Physical activity tends to _____.

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Institute of Medicine (US) Subcommittee on Military Weight Management. Weight Management: State of the Science and Opportunities for Military Programs. Washington (DC): National Academies Press (US); 2004.


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There are many components that have the right to affect body weight. The individual has actually no regulate over some of these determinants, including developmental determinants, hereditary makeup, gender, and also age. Other components that influence body weight over which the individual has actually potential regulate include level of physical task, diet, and also some environmental and social determinants. This chapter explores the relationship in between each of these components and also body weight.


DEVELOPMENTAL DETERMINANTS

It has actually been postulated that tbelow are times throughout people"s lives once expocertain to particular factors may rise their hazard for the onset of excessive weight. These times have actually been termed “important periods.” If these instrumental durations, in addition to the influential determinants, deserve to be clearly defined, it might be feasible to determine individuals at boosted hazard for the breakthrough and persistence of overweight and obesity in adulthood. The prenatal duration, the period of adiposity rebound, and adolescence have actually been proposed as instrumental periods in childhood (Dietz, 1994); pregnancy and also the immediate postpartum period have been proposed as instrumental periods for women in adulthood.


Prenatal Factors

Although the information are topic to a variety of interpretations, it has been documented in both animals and people that females who are severely food minimal throughout the first one to 2 trimesters of pregnancy have actually progeny who have a higher ubiquity of weight problems, diabetes, insulin resistance, and also hypertension later on in life. Progeny of survivors of the Dutch famine in World War II demonstrated a greater pervasiveness of weight problems and also diabetes (Ravelli et al., 1976), although this conclusion was questioned by later on research studies (Jackkid et al., 1996; Susser and also Stein, 1994). Malnutrition in utero likewise has been reported to bring about increased obesity and its complications later in life (Stanner et al., 1997). Lower birth weights additionally seem to be linked via raised top body visceral adiposity in later on life via its attendant raised danger of cardiovascular illness (Oken and also Gillguy, 2003; Rogers, 2003). Due to the fact that people from a lower socioeconomic background are even more likely to be exposed to malnutrition during gestation or beforehand childhood, the pervasiveness of weight problems in such subgroups can be expected to be higher.


Adiposity Rebound

Adiposity rises from birth until approximately 1 year of age, then declines to a minimum at about 6 years of age. The term “adiposity rebound” refers to the boost in body mass index (BMI) and also body fat that occurs after this nadir in youngsters in between the ages of 5 and 7 years. Children enduring adiposity rebound at an previously age show up to have actually a three- to sixfold higher risk of increased adult BMI than do other children (Whitaker et al., 1998). He and Karlberg (2002) demonstrated, with the development of probcapacity charts based on 3,650 kids complied with from birth to 18 years of age, that children who experienced this rebound prior to 8 years of age have actually a greater risk of adulthood excessive weight. However before, Guo and coemployees (2000), utilizing serial BMI data from the Fels Longitudinal research demonstrated that while tbelow was no association in between at an early stage age at adiposity rebound and also adult BMI condition in males, after managing for results of birth weight, adult physical task, alcohol and cigarette use, tright here was approximately twice the hazard for overweight via at an early stage rebound in woguys.

Casupplies of beforehand adiposity rebound have actually been otherwise attributed to progressed skeletal maturity (Roland-Cachera et al., 1984; Williams and also Dickson, 2002), high protein intake (Roland-Cachera et al., 1995), and also parental BMI (Dorosty et al., 2000). Cameron and Demerath (2002) concluded after substantial review of the accessible scientific literature that the evidence is still not clear around whether age at adiposity rebound is an essential period for the development of excessive weight, but that beforehand adiposity rebound might well be a statistical predictor of later obesity because of its strong connection with at an early stage adiposity and also sped up maturation, both of which are established markers of later danger of obesity.


Adolescence

Although just 30 percent of adult excessive weight begins throughout childhood, 70 percent of the adult weight problems that begins in childhood may start throughout adolescence (Dietz, 1994). Adolescent weight problems is linked through a selection of adverse health effects in adulthood, including at an early stage mortality in males and enhanced risks of coronary heart condition, diabetes, and also colorectal cancer (Miller, 1988; Must et al., 1992; Wylie-Rosett, 1988). Most of these dangers were only slightly attenuated by adjustment for adult weight problems, which says that weight problems during adolescence may identify the hazard of these later complications regardmuch less of whether or not the individuals are obese adults.

While total fatness is an important consideration once evaluating developpsychological elements of weight problems, a second consideration is adipose tconcern circulation. Visceral adipose tissue has an independent result on obesity-linked comorbidities (Emery et al., 1993) that is separate from that of total body fat, although the developpsychological aspects of visceral adipose tworry deposition have not been well stupassed away. Amongst children, visceral adiposity shows up to be connected through an enhanced hazard of cardiovascular hazard determinants such as elevated triglycerides and reduced high-density lipoproteins that are independent of complete body fat (Caprio et al., 1996; Gutin et al., 1994). However before, the periods at which these relationships appear remain unclear. Cross-sectional studies imply that visceral adipose tissue deplace is not noted prior to adolescence, however rises rapidly at that time.


Adulthood

The period after adolescence has not been intensively stupassed away, although roughly two-thirds of adult excessive weight starts after adolescence. Whether added critical periods exist in adulthood is less certain, but pregnancy and also postpartum might constitute one such duration for a subcollection of women (Williamboy et al., 1994). Postpartum weight retention appears to range from 0.5 to 4.8 kg for the majority of women (Johnston, 1991), however African-Amerihave the right to mothers might be twice as most likely to retain 9.1 kg (20 lb) or more postpartum than Caucasian mothers (Parker and Abrams, 1993). Boardley and also colleagues (1995) discovered that African-Amerideserve to womales ate more and also were much less physically energetic postpartum than were the Caucasian women in their sample. When the feasible constarting factors of prepregnancy weight, gestational weight obtain, prenatal physical activity, parity, and also socioeconomic status were managed, African-Amerideserve to womales still maintained even more weight in the postpartum period than did Caucasian women. Results of a number of recent researches suggest that feasible hereditary factors may be connected in the tendency to retain weight postpartum. One research uncovered that in women via normal prepregnancy BMIs, high first-trimester serum leptin concentrations (a protein hormone encoded by the obese gene) correlated via increased gestational weight get and postpartum weight retention (Stein et al., 1998). In an additional research, womales within 12 months of the birth of their first boy who were homozygous for the 825T allele of the G-protein ß3, taken into consideration a “thrifty” genoform, had significantly higher BMIs and postpartum weight retention than womales that did not bring the genoform (Gütersohn et al., 2000). No impact of the genotype was oboffered among women who had actually never before given birth, suggesting a pregnancy-specific phenomenon. In enhancement, this partnership was just oboffered among women that engaged in low levels of physical task, sustaining the concept that physical activity might mitigate impacts of genetic endowment on the potential for postpartum weight retention. Whether this particular hereditary variation in this certain G protein is causally linked to the oboffered distinctions in BMI and weight retention or is merely a marker for the responsible mutation, and what the device might be, are both inquiries that require additionally investigation (Feldmale and also Hegele, 2000).


GENETIC DETERMINANTS

The understanding of the genetic impacts on overweight and excessive weight in people has actually raised dramatically. Individuals show significant heterogeneity in their body weight and body fatness responses to transformed power balance, dietary components, and also transforming activity levels. It is now well-establimelted that overweight and excessive weight have a significant hereditary component, with approximates of the contribution of genetic variation to oboffered variation in obesity-connected phenokinds (such as BMI, fat mass, and leptin levels) varying from 30 to 70 percent (Comuzzie et al., 1993, 1994, 1996). However, little is yet known around the particular reasons of heterogeneity (Pérusse and also Bouchard, 1999). It appears clear that power metabolism and neural regulate of appetite are connected in regulating body weight and also might contribute to the etiology of weight problems. Studies of relaxing metabolic price display that the variation within families is less than the variation among family members (Bogardus et al., 1986).

Several research studies have evaluated the potential mechanisms whereby hereditary determinants may add to weight problems. One of the mechanisms through which differences in power metabolism might add to excessive weight might involve defects in uncoupling proteins (UCP). Several types of uncoupling proteins have actually been determined. Fleury and also colleagues (1997) initially explained huguy uncoupling protein 2 (UCP-2) and its web links to excessive weight and hyperinsulinemia. Boucdifficult (1997) noted that markers near the UCP-2 gene in human beings are connected to differences in resting metabolic rate. Hence, hereditary distinctions in UCP-2, and also possibly various other UCPs, may add to human weight problems.

Tright here is a group of at leastern 20 Mendelian syndromes in which excessive weight is a component, including Prader-Willi, Bardet-Biedl, Borjeboy, Cohen, and also Wilson-Turner (Gunay-Aygun et al., 1997; Reed et al., 1995). These genetic disorders are rare, and also family researches perform not suggest that the genes responsible for these syndromes are associated in the widespread develops of humale obesity. For more than 99 percent of obese humans, the genetic basis of their obesity is unrecognized.


Animal Models of Genetic Obesity

The strongest evidence for genetic weight-regulating mechanisms is the current elucidation of single gene defects that are connected through extreme weight obtain in pets. Single gene mutations can indisputably reason weight problems in both rodent models and also in humans. In rodents, such mutations have been identified in at leastern 5 genes: the obese gene for the circulating adipose tissue-secreted variable leptin; the db gene for the receptor of leptin; the agouti yellow mutation, which controls hair color in mice via the production of melanin pigments (via its human indistinguishable, agouti signaling protein gene); the fat mutation in the carboxipeptidase E gene, which is a prohormone handling enzyme; and also the tub mutation, the feature of which has actually yet to be identified. Of the five gene assets that currently have been linked through weight regulation, leptin is the finest identified. Genetic defects in leptin are associated with extreme obesity in both humans and laboratory pets. In enhancement, serum concentrations of leptin are elevated in close proportion to body fat in obese civilization with no defect in the leptin gene. Recent studies present that management of recombinant leptin to lean and also obese people outcomes in dose-dependent weight loss (Heymsfield et al., 1999). Additional research study is essential to assess the potential role of leptin in weight problems therapy.


Familial Aggregation of Risk for Obesity

Using the thorough Danish fostering registry, Stunkard and colleagues (1986) discovered that embraced children that were raised independently from their organic parents had actually body weights closer to those of their biological parents than to those of their adoptive parental fees. The kids in this examine were separated from their parents at a very early age, generally prior to 3 months, so the possibility for the biological parents to instill eating and also activity actions was exceptionally limited. Another study of adoptees confirmed a far-ranging hereditary influence on weight problems, but none of the environmental indicators evaluated were discovered to add, although a number of the conditions considered have previously been linked via obesity (Sorensen et al., 1998). Stunkard and colleagues (1986) estimated that as much as 70 percent of the variance in the event of weight problems can be attributed to genetic components, but other authors have actually postulated that as little as 20 percent of the variance is due to hereditary components. The basic agreement is that hereditary determinants account for about 30 to 50 percent of the variance in the event of weight problems (Bouctough, 1997).

Twin research studies carry out the many exceptional clinical proof that genetic factors play a vital duty in the etiology of excessive weight in people. Stunkard and colleagues (1990) studied identical and also nonthe same twins that were reared together and also others that were reared acomponent. They found a high correlation of body weight among the same twins, also if they were reared acomponent. Bouchard and colleagues (1990) studied twins who were isolated in the Canadian wilderness through no accessibility to foods items various other than those offered by the investigators. Identical twins were overfed for a duration of 100 days, and their gains in body weight and also adipose tworry were evaluated. There was a closer association of both body weight and also intra-abdominal adipose tconcern (visceral fat) within twin pairs than among twin pairs.

The maximal heritcapacity of excessive weight has actually been approximated to range from 30 to 50 percent, based on a evaluation of family members researches (Chagnon et al., 2000). Although extensive initiatives have actually been made to determine mutations in the genes determined as obesity-connected in rodents and in other candiday genes for excessive weight in people, to date just a handful of people have been identified through mutations in any of the genes that have actually produced obesity in rodents. Specifically, numerous people have actually been identified through mutations in the leptin gene or its receptor, however no people have yet been uncovered through mutations in the various other genes established in rodents.

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In full, single gene mutations have actually been figured out as responsible for weight problems in 25 persons, with these mutations appearing in 7 genes (12 different mutations) (Pérusse et al., 1999) or in 5 genes (Chagnon et al., 2000). Studies of quantitative trait loci (QTL) in rodents have argued at leastern 98 different QTLs linked with weight problems (Chagnon et al., 2000).

At this time, the major effort in the search for particular genes that contribute to human overweight and excessive weight is based upon the use of genome scanning. In genome scanning, affiliation evaluation is carried out to determine QTLs that affect the specific phenoform under research. The use of genome scanning has gave proof of QTLs that influence body weight and also the variety of fat cells (Chagnon et al., 2000).

Comparichild of the dangers of excessive weight in sposupplies and also in first-level relatives has actually said that genetic determinants might be of higher prominence in even more significant obesity (Katzmarzyk et al., 2000). Amongst the members of families that contain at least one morbidly obese perkid, a major gene result was transmitted in a coleading fashion, suggesting a gene-atmosphere interaction (Rice et al., 1999). Both multifactorial and also major gene impacts have actually been suggested. Efforts are recurring to determine the genetic and molecular basis of overweight and obesity, and also it is likely that many genes (and within these genes and also their promoters, many different mutations or variants) that are responsible for the hereditary variation of excessive weight in people will be established.

The breakthrough of obesity most likely involves a mix of mutual environment and also common hereditary propensities. The quick increase in pervasiveness of obesity in the USA, as well as in many type of other countries, throughout all age teams might reflect a removal of environmental constraints (e.g., high levels of day-to-day task and food availability) on the expression of excessive weight genokinds. Knowledge of the hereditary components of excessive weight is not most likely to be helpful to the military in the near term, however identification of markers of potential hazard of obesity may well have actually implications for future screening.


AGE

Cross-sectional and longitudinal studies indicate a progressive rise in the average BMI of Americans approximately the eras of 50 to 60 years (IOM, 1995). This trend is similar, through some variation, across males and females and also throughout all evaluated ethnic groups. Population research studies likewise show a decrease in body weight and also BMI among the elderly, generally in the seventh and also eighth decades (IOM, 1995; Kuczmarski et al., 1994; NHLBI, 1998). The same fads have been figured out in alters in complete body fat and also percent body fat (Chumlea et al., 2002). Overweight and weight problems thus reach maximal rates among middle-aged adults. This pattern is shown in Figure 3-1.


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FIGURE 3-1

The prevalence (%) of overweight and weight problems of males and also womales by age in the UNITED STATE population. Preweight problems = body mass index (BMI) of 25–29.9, course I obesity = BMI of 30–34.9, course II excessive weight = BMI of 35–39.9, and course III weight problems (even more...)


The age-related body mass rise approximately the fifth and also 6th years is accompanied by added anatomical, structural, and also body compositional transforms. Stature declines from about age 30 onward, with prices in women much faster than those in guys and also for postmenopausal woguys quicker than their premenopausal counterparts. Declining stature accounts for a tiny percentage of the age-connected rise in BMI (Gallagher et al., 1996).

Many weight-management professionals agree that body weight becomes increasingly even more tough to maintain via age, however tbelow shows up to be bit rationale for increasing the top BMI range constant through excellent health and wellness as individuals become older. Williams (1997) indicated that body weight and linked circumferences would certainly increase via proceeding age unmuch less food intake is decreased and physical task is substantially increased.

A huge variety of cross-sectional studies, however, perform show that body fat boosts via age, also after managing for transforms in body weight and also physical task levels (Baumgartner et al., 1995; Flynn et al., 1989; Forbes, 1987; Forbes and 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 intend body-fat content in nonworking out civilian women via a BMI of 25 raised from 30 percent for those between the eras of 17 and also twenty years to 36 percent for those ages 40 years and older. The implication of this is that lean body mass and also, commonly, skeletal mass, decrease with age. Additionally, partitioning of adipose tissue between the subcutaneous and also visceral compartments is likewise moderated by age (Borkan et al., 1983). Men have actually more visceral adipose tproblem than do womales at all periods, and also the price of visceral adipose tissue increase via age is higher in males than in women (Blaak, 2001).

In comparison to body fat, skeletal muscle mass declines via age beginning about the third decade of life (Dutta and Hadley, 1995). This monitoring is true not just for the basic populace, yet it is likewise noticeable in armed forces personnel (USAF, 1975). The prices of decline might accelerate after the oncollection of menopause in woguys (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 minerals through progressing age and are existing also after regulating for loss in body weight (Gallagher et al., 2000). The mechanisms of body composition change through aging are multifactorial and include physical intask, diet, and hormonal and also cytokine alterations. The loss of lean mass and gain in fat mass occur even with no evident readjust in body weight. Since lean mass contributes the larger share of metabolic task, total power expenditure throughout remainder or low task will certainly likewise decrease proportionally through the loss of lean mass.

Total energy expenditure and also for this reason, power requirements, decrease through advancing age (Tzankoff and also Norris, 1978). Physical task levels are lower in older individuals, which account for a section of the energy expenditure reduction that comes via aging. Resting power needs are additionally lower in the elderly, due mainly to decreases in all metabolically active tworries, including skeletal muscle, brain, and also visceral organs. In laboratory pets, the heat developed by tconcerns per unit of mass decreases with age (a decrease in the certain resting energy expenditure of organs), but it continues to be unparticular whether this monitoring additionally applies to people. The practice of resistance training by human being over the age of 50 years may improve fat-complimentary mass, mainly skeletal muscle, and also thereby assist offset the age-connected decline in relaxing metabolic rate (Hill and Saris, 1998; Tzankoff and Norris, 1977). In woguys, loss of ovarian function accounts for a reduced rate of as a whole warmth production compared with that observed in premenopausal woguys (Poehlmale and Tchernof, 1998). Therefore, both older men and also women have reduced rates of power expenditure and, unless counterbalanced by raised physical activity and reduced food intake, older individuals, in general, will get weight over time.


RACE/ETHNICITY

Whether tright here are racial/ethnic differences in response to the miscellaneous components of weight administration is a legitimate research question that has been explored to only a moderate level. File from National Health and Nutrition Examination Surveys (NHANES) clearly suggest that tbelow are racial/ethnic distinctions in the pervasiveness of overweight and excessive weight. Flegal and also coemployees (2002), reporting on 1999–2000 NHANES data, figured out that in guys two decades of age and also older, the prevalence of overweight (BMI ≥ 25) was 67.4 percent for non-Hispanic whites, 60.7 percent for non-Hispanic blacks, and also 74.7 percent for Mexihave the right to Americans. The distinctions were not statistically substantial, but sample sizes were reasonably small. However, for woguys eras twenty years and older, the prevalence of overweight was 57.3 percent in non-Hispanic whites, 77.3 percent in non-Hispanic blacks, and 71.9 percent in Mexican Americans. The difference in ubiquity between non-Hispanic white and non-Hispanic black womales was statistically considerable (Flegal et al., 2002). The causes of these differences in the pervasiveness of overweight have not been plainly determined, however are likely to be a combination of physiology, society, and also actions.

The relationship of BMI to percent body fat is also influenced by race/ ethnicity. Fernandez and colleagues (2003) newly reported the results of an evaluation of 11 cross-sectional studies including body composition assessments of African-Amerideserve to men and also woguys, Hispanic-Amerihave the right to guys and womales, and also European-Amerihave the right to guys and womales. The average age ranged from 42.6 to 50.8 years, and the average BMI ranged from 25.1 (European-American women) to 29.8 (African-American women). Total body fat was measured using dual-energy X-ray absorptiomeattempt. There were no distinctions in the estimation of percent body fat from BMI for males across ethnic groups. However before, for woguys via BMIs much less than 30, Hispanic-Amerihave the right to woguys had actually a significantly better percent of body fat at a provided BMI than did African-Amerideserve to or European-American women. However before, at BMIs greater than 35, European-Amerideserve to womales had a higher percent body fat than either of the other two teams of womales. Some previously studies have actually reported greater fat complimentary mass in African-American women compared via Caucasian women through the same BMI, primarily due to the greater skeletal mass in African-American woguys (Gallagher et al., 1996; Ortiz et al., 1992).

A variety of research studies have actually examined feasible physiological factors for these race/ethnic differences. Foster and also colleagues (1997) explored distinctions in relaxing energy expenditure (REE) in between obese African-Amerihave the right to women and also Caucasian-Amerideserve to women. They found that REE was a lot of closely associated to body weight and also that African-Amerideserve to womales had actually reduced REE than Caucasian-Amerideserve to women. Melby and also coemployees (2000) examined behavior and also physiological characteristics pertained to obesity danger in young, sedentary, nonobese African-Amerihave the right to and Caucasian-Amerideserve to woguys. The 2 groups were similar in age and anthropometric qualities. Parameters examined consisted of REE, respiratory exadjust prices (RER), insulin sensitivity, and maximal oxygen consumption. REE was 3 to 4 percent reduced in African-American women, yet the difference was not statistically substantial. However before, the resting RER was considerably reduced in African-American womales. The African-Amerihave the right to women additionally had significantly lower insulin sensitivity values that led to better acute phase insulin response to glucose. Total daily power expenditure and also physical task energy expenditure were substantially reduced in the African-Amerihave the right to womales.

Tanner and coworkers (2002) newly figured out a connection between muscle fiber type and also obesity. In a study of lean and obese African-Amerihave the right to and Caucasian womales, type I muscle fibers (sluggish twitch, oxidative muscle fibers) were significantly reduced in obese women compared with the lean women, and also kind IIb fibers (quick twitch, glycolytic muscle fibers) were considerably boosted. These distinctions in between lean and obese women were better in African-Americans than in Caucasians. The type IIb phenotype is insulin resistant and also deficient with regard to lipid disposal. The authors speculated that the pervasiveness of the kind II fibers could bring about partitioning lipid toward storage in skeletal muscle or adipose tproblem rather than oxidation within the skeletal muscle, causing a positive fat balance.

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A variety of researches have actually likewise examined social and behavior determinants that might contribute to the distinction in the ubiquity of overweight between African-Amerideserve to and also Caucasian womales (Kumanyika et al., 1993; Stevens et al., 1994). Attitudinal and also behavioral components that limit the capability of some African-American women to shed weight or preserve weight loss have been established. Regardless of whether or not they were overweight, African-American woguys were half as likely as Caucasian women to consider themselves overweight. Tbelow is a a lot higher cultural tolerance of overweight among African-Americans, and they have different body image perceptions. Although African-Amerideserve to woguys responded physiologically to a weight-reduction program in the exact same manner as Caucasian woguys, their drop-out price from the program was double that of Caucasian womales (Glass et al., 2002).