The influence of reduced insulin sensitivity via short-term reductions in physical activity on cardiac baroreflex sensitivity during acute hyperglycemia.

Reduced insulin sensitivity and impaired glycemic control are among the consequences of physical inactivity and have been associated with reduced cardiac baroreflex sensitivity (BRS). However, the effect of reduced insulin sensitivity and acute hyperglycemia following glucose consumption on cardiac BRS in young, healthy subjects has not been well characterized. We hypothesized that a reduction in insulin sensitivity via reductions in physical activity would reduce cardiac BRS at rest and following an oral glucose tolerance test (OGTT). Nine recreationally active men (23 ± 1 yr; >10,000 steps/day) underwent 5 days of reduced daily physical activity (RA5) by refraining from planned exercise and reducing daily steps (<5,000 steps/day). Spontaneous cardiac BRS (sequence technique) was compared at rest and for 120 min following an OGTT at baseline and after RA5. A substudy (n = 8) was also performed to independently investigate the influence of elevated insulin alone on cardiac BRS using a 120-min hyperinsulinemic-euglycemic clamp. Insulin sensitivity (Matsuda index) was significantly reduced following RA5 (BL 9.2 ± 1.3 vs. RA5 6.4 ± 1.1, P < 0.001). Resting cardiac BRS was unaffected by RA5 and significantly reduced during the OGTT similarly at baseline and RA5 (baseline 0 min, 28 ± 4 vs. 120 min, 18 ± 4; RA5 0 min, 28 ± 4 vs. 120 min, 21 ± 3 ms/mmHg). Spontaneous cardiac BRS was also reduced during the hyperinsulinemic-euglycemic clamp (P < 0.05). Collectively, these data demonstrate that acute elevations in plasma glucose and insulin can impair spontaneous cardiac BRS in young, healthy subjects, and that reductions in cardiac BRS following acute hyperglycemia are unaffected by reduced insulin sensitivity via short-term reductions in physical activity.

A pilot study examining the effects of consuming a high-protein vs normal-protein breakfast on free-living glycemic control in overweight/obese 'breakfast skipping' adolescents.

To examine whether the daily consumption of normal-protein (NP) vs higher-protein (HP) breakfasts improve free-living glycemic control in overweight/obese, 'breakfast skipping' adolescents. Twenty-eight healthy, but overweight, teens (age: 19±1 year; BMI: 29.9±0.8 kg m(-2)) completed a 12-week randomized parallel-arm study in which the adolescents consumed either a 350 kcal NP breakfast (13 g protein) or HP breakfast (35 g protein). Pre- and post-study 24-h blood glucose measures were assessed using continuous glucose monitoring. Although no main effects of time or group were detected, time by group interactions were observed. Post hoc pairwise comparisons assessing the post-pre changes revealed that the daily consumption of the HP breakfasts tended to reduce the 24-h glucose variability (s.d.) vs NP (-0.17±0.09 vs +0.09±0.10 s.d.; P=0.06) and tended to reduce the time spent above the high glucose limit (-292±118 vs -24±80 min; P=0.09). The consumption of the HP breakfasts also reduced the 24-h maximal (peak) glucose response (-0.94±0.36 vs +0.30±0.18 mmol l(-1); P<0.01) and reduced postprandial glucose fluctuations (-0.88±0.44 vs +0.49±0.34 mmol l(-1); P<0.03) vs NP. These data suggest that the daily addition of a HP breakfast, containing 35 g of high-quality protein, has better efficacy at improving free-living glycemic control compared with a NP breakfast in overweight/obese, but otherwise healthy, 'breakfast skipping' adolescents.

The effect of breakfast type and frequency of consumption on glycemic response in overweight/obese late adolescent girls.

BACKGROUND/OBJECTIVES: The primary aim was to examine the daily glycemic response to normal-protein (NP) vs higher-protein (HP) breakfasts in overweight adolescents who habitually skip breakfast (H-BS). The secondary aim examined whether the glycemic response to these meals differed in H-BS vs habitual breakfast consumers (H-BC). SUBJECTS/METHODS: Thirty-five girls (age: 19 ± 1 year; body mass index: 28.4 ± 0.7 kg/m(2)) participated in the semi-randomized crossover-design study. The participants were grouped according to habitual breakfast frequency. H-BS (n = 20) continued to skip breakfast (BS) or consumed a NP (12 g protein) or HP (32 g protein) breakfast for 3 days, whereas the H-BC (n = 15) completed the NP and HP breakfast conditions for 3 days. On day 4 of each pattern, an 8 h testing day was completed. The respective breakfast and a standard lunch meal were provided, and plasma was collected to assess morning, afternoon, and total glucose and insulin area under the curves (AUC). RESULTS: In H-BS, the addition of a HP breakfast increased total glucose AUC vs BS (P < 0.05), whereas NP breakfast increased total insulin AUC vs BS (P < 0.05). In H-BC, the HP breakfast reduced morning, afternoon and total glucose AUCs vs NP (all, P < 0.05). No differences in insulin were detected. When comparing the HP-NP differential glycemic responses between groups, H-BS experienced greater afternoon and total glucose AUCs following HP vs NP breakfasts (both, P<0.05). No differences in insulin responses were observed between groups. CONCLUSIONS: Novel differences in the glucose response to HP vs NP breakfasts were observed and were influenced by the frequency of habitual breakfast consumption in overweight adolescents.

Estrogen and progesterone exposure is reduced in response to energy deficiency in women aged 25-40 years.

BACKGROUND: Alterations in circulating steroids are believed to be important mediators of the impact that diet and exercise have on breast cancer risk and changes in bone density. This study aimed to test the hypothesis that moderate exercise training combined with caloric restriction would produce significant menstrual disturbances and alterations in ovarian steroids in premenopausal women. METHODS: Sedentary premenopausal women (25-40 years; body mass index: 23.6 +/- 0.6 kg/m(2)) assigned to either a light conditioning (LC, n = 9) or an exercise combined with caloric restriction group (EX + CR, n = 24) were studied for one screening, one baseline and four intervention periods equivalent to the length of subjects' menstrual cycles. Exercise consisted of supervised training sessions, i.e. two LC or four EX + CR times per week, 30-60 min at a moderate intensity. The EX + CR group was prescribed a diet representing a caloric restriction of 20-35% below baseline energy requirements, whereas the LC group remained eucaloric. Ovarian steroid exposure was determined with daily urinary estrone-1- and pregnanediol glucuronides (E1G and PdG, respectively) and mid-cycle urinary LH measures. Fitness, body composition, and serum sex hormone binding globulin (SHBG) and serum estradiol (E2) were assessed repeatedly. RESULTS: The intervention produced significant increases in VO(2) max and decreases in both body weight (-3.7 +/- 0.5 kg; ranged from -8.8 to +1.8 kg) and percent body fat (-4.5 +/- 0.7%; ranged from -12 to +0.3%), which were attributable primarily to changes in the EX + CR subjects (time x group; P < 0.05). Serum E2 and urinary E1G and PdG concentrations declined significantly across the intervention period (time; P < 0.05), whereas SHBG increased transiently (time; P < 0.05) in the EX + CR subjects, with no significant changes observed in the LC group. The decrease in E1G area under the curve was significantly related to the daily energy deficit (R =0.61; P = 0.003), not the amount of weight lost. There was no significant impact of the intervention on menstrual cyclicity or the incidence of menstrual disturbances in either group. CONCLUSIONS: A moderate aerobic exercise training program combined with modest weight loss in accordance with recommended guidelines produces significant reductions in ovarian steroid exposure without disrupting menstrual cyclicity in premenopausal women aged 25-40 years. Exposure to a daily energy deficit is a stronger predictor of the decline in estrogen exposure than decreases in body weight.

The addition of a protein-rich breakfast and its effects on acute appetite control and food intake in 'breakfast-skipping' adolescents.

BACKGROUND: Breakfast skipping (BS) is closely associated with overeating (in the evening), weight gain and obesity. It is unclear whether the addition of breakfast, with emphasis on dietary protein, leads to better appetite and energy intake regulation in adolescents. OBJECTIVE: The purpose of the study was to examine the impact of addition of a normal-protein (PN) breakfast vs protein-rich (PR) breakfast on appetite and food intake in 'breakfast-skipping' adolescents. SUBJECTS AND DESIGN: A total of 13 adolescents (age 14.3+/-0.3 years; body mass index percentile 79+/-4 percentile; skipped breakfast 5+/-1 x per week) randomly completed 3 testing days that included a PN (18+/-1 g protein), PR (48+/-2 g protein) or BS. Breakfast was 24% of estimated daily energy needs. Appetite, satiety and hormonal responses were collected over 5 h followed by an ad libitum lunch and 24-h food intake assessments. RESULTS: Perceived appetite was not different following PN vs BS; PR led to greater reductions vs BS (P<0.01) and PN (P<0.001). Fullness was greater following both breakfast meals vs BS (P<0.01) but was not different between meals. Ghrelin was not different among treatments. Greater PYY concentrations were observed following both breakfast meals vs BS (P<0.01) but was not different between meals. Lunch energy intake was not different following PN vs BS; PR led to fewer kcal consumed vs BS (P<0.01) and PN (P<0.005). Daily food intake was not different among treatments. CONCLUSIONS: Breakfast led to increased satiety through increased fullness and PYY concentrations in 'breakfast skipping' adolescents. A breakfast rich in dietary protein provides additional benefits through reductions in appetite and energy intake. These findings suggest that the addition of a protein-rich breakfast might be an effective strategy to improve appetite control in young people.

Effects of solid versus liquid meal-replacement products of similar energy content on hunger, satiety, and appetite-regulating hormones in older adults.

OBJECTIVE: To examine whether solid versus liquid meal-replacement products differentially affect appetite and appetite-regulating hormones in older adults. METHODS: On two occasions, 9 subjects (age: 61+/-3 years; BMI: 25.6+/-1.3 kg/m (2)) consumed 25% of daily energy needs as solid or liquid meal-replacements of similar energy contents. Blood and appetite ratings were collected over 4 hours. RESULTS: The post-prandial hunger composite (area under the curve) was lower following the solid versus liquid meal-replacement (p<0.005) and remained below baseline over 4 hours (p<0.05). Similar responses were observed with the desire to eat. The insulin and ghrelin composites were lower following the solid trial compared to the liquid [insulin: 5825 (range: 4676-11639) VS. 7170 (4472-14169) uIU/l x 240 min, p<0.01; ghrelin: -92798 (range: -269130-47528) VS. -56152 (range: -390855-30840) pg/ml x 240 min, p<0.05]. Ghrelin also remained below baseline over 4 hours (p<0.05). No differences in cholecystokinin and leptin were observed between products. CONCLUSION: The consumption of comparable meal-replacement products in solid versus liquid versions with similar energy contents led to differential appetitive responses and should not be viewed as dietary equivalents in older adults.

Meal energy content is related to features of meal-related ghrelin profiles across a typical day of eating in non-obese premenopausal women.

UNLABELLED: Some features of the meal-related profile of ghrelin correspond to acute energy intake, suggesting a role in short-term energy homeostasis. Yet, no studies have examined this relationship across a typical day of eating when effects of time of day and or cumulative energy intake may also exist. AIM OF STUDY: To examine the relation between ghrelin and acute energy intake by quantifying changes in ghrelin over 24 hours in response to three typical meals and a snack occurring throughout the day. METHODS: Fourteen non-obese women consumed three meals and a snack at specific times; total ghrelin was measured repeatedly over 24 hours. RESULTS: Significant correlations existed between: 1) meal calories and the post-meal trough (r = - 0.36; p < 0.05), and 2) the sum of breakfast and lunch calories and subsequent dinner rise (r = - 0.45; p < 0.02) and 3) the sum of breakfast and lunch calories and dinner peak (r = - 0.54; p < 0.003). Thus, as energy intake increased across the day, pre-meal rises of subsequent meals were reduced. CONCLUSION: Meal-related profiles of ghrelin are not only associated with the energy content of specific meals, but also with the accumulated calories prior to a subsequent meal, suggesting a role in the modulation of acute energy homeostasis.

Circulating ghrelin is sensitive to changes in body weight during a diet and exercise program in normal-weight young women.

Ghrelin is directly involved with short-term regulation of energy balance. Although circulating levels of ghrelin are elevated in anorexia nervosa and reduced in obesity, the role of ghrelin in regulating long-term energy balance in healthy women has not been investigated. We examined the effects of a 3-month energy deficit-imposing diet and exercise intervention on circulating ghrelin in normal-weight, healthy women. Body composition, resting metabolic rate, and serum ghrelin were measured at pre-, mid-, and postintervention in controls (n = 7), who performed no exercise, and exercising women who remained weight stable (n = 5) or lost weight (n = 10). Exercise training occurred five times per week, and subjects were fed a specific diet. Ghrelin significantly increased over time (770 +/- 296 to 1322 +/- 664 pmol/liter) in the weight-loss group compared with the controls and the weight-stable group (P < 0.05). Changes in ghrelin were negatively correlated with changes in body weight (r = -0.61; P < 0.05). Body fat, body weight, and resting metabolic rate significantly decreased in the weight-loss group before the increase in ghrelin. These findings suggest that ghrelin responds in a compensatory manner to changes in energy homeostasis in healthy young women, and that ghrelin exhibits particular sensitivity to changes in body weight.