This research studied the preferences reported by women and men about their Ideal Body Image for the Opposite Sex (IBIOS), and its association with body mass index (BMI). It also analysed the preferences of each sex for a woman’s ideal body image (W-IBI) and a man’s ideal body image (M-IBI). A total of 450 participants aged 18–70 years with different weights were studied. Their IBIOS was assessed using standard figural stimuli. The sample was divided in four groups by sex and age (<45 years; ≥45 years). Sex and age differences in IBIOS, as well as sex differences in the preferences for a woman’s ideal body image (W-IBI) and a man’s ideal body image (M-IBI), were tested using a non-parametric Mann-Whitney U test. The association between IBIOS and BMI was analysed using Spearman’s correlation. In all groups, the most chosen silhouette as IBIOS was number 4. In the under-45 years group, women chose bigger silhouettes for the opposite sex than men did (p<0.05). In this age group women chose as ideal smaller silhouettes for the female body than men did (p<0.01). In addition, women and men in the younger age group and with normal weight chose smaller silhouettes, while those who were overweight or obese selected larger silhouettes (p<0.001). Age was found to be a relevant factor in IBIOS preferences, and in the association between IBIOS and nutritional status as measured by BMI, which was only observed to be significant in the younger age group.

The aim of this research was to analyse variation in body image perception and satisfaction by age, sex and nutritional status in an adult sample from the Basque Country, Spain. A case-control study was performed for 227 women and 178 men aged 18–70 years. Stunkard’s silhouettes were used to evaluate Current Body Image (CBI) and Ideal Body Image (IBI), as well as dissatisfaction and inconsistency scores. Nutritional status was assessed following the WHO criteria for BMI in an adult population. The sample was divided into four groups based on sex and age (early adulthood <45 years, and middle/older adulthood ≥45 years). The Mann–Whitney U test was employed to evaluate sex and age differences, and the Gamma coefficient to assess the association between body image variables and nutritional status. Significant age differences in CBI (p<0.05) and sex differences in IBI (p<0.001) were detected. Both variables showed a positive association with BMI (p<0.01), which indicates that BMI is a biological characteristic related to body image satisfaction and influences participants’ perception of themselves. Dissatisfaction scores showed that both sex and age differences (p<0.05) were negatively associated with BMI (p<0.001). Only participants ≥45 years presented sex differences in inconsistency scores (p<0.05); this variable was associated with BMI in women (p<0.01). Preferences in body image showed sexual dimorphism, with women preferring thinner bodies than men – a pattern observed in many Western populations – linked in part to sociocultural pressures. Women were more dissatisfied with their bodies than men; a higher dissatisfaction was observed in older relative to younger participants. The results confirm the association between nutritional status and body size perception and satisfaction, but also the relationship between nutritional status and the reliability with which women can classify themselves; in men, this relationship was not as clear.

Whether monozygotic (MZ) and dizygotic (DZ) twins differ from each other in a variety of phenotypes is important for genetic twin modeling and for inferences made from twin studies in general. We analyzed whether there were differences in individual, maternal and paternal education between MZ and DZ twins in a large pooled dataset. Information was gathered on individual education for 218,362 adult twins from 27 twin cohorts (53% females; 39% MZ twins), and on maternal and paternal education for 147,315 and 143,056 twins respectively, from 28 twin cohorts (52% females; 38% MZ twins). Together, we had information on individual or parental education from 42 twin cohorts representing 19 countries. The original education classifications were transformed to education years and analyzed using linear regression models. Overall, MZ males had 0.26 (95% CI [0.21, 0.31]) years and MZ females 0.17 (95% CI [0.12, 0.21]) years longer education than DZ twins. The zygosity difference became smaller in more recent birth cohorts for both males and females. Parental education was somewhat longer for fathers of DZ twins in cohorts born in 1990–1999 (0.16 years, 95% CI [0.08, 0.25]) and 2000 or later (0.11 years, 95% CI [0.00, 0.22]), compared with fathers of MZ twins. The results show that the years of both individual and parental education are largely similar in MZ and DZ twins. We suggest that the socio-economic differences between MZ and DZ twins are so small that inferences based upon genetic modeling of twin data are not affected.

We analyzed birth order differences in means and variances of height and body mass index (BMI) in monozygotic (MZ) and dizygotic (DZ) twins from infancy to old age. The data were derived from the international CODATwins database. The total number of height and BMI measures from 0.5 to 79.5 years of age was 397,466. As expected, first-born twins had greater birth weight than second-born twins. With respect to height, first-born twins were slightly taller than second-born twins in childhood. After adjusting the results for birth weight, the birth order differences decreased and were no longer statistically significant. First-born twins had greater BMI than the second-born twins over childhood and adolescence. After adjusting the results for birth weight, birth order was still associated with BMI until 12 years of age. No interaction effect between birth order and zygosity was found. Only limited evidence was found that birth order influenced variances of height or BMI. The results were similar among boys and girls and also in MZ and DZ twins. Overall, the differences in height and BMI between first- and second-born twins were modest even in early childhood, while adjustment for birth weight reduced the birth order differences but did not remove them for BMI.

A trend toward greater body size in dizygotic (DZ) than in monozygotic (MZ) twins has been suggested by some but not all studies, and this difference may also vary by age. We analyzed zygosity differences in mean values and variances of height and body mass index (BMI) among male and female twins from infancy to old age. Data were derived from an international database of 54 twin cohorts participating in the COllaborative project of Development of Anthropometrical measures in Twins (CODATwins), and included 842,951 height and BMI measurements from twins aged 1 to 102 years. The results showed that DZ twins were consistently taller than MZ twins, with differences of up to 2.0 cm in childhood and adolescence and up to 0.9 cm in adulthood. Similarly, a greater mean BMI of up to 0.3 kg/m2 in childhood and adolescence and up to 0.2 kg/m2 in adulthood was observed in DZ twins, although the pattern was less consistent. DZ twins presented up to 1.7% greater height and 1.9% greater BMI than MZ twins; these percentage differences were largest in middle and late childhood and decreased with age in both sexes. The variance of height was similar in MZ and DZ twins at most ages. In contrast, the variance of BMI was significantly higher in DZ than in MZ twins, particularly in childhood. In conclusion, DZ twins were generally taller and had greater BMI than MZ twins, but the differences decreased with age in both sexes.

For over 100 years, the genetics of human anthropometric traits has attracted scientific interest. In particular, height and body mass index (BMI, calculated as kg/m2) have been under intensive genetic research. However, it is still largely unknown whether and how heritability estimates vary between human populations. Opportunities to address this question have increased recently because of the establishment of many new twin cohorts and the increasing accumulation of data in established twin cohorts. We started a new research project to analyze systematically (1) the variation of heritability estimates of height, BMI and their trajectories over the life course between birth cohorts, ethnicities and countries, and (2) to study the effects of birth-related factors, education and smoking on these anthropometric traits and whether these effects vary between twin cohorts. We identified 67 twin projects, including both monozygotic (MZ) and dizygotic (DZ) twins, using various sources. We asked for individual level data on height and weight including repeated measurements, birth related traits, background variables, education and smoking. By the end of 2014, 48 projects participated. Together, we have 893,458 height and weight measures (52% females) from 434,723 twin individuals, including 201,192 complete twin pairs (40% monozygotic, 40% same-sex dizygotic and 20% opposite-sex dizygotic) representing 22 countries. This project demonstrates that large-scale international twin studies are feasible and can promote the use of existing data for novel research purposes.

The objective of the present study was to compare different methods for evaluating body fat percentage (BF%) (anthropometric methods and bioelectrical impedance analysis) in university students. Subjects were 653 healthy students whose mean age, body height, body weight and BMI were 21·1 (SD 2·5) years, 166·0 (SD 8·4) cm, 62·8 (SD 11·0) kg and 22·7 (SD 3·1) kg/m2, respectively. Results showed that BMI is a poor predictor of body fatness since the sensitivity was low in comparison with the reference method (Siri equation). The lowest values of BF% were obtained using the reference method (Siri equation) (21·8 (SD 6·8)%). The two methods with the highest agreement were Siri and Lean (mean difference, −0·5), followed by Brozek (mean difference, −1·4) and Deurenberg (mean difference, −1·5). The largest mean difference for BF% was between Siri and impedance (−4·5). Although the methods and/or equations used in the present study have been commonly utilised to estimate BF% in young adults, the results must be interpreted with caution in the diagnosis and monitoring of overweight and obesity.