Angelo Tremblay

Regional distribution of body fat, plasma lipoproteins, and cardiovascular disease.

Several epidemiological studies have reported that the regional distribution of body fat is a significant and independent risk factor for cardiovascular disease (CVD) and related mortality. Although these associations are well established, the causal mechanisms are not fully understood. Numerous studies have, however, shown that specific topographic features of adipose tissue are associated with metabolic complications that are considered as risk factors for CVD such as insulin resistance, hyperinsulinemia, glucose intolerance and type II diabetes mellitus, hypertension, and changes in the concentration of plasma lipids and lipoproteins. The present article summarizes the evidence on the metabolic correlates of body fat distribution. Potential mechanisms for the association between body fat distribution, metabolic complications, and CVD are reviewed, with an emphasis on plasma lipoprotein levels and plasma lipid transport. From the evidence available, it seems likely that subjects with visceral obesity represent the subgroup of obese individuals with the highest risk for CVD. Although body fat distribution is now considered as a more significant risk factor for CVD and related death rate than obesity per se, further research is clearly needed to identify the determinants of body fat distribution and the causal mechanisms involved in the metabolic alterations. It appears certain, however, that an altered plasma lipid transport is a significant component of the relation between body fat distribution and CVD.

The response to long-term overfeeding in identical twins.

We undertook this study to determine whether there are differences in the responses of different persons to long-term overfeeding and to assess the possibility that genotypes are involved in such differences. After a two-week base-line period, 12 pairs of young adult male monozygotic twins were overfed by 4.2 MJ (1000 kcal) per day, 6 days a week, for a total of 84 days during a 100-day period. The total excess amount each man consumed was 353 MJ (84,000 kcal). During overfeeding, individual changes in body composition and topography of fat deposition varied considerably. The mean weight gain was 8.1 kg, but the range was 4.3 to 13.3 kg. The similarity within each pair in the response to overfeeding was significant (P less than 0.05) with respect to body weight, percentage of fat, fat mass, and estimated subcutaneous fat, with about three times more variance among pairs than within pairs (r approximately 0.5). After adjustment for the gains in fat mass, the within-pair similarity was particularly evident with respect to the changes in regional fat distribution and amount of abdominal visceral fat (P less than 0.01), with about six times as much variance among pairs as within pairs (r approximately 0.7). We conclude that the most likely explanation for the intrapair similarity in the adaptation to long-term overfeeding and for the variations in weight gain and fat distribution among the pairs of twins is that genetic factors are involved. These may govern the tendency to store energy as either fat or lean tissue and the various determinants of the resting expenditure of energy.

How much physical activity is enough to prevent unhealthy weight gain? Outcome of the IASO 1st Stock Conference and consensus statement

A consensus meeting was held in Bangkok, 21–23 May 2002, where experts and young scientists in the field of physical activity, energy expenditure and body‐weight regulation discussed the different aspects of physical activity in relation to the emerging problem of obesity worldwide. The following consensus statement was accepted unanimously.

Visceral Obesity in Men: Associations With Glucose Tolerance, Plasma Insulin, and Lipoprotein Levels

The relations of regional adipose tissue (AT) distribution measured by computed tomography (CT) to plasma insulin-glucose homeostasis and lipoprotein-lipid levels were studied in 58 obese and 29 lean control men. In the group of obese men, the visceral AT area measured by CT was positively correlated with fasting plasma triglyceride and insulin levels and with glucose and insulin areas under the curves measured during a 75-g oral glucose tolerance test. Visceral AT area was also negatively associated with plasma high-density lipoprotein (HDL) and HDL2 cholesterol levels. The relative accumulation of abdominal fat, estimated by the ratio of abdominal to femoral AT areas obtained by CT, was also a significant correlate of indices of carbohydrate metabolism and was the best univariate correlate of plasma lipoprotein levels. No significant associations were observed between the visceral AT area, the ratio of abdominal to femoral AT areas, and indices of carbohydrate and lipoprotein metabolism in the group of lean men. On the other hand, the subcutaneous abdominal AT area was a significant correlate of the glucose area under the curve in both groups of men, but this association was not independent from the percentage of total body fat. No relationship was observed between the femoral AT area and indices of carbohydrate metabolism in either lean or obese groups. In obese men, however, the femoral AT area was negatively correlated with plasma triglyceride concentration and positively correlated with plasma HDL and HDL2 cholesterol levels. Comparison between two subgroups of equally obese men showing either low or high levels of visceral AT and a group of lean men generally revealed that only obese men with high levels of visceral AT showed significant metabolic alterations compared with lean men. These results demonstrate that the amount of visceral AT and the ratio of abdominal to femoral AT measured by CT are important correlates of the alterations in carbohydrate and lipoprotein metabolism observed in obese men. In addition, our results suggest that obesity is required to observe significant associations between body fat distribution measured by CT and metabolic variables. Finally, we suggest that, in men, a high accumulation of femoral fat may be protective against the adverse effects of obesity, particularly abdominal obesity, on plasma lipoprotein levels.

Role of Deep Abdominal Fat in the Association Between Regional Adipose Tissue Distribution and Glucose Tolerance in Obese Women

Computed tomography (CT) was used to study the association between adipose tissue localization and glucose tolerance in a sample of 52 premenopausal obese women aged 35.7 ± 5.5 yr (mean ± SD) and with a body fat of 45.9 ± 5.5%. Body-fat mass and the body mass index (BMI) were significantly correlated with plasma glucose, insulin, and connecting peptide (C-peptide) areas after glucose (75 g) ingestion (.40 ≥ r ≤ .51, P < .01). Trunk-fat accumulation and the size of fat cells in the abdomen displayed highly significant correlations with postglucose insulin levels. The C-peptide area was also positively correlated with abdominal fat cell size (r = .76, P < .01) and was more closely associated with the sum of trunk skin folds (r = .59, P <.001) than with the extremity skin folds (r = .29, P < .05). Subcutaneous and deep-abdominal-fat areas measured by CT displayed comparable associations with the plasma insulin area (r = .44 and .49, respectively; P < .001) but marked differences in the associations with glucose tolerance. Indeed, subcutaneous abdominal fat was not significantly correlated with the glucose area, whereas deep abdominal fat showed a significant correlation (r = .57, P < .001) with the glucose area. Midthigh fat deposition measured by CT was not, however, correlated with plasma glucose, insulin, or C-peptide areas. Partial correlation analyses indicated that the effect of accumulation of deep abdominal fat on glucose tolerance was independent from total adiposity and that no association was observed between total adiposity and glucose tolerance after control for accumulation of deep abdominal fat. These results emphasize the importance of deep abdominal fat as an independent correlate of glucose tolerance in obese women.

Assessment of adipose tissue distribution by computed axial tomography in obese women: association with body density and anthropometric measurements

1. Abdominal obesity is associated with numerous metabolic complications. Deep abdominal adipose tissue is critical in the association between the level of abdominal obesity and cardiovascular risk factors. 2. Adipose tissue localization was assessed by computed axial tomography (CAT), and its association with body density and anthropometric measurements was investigated in a sample of fifty-one obese women (percentage body fat 45.9 (SD 5.6)) aged 35.7 (SD 5.5) years. The CAT scans were performed at three levels: lower chest, abdomen and mid-thigh. 3. The total adipose tissue volume computed from these three scans was highly correlated with body fat mass (r 0.94, P less than 0.001). The proportion of deep abdominal fat as measured by the ratio of deep: total adipose tissue areas at the abdominal level was not significantly correlated with body fat mass, but it was moderately associated with the ratio of waist: hip circumferences (WHR) (r 0.49, P less than 0.001). The absolute amount of deep abdominal fat was, however, significantly correlated with body fat mass (r 0.72, P less than 0.001). 4. The subscapular (r 0.38) and the abdominal (r 0.38) skinfolds were the only two skinfolds that were significantly associated with the proportion of deep abdominal fat (P less than 0.01). These skinfolds were also those which showed the highest correlation with the absolute amount of deep abdominal fat (r 0.65, P less than 0.001, for both skinfolds). 5. A three-site CAT-scan procedure can be used for the estimation of body fat mass in premenopausal obese women. 6. In these obese women, there was no significant association between total adiposity and the proportion of deep adipose tissue at the abdominal level. 7. In premenopausal obese women, the absolute amount of deep abdominal fat can be predicted from anthropometric measurements with more accuracy than the relative amount of deep abdominal fat.

Short sleep duration is associated with reduced leptin levels and increased adiposity: Results from the Quebec family study.

Objective: To explore cross‐sectional associations between short sleep duration and variations in body fat indices and leptin levels during adulthood in a sample of men and women involved in the Québec Family Study.

Impact of exercise intensity on body fatness and skeletal muscle metabolism.

The impact of two different modes of training on body fatness and skeletal muscle metabolism was investigated in young adults who were subjected to either a 20-week endurance-training (ET) program (eight men and nine women) or a 15-week high-intensity intermittent-training (HIIT) program (five men and five women). The mean estimated total energy cost of the ET program was 120.4 MJ, whereas the corresponding value for the HIIT program was 57.9 MJ. Despite its lower energy cost, the HIIT program induced a more pronounced reduction in subcutaneous adiposity compared with the ET program. When corrected for the energy cost of training, the decrease in the sum of six subcutaneous skinfolds induced by the HIIT program was ninefold greater than by the ET program. Muscle biopsies obtained in the vastus lateralis before and after training showed that both training programs increased similarly the level of the citric acid cycle enzymatic marker. On the other hand, the activity of muscle glycolytic enzymes was increased by the HIIT program, whereas a decrease was observed following the ET program. The enhancing effect of training on muscle 3-hydroxyacyl coenzyme A dehydrogenase (HADH) enzyme activity, a marker of the activity of beta-oxidation, was significantly greater after the HIIT program. In conclusion, these results reinforce the notion that for a given level of energy expenditure, vigorous exercise favors negative energy and lipid balance to a greater extent than exercise of low to moderate intensity. Moreover, the metabolic adaptations taking place in the skeletal muscle in response to the HIIT program appear to favor the process of lipid oxidation.

The effect of obesity on chronic respiratory diseases: pathophysiology and therapeutic strategies

Sedentary lifestyles and increased pollution brought about by industrialization pose major challenges to the prevention of both obesity and chronic respiratory diseases such as chronic obstructive pulmonary disease (COPD), asthma, obstructive sleep apnea and obesity hypoventilation syndrome. Obesity has emerged as an important risk factor for these respiratory diseases, and in many instances weight loss is associated with important symptomatic improvement. Moreover, obesity may influence the development and presentation of these diseases. In this article, we review the current understanding of the influence of obesity on chronic respiratory diseases and the clinical management of obesity concurrent with asthma, COPD, obstructive sleep apnea or obesity hypoventilation syndrome.

Adipose tissue distribution and plasma lipoprotein levels in obese women. Importance of intra-abdominal fat.

Prospective studies have shown that excess abdominal fat Is associated with an Increased risk of coronary heart disease and related death. We used computed axial tomography (CAT) to assess the association between deep and subcutaneous abdominal adipose tissue and plasma lipoprotein levels In a sample of 52 premenopausal obese women aged 35.7±5.5 years (mean±SD). Whereas the plasma lipoprotein concentrations were not significantly correlated with fat mass, the data obtained by CAT Indicated that the absolute amount of deep abdominal fat was negatively correlated with high density lipoprotein cholesterol (HDL-CHOL) levels (r=−0.35, /x 0.01), as well as with HDL-CHOL/low density lipoprotein (LDL)-CHOL, HDL- apoprotein-(apo) A-l/LDL-apo B, and HDL2-CHOL/HDL,-CHOL ratios (−0.32srs-0.40, 0.05>p<0.01). Adipose tissue deposition at the mid-thigh region determined by CAT did not show any significant relationship with plasma lipoprotein levels. When subgroups of women with comparable ages and adiposity but with high and low Intra-abdominal fat accumulation were compared, women with a high accumulation of Intra-abdominal fat displayed significantly lower HDL-CHOL (p<0.001), HDLj- CHOL (p<0.001), HDL3-CHOL (p<0.01), and HDL-apo A-l (p<0.05) levels, as well as reduced HDL-CHOL/LDL-CHOL (p<0.01), HDL-apo A-l/LDL-apo B (p<0.05), and HDL2-CHOL/HDL4-CHOL ratios (p<0.05) in comparison with obese women with low accumulations of Intra-abdominal fat These data Indicate that, in a sample of obese women, body fat distribution, especially Intra-abdominal fat accumulation, is a significant correlate of plasma lipoprotein levels Independent of total fatness.