The validity of predicted body fat percentage from body mass index and from impedance in samples of five European populations

Body fat and body-mass index among a multiethnic sample of college-age men and women

Obesity prevalence and average body composition vary by US race and gender. Asian Americans have the lowest prevalence of obesity. Relying on body-mass index (BMI) to estimate obesity prevalence may misclassify subgroups that appear normally weighted but have excess body fat. We evaluated percentage body fat (PBF) and BMI to determine whether BMI reflects PBF consistently across different races. 940 college students were recruited from a local public university over four consecutive years. We measured PBF by bioelectrical impedance analysis (BIA), weight by physicians' scales, and height with stadiometers. Our sample comprised Asians (49%), Caucasians (23%), Hispanics (7%), and Other (21%). Participants averaged 21.4 years old; BMI was 22.9 kg/m(2); PBF was 24.8%. BMI and PBF varied significantly by race and gender (P value = 0.002 and 0.005 for men; 0.0009 and 0.0008 for women). Asian-American women had the lowest BMI (21.5 kg/m(2)) but the second highest PBF (27.8%). Linear association between BMI and PBF was the weakest (r (2) = 0.09) among Asian-American women and BMI had the poorest sensitivity (37%) to detect PBF. The high PBF with low BMI pattern exhibited by Asian-American women suggests that they could escape detection for obesity-related disease if BMI is the sole measure that estimates body composition.

BMI and an anthropometry-based estimate of fat mass percentage are both valid discriminators of cardiometabolic risk: a comparison with DXA and bioimpedance

OBJECTIVE

To determine whether categories of obesity based on BMI and an anthropometry-based estimate of fat mass percentage (FM% equation) have similar discriminative ability for markers of cardiometabolic risk as measurements of FM% by dual-energy X-ray absorptiometry (DXA) or bioimpedance analysis (BIA).

DESIGN AND METHODS

A study of 40-79-year-old male (n = 205) and female (n = 388) Finns. Weight, height, blood pressure, triacylglycerols, HDL cholesterol, and fasting blood glucose were measured. Body composition was assessed by DXA and BIA and a FM%-equation.

RESULTS

For grade 1 hypertension, dyslipidaemia, and impaired fasting glucose >6.1 mmol/L, the categories of obesity as defined by BMI and the FM% equation had 1.9% to 3.7% (P < 0.01) higher discriminative power compared to DXA. For grade 2 hypertension the FM% equation discriminated 1.2% (P = 0.05) lower than DXA and 2.8% (P < 0.01) lower than BIA. Receiver operation characteristics confirmed BIA as best predictor of grade 2 hypertension and the FM% equation as best predictor of grade 1 hypertension. All other differences in area under curve were small (≤0.04) and 95% confidence intervals included 0.

CONCLUSIONS

Both BMI and FM% equations may predict cardiometabolic risk with similar discriminative ability as FM% measured by DXA or BIA.

Physical activity, body composition and physical self-esteem: a 3-year follow-up study among adolescents in Sweden

AIMS

To measure physical activity by means of daily pedometer steps, body composition, expressed as body mass index (BMI) and bioelectrical impedance as percent body fat, and perceived physical self-esteem and additionally, to evaluate eventual predictors for a healthy lifestyle i.e., highly physically active, normal weighted and a high physical self-esteem in a follow-up group.

METHODS

During autumn 2000 physical activity level was assessed and BMI was calculated in 871 children aged 7-14 in south eastern Sweden and in 501 of these, physical self-esteem were also assessed. During autumn 2003 a total of 375 adolescents aged 15-18 were assessed using the same methodology and additionally percent body fat was measured. Ninety-three of these adolescents (46 girls), were also measured in 2000 and they formed the follow-up group.

RESULTS

In the follow-up group a significant increase in BMI and stability in physical self-esteem in boys and girls, and in boys a significant decrease in daily steps was found 3 years later. Strongest predictor to be highly physically active, maintain normal BMI and high self-esteem 3 years later, i.e., to have a healthy lifestyle, was for girls increased self-esteem and for boys a decreased BMI.

CONCLUSION

Consequently, for a healthy lifestyle, promoting physical self-esteem in girls and weight control in boys is of great importance in early adolescence.

The evolution of human fatness and susceptibility to obesity: an ethological approach

Human susceptibility to obesity is an unusual phenomenon amongst animals. An evolutionary analysis, identifying factors favouring the capacity for fat deposition, may aid in the development of preventive public health strategies. This article considers the proximate causes, ontogeny, fitness value and evolutionary history of human fat deposition. Proximate causes include diet composition, physical activity level, feeding behaviour, endocrine and genetic factors, psychological traits, and exposure to broader environmental factors. Fat deposition peaks during late gestation and early infancy, and again during adolescence in females. As in other species, human fat stores not only buffer malnutrition, but also regulate reproduction and immune function, and are subject to sexual selection. Nevertheless, our characteristic ontogenetic pattern of fat deposition, along with relatively high fatness in adulthood, contrasts with the phenotype of other mammals occupying the tropical savannah environment in which hominids evolved. The increased value of energy stores in our species can be attributed to factors increasing either uncertainty in energy availability, or vulnerability to that uncertainty. Early hominid evolution was characterised by adaptation to a more seasonal environment, when selection would have favoured general thriftiness. The evolution of the large expensive brain in the genus Homo then favoured increased energy stores in the reproducing female, and in the offspring in early life. More recently, the introduction of agriculture has had three significant effects: exposure to regular famine; adaptation to a variety of local niches favouring population-specific adaptations; and the development of social hierarchies which predispose to differential exposure to environmental pressures. Thus, humans have persistently encountered greater energy stress than that experienced by their closest living relatives during recent evolution. The capacity to accumulate fat has therefore been a major adaptive feature of our species, but is now increasingly maladaptive in the modern environment where fluctuations in energy supply have been minimised, and productivity is dependent on mechanisation rather than physical effort. Alterations to the obesogenic environment are predicted to play a key role in reducing the prevalence of obesity.

Comparison of hand-to-hand bioimpedance and anthropometry equations versus dual-energy X-ray absorptiometry for the assessment of body fat percentage in 17-18-year-old conscripts

In the present study, hand-to-hand bioelectrical impedance analysis (BIA), skinfold (SKF) thickness and height-weight (body mass index, BMI)-based equations and dual-energy X-ray absorptiometry (DEXA), as a criterion method, were compared with each other in the assessment of body fat percentage (BF%) in 17-18-year-old Estonian conscripts (n = 32). The Omron BF body fat monitor estimated that BF% was lower than that of the criterion method DEXA. The difference between DEXA and Omron BF 300 (III) was higher (1.1 +/- 3.0%; P = 0.04) and that between DEXA and Omron BF 306 lower (0.2 +/- 3.0%; P>0.05). Omron BF 300 (I) and (II) (series 8) had intermediate difference (0.9 +/- 3.0 and 0.9 +/- 3.0; P>0.05) when compared with DEXA. Three anthropometric equations estimated a higher BF% than cthat of DEXA. The Durnin & Womersley SKF equation BF% (1.0 +/- 2.4; P = 0.03) was higher than that of the DEXA. Deurenberg et al. and Gallagher et al. BMI-based equations overestimation yielded 0.9 +/- 3.7 and 0.6 +/- 3.8 BF% (P>0.05). From the anthropometric equations, only the Deurenberg et al. SKF equation slightly underestimated 0.5 +/- 3.4 BF% (P>0.05). DEXA-assessed BF% had highest correlation with SKF equations (r = 0.93), less so with BIA (r = 0.88-0.89) and lowest with BMI equation-assessed BF% (r = 0.81-0.84). All values were significant at P<0.001. We can conclude that the Omron BF 306 body fat monitor and the anthropometric Deurenberg et al. SKF equation yielded results close to the DEXA BF%.

Validation of skinfold thickness and hand-held impedance measurements for estimation of body fat percentage among Singaporean Chinese, Malay and Indian subjects

Body fat percentage (BF%) was measured in 298 Singaporean Chinese, Malay and Indian men and women using a chemical four-compartment model consisting of fat, water, protein and mineral (BF%4C). In addition, weight, height, skinfold thickness and segmental impedance (from hand to hand) was measured. Body fat percentage was predicted using prediction equations from the literature (for skinfolds BF%SKFD) and using the manufacturer's software for the hand-held impedance analyser (BF%IMP). The subjects ranged in age from 18-70 years and in body mass index from 16.0 to 40.2 kg/m2. Body fat ranged from 6.5 to 53.3%. The biases for skinfold prediction (BF%4C-BF%SKFD, mean +/- SD) were -0.4+/-3.9, 2.3+/-4.1 and 3.1+/-4.2 in Chinese, Malay and Indian women, respectively, the Chinese being different from the Malays and Indians. The differences were significant from zero (P < 0.05) in the Malays and Indians. For the men, the biases were 0.5+/-3.8, 0.0+/-4.8 and 0.9+/-4.0 in Chinese, Malays and Indians, respectively. These biases were not significantly different from zero and not different among the ethnic groups. The biases for hand-held impedance BF% were -0.7+/-4.5, 1.5+/-4.4 and 0.4+/-3.8 in Chinese, Malay and Indian women. These biases were not significantly different from zero but the bias in the Chinese was significantly different from the biases in the Malays and Indians. In the Chinese, Malay and Indian men, the biases of BF%IMP were 0.7+/-4.6, 1.9+/-4.8 and 2.0+/-4.4, respectively. These biases in Malay and Indian men were significantly different from zero and significantly different from the bias in Chinese men. The biases were correlated with level of body fat and age, and also with relative arm span (arm span/height) for impedance. After correction, the differences in bias among the ethnic groups disappeared. The study shows that the biases in predicted BF% differ between ethnic groups, differences that can be explained by differences in body composition and differences in body build. This information is important and should be taken into account when comparing body composition across ethnic groups using predictive methods.