不同干预方式对超重、肥胖青少年体重指数和体脂含量的影响

目的 观察不同干预方式对超重、肥胖青少年体重指数(BMI)和体脂含量的影响,以期得到合理有效的青少年减重方案.方法 选择北京市某初中67名超重、肥胖学生为研究对象,采用随机配伍法随机分为对照组(n=16)、膳食干预组(n=22)和综合干预组(膳食+运动,n=29)3组,观察干预前后BMI和体脂率的变化情况.结果 膳食干预组(P=0.000)和综合干预组(P=0.018)试验后的BMI明显低于试验前,膳食干预组BMI的降低幅度明显大于对照组(P=0.035).膳食干预组(P=0.000,P=0.013)和综合干预组(P=0.000,P=0.000)试验后的躯干和全身体脂率均明显低于试验前,综合于预组躯干和全身体脂率的降低幅度明显大于对照组(P=0.005,P=0.003).结论 膳食和综合干预都可使青少年达到减重效果,综合干预效果更佳.

Abstract：

Objective To observe the effects of different interventions on the body mass index (BMI) and body fat content in overweight and obese adolescents, with an attempt to design reasonable weight relief program.Methods Totally 67 overweight or obese adolescents from a middle school of Beijing were randomly divided into three groups: control group ( n = 16 ), diet intervention group ( n= 22), and combined interventions group ( n =29). The changes of BMI and body fat rate (BFR) were observed. Results BMI significantly decreased after interventions ( diet intervention group: P = 0. 000; combined interventions group: P = 0. 018 ); the change of BMI in diet intervention group was significantly larger than that in control group ( P = 0. 035 ). The trunk and body BFRs also significantly decreased after interventions (diet intervention group: P=0. 000, P = 0. 013; combined interventions group: P = 0. 000, P = 0. 000 ); the changes of trunk and body BFRs were significantly larger in combined interventions group than those in control group ( P = 0.005, P = 0. 003 ). Conclusion Diet intervention and combined interventions are both effective in achieving weight loss in adolescents, and combined interventions have superior effectiveness.     

Anthropometric body fat composition reference values in Spanish adolescents. The AVENA Study

OBJECTIVE: To determine reference values for body mass index (BMI), sum of six skinfolds (sigma6 skinfolds) and body fat percentage (BF%) in Spanish adolescents aged 13-18 years, included in the AVENA Study (Alimentación y Valoración del Estado Nutricional en Adolescentes: Food and Assessment of the Nutritional Status of Adolescents). DESIGN: Multicentre cross-sectional study. SETTING: Representative sample of Spanish adolescents. SUBJECTS: The population was selected by means of a multiplestep, simple random sampling. The final number of subjects included in the AVENA Study was 2859 adolescents; 2160 adolescents had a complete set of anthropometric measurements and were then included in this study (1109 males and 1051 females). INTERVENTIONS: Weight, height and six skinfold thicknesses were measured. As indices of total adiposity, we calculated BMI, summation sigma6 skinfolds and BF% with the formulas described by Slaughter et al. RESULTS: Sigma6 skinfolds and BF% in each age group were significantly higher in females than in males. In males, age showed a significant effect for BMI, sigma6 skinfolds and BF%; however, in females, the effect was only significant for BF%. The percentile distribution was more disperse towards higher sigma6 skinfolds and BF% values in males when compared with females. CONCLUSIONS: The presented percentile values will help us to classify adolescents in comparison with a well-established reference population, and to estimate the proportion of adolescents with high or low adiposity amounts. SPONSORSHIP: The AVENA-Study was supported by the Spanish Ministry of Health (FIS 00/0015), and grants from Panrico SA, Madaus SA and Procter and Gamble SA. This study was also supported by Instituto de Salud Carlos III (Spain), RCESP (C03/09) and Spanish Ministry of Education (AP2003-2128).     

Limits of body mass index to detect obesity and predict body composition

Body mass index (BMI) is commonly used to identify obesity. In this study, we determined how accurately BMI could determine body composition and identify obese from non-obese individuals. Fat-free mass and body fat were determined with bioelectrical impedance. Adiposity was calculated as body fat per body mass and as body fat divided by body height (m2). Obesity was defined as a BMI of at least 30 kg/m2 or an amount of body fat of at least 25% of total body mass for men and at least 30% for women. Obesity as defined by percentage of body fat was always present with a BMI of at least 30 kg/m2. However, 30% of men and 46% of women with a BMI below 30 kg/m2 had obesity levels of body fat. The greatest variability in the prediction of percentage of body fat and body fat divided by height (m2) from regression equations using BMI was at a BMI below 30 kg/m2. In conclusion, using impedance-derived body-fat mass as the criterion, people with BMI of at least 30 kg/m2 are obese. However, significant numbers of people with a BMI below 30 kg/m2 are also obese and thus misclassified by BMI. Percent of body fat and body fat divided by height (m2) are predictable from BMI, but the accuracy of the prediction is lowest when the BMI is below 30 kg/m2. Therefore, measurement of body fat is a more appropriate way to assess obesity in people with a BMI below 30 kg/m2.     

Screening performances of the International Obesity Task Force body mass index cut-off values in adolescents

OBJECTIVE: To try to improve the International Obesity Task Force (IOTF) BMI cut-off values, in terms of prediction of body fat percentage assessed by dual-energy X-ray absorptiometry (DXA), in adolescents. METHODS: Cross-sectional survey of the adolescents from the city of Zaragoza (Spain). For this analysis we have included 286 adolescents (116 boys and 170 girls) aged 13.0-17.9 years. Body mass index (BMI) was calculated as body weight (kg), divided by height (m) squared. The percentage of body fat (BF%) was estimated by the use of DXA. RESULTS: We have calculated, new BMI cut-off values (AVENA cut-offs) to predict BF%, for boys and girls in each age group. In male adolescents, sensitivity was higher with the IOTF cut-offs (0.71, 95th C.I.: 0.44, 0.90) than with the AVENA ones (0.53, 95th C.I.: 0.28, 0.77), and specificity was very similar with both cut-off values (0.86 and 0.88, respectively), the differences being not statistically significant. In girls, both sensitivities (0.75 and 0.79, respectively) and specificities (0.90 and 0.92, respectively) were very similar with both cut-off values, and the differences, not significant. CONCLUSIONS: Optimization of the IOTF BMI cut-off values, in terms of BF%, seems not to be possible in adolescents. The IOTF criteria should be used only for overweight and obesity screening; however, in clinical settings, a more accurate measure of body fat should be recommended.     

Excess body fat negatively affects bone mass in adolescents

ObjectiveThe aim of this study was to investigate the effects of excess body fat on bone mass in overweight, obese, and extremely obese adolescents.MethodsThis study included 377 adolescents of both sexes, ages 10 to 19 y. Weight, height, body mass index (BMI), bone age, bone mineral content (BMC), and bone mineral density (BMD) were obtained by dual-energy x-ray absorptiometry. The results were adjusted for chronological age and bone age. Comparisons according to nutritional classification were performed by analysis of variance, followed by Tukey test. Linear regression models were used to explain the variation in BMD and BMC in the L1–L4 lumbar spinal region, proximal femur, and whole body in relation to BMI, lean mass, fat mass (FM), and body fat percentage (BF%), considering P < 0.05.ResultsFor all nutritional groups, average bone age was higher than chronological age. In both sexes, weight and BMI values increased from eutrophic to extremely obese groups, except for BMD and BMC, which did not differ among male adolescents, and were smaller in extremely obese than in obese female adolescents (P < 0.01). Significant differences were observed for FM and BF% values among all nutritional groups (P < 0.01). Positive, moderate to strong correlations were detected between BMD and BMC for BMI, lean mass, and FM. A negative and moderate correlation was found between BMC and BF%, and between BMD and BF% at all bone sites analyzed in males and between BF% and spine and femur BMD, in females.ConclusionThe results reveal a negative effect of BF% on bone mass in males and indicate that the higher the BF% among overweight adolescents, the lower the BMD and BMC values.     

Sedentarism affects body fat mass index and fat-free mass index in adults aged 18 to 98 years

OBJECTIVE: Body mass index does not discriminate body fat from fat-free mass or determine changes in these parameters with physical activity and aging. Body fat mass index (BFMI) and fat-free mass index (FFMI) permit comparisons of subjects with different heights. This study evaluated differences in body mass index, BFMI, and FFMI in physically active and sedentary subjects younger and older than 60 y and determined the association between physical activity, age, and body composition parameters in a healthy white population between ages 18 and 98 y. METHODS: Body fat and fat-free mass were determined in healthy white men (n = 3549) and women (n = 3184), between ages 18 and 98 y, by bioelectrical impedance analysis. BFMI and FFMI (kg/m2) were calculated. Physical activity was defined as at least 3 h/wk of endurance-type activity for at least 2 mo. RESULTS: Physically active as opposed to sedentary subjects were more likely to have a low BFMI (men: odds ratio [OR], 1.4; confidence interval [CI], 0.7-2.5; women: OR 1.9, CI 1.6-2.2) and less likely to have very high BFMI (men: OR, 0.2; CI, 0.1-0.2; women: OR, 0.1; CI, 0.02-0.2), low FFMI (men: OR, 0.5; CI, 0.3-0.9; women: OR, 0.7; CI, 0.6-0.9), or very high FFMI (men: OR, 0.6; CI, 0.4-0.8; women: OR, 0.7; CI, 0.5-1.0). Compared with subjects younger than 60 y, those older than 60 y were more like to have very high BFMI (men: OR, 6.5; CI, 4.5-9.3; women: OR, 14.0; CI, 9.6-20.5), and women 60 y and older were less likely to have a low BFMI (OR, 0.4; CI, 0.2-0.5). CONCLUSIONS: A clear association was found between low physical activity or age and height-normalized body composition parameters (BFMI and FFMI) derived from bioelectrical impedance analysis. Physically active subjects were more likely to have high or very high or low FFMI. Older subjects had higher body weights and BFMI.     

Body mass index as an estimate of body fat

Body mass index (BMI) was compared with percentage body fat (%Fat) measured by dual energy X-ray absorptiometry (DXA) in 233 adolescent schoolgirl volunteers and 179 adult female patients. Repeat measurements were made on 67 of the adolescents and 51 of the adults. The correlations between BMI and %Fat were established from the 300 adolescent measurements and the 230 adult measurements. Although highly significant relationships were found between BMI and %Fat, only 58% of the variance in %Fat in adolescents and 66% in adults could be predicted by BMI. At the 95% confidence levels, a BMI of 20 kg m⁻² can correspond to a range of 18–33% body fat in adolescents and 13–32% in adults. Without any change in BMI, an adolescent's percentage fat can change by as much as -3% to + 7%. For an individual adult the same BMI can correspond to changes in fat of ±5%. Since the strength of prediction of percentage body fat from BMI is poor, caution should be exercised in its use for eating disorders research. © 1995 by John Wiley & Sons, Inc.     

Optimal cutoff values for overweight: using body mass index to predict incidence of hypertension in 18- to 65-year-old Chinese adults

Studies aimed at identifying BMI cutoffs representing increased diseased risk for Asians are typically based on cross-sectional studies. This study determines an optimal BMI cutoff for overweight that represents elevated incidence of hypertension in Chinese adults with data from the China Health and Nutrition Survey 2000-2004 prospective cohort. Cumulative incidence was calculated by dividing new cases of hypertension over the study period by the total at-risk population, aged 18-65 y, in 2000. Sex-specific receiver operating characteristic curves were used to assess the sensitivity and specificity of BMI as a predictor of hypertension incidence. Four-year cumulative incidences of hypertension (13% for women and 19% for men) were related (P < 0.005) to the increase in BMI. The crude area under the curves (AUC) were 0.62 (95% CI: 0.59-0.65) and 0.62 (95% CI: 0.58-0.65) for men and women, respectively; the age-adjusted AUC were 0.68 (95% CI: 0.65-0.70) and 0.71 (95% CI: 0.68-0.74) for men and women, respectively. A BMI of 23.5 kg/m(2) for women and 22.5 kg/m(2) for men provided the highest sensitivity and specificity (60%). The finding was consistent in different age groups. A BMI level of 25 kg/m(2) provided lower sensitivities (36% for women and 29% for men) with higher specificities (80% for women and 85% for men). Our study supported the hypothesis that the BMI cutoff to define overweight should be lower in Chinese than that in Western populations.     

Ethnic differences in the relationship between body mass index and percentage body fat among Asian children from different backgrounds

Overweight and obesity in Asian children are increasing at an alarming rate; therefore a better understanding of the relationship between BMI and percentage body fat (%BF) in this population is important. A total of 1039 children aged 8-10 years, encompassing a wide BMI range, were recruited from China, Lebanon, Malaysia, The Philippines and Thailand. Body composition was determined using the 2H dilution technique to quantify total body water and subsequently fat mass, fat-free mass and %BF. Ethnic differences in the BMI-%BF relationship were found; for example, %BF in Filipino boys was approximately 2 % lower than in their Thai and Malay counterparts. In contrast, Thai girls had approximately 2.0 % higher %BF values than in their Chinese, Lebanese, Filipino and Malay counterparts at a given BMI. However, the ethnic difference in the BMI-%BF relationship varied by BMI. Compared with Caucasian children of the same age, Asian children had 3-6 units lower BMI at a given %BF. Approximately one-third of the obese Asian children (%BF above 25 % for boys and above 30 % for girls) in the study were not identified using the WHO classification and more than half using the International Obesity Task Force classification. Use of the Chinese classification increased the sensitivity. Results confirmed the necessity to consider ethnic differences in body composition when developing BMI cut-points and other obesity criteria in Asian children.     

Impact of calcium intake on body mass index in Venezuelan adolescents

The prevalence of overweight and obesity is increasing worldwide, affecting approximately 15% of adolescents in Venezuela, 17% in United States, and more than 30% in Mexico and Puerto Rico. Recent studies have shown that dietary calcium and dairy intake are associated with body fat. These studies show that a high calcium intake results in low body mass index (BMI). Therefore, the objective of the present study is to relate calcium intake from foods rich in calcium-rich foods to body weight and BMI in a random sample of 100 adolescents, aged 13-18 years. Anthropometric measurements (weight and height) were obtained for each participant, who also completed a food frequency questionnaire (FFQ), modified with calcium-rich foods. Dietary calcium consumption was 1076+/-534 mg/d among the adolescents, which represented an adequacy of 90%. A negative and significant association was found between calcium intake and BMI in the boys aged 13-15 years (r=-0.39, p<0.05). This population subgroup exhibited the widest range of BMI values among all groups evaluated. This correlation was not found among the older boys (aged 16-18 years) or girls, in which BMI was in the normal range and with relatively high calcium intake. In conclusion, we found that high calcium intake in younger boys was related to a lower BMI. A high calcium intake, not only helps to maintain a healthy body weight, but also is essential for acquiring peak bone mass in this crucial stage of life.     

A test of the resource security and the body mass index reference point hypotheses of body dissatisfaction amongst adolescents in eight countries

Objective. This study aimed to identify cultural-level variables that may influence the extent to which adolescents from different cultural groups are dissatisfied with their bodies.

Design. A sample of 1730 male and 2000 female adolescents from Australia, Fiji, Malaysia, Tonga, Tongans in New Zealand, China, Chile, and Greece completed measures of body satisfaction, and the sociocultural influences on body image and body change questionnaire, and self-reported height and weight. Country gross domestic product and national obesity were recorded using global databases.

Results. Prevalence of obesity/overweight and cultural endorsement of appearance standards explained variance in individual-level body dissatisfaction (BD) scores, even after controlling for the influence of individual differences in body mass index and internalization of appearance standards.

Conclusions. Cultural-level variables may account for the development of adolescent BD.     

PIXImus DXA with different software needs individual calibration to accurately predict fat mass

OBJECTIVE: To validate GE PIXImus2 DXA fat mass (FM) estimates by chemical analysis, to compare previously published correction equations with an equation from our machine, and to determine intermachine variation. RESEARCH METHODS AND PROCEDURES: C57BL/6J (n = 16) and Aston (n = 14) mice (including ob/ob), Siberian hamsters (Phodopus sungorus) (n = 15), and bank voles (Clethrionomys glareolus) (n = 37) were DXA scanned postmortem, dried, then fat extracted using a Soxhlet apparatus. We compared extracted FM with DXA-predicted FM corrected using an equation designed using wild-type animals from split-sample validation and multiple regression and two previously published equations. Sixteen animals were scanned on both a GE PIXImus2 DXA in France and a second machine in the United Kingdom. RESULTS: DXA underestimated FM of obese C57BL/6J by 1.4 +/- 0.19 grams but overestimated FM for wild-type C57BL/6J (2.0 +/- 0.11 grams), bank voles (1.1 +/- 0.09 grams), and hamsters (1.1 +/- 0.13 grams). DXA-predicted FM corrected using our equation accurately predicted extracted FM (accuracy 0.02 grams), but the other equations did not (accuracy, -1.3 and -1.8 grams; paired Student's t test, p < 0.001). Two similar DXA instruments gave the same FM for obese mutant but not lean wild-type animals. DISCUSSION: DXA using the same software could use the same correction equation to accurately predict FM for obese mutant but not lean wild-type animals. PIXImus machines purchased with new software need validating to accurately predict FM.     

Diagnosis of overweight in adolescents: comparative study of the performance different criteria for body mass index

OBJECTIVE: In an attempt to simplify the screening process for detecting obesity in adolescence, the performance of different cutoff values for body mass index (BMI) was assessed in a population-based cohort in Southern Brazil. METHODS: A total of 493 adolescents aged 15-16 years who lived in the city of Pelotas, Brazil, were studied. Obesity was defined according to the WHO criteria taking into account age and sex (a BMI equal to or greater than the 85th percentile of the NHANES I reference, plus subscapular and triceps skinfold equal to or greater than the 90th percentile of the same reference). Different BMI cutoff values were used to assess their specificity and sensitivity. RESULTS: For boys, BMI>/=25 kg/m(2) showed the best performance for detecting obesity, with a sensitivity of 90% and only 5% of false positives. The Brazilian proposed criteria that was used had 100% sensitivity but up to 23% of false positives. Higher cutoff values were also tested, but there was a slight increase in specificity, accompanied by a marked reduction in sensitivity. CONCLUSIONS: The BMI cutoff of 25 kg/m(2) presented the best performance for screening obesity in the studied sample, and it is recommended for adolescents aged 15 and more in populations with similar characteristics. It provides a single cutoff value to be used in primary health services, eliminating the need for age and sex-specific values and skinfold measurements, and it is also consistent with the cutoff value proposed to identifying overweight adults.     

Body composition interpretation. Contributions of the fat-free mass index and the body fat mass index

OBJECTIVE: Low and high body mass index (BMI) values have been shown to increase health risks and mortality and result in variations in fat-free mass (FFM) and body fat mass (BF). Currently, there are no published ranges for a fat-free mass index (FFMI; kg/m(2)), a body fat mass index (BFMI; kg/m(2)), and percentage of body fat (%BF). The purpose of this population study was to determine predicted FFMI and BFMI values in subjects with low, normal, overweight, and obese BMI. METHODS: FFM and BF were determined in 2986 healthy white men and 2649 white women, age 15 to 98 y, by a previously validated 50-kHz bioelectrical impedance analysis equation. FFMI, BFMI, and %BF were calculated. RESULTS: FFMI values were 16.7 to 19.8 kg/m(2) for men and 14.6 to 16.8 kg/m(2) for women within the normal BMI ranges. BFMI values were 1.8 to 5.2 kg/m(2) for men and 3.9 to 8.2 kg/m(2) for women within the normal BMI ranges. BFMI values were 8.3 and 11.8 kg/m(2) in men and women, respectively, for obese BMI (>30 kg/m(2)). Normal ranges for %BF were 13.4 to 21.7 and 24.6 to 33.2 for men and women, respectively. CONCLUSION: BMI alone cannot provide information about the respective contribution of FFM or fat mass to body weight. This study presents FFMI and BFMI values that correspond to low, normal, overweight, and obese BMIs. FFMI and BFMI provide information about body compartments, regardless of height.     

体质指数与皮褶厚度测量体脂含量准确度

目的了解身体质量指数法、皮褶厚度测量法和体成分仪判断人体肥胖的准确程度。方法将312名大学生分别测量体质指数、皮褶厚度,并计算肥胖程度,把计算结果和体成分仪判断结果相比较,从而了解身体质量指数法和皮褶厚度测量法对身体肥胖程度判断的准确程度。结果 3种方法对普通人群肥胖程度的判断基本一致,但均有部分差异。结论和体成分仪相比,体质指数法不如皮褶厚度法准确,适用范围较小。     

Dietary calcium is associated with body mass index and body fat in American Indians

American Indians have a high prevalence of obesity. Evidence supports a relationship between increased dietary calcium intake and lower body weight. This study was conducted to investigate the association between dietary calcium intake, BMI, and percentage of body fat (PBF) in American Indians (ages 47-79 y) in the Strong Heart Study (SHS) (2nd exam, 1992-1995). SHS data were compared with data for the general U.S. adult population from the NHANES III (1988-1994). BMI was calculated as kg/m(2). PBF was estimated by bioelectrical impedance using an equation based on total body water. The clinical examination included measures of blood chemistry. Dietary data were collected using a 24-h dietary recall. Calcium intake was significantly lower in SHS participants than in age-matched NHANES III participants. Mean calcium intake in the SHS was 680 mg/d (range: 103-4574 mg/d) for men and 610 mg/d (range: 71-4093 mg/d) for women (P < 0.001). After adjustment for potential confounders, BMI and PBF were lower by 0.80 kg/m(2) (95% CI: -1.53 to -0.08, P = 0.046) and 1.28% (95% CI: -2.10 to -0.47, P = 0.011) in SHS participants with higher (> or = 873 mg/d in the 5th quintile) vs. lower calcium intake (<313 mg/d in the 1st quintile). No relation between calcium intake and BMI or PBF was observed in NHANES III participants. Our data may be used to develop nutritional interventions aimed at weight control in culturally appropriate clinical trials.