Weight Management State of the Science and Opportunities for Military Programs (2003) / Chapter Skim
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3 Factors That Infuence Body Weight
3 Factors That Infuence Body Weight
Pages 57-78
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From page 57... ...
Other factors that influence body weight over which the individual has potential control include level of physical activity, diet, and some environmental and social factors. This chapter explores the relationship between each of these factors and body weight.
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From page 58... ...
, using serial BMI data from the Fels Longitudinal study demonstrated that while there was no association between early age at adiposity rebound and adult BMI status in men, after controlling for effects of birth weight, adult physical activity, alcohol and cigarette use, there was approximately twice the risk for overweight with early rebound in women. Causes of early adiposity rebound have been variously attributed to advanced skeletal maturity (Roland-Cachera et al., 1984; Williams and Dickson, 2002)
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From page 59... ...
When the possible confounding factors of prepregnancy weight, gestational weight gain, prenatal physical activity, parity, and socioeconomic status were controlled, African-American women still retained more weight in the postpartum period than did Caucasian women. Results of several recent studies suggest that possible genetic factors may be involved in the tendency to retain weight postpartum.
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From page 60... ...
GENETIC DETERMINANTS The understanding of the genetic influences on overweight and obesity in humans has increased dramatically. Individuals show significant heterogeneity in their body weight and body fatness responses to altered energy balance, dietary components, and changing activity levels.
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From page 61... ...
In addition, serum concentrations of leptin are elevated in close proportion to body fat in obese people with no defect in the leptin gene. Recent studies show that administration of recombinant leptin to lean and obese individuals results in dose-dependent weight loss (Heymsfield et al., 1999~.
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From page 62... ...
The use of genome scanning has provided evidence of QTLs that influence body weight and the number of fat cells (Chagnon et al., 2000~. Comparison of the risks of obesity in spouses and in first-degree relatives has suggested that genetic factors may be of greater prominence in more severe obesity (Katzmarzyk et al., 2000~.
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From page 63... ...
The same trends have been identified in changes in total body fat and percent body fat (Chumlea et al., 20021. Overweight and obesity thus reach maximal rates among middle-aged adults.
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From page 64... ...
Physical activity levels are lower in older individuals, which account for a portion of the energy expenditure reduction that comes with aging. Resting energy requirements are also lower in the elderly, due largely to decreases in all metabolically active tissues, including skeletal muscle, brain, and visceral organs.
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From page 65... ...
Thus, both older men and women have lower rates of energy expenditure and, unless counterbalanced by increased physical activity and reduced food intake, older individuals, in general, will gain weight over time. RACE/ETHNICITY Whether there are racial/ethnic differences in response to the various components of weight management is a legitimate research question that has been explored to only a moderate extent.
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From page 66... ...
Total daily energy expenditure and physical activity energy expenditure were significantly lower in the African-American women. Tanner and coworkers (2002)
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From page 67... ...
Physical activity represents an important component of volitional energy expenditure. Modern transportation and other conveniences have reduced the need for energy expenditure in the form of physical exertion.
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From page 68... ...
found that an association exists between habitual physical activity and maintenance of resting metabolic rate in middleaged women. Physical activity also may reduce the incidence of chronic diseases by favorably altering blood lipid profiles, reducing body fat, and improving lean body mass (Eliakim et al., 1997; Schwartz et al., 1991; Wei et al., 1997; Wilbur et al., 1999~.
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From page 69... ...
Increased energy consumption, decreased energy expenditure, or both can result in positive energy balance. While the etiology of obesity is multifactoral, the common characteristic of all obese people is excessive energy storage in the form of body fat.
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From page 70... ...
Compared with dietary fat, CHOs require additional energy expenditure for digestion, assimilation, and conversion to fat. When energy intake exceeds expenditure, 23 percent of energy consumed is required to convert and store CHO as fat, compared with only 3 percent to store fat.
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From page 71... ...
Results of a small study suggest that the amount of energy required to maintain body weight may be related to the proportion of fat in the diet, regardless of an individual's weight status (Prewitt et al., 1991~. These findings suggest that dietary fat may promote greater weight gain and body-fat accumulation than expected on the basis of energy intake alone.
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From page 72... ...
a highprotein diet preserves lean body mass during weight loss; and (4) the thermogenic effect of protein is the highest of the three macronutrients, resulting in increased energy expenditure for a similar intake.
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From page 73... ...
Data were taken from four national food-consumption surveys covering the period 1977 to 1996. Food consumption was estimated as energy intake in kcal and as average portion sizes using food models to assist respondents in identifying portion size.
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From page 74... ...
The presence of food in virtually every circumstance of daily life, from fast-food outlets to vending machines, encourages and allows individuals to consume multiple calorically dense meals and snacks per day (Bell et al., 1998; Rolls, 2000~. PHYSIOLOGICAL FACTORS A number of phenotypic characteristics have been associated with the risk of weight gain, notably alterations in nonvolitional components of energy expenditure.
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From page 75... ...
found that an association exists between physical activity and maintaining RMR in middle-aged women. The thermic effect of feeding usually accounts for 5 to 10 percent of daily energy expenditure and varies between lean and obese individuals (Astrup, 19961.
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From page 76... ...
In addition, fat intake has also increased steadily, although the relative intake of fat has been decreasing since the 1970s (Putnam and Allshouse, 1999~. This decrease in fat intake has been associated with an increase in average total energy intake (Bray and Popkin, 1998~.
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From page 77... ...
Thus, dietary change is strongly associated with increased weight in both of these carefully studied population groups. The same phenomenon is observed in studies of South Asians who have migrated to the United Kingdom and who have modified their diet and physical activity patterns (McKeigue et al., 1992~.
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From page 78... ...
Maintenance of fitness and appropriate body-fat standards by military personnel is affected by each individual's genetics, developmental history, physiology, age, physical activity level, environment, diet, ethnicity, and social background.
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