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You are watching: Which factor correlates with weight gain among children and adults in recent decades?

Institute of medication (US) Subcommittee on military Weight Management. Weight Management: State that the Science and also Opportunities for army Programs. Washington (DC): national Academies push (US); 2004.


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There are plenty of factors that can influence body weight. The individual has actually no manage over some of these factors, including developmental determinants, genetic makeup, gender, and age. Other determinants that affect body weight over i m sorry the individual has potential regulate include level of physics activity, diet, and some environmental and social factors. This thing explores the relationship between each of this factors and also body weight.


DEVELOPMENTAL DETERMINANTS

It has been postulated the there room times during people\"s lives once exposure to details factors may boost their threat for the onset of obesity. These times have been termed “critical periods.” If these critical periods, in addition to the influential factors, deserve to be plainly defined, it may be feasible to recognize individuals at enhanced risk for the development and persistence the overweight and also obesity in adulthood. The prenatal period, the duration of adiposity rebound, and also adolescence have been propose as vital periods in childhood (Dietz, 1994); pregnancy and also the instant postpartum period have to be proposed as an important periods for ladies in adulthood.


Prenatal Factors

Although the data are subject come a variety of interpretations, it has actually been recorded in both animals and humans the females who room severely food minimal during the very first one to two trimesters that pregnancy have progeny who have actually a higher prevalence that obesity, diabetes, insulin resistance, and hypertension later on in life. Progeny the survivors that the Dutch scarcity in civilization War II demonstrated a greater prevalence of obesity and also diabetes (Ravelli et al., 1976), although this conclusion was wondered about by later studies (Jackson et al., 1996; Susser and Stein, 1994). Malnutrition in utero also has to be reported to result in raised obesity and also its complications later in life (Stanner et al., 1997). Reduced birth weights likewise seem come be linked with increased upper human body visceral adiposity in later life v its attendant boosted risk that cardiovascular condition (Oken and Gillman, 2003; Rogers, 2003). Since individuals native a lower socioeconomic elevator are more likely to it is in exposed to malnutrition throughout gestation or early on childhood, the prevalence of weight problems in such subgroups can be supposed to be higher.


Adiposity Rebound

Adiposity rises from birth until approximately 1 year that age, then decreases to a minimum at around 6 years of age. The hatchet “adiposity rebound” describes the rise in human body mass table of contents (BMI) and also body fat the occurs ~ this nadir in children between the ages of 5 and 7 years. Kids experiencing adiposity rebound in ~ an earlier age show up to have a three- to sixfold better risk of increased adult BMI than execute other youngsters (Whitaker et al., 1998). He and also Karlberg (2002) demonstrated, through the development of probability charts based on 3,650 youngsters followed from bear to 18 year of age, that children who skilled this rebound prior to 8 year of period have a greater risk the adulthood obesity. However, Guo and coworkers (2000), making use of serial BMI data indigenous the Fels Longitudinal study demonstrated that while there was no association between early period at adiposity rebound and also adult BMI standing in men, after controlling for results of bear weight, adult physics activity, alcohol and cigarette use, over there was around twice the threat for overweight with early on rebound in women.

Causes of early adiposity rebound have actually been otherwise attributed to progressed skeletal maturity (Roland-Cachera et al., 1984; Williams and Dickson, 2002), high protein entry (Roland-Cachera et al., 1995), and parental BMI (Dorosty et al., 2000). Cameron and also Demerath (2002) concluded after substantial review of the available scientific literature that the evidence is still no clear about whether period at adiposity cant is a an important period because that the development of obesity, but that early adiposity rebound can well it is in a statistics predictor of later obesity because of its solid relationship with early on adiposity and sped up maturation, both of i beg your pardon are developed markers of later on risk that obesity.


Adolescence

Although just 30 percent that adult obesity starts during childhood, 70 percent that the adult obesity that starts in childhood may start during adolescence (Dietz, 1994). Adolescent obesity is connected with a range of disadvantage health effects in adulthood, including early mortality in men and also increased threats of coronary love disease, diabetes, and also colorectal cancer (Miller, 1988; must et al., 1992; Wylie-Rosett, 1988). Most of these dangers were just slightly attenuated by adjustment because that adult obesity, which argues that obesity during adolescence may recognize the threat of these later on complications nevertheless of even if it is or not the people are obese adults.

While full fatness is vital consideration when assessing developmental aspects of obesity, second consideration is adipose tissue distribution. Visceral adipose tissue has an independent effect on obesity-associated comorbidities (Emery et al., 1993) that is separate from that of complete body fat, although the developmental aspects of visceral adipose tissue deposition have not to be well studied. Among children, visceral adiposity shows up to be connected with an raised risk that cardiovascular risk components such together elevated triglycerides and reduced high-density lipoproteins that room independent of complete body fat (Caprio et al., 1996; Gutin et al., 1994). However, the ages at which this relationships appear remain unclear. Cross-sectional studies suggest that visceral adipose tissue deposition is not significant before adolescence, yet increases quickly at the time.


Adulthood

The duration after adolescence has actually not been intensively studied, although around two-thirds of adult obesity begins after adolescence. Even if it is additional an essential periods exist in adulthood is less certain, however pregnancy and also postpartum may constitute one such period for a subset of women (Williamson et al., 1994). Postpartum weight retention shows up to range from 0.5 come 4.8 kg for most women (Johnston, 1991), but African-American mothers may be double as likely to maintain 9.1 kg (20 lb) or more postpartum than Caucasian mother (Parker and Abrams, 1993). Boardley and also colleagues (1995) uncovered that African-American women ate more and were less physically energetic postpartum than were the Caucasian ladies in your sample. As soon as the feasible confounding factors of prepregnancy weight, gestational weight gain, prenatal physics activity, parity, and also socioeconomic standing were controlled, African-American ladies still retained an ext weight in the postpartum duration than walk Caucasian women. Outcomes of several recent studies imply that feasible genetic factors may be associated in the propensity to retain weight postpartum. One study found that in women with normal prepregnancy BMIs, high first-trimester serum leptin concentration (a protein hormone encoded by the obese gene) correlated with raised gestational load gain and postpartum weight retention (Stein et al., 1998). In one more study, ladies within 12 month of the bear of their first child who were homozygous because that the 825T allele that the G-protein ß3, taken into consideration a “thrifty” genotype, had actually significantly greater BMIs and postpartum load retention 보다 women that did not bring the genotype (Gütersohn et al., 2000). No result of the genotype to be observed amongst women who had actually never given birth, arguing a pregnancy-specific phenomenon. In addition, this connection was just observed among women who involved in low levels of physics activity, sustaining the idea the physical activity may mitigate impacts of genetic endowment top top the potential for postpartum load retention. Even if it is this details genetic sports in this specific G protein is causally attached to the observed differences in BMI and also weight retention or is simply a marker because that the responsible mutation, as well as what the mechanism can be, are both concerns that require more investigation (Feldman and also Hegele, 2000).


GENETIC DETERMINANTS

The understanding of the hereditary influences on overweight and also obesity in humans has increased dramatically. People show far-ranging heterogeneity in your body weight and also body fatness responses to altered energy balance, diet components, and transforming activity levels. That is now well-established the overweight and obesity have actually a far-ranging genetic component, with approximates of the donation of genetic variation to it was observed variation in obesity-related phenotypes (such together BMI, fat mass, and leptin levels) varying from 30 come 70 percent (Comuzzie et al., 1993, 1994, 1996). However, little is however known about the details causes that heterogeneity (Pérusse and Bouchard, 1999). It seems clear that power metabolism and neural regulate of appetite are associated in regulating body weight and also may contribute to the etiology the obesity. Researches of relaxing metabolic rate show that the sports within families is much less than the variation among families (Bogardus et al., 1986).

Several studies have actually evaluated the potential mechanisms by which genetic determinants may contribute to obesity. One of the mechanisms through which differences in energy metabolism may add to obesity might involve defects in uncoupling proteins (UCP). Several types of uncoupling proteins have been identified. Fleury and colleagues (1997) an initial described person uncoupling protein 2 (UCP-2) and its links to obesity and also hyperinsulinemia. Bouchard (1997) detailed that markers near the UCP-2 gene in human beings are linked to distinctions in resting metabolic rate. Thus, genetic distinctions in UCP-2, and also perhaps various other UCPs, may add to person obesity.

There is a team of at least 20 Mendelian syndromes in which obesity is a component, consisting of Prader-Willi, Bardet-Biedl, Borjeson, Cohen, and also Wilson-Turner (Gunay-Aygun et al., 1997; Reed et al., 1995). These hereditary disorders are rare, and family studies do not suggest that the genes responsible because that these syndromes are involved in the usual forms of person obesity. For more than 99 percent the obese humans, the genetic basis that their excessive weight is unknown.


Animal Models of genetic Obesity

The strongest proof for hereditary weight-regulating mechanisms is the recent elucidation of solitary gene defects that are linked with excessive weight get in animals. Single gene mutations can indisputably cause obesity in both rodent models and in humans. In rodents, together mutations have been established in in ~ least 5 genes: the obese gene because that the circulating adipose tissue-secreted factor leptin; the db gene because that the receptor of leptin; the agouti yellow mutation, i m sorry controls hair shade in mice v the production of melanin pigments (with its human being equivalent, agouti signaling protein gene); the fat mutation in the carboxipeptidase E gene, i beg your pardon is a prohormone processing enzyme; and also the tub mutation, the role of which has yet to it is in determined. That the five gene products that at this time have been associated with weight regulation, leptin is the best characterized. Genetic defects in leptin are associated with too much obesity in both humans and also laboratory animals. In addition, serum concentrations of leptin space elevated in near proportion to human body fat in obese civilization with no defect in the leptin gene. Current studies display that administration of recombinant leptin to lean and also obese people results in dose-dependent load loss (Heymsfield et al., 1999). Additional research is needed to evaluate the potential role of leptin in obesity treatment.


Familial Aggregation of danger for Obesity

Using the substantial Danish fostering registry, Stunkard and colleagues (1986) uncovered that adopted children that were raised separately from their organic parents had actually body weights closer come those that their organic parents 보다 to those of your adoptive parents. The children in this study were separated from your parents at a very early age, generally before 3 months, for this reason the chance for the organic parents come instill eating and activity habits was really limited. An additional study of adoptees verified a far-ranging genetic influence on obesity, yet none the the environmental indicators evaluated were uncovered to contribute, although a variety of the problems considered have previously been connected with obesity (Sorensen et al., 1998). Stunkard and colleagues (1986) approximated that as much as 70 percent that the variance in the event of obesity can be attributed to hereditary factors, however other authors have postulated that as tiny as 20 percent that the variance is as result of genetic factors. The general agreement is the genetic determinants account for around 30 to 50 percent of the variance in the occurrence of obesity (Bouchard, 1997).

Twin studies carry out the many impressive clinical evidence that genetic determinants play critical role in the etiology of weight problems in humans. Stunkard and colleagues (1990) studied identical and nonidentical twins who were reared together and others who were reared apart. They found a high correlation of body weight among identical twins, even if they to be reared apart. Bouchard and also colleagues (1990) learned twins who were isolated in the Canadian wilderness through no accessibility to foods other 보다 those provided by the investigators. Identical twins to be overfed because that a duration of 100 days, and also their gains in human body weight and also adipose organization were evaluated. There to be a closer combination of both human body weight and also intra-abdominal adipose tissue (visceral fat) within pair pairs than among twin pairs.

The maximal heritability the obesity has been approximated to selection from 30 come 50 percent, based upon a testimonial of family studies (Chagnon et al., 2000). Back extensive initiatives have to be made to identify mutations in the genes established as obesity-associated in rodents and also in various other candidate genes for weight problems in humans, to day only a grasp of individuals have been figured out with mutations in any kind of of the gene that have produced obesity in rodents. Specifically, number of humans have been established with mutations in the leptin gene or that is receptor, yet no individuals have yet been found with mutations in the various other genes determined in rodents.

In total, solitary gene mutations have been determined as responsible for weight problems in 25 persons, through these mutations appearing in 7 genes (12 different mutations) (Pérusse et al., 1999) or in 5 genes (Chagnon et al., 2000). Researches of quantitative properties loci (QTL) in rodents have argued at least 98 different QTLs connected with obesity (Chagnon et al., 2000).

Currently, the major effort in the find for certain genes that add to person overweight and also obesity is based upon the usage of genome scanning. In genome scanning, linkage evaluation is carried out to recognize QTLs that influence the certain phenotype under study. The usage of genome scanning has listed evidence of QTLs that influence body weight and also the variety of fat cells (Chagnon et al., 2000).

Comparison that the threats of excessive weight in spouses and in first-degree family members has suggested that genetic factors may be of higher prominence in an ext severe weight problems (Katzmarzyk et al., 2000). Among the members of families that save on computer at the very least one morbidly obese person, a major gene effect wastransfer in a codominant fashion, suggesting a gene-environment interaction (Rice et al., 1999). Both multifactorial and major gene results have to be suggested. Efforts are recurring to identify the genetic and molecular communication of overweight and obesity, and it is likely that plenty of genes (and within these genes and their promoters, plenty of different mutations or variants) that are responsible because that the genetic variation of weight problems in humans will be identified.

The advance of weight problems likely requires a combination of mutual environment and also shared hereditary propensities. The rapid boost in pervasiveness of obesity in the united States, and also in many other countries, across all period groups might reflect a removal of ecological constraints (e.g., high level of daily activity and food availability) top top the expression of obesity genotypes. Expertise of the genetic materials of weight problems is not most likely to be advantageous to the armed forces in the close to term, yet identification of markers of potential risk of obesity may well have actually implications because that future screening.


AGE

Cross-sectional and longitudinal studies indicate a gradual increase in the typical BMI the Americans up to the eras of 50 to 60 year (IOM, 1995). This tendency is similar, v some variation, across males and females and across all evaluated country groups. Populace studies likewise indicate a decrease in human body weight and BMI amongst the elderly, usually in the seventh and eighth years (IOM, 1995; Kuczmarski et al., 1994; NHLBI, 1998). The very same trends have actually been determined in changes in total body fat and also percent human body fat (Chumlea et al., 2002). Overweight and also obesity therefore reach maximal rates amongst middle-aged adults. This sample is displayed in number 3-1.


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FIGURE 3-1

The prevalence (%) that overweight and obesity the men and women by age in the U.S. Population. Preobesity = human body mass index (BMI) the 25–29.9, class I obesity = BMI that 30–34.9, class II excessive weight = BMI the 35–39.9, and also class III obesity (more...)


The age-related human body mass boost up to the fifth and sixth decades is attach by additional anatomical, structural, and also body compositional changes. Stature declines from around age 30 onward, with prices in women much faster than those in men and for postmenopausal women much faster than your premenopausal counterparts. Declining stature accounts for a small part of the age-related increase in BMI (Gallagher et al., 1996).

Many weight-management professionals agree that body weight becomes increasingly more an overwhelming to keep with age, however there shows up to be tiny rationale for enhancing the top BMI variety consistent with an excellent health together individuals end up being older. Williams (1997) shown that body weight and associated circumferences would increase with advancing age unless food input is reduced and also physical activity is significantly increased.

A huge number that cross-sectional studies, however, do show that body fat boosts with age, even after controlling for changes in body weight and also physical task levels (Baumgartner et al., 1995; Flynn et al., 1989; Forbes, 1987; Forbes and also Reina, 1970; Gallagher et al., 1996, 1997; Noppa et al., 1980; Novak, 1972; Steen et al., 1979). Gallagher and also colleagues (1996) demonstrated that the typical body-fat contents in nonexercising civilian women v a BMI that 25 boosted from 30 percent for those in between the ages of 17 and twenty years to 36 percent because that those periods 40 years and older. The implicitly of this is the lean human body mass and, frequently, bones mass, decrease with age. Additionally, partitioning of adipose tissue in between the subcutaneous and visceral compartments is likewise moderated by period (Borkan et al., 1983). Men have much more visceral adipose tissue than carry out women at every ages, and the price of visceral adipose tissue rise with age is better in men than in ladies (Blaak, 2001).

In comparison to body fat, bones muscle mass declines with period beginning approximately the third decade the life (Dutta and Hadley, 1995). This observation is true not just for the general population, but it is additionally evident in army personnel (USAF, 1975). The prices of decline may advice after the start of menopause in females (Aloia et al., 1991) and for both genders in the seventh and also eighth years (Flynn et al., 1989). Losses of skeletal muscle parallel alters in skeletal mineral with progressing age and are present even after regulating for ns in body load (Gallagher et al., 2000). The mechanisms of human body composition readjust with aging space multifactorial and include physics inactivity, diet, and also hormonal and also cytokine alterations. The ns of skinny mass and also gain in fat mass occur also with no apparent change in human body weight. Since lean mass contributes the larger share the metabolic activity, complete energy expenditure throughout rest or low task will additionally decrease proportionally with the lose of skinny mass.

Total energy expenditure and also thus, power requirements, decrease v advancing period (Tzankoff and Norris, 1978). Physical activity levels are lower in larger individuals, which account for a part of the energy expenditure reduction that comes v aging. Resting power requirements are additionally lower in the elderly, due mostly to decreases in every metabolically active tissues, including skeletal muscle, brain, and also visceral organs. In laboratory animals, the heat developed by tissues per unit of mass decreases with age (a to decrease in the certain resting energy expenditure that organs), however it remains uncertain even if it is this observation additionally applies come humans. The exercise of resistance cultivate by human being over the age of 50 year may enhance fat-free mass, primarily skeletal muscle, and thereby aid offset the age-related decline in resting metabolic rate (Hill and also Saris, 1998; Tzankoff and also Norris, 1977). In women, ns of ovarian duty accounts for a reduced rate of overall heat production contrasted with that observed in premenopausal ladies (Poehlman and also Tchernof, 1998). Thus, both enlarge men and women have actually lower rates of power expenditure and, uneven counterbalanced by boosted physical task and diminished food intake, enlarge individuals, in general, will gain weight end time.


RACE/ETHNICITY

Whether there space racial/ethnic distinctions in an answer to the various contents of weight administration is a legitimate research question that has actually been discover to only a center extent. Data from nationwide Health and Nutrition check Surveys (NHANES) plainly indicate the there are racial/ethnic distinctions in the pervasiveness of overweight and obesity. Flegal and coworkers (2002), reporting on 1999–2000 NHANES data, established that in men two decades of age and also older, the ubiquity of overweight (BMI ≥ 25) was 67.4 percent for non-Hispanic whites, 60.7 percent for non-Hispanic blacks, and also 74.7 percent because that Mexican Americans. The differences were no statistically significant, but sample sizes were relatively small. However, for ladies ages two decades and older, the prevalence of overweight to be 57.3 percent in non-Hispanic whites, 77.3 percent in non-Hispanic blacks, and 71.9 percent in mexican Americans. The difference in prevalence in between non-Hispanic white and non-Hispanic black ladies was statistically far-ranging (Flegal et al., 2002). The causes of these differences in the ubiquity of overweight have not been plainly identified, however are most likely to it is in a combination of physiology, culture, and behavior.

The partnership of BMI to percent body fat is also impacted by race/ ethnicity. Fernandez and also colleagues (2003) newly reported the outcomes of an analysis of 11 cross-sectional studies entailing body composition assessments that African-American men and also women, Hispanic-American men and women, and European-American men and women. The average age ranged indigenous 42.6 to 50.8 years, and the median BMI ranged indigenous 25.1 (European-American women) to 29.8 (African-American women). Full body fat was measured making use of dual-energy X-ray absorptiometry. There were no differences in the estimation of percent human body fat native BMI because that men across ethnic groups. However, for women with BMIs much less than 30, Hispanic-American women had actually a significantly higher percent of body fat in ~ a given BMI 보다 did African-American or European-American women. However, in ~ BMIs higher than 35, European-American women had a greater percent body fat 보다 either the the other two teams of women. Some previously studies have actually reported greater fat cost-free mass in African-American women compared with Caucasian women through the exact same BMI, primarily as result of the greater skeletal massive in African-American females (Gallagher et al., 1996; Ortiz et al., 1992).

A variety of studies have examined feasible physiological reasons for these race/ethnic differences. Foster and colleagues (1997) explored differences in resting energy expenditure (REE) in between obese African-American women and also Caucasian-American women. They uncovered that REE to be most very closely correlated to human body weight and also that African-American women had actually lower REE than Caucasian-American women. Melby and also coworkers (2000) check behavioral and also physiological attributes related to weight problems risk in young, sedentary, nonobese African-American and also Caucasian-American women. The two teams were comparable in age and anthropometric characteristics. Parameters examined had REE, respiratory tract exchange rates (RER), insulin sensitivity, and also maximal oxygen consumption. REE was 3 to 4 percent lower in African-American women, but the difference was not statistically significant. However, the resting RER was considerably lower in African-American women. The African-American women likewise had substantially lower insulin sensitivity values that result in greater acute phase insulin solution to glucose. Full daily power expenditure and also physical task energy expenditure were substantially lower in the African-American women.

Tanner and also coworkers (2002) recently determined a relationship between muscle fiber form and obesity. In a study of lean and also obese African-American and Caucasian women, form I muscle yarn (slow twitch, oxidative muscle fibers) were considerably reduced in obese women compared with the skinny women, and form IIb fibers (fast twitch, glycolytic muscle fibers) were considerably increased. This differences in between lean and also obese females were better in African-Americans than in Caucasians. The type IIb phenotype is insulin resistant and also deficient through regard come lipid disposal. The writer speculated that the ubiquity of the form II yarn might result in partitioning lipid towards storage in bones muscle or adipose tissue quite than oxidation in ~ the skeleton muscle, causing a positive fat balance.

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A number of studies have additionally examined social and also behavioral factors that may contribute to the distinction in the pervasiveness of overweight between African-American and Caucasian females (Kumanyika et al., 1993; Stevens et al., 1994). Attitudinal and behavioral determinants that limit the capability of some African-American females to shed weight or preserve weight loss have been identified. Regardless of even if it is or no they were overweight, African-American females were half as most likely as Caucasian ladies to think about themselves overweight. There is a lot greater social tolerance the overweight amongst African-Americans, and also they have various body picture perceptions. Return African-American females responded physiologically come a weight-reduction regimen in the very same manner as Caucasian women, their drop-out price from the regime was double that that Caucasian females (Glass et al., 2002).