Narumi Nagai

This study was designed to investigate the effect of skipping breakfast and macro-nutrient balance on postprandial blood glucose (BG), satiety, energy expenditure (EE), and autonomic nervous system (ANS) activity in healthy subjects with and without polymorphism of the uncoupling protein-1 (UCP 1) gene. Eight healthy young subjects were given breakfast and lunch (CC ; high-carbohydrate meal (HC) + HC, SC ; no breakfast + doubled HC lunch, FF ; high-fat meal (HF) + HF, SF ; no breakfast + doubled HF lunch) at random on four different days. The total calories of each test diet were the same and were adjusted individually to each subject's body-mass (22 kcal/kg). BG, satiety score, EE and ANS activity were measured before breakfast and at 30-minutes intervals for 6 hours after breakfast. During the first 3 hours significantly higher BG, satiety scores, and EE were found after the CC test, than after the FF test. Postprandial thermogenesis during the 6 hours after the CC test was higher than after the other diets. The ANS seemed to play a role in the higher level of satiety and thermogenesis ; however, the difference in ANS activity was not significant. The subjects with the GG allele of the UCP 1 gene showed lower postprandial thermogenesis. In conclusion, a HC meal for breakfast and well-regulated diet can contribute to the prevention of obesity in individuals with normal glucose tolerance. Our results suggest that genetic background is also important to prevention of obesity.

The present study was designed to investigate the metabolic and sympathetic responses to a high-fat meal in humans. Fourteen young men (age: 23.6 +/- 0.5 y, BMI: 21.3 +/- 0.4 kg/m2) were examined for energy expenditure and fat oxidation measured by indirect calorimetry for 3.5 h after a high-fat (70%, energy from fat) or an isoenergetic low-fat (20% energy from fat) meal served in random order. The sympathetic nervous system (SNS) activity was assessed using power spectral analysis of heart rate variability (HRV). After the high-fat meal, increases in thermoregulatory SNS activity (very low-frequency component of HRV, 0.007-0.035 Hz, 577.4+/-45.9 vs. 432.0+/-49.3 ms2, p<0.05) and fat oxidation (21.0+/-5.3 vs. 13.3+/-4.3 g, p<0.001) were greater than those after the low-fat meal. However, thermic effects of the meal (TEM) were lower after the high-fat meal than after the low-fat meal (27.5+/-11.2 vs. 36.1+/-10.9 kcal, p<0.05). In conclusion, the high-fat meal can stimulate thermoregulatory SNS and lipolysis, but resulted in lower TEM, suggesting that a high proportion of dietary fat intake, even with a normal daily range of calories, may be a potent risk factor for further weight gain.

This paper summarizes my Basmajian keynote presentation at the 2004 International Society of Electrophysiology and Kinesiology Conference. I dedicate this paper to Dr. Herbert A. deVries, the mentor of my research career. The following topics will be covered from the standpoint of Electrophysiology and Kinesiology for health and disease: (1) electromechanical manifestations of neuromuscular fatigue and muscle soreness, (2) cardiac depolarization-repolarization characteristics of normal and patients, (3) etiology of obesity and diabetes and autonomic nervous system, and (4) functional electrical stimulation for health and disease, respectively.

The purpose of the present study was to investigate the thermic effect of food (TEF) and sympathetic nervous system (SNS) activity in obese boys. Ten obese (9.2+/-0.4 years) and 13 lean boys (8.8+/-0.4 years) were examined for energy expenditure and fat oxidation measured via indirect calorimetry for 3 hours after a high-carbohydrate (HC; 70% carbohydrate, 20% fat, and 10% protein) or a high-fat (HF; 20% carbohydrate, 70% fat, and 10% protein) meal served on 2 different days at random. The activity of the SNS was assessed by means of a power spectral analysis of the heart rate variability. The TEF, expressed as a percentage of the consumed energy, was significantly lower in obese boys than in lean boys after the HC meal; however, such a difference was not observed after the HF meal. Multiple regression analysis revealed that obesity was a significant variable contributing to the variances in the TEF induced by the HC meal. Moreover, after the HC meal, the boys with a recent onset of obesity (duration, <3 years) manifested a lower TEF as well as a reduced very low frequency component of the heart rate variability, an index of thermoregulatory SNS functions, compared with the remaining obese and lean boys. In conclusion, obese boys possessed normal metabolic and sympathetic responses to the HF meal but showed a diminished thermogenic response to the HC meal, especially during the early phase of obesity.

OBJECT: Our objective was to investigate the effect of a long-term moderate exercise program on cardiac autonomic nervous system (ANS) activity in healthy children. METHODS: Three hundred and five children aged 6-11 years participated in a 12-month school-based exercise training program (130-140 bpm, 20 min/day, 5 days/week). Cardiac ANS activities were measured using heart rate variability (HRV) power spectral analysis in resting conditions. Following the first measurement, 100 children from the lowest total power (TP) HRV were chosen as experimental samples and the same number of age-, height-, and weight-matched controls (CG) was randomly selected from the remaining children. RESULTS: In the low group (LG), all the frequency components of the HRV were significantly increased after the training period, whereas only low-frequency power was augmented in the control group (CG). CONCLUSION: Our data suggest that the 12-month moderate exercise training has a positive effect on cardiac ANS activity in the children who initially had low HRV.

OBJECTIVE: The autonomic nervous system (ANS) is a key factor in the regulation of energy balance and body fat storage; however, to what extent the physical activity during the childhood years contributes to variations in ANS function is still unclear. The present study was designed to investigate the ANS activity in lean and obese children, focusing on the differences in physical activity levels. SUBJECTS: This study was performed on 1080 school children initially recruited to the present study. In all, 24 physically active and 24 inactive obese children (greater than or equal to120% of the standard body weight) were chosen as samples. Then, 24 lean-active and 24 lean-inactive children, who were matched individually in age, gender, height, and the amount of sports activity, were carefully selected from the remaining children. MEASUREMENTS: Physical activity was classified as the frequency of participation in after-school sports activities ( active; greater than or equal to3 times per week, inactive; nothing). The ANS activities were measured during the resting condition by means of heart rate (HR) variability power spectral analysis, which enables us to identify separate frequency components, that is, low frequency (LF; 0.03 - 0.15 Hz), reflecting mixed sympathetic (SNS) and parasympathetic nervous system (PNS) activity, high frequency (HF; 0.15 - 0.5 Hz), mainly associated with PNS activity, and total power (TP; 0.03 - 0.5 Hz), evaluating the overall ANS activity. The spectral powers were log transformed for statistical testing. RESULTS: The lean-active group demonstrated lower resting HR as well as significantly higher TP, LF, and HF powers compared to the remaining groups. In contrast, the obese-inactive group showed significantly lower TP (P&lt;0.05 vs the remaining groups), LF (P&lt;0.05 vs the lean groups), and HF power (P&lt;0.05 vs the lean groups), respectively. The obese-active and lean-inactive groups were nearly identical in all spectral parameters. The correlation analysis revealed that TP among 48 inactive children was significantly and negatively associated with the percentage of body fat ( r = - 0.53, P&lt;0.001); however, such correlation among 48 active children was modest ( r = - 0.33, P = 0.02). CONCLUSION: Our data suggest that obese children possess reduced sympathetic as well as parasympathetic nervous activities as compared to lean children who have similar physical activity levels. Such autonomic reduction, associated with the amount of body fat in inactive state, might be an etiological factor of onset or development of childhood obesity. On the other hand, regular physical activities could contribute to enhance the overall ANS activity in both lean and obese children. These findings further imply that regular physical activity might be effective in preventing and treating obesity beginning in the childhood.

This study investigated whether the -3826 A-->G nucleotide variant of the uncoupling protein-1 (UCP1) gene is correlated with postprandial thermogenesis after a high fat meal in children. Healthy boys, aged 8-11 yr, were examined for resting energy expenditure and the thermic effect of a meal (TEM), which were measured by indirect calorimetry for 180 min after a high fat (70% fat, 20% carbohydrate, and 10% protein, providing 30% of the daily energy requirement) and a high carbohydrate meal (20% fat, 70% carbohydrate, and 10% protein). The sympatho-vagal activities were assessed by means of spectral analysis of the heart rate variability during the same period. Children were genotyped for UCP1 polymorphism by applying a PCR-restriction fragment length polymorphism using buccal samples. There was no reaction of sympathetic activity to the high carbohydrate meal in either the GG allele or the AA+AG group and no significant difference in TEM. However, after the high fat meal, sympathetic responses were found in both groups; further, the GG allele group showed significantly lower TEM than the AA+AG group. In conclusion, despite fat-induced sympathetic stimulation, GG allele carriers have a lowered capacity of TEM in response to fat intake, suggesting that such impaired UCP1-linked thermogenesis can have adverse effects on the regulation of body weight.

OBJECTIVE: The autonomic nervous system (ANS) plays an important role in regulating energy expenditure and body fat content; however, the extent to which the ANS contributes to pediatric obesity remains inconclusive. The aim of this study was to evaluate whether sympathetic and/or the parasympathetic nerve activities were altered in an obese pediatric population. We further examined a physiological association between the duration of obesity and the sympatho-vagal activities to scrutinize the nature of ANS alteration as a possible etiologic factor of childhood obesity. RESEARCH METHODS AND PROCEDURES: Forty-two obese and 42 non-obese healthy sedentary school children were carefully selected from 1080 participants initially recruited to this study. The two groups were matched in age, gender, and height. The clinical records of physical characteristics and development of the obese children were retrospectively reviewed to investigate the onset and progression of obesity. The ANS activities were assessed during a resting condition by means of heart rate variability power spectral analysis, which enables us to identify separate frequency components, i.e., total power (TP), low-frequency (LF) power, and high-frequency (HF) power. The spectral powers were then logarithmically transformed for statistical testing. RESULTS: The obese children demonstrated a significantly lower TP (6.77 +/- 0.12 vs. 7.11 +/- 0.04 ln ms(2), p < 0.05), LF power (6.16 +/- 0.12 vs. 6.42 +/- 0.05 ln ms(2), p < 0.05), and HF power (5.84 +/- 0.15 vs. 6.34 +/- 0.07 ln ms(2), p < 0.01) compared with the non-obese children. A partial correlation analysis revealed that the LF and HF powers among 42 obese children were negatively associated with the duration of obesity independent of age (LF: partial r = -0.55, p < 0.001; HF: partial r = -0.40, p < 0.01). The obese children were further subdivided into two groups based on the length of their obesity. All three spectral powers were significantly reduced in the obese group with obesity of >3 years (n = 18) compared to the group with obesity of <3 years. DISCUSSION: Our data indicate that obese children possess reduced sympathetic as well as parasympathetic nerve activities. Such autonomic depression, which is associated with the duration of obesity, could be a physiological factor promoting the state and development of obesity. These findings further imply that preventing and treating obesity beginning in the childhood years could be an urgent and crucial pediatric public health issue.