Long-term effects of dietary glycemic index on adiposity, energy metabolism, and physical activity in mice

A high-glycemic index (GI) diet has been shown to increase adiposity in rodents; however, the long-term metabolic effects of a low- and high-GI diet have not been examined. In this study, a total of 48 male 129SvPas mice were fed diets high in either rapidly absorbed carbohydrate (RAC; high GI) or slowly absorbed carbohydrate (SAC; low GI) for up to 40 wk. Diets were controlled for macronutrient and micronutrient content, differing only in starch type. Body composition and insulin sensitivity were measured longitudinally by DEXA scan and oral glucose tolerance test, respectively. Food intake, respiratory quotient, physical activity, and energy expenditure were assessed using metabolic cages. Despite having similar mean body weights, mice fed the RAC diet had 40% greater body fat by the end of the study and a mean 2.2-fold greater insulin resistance compared with mice fed the SAC diet. Respiratory quotient was higher in the RAC group, indicating comparatively less fat oxidation. Although no differences in energy expenditure were observed throughout the study, total physical activity was 45% higher for the SAC-fed mice after 38 wk of feeding. We conclude that, in this animal model, 1) the effect of GI on body composition is mediated by changes in substrate oxidation, not energy intake; 2) a high-GI diet causes insulin resistance; and 3) dietary composition can affect physical activity level.

A paradoxical signal intensity increase in fatty livers using opposed-phase gradient echo imaging with fat-suppression pulses

With the increase in obese and overweight children, nonalcoholic fatty liver disease has become more prevalent in the pediatric population. Appreciating subtleties of magnetic resonance (MR) signal intensity behavior from fatty livers under different imaging conditions thus becomes important to pediatric radiologists. We report an initially confusing signal behavior-increased signal from fatty livers when fat-suppression pulses are applied in an opposed-phase gradient echo imaging sequence-and seek to explain the physical mechanisms for this paradoxical signal intensity behavior. Abdominal MR imaging at 3 T with a 3-D volumetric interpolated breath-hold (VIBE) sequence in the opposed-phase condition (TR/TE 3.3/1.3 ms) was performed in five obese boys (14+/-2 years of age, body mass index >95th percentile for age and sex) with spectroscopically confirmed fatty livers. Two VIBE acquisitions were performed, one with and one without the use of chemical shift selective (CHESS) pulse fat suppression. The ratios of fat-suppressed over non-fat-suppressed signal intensities were assessed in regions-of-interest (ROIs) in five tissues: subcutaneous fat, liver, vertebral marrow, muscle and spleen. The boys had spectroscopically estimated hepatic fat levels between 17% and 48%. CHESS pulse fat suppression decreased subcutaneous fat signals dramatically, by more than 85% within regions of optimal fat suppression. Fatty liver signals, in contrast, were elevated by an average of 87% with CHESS pulse fat suppression. Vertebral marrow signal was also significantly elevated with CHESS pulse fat suppression, while spleen and muscle signals demonstrated only small signal increases on the order of 10%. We demonstrated that CHESS pulse fat suppression actually increases the signal intensity from fatty livers in opposed-phase gradient echo imaging conditions. The increase can be attributed to suppression of one partner of the opposed-phase pair that normally contributes to the destructive interference between water and fat. The result is a paradoxical increase in signal from fatty liver that will depend on both fat content and the relative longitudinal relaxation times of fat methylene protons and water.

Effects of replacing the habitual consumption of sugar-sweetened beverages with milk in Chilean children

BACKGROUND

During the nutrition transition in Chile, dietary changes were marked by increased consumption of high-energy, nutrient-poor products, including sugar-sweetened beverages (SSBs). Obesity is now the primary nutritional problem in posttransitional Chile.

OBJECTIVE

We conducted a randomized controlled trial to examine the effects on body composition of delivering milk beverages to the homes of overweight and obese children to displace SSBs.

DESIGN

We randomly assigned 98 children aged 8-10 y who regularly consumed SSBs to intervention and control groups. During a 16-wk intervention, children were instructed to drink 3 servings/d (approximately 200 g per serving) of the milk delivered to their homes and to not consume SSBs. Body composition was measured by dual-energy X-ray absorptiometry. Data were analyzed by multiple regression analysis according to the intention-to-treat principle.

RESULTS

For the intervention group, milk consumption increased by a mean (+/- SEM) of 452.5 +/- 37.7 g/d (P < 0.0001), and consumption of SSBs decreased by -711.0 +/- 33.7 g/d (P < 0.0001). For the control group, milk consumption did not change, and consumption of SSBs increased by 71.9 +/- 33.6 g/d (P = 0.04). Changes in percentage body fat, the primary endpoint, did not differ between groups. Nevertheless, the mean (+/- SE) accretion of lean body mass was greater (P = 0.04) in the intervention (0.92 +/- 0.10 kg) than in the control (0.62 +/- 0.11 kg) group. The increase in height was also greater (P = 0.01) in the intervention group (2.50 +/- 0.21 cm) than in the control group (1.77 +/- 0.20 cm) for boys but not for girls.

CONCLUSION

Replacing habitual consumption of SSBs with milk may have beneficial effects on lean body mass and growth in children, despite no changes in percentage body fat. This trial was registered at clinicaltrials.gov as NCT00149695.

Blood glucose and hormonal responses to small and large meals in healthy young and older women

Blood glucose regulation in the fasting and fed states has important implications for health. In addition, the ability to maintain normal blood glucose homeostasis may be an important determinant of an individual's capacity to regulate food intake. We tested the hypothesis that aging is associated with an impairment in the ability to maintain normal blood glucose homeostasis following the consumption of large meals but not small ones, a factor that could help to explain age-related impairments in the control of food intake and energy regulation. The subjects were eight healthy younger women (25 +/- 2 years, SD) and eight healthy older women (72 +/- 2 years) with normal body weight and glucose tolerance. Following a 36-h period when diet and physical activity were controlled, subjects consumed test meals containing 0, 1046, 2092, and 4184 kJ (simulating extended fasting, and consumption of a snack, a small meal, and a moderately large meal), with 35% of energy from fat, 48% from carbohydrate, and 17% from protein. Each subject consumed each of the test meals on a separate occasion. Serial blood samples were collected at baseline and during 5 h after consumption of the meals. Measurements were made of circulating glucose, insulin, glucagon, free fatty acids, and triglycerides. There was no significant difference between young and older women in their hormone and metabolite responses to fasting and consumption of the 1046-kJ meal. However, following consumption of 2092 and 4148 kJ, older individuals showed exaggerated responses and a delayed return to premeal values for glucose (p = .023), insulin (p = .010), triglycerides (p = .023), and the ratio of insulin to glucagon (p = .026). In conclusion, these results suggest an impairment in the hormonal and metabolite responses to large meals in older women.

A novel interaction between dietary composition and insulin secretion: effects on weight gain in the Quebec Family Study

BACKGROUND

Clinical trials of low-fat diets characteristically produce small mean long-term weight loss but a large interindividual variation in response. This variation has been attributed to psychological and behavioral factors, although biological differences may also play a role.

OBJECTIVE

The objective was to determine whether physiologic differences in insulin secretion explain differences in weight gain among individuals consuming low- and high-fat diets.

DESIGN

Of 276 individuals followed in the Quebec Family Study for a mean of 6 y, we compared those in the lowest with those in the highest dietary fat tertiles. We performed oral-glucose-tolerance tests at baseline and examined the insulin concentration at 30 min (insulin-30) as a proxy measure of insulin secretion. Six-year changes in body weight and waist circumference were the primary endpoints. We determined the associations between insulin-30 and the primary endpoints by linear regression analysis, with adjustment for potentially confounding factors.

RESULTS

Mean changes in body weight and waist circumference did not differ significantly between the lowest- and highest-fat diet groups. However, these endpoints were strongly associated with insulin-30, especially among individuals consuming the lowest-fat diet. Insulin-30 at baseline was significantly associated with 6-y weight gain (r = 0.51, P < 0.0001) and change in waist circumference (r = 0.55, P < 0.0001) in the lowest diet fat, group [corrected], but not in the highest diet fat group (r = 0.18, P = 0.086 and r = 0.20, P = 0.058, respectively) [corrected] Individuals in the highest insulin-30 and lowest dietary fat group gained 1.8 kg more than did those in the highest insulin-30 and highest dietary fat group (51%; P = 0.034); they gained 4.5 kg more than did those in the lowest insulin-30 and lowest dietary fat group (6.5-fold; P = 0.0026).

CONCLUSION

A proxy measure of insulin secretion strongly predicts changes in body weight and waist circumference over 6 y in adults, especially among those consuming lower-fat diets, which demonstrates the existence of a novel diet-phenotype interaction.

Recommendations for treatment of child and adolescent overweight and obesity

In this article, we review evidence about the treatment of obesity that may have applications in primary care, community, and tertiary care settings. We examine current information about eating behaviors, physical activity behaviors, and sedentary behaviors that may affect weight in children and adolescents. We also review studies of multidisciplinary behavior-based obesity treatment programs and information about more aggressive forms of treatment. The writing group has drawn from the available evidence to propose a comprehensive 4-step or staged-care approach for weight management that includes the following stages: (1) Prevention Plus; (2) structured weight management; (3) comprehensive multidisciplinary intervention; and (4) tertiary care intervention. We suggest that providers encourage healthy behaviors while using techniques to motivate patients and families, and interventions should be tailored to the individual child and family. Although more intense treatment stages will generally occur outside the typical office setting, offices can implement less intense intervention strategies. We not ony address specific patient behavior goals but also encourage practices to modify office systems to streamline office-based care and to prepare to coordinate with professionals and programs outside the office for more intensive interventions.

Eating disorder pathology among overweight treatment-seeking youth: Clinical correlates and cross-sectional risk modeling

Preliminary research suggests that pediatric overweight is associated with increased eating disorder pathology, however, little is known about which overweight youth are most vulnerable to eating disorder pathology. We therefore investigated 122 overweight treatment-seeking youth to describe eating disorder pathology and mental health correlates, and to identify psychopathological constructs that may place overweight youth at increased risk for eating disorder pathology. Youth participated in a comprehensive assessment of eating disorders, mood and anxiety disorders, general psychopathology, and risk variables involving semi-structured clinical interviews and self- and parent-report questionnaires prior to the initiation of weight-loss treatment. Ten youth met criteria for an eating disorder, and over one-third endorsed recent binge eating. Eating disorder pathology was associated with depressive and anxious symptoms (p's<0.001). Structural equation modeling indicated increased negative affect, teasing experience, and thin-ideal internalization, and decreased perfectionism were associated with increased eating disorder pathology. Findings corroborate earlier work indicating that eating disorder pathology is elevated and clinically significant in overweight treatment-seeking youth, bolstering the need for mental health assessment of such individuals. Cross-sectional modeling proposed key variables that relate to eating disorder pathology in overweight treatment-seeking youth, which following prospective replication, may inform the development of effective interventions for overweight and eating disorders.

Hepatic steatosis and increased adiposity in mice consuming rapidly vs. slowly absorbed carbohydrate

OBJECTIVE

Non-alcoholic fatty liver disease (NAFLD) is fast becoming a major public health concern, coincident with the increasing prevalence of obesity. Although lifestyle greatly influences development of NAFLD, the specific dietary causes remain largely unknown. The purpose of this study was to determine whether a diet high in rapidly absorbed carbohydrate (RAC) vs. slowly absorbed carbohydrate (SAC), controlled for confounding dietary factors, causes NAFLD in mice with similar body weight. An animal model was chosen because of logistical and ethical challenges to conducting this study in humans.

RESEARCH METHODS AND PROCEDURES

Male 129SvPas mice were fed diets high in either RAC (amylopectin; high glycemic index) or SAC (amylose; low glycemic index) for 25 weeks. Diets were controlled for macronutrient and micronutrient content, differing only in starch type. Body weight and composition were measured throughout the study. Hepatic and plasma triacylglycerol concentrations were quantified at the end of the study.

RESULTS

Body weight was not significantly different between the two groups. However, total body adiposity increased twice as much, in absolute terms, in the mice fed RAC vs. SAC (12.2 +/- 2.9% vs. 6.1 +/- 4.2%, p < 0.0001). Hepatic triacylglycerol content was 2-fold greater in the RAC group (20.7 +/- 9.4 vs. 9.6 +/- 4.9 mg/g, p = 0.01). In addition, plasma insulin and triacylglycerol concentrations were higher in the RAC group.

DISCUSSION

A diet high in RAC causes accumulation of fat in liver, adipose tissue, and plasma in mice. Therefore, a low glycemic index diet may help prevent or treat NAFLD in humans.

Pediatric obesity management: variation by specialty and awareness of guidelines

A survey of 2727 pediatric clinicians evaluated pediatric overweight management and awareness of Expert Committee recommendations (ECR) on obesity. Adjusted response rate was 45%. ECR awareness was reported by 24.6%. Family practice specialists (FPS) were less likely than pediatric specialists (PS) to be aware of ECR (OR, 0.46; 95% CI, 0.30-0.71). Body mass index (BMI) was never used by 25.6% to identify overweight; 35.4% did not obtain laboratory tests. Among PS but not FPS, ECR awareness was associated with BMI use (OR, 2.70; 95% CI, 1.56-4.65) and frequent follow-up (OR, 2.48; 95% CI, 1.58-3.90). FPS were more likely than PS to use BMI (OR, 1.78; 95% CI, 1.15-2.75) and obtain thyroid function tests (OR, 2.58; 95% CI, 1.53-4.37), but less likely to obtain fasting lipids (OR, 0.47; 95% CI, 0.30-0.73). Specialty differences in dietary recommendations, referrals, and barriers to treatment were identified. Pediatric overweight management guidelines should consider specialty differences and be accessible to all pediatric care providers.

Effects of a low-glycemic load vs low-fat diet in obese young adults: a randomized trial

CONTEXT

The results of clinical trials involving diet in the treatment of obesity have been inconsistent, possibly due to inherent physiological differences among study participants.

OBJECTIVE

To determine whether insulin secretion affects weight loss with 2 popular diets.

DESIGN, SETTING, AND PARTICIPANTS

Randomized trial of obese young adults (aged 18-35 years; n = 73) conducted from September 2004 to December 2006 in Boston, Mass, and consisting of a 6-month intensive intervention period and a 12-month follow-up period. Serum insulin concentration at 30 minutes after a 75-g dose of oral glucose was determined at baseline as a measure of insulin secretion. Outcomes were assessed at 6, 12, and 18 months. Missing data were imputed conservatively.

INTERVENTIONS

A low-glycemic load (40% carbohydrate and 35% fat) vs low-fat (55% carbohydrate and 20% fat) diet.

MAIN OUTCOME MEASURES

Body weight, body fat percentage determined by dual-energy x-ray absorptiometry, and cardiovascular disease risk factors.

RESULTS

Change in body weight and body fat percentage did not differ between the diet groups overall. However, insulin concentration at 30 minutes after a dose of oral glucose was an effect modifier (group x time x insulin concentration at 30 minutes: P = .02 for body weight and P = .01 for body fat percentage). For those with insulin concentration at 30 minutes above the median (57.5 microIU/mL; n = 28), the low-glycemic load diet produced a greater decrease in weight (-5.8 vs -1.2 kg; P = .004) and body fat percentage (-2.6% vs -0.9%; P = .03) than the low-fat diet at 18 months. There were no significant differences in these end points between diet groups for those with insulin concentration at 30 minutes below the median level (n = 28). Insulin concentration at 30 minutes after a dose of oral glucose was not a significant effect modifier for cardiovascular disease risk factors. In the full cohort, plasma high-density lipoprotein cholesterol and triglyceride concentrations improved more on the low-glycemic load diet, whereas low-density lipoprotein cholesterol concentration improved more on the low-fat diet.

CONCLUSIONS

Variability in dietary weight loss trials may be partially attributable to differences in hormonal response. Reducing glycemic load may be especially important to achieve weight loss among individuals with high insulin secretion. Regardless of insulin secretion, a low-glycemic load diet has beneficial effects on high-density lipoprotein cholesterol and triglyceride concentrations but not on low-density lipoprotein cholesterol concentration.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00130299.

Altering portion sizes and eating rate to attenuate gorging during a fast food meal: effects on energy intake

OBJECTIVE

Eating large amounts of food at a rapid rate, defined as gorging, may contribute to excess energy intake. We aimed to evaluate whether altering portion sizes and eating rate could decrease energy intake during an extra-large fast food meal.

METHODS

Subjects were adolescents (n = 18), 13 to 17 years of age, who reported eating fast food > or =1 time per week. BMI exceeded the 80th percentile for all subjects. Three feeding conditions were evaluated with a crossover design. Total amounts and types of foods and beverage served during the meal were held constant across conditions, equaling approximately 125% of that consumed during a baseline assessment visit when subjects were offered unlimited amounts. The meal (chicken nuggets, French fries, and cola) was presented as 1 large serving at a single time point (condition A, standard), portioned into 4 smaller servings presented at a single time point (condition B, effects of portioning), or portioned into 4 smaller servings presented at 15-minute intervals (condition C, effects of portioning and eating rate). Energy intake across conditions was compared by using analysis of variance.

RESULTS

Energy intake was not significantly different, whether expressed in kilojoules (mean +/- SEM: condition A, 5552 +/- 357 kJ; condition B, 5321 +/- 433 kJ; condition C, 5762 +/- 500 kJ) or relative to total daily energy expenditure (mean +/- SEM: condition A, 51.9 +/- 3.5%; condition B, 48.2 +/- 4.0%; condition C, 53.0 +/- 4.3%).

CONCLUSIONS

Adolescents consumed approximately 50% of energy needs regardless of manipulations in portion sizes and eating rate to attenuate gorging. This finding suggests that nutritional factors inherent to fast food, such as low levels of dietary fiber, high palatability, high energy density, high fat content, high glycemic load, and high content of sugar in liquid form promote excess energy intake.

Relationship between funding source and conclusion among nutrition-related scientific articles

BACKGROUND

Industrial support of biomedical research may bias scientific conclusions, as demonstrated by recent analyses of pharmaceutical studies. However, this issue has not been systematically examined in the area of nutrition research. The purpose of this study is to characterize financial sponsorship of scientific articles addressing the health effects of three commonly consumed beverages, and to determine how sponsorship affects published conclusions.

METHODS AND FINDINGS

Medline searches of worldwide literature were used to identify three article types (interventional studies, observational studies, and scientific reviews) about soft drinks, juice, and milk published between 1 January, 1999 and 31 December, 2003. Financial sponsorship and article conclusions were classified by independent groups of coinvestigators. The relationship between sponsorship and conclusions was explored by exact tests and regression analyses, controlling for covariates. 206 articles were included in the study, of which 111 declared financial sponsorship. Of these, 22% had all industry funding, 47% had no industry funding, and 32% had mixed funding. Funding source was significantly related to conclusions when considering all article types (p = 0.037). For interventional studies, the proportion with unfavorable conclusions was 0% for all industry funding versus 37% for no industry funding (p = 0.009). The odds ratio of a favorable versus unfavorable conclusion was 7.61 (95% confidence interval 1.27 to 45.73), comparing articles with all industry funding to no industry funding.

CONCLUSIONS

Industry funding of nutrition-related scientific articles may bias conclusions in favor of sponsors' products, with potentially significant implications for public health.

Inflammation and changes in metabolic syndrome abnormalities in US adolescents: findings from the 1988-1994 and 1999-2000 National Health and Nutrition Examination Surveys

BACKGROUND

Understanding of C-reactive protein (CRP) in adult metabolic syndrome is increasing; however, this relationship in children is less clear.

METHODS

We compared the prevalence of metabolic abnormalities and metabolic syndrome in fasting 12- to 19-year-olds from the 1999-2000 and 1988-1994 National Health and Nutrition Examination Survey (NHANES). In the more recent dataset we explored the relationship between metabolic abnormalities and CRP as measured by a high-sensitivity assay.

RESULTS

The prevalence of central obesity, low HDL-cholesterol, and hypertension increased between the 2 surveys. Three or more abnormalities (metabolic syndrome) were found in 12.7% [95% confidence interval (CI), 10.0%-15.4%] of fasting adolescents from the 1999-2000 survey, compared with 9.2% (95% CI, 7.8%-10.6%; P < 0.001) in the 1988-1994 dataset, with increases also seen in sex and ethnic/racial subgroups. Increases in metabolic syndrome were primarily attributable to increasing body mass index (BMI); prevalence of BMI at or above the 85th percentile increased from 25.9% to 30.5%. Metabolic syndrome was much more prevalent in overweight compared with normal-weight adolescents (38.6% vs 1.4%; P < 0.001). Median CRP increased with increasing numbers of metabolic abnormalities and was higher in adolescents with metabolic syndrome than in those without. CRP was higher in adolescents with BMI at or above the 85th percentile than those with normal BMI.

CONCLUSIONS

Metabolic abnormalities and the metabolic syndrome phenotype are increasingly prevalent in US adolescents, attributable in part to the increasing incidence of overweight. Adolescents with more metabolic abnormalities have higher CRP, which may be an indicator of greater metabolic derangement and future cardiovascular risk.