Physiological regulation of food intake

Exploring racial differences in the obesity gender gap

PURPOSE

To investigate whether the gender gap in obesity prevalence is greater among U.S. blacks than whites in a study designed to account for racial differences in socioeconomic and environmental conditions.

METHODS

We estimated age-adjusted, race-stratified gender gaps in obesity (% female obese - % male obese, defined as body mass index ≥30 kg/m(2)) in the National Health Interview Survey 2003 and the Exploring Health Disparities in Integrated Communities-Southwest Baltimore 2003 study (EHDIC-SWB). EHDIC-SWB is a population-based survey of 1381 adults living in two urban, low-income, racially integrated census tracts with no race difference in income.

RESULTS

In the National Health Interview Survey, the obesity gender gap was larger in blacks than whites as follows: 7.7 percentage points (ppts; 95% confidence interval (CI): 3.4-11.9) in blacks versus -1.5 ppts (95% CI: -2.8 to -0.2) in whites. In EHDIC-SWB, the gender gap was similarly large for blacks and whites as follows: 15.3 ppts (95% CI: 8.6-22.0) in blacks versus 14.0 ppts (95% CI: 7.1-20.9) in whites.

CONCLUSIONS

In a racially integrated, low-income urban community, gender gaps in obesity prevalence were similar for blacks and whites.

Intragastric pressure as a determinant of food intake

BACKGROUND

Different studies indicated a correlation between intragastric pressure (IGP) and satiation. Our aim was to investigate this correlation while artificially increasing the IGP.

METHODS

In 12 fasted healthy volunteers an infusion catheter and a manometry probe were positioned intragastrically. Intragastric pressure was increased using a custom-made belt before or progressively during intragastric nutrient infusion. Nutrient drink (1.5 kcal mL(-1)) was intragastrically infused at 60 mL min(-1) . The subjects scored satiation using a 6-point Likert scale until maximum, when the infusion ended and the belt was released. Results are presented as mean ± S.E.M. and compared using a paired t-test.

KEY RESULTS

When the belt was tightened before the nutrient infusion, fasting IGP was significantly increased (13.6 ± 1.3 vs 9.6 ± 0.9 mmHg; P < 0.05) but no differences in satiation could be observed. When progressively tightening the belt during nutrient infusion the IGP increased with 0.43 ± 0.04 mmHg per minute while in control experiments this was 0.28 ± 0.05 mmHg per minute (P < 0.01). During the latter experiment satiation linearly increased with 0.35 ± 0.03 and 0.29 ± 0.02 units per minute until maximal satiation (P < 0.01) while maximum volume consumed was 926 ± 66 and 1095 ± 82 mL when progressively increasing the IGP vs control respectively (P < 0.01).

CONCLUSIONS & INFERENCES

These findings indicate that IGP per se does not affect satiation but that a gradual IGP increase during food intake is associated with decreased food intake, indicating that gastric accommodation is an important determinant of food intake.

Review article: the role of gastric motility in the control of food intake

BACKGROUND

From a classical point of view, gastric motility acts to clear the stomach between meals, whereas postprandial motility acts to provide a reservoir for food, mixing and grinding the food and to assure a controlled flow of food to the intestines.

AIM

To summarise findings that support the role of gastric motility as a central mediator of hunger, satiation and satiety.

METHODS

A literature review using the search terms 'satiety', 'satiation' and 'food intake' was combined with specific terms corresponding to the sequence of events during and after food intake.

RESULTS

During food intake, when gastric emptying of especially solids is limited, gastric distension and gastric accommodation play an important function in the regulation of satiation. After food intake, when the stomach gradually empties, the role of gastric distension in the determination of appetite decreases and the focus will shift to gastric emptying and intestinal exposure of the nutrients. Finally, we have discussed the role of the empty stomach and the migrating motor complex in the regulation of hunger signals.

CONCLUSIONS

Our findings indicate that gastric motility is a key mediator of hunger, satiation and satiety. More specifically, gastric accommodation and gastric emptying play important roles in the regulation of gastric (dis)tension and intestinal exposure of nutrients and hence control satiation and satiety. Correlations between gastric accommodation, gastric emptying and body weight indicate that gastric motility can also play a role in the long-term regulation of body weight.

Parental influence on children's early eating environments and obesity risk: implications for prevention

Most childhood obesity prevention efforts have focused on school-age children and adolescents and have had limited success. We argue that the first years of life, including the prenatal period, the postnatal suckling period and the transition to the modified adult diet, may provide opportunities for preventive interventions. These early periods are characterized by high plasticity and rapid transitions, and parents have a high degree of control over children's environments and experiences. Observational and experimental evidence reveal persistent effects of early environments on eating behavior and obesity risk, suggesting that interventions should be tested during these early periods. The central task parents have in early development points to their potential as key targets and agents of change in early preventive interventions. In this paper, we review evidence of early environmental effects on children's eating and obesity risk, highlighting ways that parental feeding practices and parents' own behaviors impact these outcomes and calling for further experimental research to elucidate whether these factors are indeed promising targets for childhood obesity preventive interventions.

Sex differences in obesity rates in poor countries: evidence from South Africa

Globally, men and women face markedly different risks of obesity. In all but of handful of (primarily Western European) countries, obesity is much more prevalent among women than men. We examine several potential explanations for this phenomenon. We analyze differences between men and women in reports and effects of potential underlying causes of obesity-childhood and adult poverty, depression, and attitudes about obesity. We evaluate the evidence for each explanation using data collected in an urban African township in the Cape Town metropolitan area. Three factors explain the greater obesity rates we find among women. Women who were nutritionally deprived as children are significantly more likely to be obese as adults, while men who were deprived as children face no greater risk. In addition, women of higher adult socioeconomic status are significantly more likely to be obese, which is not true for men. These two factors - childhood circumstances and adult SES - can fully explain the difference in obesity rates between men and women that we find in our sample. More speculatively, in South Africa, women's perceptions of an 'ideal' female body are larger than men's perceptions of the 'ideal' male body, and individuals with larger 'ideal' body images are significantly more likely to be obese.

Overnight hypoxic exposure and glucagon-like peptide-1 and leptin levels in humans

Altitude exposure has been associated with loss of appetite and weight loss in healthy humans; however, the endocrine factors that contribute to these changes remain unclear. Leptin and glucagon-like peptide-1 (GLP-1) are peptide hormones that contribute to the regulation of appetite. Leptin increases with hypoxia; however, the influence of hypoxia on GLP-1 has not been studied in animals or humans to date. We sought to determine the influence of normobaric hypoxia on plasma leptin and GLP-1 levels in 25 healthy humans. Subjects ingested a control meal during normoxia and after 17 h of exposure to normobaric hypoxia (fraction of inspired oxygen of 12.5%, simulating approximately 4100 m). Plasma leptin was assessed before the meal, and GLP-1 was assessed premeal, at 20 min postmeal, and at 40 min postmeal. We found that hypoxia caused a significant elevation in plasma leptin levels (normoxia, 4.9 +/- 0.8 pg.mL-1; hypoxia, 7.7 +/- 1.5 pg.mL-1; p < 0.05; range, -16% to 190%), no change in the average GLP-1 response to hypoxia, and only a small trend toward an increase in GLP-1 levels 40 min postmeal (fasting, 15.7 +/- 0.9 vs 15.9 +/- 0.7 pmol.L-1; 20 min postmeal, 21.7 +/- 0.9 vs 21.8 +/- 1.2 pmol.L-1; 40 min postmeal, 19.5 +/- 1.2 vs. 21.0 +/- 1.2 pmol.L-1 for normoxia and hypoxia, respectively; p > 0.05 normoxia vs hypoxia). There was a correlation between SaO2 and leptin after the 17 h exposure (r = 0.45; p < 0.05), but no relation between SaO2 and GLP-1. These data confirm that leptin increases with hypoxic exposure in humans. Further study is needed to determine the influence of hypoxia and altitude on GLP-1 levels.

Transcriptional profiling of chromosome 17 quantitative trait Loci for carbohydrate and total calorie intake in a mouse congenic strain reveals candidate genes and pathways

BACKGROUND/AIMS

The genetic basis for ingestive behaviors is virtually unknown. Quantitative trait loci (QTLs) for carbohydrate and energy intake map to mouse chromosome 17 and were previously confirmed by a congenic strain bearing CAST/Ei (CAST) donor segment on the C57BL/6J (B6) background.

METHODS

We used microarray technology to facilitate gene identification. Gene expression was compared between the B6.CAST-17 (BC-17) congenic and B6 strains in two diets: (1) chow, and (2) carbohydrate/protein vs. fat/protein.

RESULTS

Within the QTL and unique to macronutrient selection, Agpat1 (acylglycerol-3-phosphate O-acyltransferase 1) was differentially expressed in hypothalamus. Irrespective of diet, the gene with the highest fold difference in congenic mice was trefoil factor 3 (Tff3) in liver. Several genes involved in fat metabolism were decreased in carbohydrate-preferring congenic mice, while genes associated with carbohydrate metabolism were increased. In particular, the glyoxalase pathway was enhanced including Glo1, Glo2, and dLDH. Higher expression of Glo1 mRNA in BC-17 congenic mice corresponded to increased protein expression revealed by Western blot, and to higher GLO1 activity in blood.

CONCLUSION

These genes represent new candidates for nutrient intake phenotypes. We propose that increased GLO1 in the BC-17 strain supports its need to protect against dietary oxidants resulting from high carbohydrate intake.

Elevated hypothalamic orexin signaling, sensitivity to orexin A, and spontaneous physical activity in obesity-resistant rats

Selectively-bred obesity-resistant [diet resistant (DR)] rats weigh less than obesity-prone [diet-induced obese (DIO)] rats, despite comparable daily caloric intake, suggesting phenotypic energy expenditure differences. Human data suggest that obesity is maintained by reduced ambulatory or spontaneous physical activity (SPA). The neuropeptide orexin A robustly stimulates SPA. We hypothesized that DR rats have greater: 1) basal SPA, 2) orexin A-induced SPA, and 3) preproorexin, orexin 1 and 2 receptor (OX1R and OX2R) mRNA, compared with DIO rats. A group of age-matched out-bred Sprague-Dawley rats were used as additional controls for the behavioral studies. DIO, DR, and Sprague-Dawley rats with dorsal-rostral lateral hypothalamic (rLHa) cannulas were injected with orexin A (0, 31.25, 62.5, 125, 250, and 500 pmol/0.5 microl). SPA and food intake were measured for 2 h after injection. Preproorexin, OX1R and OX2R mRNA in the rLHa, and whole hypothalamus were measured by real-time RT-PCR. Orexin A significantly stimulated feeding in all rats. Orexin A-induced SPA was significantly greater in DR and Sprague-Dawley rats than in DIO rats. Two-mo-old DR rats had significantly greater rLHa OX1R and OX2R mRNA than DIO rats but comparable preproorexin levels. Eight-mo-old DR rats had elevated OX1R and OX2R mRNA compared with DIO rats, although this increase was significant for OX2R only at this age. Thus DR rats show elevated basal and orexin A-induced SPA associated with increased OX1R and OX2R gene expression, suggesting that differences in orexin A signaling through OX1R and OX2R may mediate DIO and DR phenotypes.

Peripheral metabolic responses to prolonged weight reduction that promote rapid, efficient regain in obesity-prone rats

Weight regain after weight loss is the most significant impediment to long-term weight reduction. We have developed a rodent paradigm that models the process of regain after weight loss, and we have employed both prospective and cross-sectional analyses to characterize the compensatory adaptations to weight reduction that may contribute to the propensity to regain lost weight. Obese rats were fed an energy-restricted (50–60% kcal) low-fat diet that reduced body weight by 14%. This reduced weight was maintained for up to 16 wk with limited provisions of the low-fat diet. Intake restriction was then removed, and the rats were followed for 56 days as they relapsed to the obese state. Prolonged weight reduction was accompanied by 1) a persistent energy gap resulting from an increased drive to eat and a reduced expenditure of energy, 2) a higher caloric efficiency of regain that may be linked with suppressed lipid utilization early in the relapse process, 3) preferential lipid accumulation in adipose tissue accompanied by adipocyte hyperplasia, and 4) humoral adiposity signals that underestimate the level of peripheral adiposity and likely influence the neural pathways controlling energy balance. Taken together, long-term weight reduction in this rodent paradigm is accompanied by a number of interrelated compensatory adjustments in the periphery that work together to promote rapid and efficient weight regain. These metabolic adjustments to weight reduction are discussed in the context of a homeostatic feedback system that controls body weight.