S. S. Guo

Body mass index during childhood, adolescence and young adulthood in relation to adult overweight and adiposity: the Fels Longitudinal Study.

BACKGROUND: Childhood overweight develops during ‘critical periods’, but the relationship of body mass index (BMI) patterns during ‘critical periods’ from childhood into adulthood with subsequent overweight and adiposity has not been previously investigated. BMI patterns during early childhood, pubescence and post-pubescence and their independent effects on overweight and body fatness at 35–45 y of age were examined along with birth weight and the effects of adult lifestyle factors.METHODS: BMI parameters describing the timing, velocity minimum (min) and maximum (max) values from 2 to 25 y of age were related to adulthood BMI values and total and percentage body fat (TBF, %BF) at 35–45 y. These data were from 180 males and 158 females in the Fels Longitudinal Study.RESULTS: There was no sex difference in the timing of BMI rebound, but the age of BMI maximum velocity and maximum BMI were both earlier in girls. Children with an earlier BMI rebound had larger BMI values at rebound and at maximum velocity. Children who reached maximum BMI at later age had larger maximum BMI values. Maximum BMI was a strong predictor for adult BMI and in females, a strong predictor of adulthood TBF and %BF. Maximum BMI was closely related to maximum BMI velocity in females and in males, BMI at maximum velocity is a strong predictor of TBF and %BF.CONCLUSIONS: Changes in childhood BMI were related to adult overweight and adiposity more so in females than males. BMI rebound is a significant important period related to overweight at 35–45 y in females but not in males. However BMI patterns during and post-adolescence were more important than the BMI rebound for adulthood TBF and %BF status. There is marked tracking in BMI from approximately 20 y into 35–45 y. The pattern of BMI changes from 2 to 25 y had stronger effects on subsequent adult overweight than birth weight and adult lifestyle variables.

Age- and maturity-related changes in body composition during adolescence into adulthood: The Fels Longitudinal Study

OBJECTIVES: To examine patterns of change in total body fat (TBF), percent body fat (%BF), and fat-free mass (FFM), from 8--20 y of age and the effect of rate of skeletal maturation. To determine the degree of tracking of body composition for individuals from childhood into adulthood.RESEARCH DESIGN: Annual serial data for TBF, %BF and FFM from underwater weighing using a multicomponent body composition model were collected from 130 CAUcasian males and 114 CAUcasian females between 1976 and 1996. Rate of maturation was defined as FELS skeletal age (SA) less chronological age (CA). Random effects models were used to evaluate general patterns of change and tracking of individual serial data over the 12 y age range.RESULTS: Changes in TBF followed a quadratic model for males and for females with declining rates of change. Changes for %BF followed a cubic model for males and females. General patterns of change for FFM followed a cubic model for males and a quadratic model for females. TBF for males and females increased with age, but the rates of change declined with age. %BF for females increased from age 8–20 y. For males, %BF increased with age, but the positive rates of change declined and became a negative when aged about 13 y and reached a minimum at about the age of 15 y. The rate of change for %BF increased thereafter. FFM for males and females increased with age, but the rates of change decreased with age. The extent of tracking is inversely related to the length of the time interval. At the same age, rapidly-maturing children have significantly larger amounts of TBF, %BF and FFM than slow-maturing children. Tracking in body composition for individuals persisted from childhood to adulthood.CONCLUSIONS: (1) There are gender-associated differences in these patterns of change for %BF and FFM but not for TBF; (2) TBF, %BF and FFM increased with increased rates of maturation; (3) significant tracking in body composition for individuals persists from childhood to adulthood.

Comparison of percent body fat estimates using air displacement plethysmography and hydrodensitometry in adults and children.

PURPOSE: The purpose of the study was to compare estimates of body density and percentage body fat from air displacement plethysmography (ADP) to those from hydrodensitometry (HD) in adults and children and to provide a review of similar recent studies.METHODS: Body density and percentage body fat (% BF) were assessed by ADP and HD on the same day in 87 adults aged 18–69 y (41 males and 46 females) and 39 children aged 8–17 y (19 males and 20 females). Differences between measured and predicted thoracic gas volumes determined during the ADP procedure and the resultant effects of those differences on body composition estimates were also compared. In a subset of 50 individuals (31 adults and 19 children), reliability of ADP was measured and the relative ease or difficulty of ADP and HD were probed with a questionnaire.RESULTS: The coefficient of reliability between %BF on day 1 and day 2 was 96.4 in adults and 90.1 in children, and the technical error of measurement of 1.6% in adults and 1.8% in children. Using a predicted rather than a measured thoracic gas volume did not significantly affect percentage body fat estimates in adults, but resulted in overestimates of percentage body fat in children. Mean percentage body fat from ADP was higher than percentage body fat from HD, although this was statistically significant only in adults (29.3 vs 27.7%, P<0.05). The 95% confidence interval of the between-method differences for all subjects was −7 to +9% body fat, and the root mean square error (r.m.s.e.) was approximately 4% body fat. In the subset of individuals who were asked to compare the two methods, 46 out of 50 (92%) indicated that they preferred the ADP to HD.CONCLUSION: ADP is a reliable method of measuring body composition that subjects found preferable to underwater weighing. However, as shown here and in most other studies, there are differences in percentage body fat estimates assessed by the two methods, perhaps related to body size, age or other factors, that are sufficient to preclude ADP from being used interchangeably with underwater weighing on an individual basis.

Mechanical and physiologic modifiers and bioelectrical impedance spectrum determinants of body composition

Fat-free mass and total and percentage body fat were determined by dual-energy X-ray absorptiometry (DXA) and total-body and segmental impedance measures were taken at 16 frequencies from 5 to 1300 kHz in a sample of white men and women aged 18-30 y. Plots of total-body and segmental impedance against frequency for each individual indicated that the general shape of these curves was described by the same mathematical function consisting of three components-ai, bi, and ci,-that contain information derived from the individual measurements of impedance summarized across the spectrum of current frequencies. Total-body and segmental multifrequency impedance were significantly correlated with hemoglobin, hematocrit, and serum sodium, potassium, creatinine, and osmolality. Regression models of body composition with total-body or segmental impedance measures at discrete frequencies or the impedance spectrum variables were similar to corresponding findings for impedance models at 50 kHz. The segmental impedance spectrum variables for total and percentage body fat and the ratios of low- to high-frequency impedance from the trunk were significantly associated with total body fatness as measured by DXA.

16 – The Assessment of Human Growth

This chapter provides an overview of old and new methods of assessing the physical growth status of children. Today, a measure of growth should include an amount of body composition along with usual measures of stature and weight. A big child may be an obese child rather than one who is healthy and well-fed, as in the past. Obesity in childhood is strongly linked with subsequent overweight and obesity in adulthood and its cardiovascular consequences. Because of the increased prevalence of obesity around the world, these growth assessments should include a computation of BMI at a minimum and possibly triceps and subscapular skinfolds. If possible, more informative measures of body composition should be considered. One can also measure the amount of muscle tissue and density of bone in growing children. Both these tissues can be assessed with a minuscule exposure to radiation. Measures of bone mineral content and bone mineral density allow us to identify children with potential risk for osteoporosis later in adulthood. Measuring the growth status of a childs body composition provides an opportunity to treat risk factors for some chronic adult diseases at their conception, when treatment can be most effective.

ADULT CHANGES IN BODY COMPOSITION ARE ASSOCIATED WITH CHANGES IN CHOLESTEROL LEVELS : THE FELS LONGITUDINAL STUDY

Serial data from 507 adult participants in the Fels Longitudinal Study were used to study relationships between average annual changes in serum cholesterol levels and annual changes in total body fat, fat-free mass, percent body fat or body mass index in men and women aged 18-45 years or 45-65 years. Average annual changes in adiposity before and after 45 years of age for men and women show statistically significant, strong, positive relationships with corresponding changes in cholesterol levels.