Body mass index (BMI) has various deficiencies as a measure of obesity, especially when the BMI measure is based on self-reported height and weight. BMI is an indirect measure of body fat compared with more direct approaches such as bioelectrical impedance. Moreover, BMI does not necessarily reflect the changes that occur with age. The proportion of body fat increases with age, whereas muscle mass decreases, but corresponding changes in height, weight and BMI may not reflect changes in body fat and muscle mass. Both the sensitivity and specificity of BMI have been shown to be poor. Additionally, the relation between BMI and percentage of body fat is not linear and differs for men and women. The consequences of the errors in the measurement of obesity with BMI depend on whether they are differential or nondifferential. Differential misclassification, a potentially greater problem in case-control and cross-sectional studies than in prospective cohort studies, can produce a bias toward or away from the null. Nondifferential misclassification produces a bias toward the null for a dichotomous exposure; for measures of exposure that are not dichotomous, the bias may be away from the null. In short, the use of BMI as a measure of obesity can introduce misclassification problems that may result in important bias in estimating the effects related to obesity.

BMI-related errors in the measurement of obesity.

Women have more body fat than men, but in contrast to the deleterious metabolic consequences of the central obesity typical of men, the pear-shaped body fat distribution of many women is associated with lower cardiometabolic risk. To understand the mechanisms regulating adiposity and adipose tissue distribution in men and women, significant research attention has focused on comparing adipocyte morphological and metabolic properties, as well as the capacity of preadipocytes derived from different depots for proliferation and differentiation. Available evidence points to possible intrinsic, cell autonomous differences in preadipocytes and adipocytes, as well as modulatory roles for sex steroids, the microenvironment within each adipose tissue, and developmental factors. Gluteal-femoral adipose tissues of women may simply provide a safe lipid reservoir for excess energy, or they may directly regulate systemic metabolism via release of metabolic products or adipokines. We provide a brief overview of the relationship of fat distribution to metabolic health in men and women, and then focus on mechanisms underlying sex differences in adipose tissue biology.

/pdf/sex-differences-in-human-adipose-tissues-the-biology-of-pear-2eiz6mrl65.pdf

Sex differences in human adipose tissues - the biology of pear shape

Food waste contributes to excess consumption of freshwater and fossil fuels which, along with methane and CO(2) emissions from decomposing food, impacts global climate change. Here, we calculate the energy content of nationwide food waste from the difference between the US food supply and the food consumed by the population. The latter was estimated using a validated mathematical model of metabolism relating body weight to the amount of food eaten. We found that US per capita food waste has progressively increased by approximately 50% since 1974 reaching more than 1400 kcal per person per day or 150 trillion kcal per year. Food waste now accounts for more than one quarter of the total freshwater consumption and approximately 300 million barrels of oil per year.

https://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0007940&type=printable

The Progressive Increase of Food Waste in America and Its Environmental Impact

The magnitude of association between overweight and obesity and the risk of diabetes: A meta-analysis of prospective cohort studies

Sex differences in human adipose tissues一■the biology of pear shape

Objective To study the effects of sex, age and race on the relation between body mass index (BMI) and measured percent body fat (%fat) Design Cross-sectional validation study of sedentary individuals Subjects The Heritage Family Study cohort of 665 black and white men and women who ranged in age from 17 to 65 y Measurements Body density determined from hydrostatic weighing Percentage body fat determined with gender and race-specific, two-compartment models BMI determined from height and weight, and sex and race in dummy coded form Results Polynomial regression showed that the relationship between %fat and BMI was quadratic for both men and women A natural log transformation of BMI adjusted for the non-linearity Test for homogeneity of log transformed BMI and gender showed that the male-female slopes were within random variance, but the intercepts differed For the same BMI, the %fat of females was 104% higher than that of males General linear models analysis of the women's data showed that age, race and race-by-BMI interaction were independently related to %fat The same analysis applied to the men's data showed that %fat was not just a function of BMI, but also age and age-by-BMI interaction Multiple regression analyses provided models that defined the bias Conclusions These data and results published in the literature show that BMI and %fat relationship are not independent of age and gender These data showed a race effect for women, but not men The failure to adjust for these sources of bias resulted in substantial differences in the proportion of subjects defined as obese by measured %fat

The effect of sex, age and race on estimating percentage body fat from body mass index: The Heritage Family Study.

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The effect of sex, age and race on estimating percentage body fat from body mass index: The Heritage Family Study.