diabetes susceptibility variants recently identified through GWAS and glucose homeostasis response to exercise. Our results extend those of previous studies showing that Ala carriers appear to be more responsive to beneficial health effects of lifestyle interventions.

Evidence for interaction between PPARG Pro12Ala and PPARGC1A Gly482Ser polymorphisms in determining type 2 diabetes intermediate phenotypes in overweight subjects

BACKGROUND

The peroxisome proliferator-activated receptor-gamma ( PPARG) Pro12Ala and the PPARG co-activator-1alpha ( PPARGC1A) Gly482Ser polymorphisms (SNPs) have been associated with type 2 diabetes mellitus (T2DM) risk. We hypothesized that independent and interactive effects of the PPARG Pro12Ala and PPARGC1A Gly482Ser polymorphisms influence T2DM intermediate phenotypes.

MATERIAL AND METHODS

PPARG Pro12Ala and PPARGC1A Gly482Ser SNPs were studied in 680 non diabetic subjects who underwent a 75 g oral glucose tolerant test (OGTT). Glucose and insulin plasma levels in the fasting state and derived from the OGTT were included in the present study.

RESULTS

We found significant independent effects of the PPARG and PPARGC1A variants on fasting insulin levels (p=0.02 for both), HOMA-IR (p=0.03 and p=0.02, respectively), insulin area under the curve (AUC) (p=0.007 and p=0.006, respectively) and 2-h glucose levels (p=0.02 for PPARGC1A). Furthermore, significant gene-gene interactions were found for fasting insulin, HOMA-IR and insulin AUC (p=0.03 for all). Carriers of the PPARGC1A Gly allele who were also PPARG Ala-carriers had higher fasting insulin levels (p=0.02), HOMA-IR (p=0.01) and insulin AUC (p=0.01) compared to the Ser/Ser-Ala+genotype combination, whereas no differences between the PPARGC1A genotypes among the PPARG Pro/Pro carriers were observed.

CONCLUSION

Together, these results showed that PPARG Pro12Ala and PPARGC1A Gly482Ser variants are associated, alone and in interaction, with insulin and glucose homeostasis and suggest that gene-gene interactions should be taken into account in candidate gene studies of T2DM to identify subjects with markedly different risks of developing the disease.

Genetic factors in the regulation of adipose tissue distribution

This paper reviews current data concerning the role of the genotype in human variation in fat distribution and its contribution in regulating fat deposition in various regions of the body, primarily the lower trunk area. After statistical control over age, gender and total amount of subcutaneous fat, one finds an additive genetic effect of about 20-25% of remaining human variance in amount of lower trunk fat and in the relative proportion of lower trunk versus extremity fat. In spite of such a moderate genetic effect in fat distribution, the preferential site of fat deposition when exposed to chronic overfeeding is largely determined by one's genotype. Characteristics of regional adipose tissue metabolism and morphology are probably involved in mediating some of these genetic effects but other regulatory mechanisms are undoubtedly implicated.

Physical training and changes in regional adipose tissue distribution

Obesity has been associated with numerous metabolic complications, such as changes in the concentration and/or composition of plasma lipoproteins, glucose intolerance and hyperinsulinemia leading to diabetes and hypertension. The relation of obesity to cardiovascular disease has not, however, been consistently reported. Recent prospective studies have clearly indicated that the distribution of adipose tissue was a significant cardiovascular risk factor and numerous studies have shown that metabolic disturbances were more closely associated with the level of abdominal fat than excess adiposity per se. As obese men generally store their energy excess in the abdominal region and women in the peripheral fat depots, the metabolic complications of obesity seem to be more closely related to adiposity in men than in women. It is suggested that the sex dimorphism observed in adipose tissue localization could partly explain the greater cardiovascular risk associated with obesity in men than in women. Indeed, obese women with a "male" (abdominal) distribution of body fat have greater metabolic complications than women with lower body fat. When aerobic exercise-training is used to induce weight loss, men generally lose more fat than women. In men, the loss of adipose tissue appears to be central, potentially reducing the risk of cardiovascular disease, whereas a relative resistance to fat loss is observed in women compared to men. Although resistance to fat loss is noted in women, those with a "male" distribution of adipose tissue (high waist-to-hip ratio and high intra-abdominal fat deposition) and with associated metabolic complications greatly benefit from aerobic exercise-training.(ABSTRACT TRUNCATED AT 250 WORDS)

FTO: the first gene contributing to common forms of human obesity

Genome-wide association, the latest gene-finding strategy, has led to the first major success in the field of obesity genetics with the discovery of FTO (fat mass and obesity associated gene) as an obesity-susceptibility gene. A cluster of variants in the first intron of FTO showed a strong and highly significant association with obesity-related traits in three independent genome-wide association studies, a finding that has been replicated in several other studies including adults and children of European descent. Homozygotes for the risk allele weigh on average 3-4 kg more and have a 1.67-fold increased risk of obesity compared with those who did not inherit a risk allele. We are still at an early stage in our understanding of the pathways through which FTO confers to increased obesity risk. Studies in humans and rodents have suggested a central role for FTO through regulation of food intake, whereas others have proposed a peripheral role through an effect on lipolytic activity in adipose tissue. There is no doubt that many more obesity-susceptibility loci remain to be discovered. Progress on this front will therefore require major collaborative efforts and pooling of compatible datasets. We stand to learn a lot about the genetic architecture of human obesity in the coming years. The expectations are high but many challenges remain. Among the latter, translating new advances into useful guidelines for prevention and treatment of obesity will be the most demanding.