Influence of physical activity and dietary restraint on

Influence of physical activity and dietary restraint on resting energy expenditure in young nonobese females E m T.

~EHLMIAN~

Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by Renmin University of China on 06/04/13 For personal use only.

Division of Endocrinology, Metabslisan and Nutrition, Department of Mediciae, College sf Medicine, Universiv of Vennsnt, Burlington, VT 05405, U. S. A.

HELENE VIERS Department of Nutritional Sciences, University of Vermont, Burlington, VT 05405, U. S. A. AND

MARKDETZEW Department of Psychology, Uaiversity of Vemsnt, Burlington, VT 05405, U. S.A. Received June 26, 1990 ~ ~ E H L M E. AM T.,, VIERS,M. E , and DETZER,M. 1991. Influence of physical activity and dietary restraint s n resting energy expenditure in young nonobese females. Can. J. Phy siol. Pharmacol. 69: 320 - 326. An understanding of the physiological and behavioral determinants of resting energy requirements is important to nutritional considerations in females. We examined the influence of endurance training and self-reported dietary restraint on resting metabolic rate and fasting plasma hormones in 44 nonobese females characterized for body composition, maximal aerobic power (Vo, max), and daily energy intake. To examine the association of metabolic rate and dietary restraint with hormonal status, fasting plasma levels of insulin, glucose, and thyroid hormones (total and free fractions of thyroxine and triiodothyronine) were determined. Hn univariate analysis, resting metabolic rate (kcal - min-') was positively related to V+ max (L . min-') (r = 0.54; g < 0.81). This relationship, however, was partially dependent on body size, since fat-free mass was also related to resting metabolic rate (8- = 0.42; p < 0.01) and Vo, max (L - min- ') (r 7 0.75; p < 0.01). After controlling for fat-free weight using partial correlation analysis, the relation between R M W and V% max was weaker but still significant (partid r = 0.38; p < 0.85). On the other hand, high levels of dietary restraint were associated with higher levels of body fat (r = 0.31; p < 0.05) and a lower resting metabolic rate (r = -0.29; p = 0.07). These associations persisted after control for differences in fat-free mass. Total energy intake as well as total and free levels of triiodothyronine were not related to resting metabolic rate or level of dietary restraint. Our results suggest that the level of endurance training (i.e., Vo, max) and dietary restraint, independent of differences in fat-free mass, contribute to individual variation in resting metabolic rate of nonobese females. These firmdings appear to be unrelated to fasting plasma concentrations of thyroid hormones. Whereas high levels of endurance training are associated with increased energy requirements at rest, higher levels of dietary restraint are associated with a lower resting metabolic rate and possibly a propensity to gain body fat. Key woP.Bs: endurance training, dietary restraint, resting metabolic rate, females, energy intake. ~ E H L M AE. M To, , VIERS,H. F., et DETZER,M. 1991. Influence of physical activity and dietary restraint on resting energy expenditure in young nonobese females. Can. J. Physiol. Phamacd. 69 : 320 -326. Du point de vue nutritionnel, il est important de comprendre Zes determinants cornpsrtementaux et physiologiques vis-h-vis des besoins CnergCtiques au repos chez le sujet ferninin. Nous avons examin6 l'effet de l'entrainement d'endurance et d'une restriction alimentaire auto-CvaluCe sur le k u x de mttabolisme au repos (TMR) et sur les hormones plasmatiques jeun, chez 44 sujets ferninins non obkses, dont on a CvaluC la composition corpsrelle, la puissance a6robie maximle (Vs, max) et I'appsrt CnergCtique quotidien. Pour examiner les liens entre le h u x de mttabolisrne, la restriction alimentaire et 1'Ctat hormonal, nous avons dtterrnint les taux plasmatiques h jeun d'insuline, de glucose et d'hormones thyroidiennes (fractions totales et Zibres de thyroxine et de triiodothyronine). Dam une analyse univariCe, le tmx de mttabolisme au repos (kcal min-9 ttait reliC positivement at Ia Vo2 rnax (L min-I) (8- = 0,54; p < 0,01). Toutefois, cette relation dtcoulait partiellement de la dimension corporelle, puisque la masse libre de graisse a aussi CtC relike au taux de mCtabolisme au repos (r = 0,42; p < 0,01) et h la Vs, max (L . min-') (r = 8,75; p < 0,01). Aprks avoir @cartela compsante m s s e libre de graisse, en utilisant une analyse de corrtlation partielle, la corrC%ationentre TMR et Vo, "ax a ttC plus faible, bien que toaajours significative ( r partiel = 0,38; p < 0,05). Par ailleurs, les h u t s taux de restriction alimentaire ont CtC associCs h des taux plus tlevCs de graisse corporelle (r = 0,3B; p < 0,05) et h un taux de mCtabolisme au reprss plus faible (r = 0,29; g = 0,67). Ces corrtlations ont persist6 apr&scontrdle des diffkrences dans la masse libre de graisse. L'apport Cnergttique total ainsi que les taux libres et totaux de triidsthyronine n'ont pas t t t relits au taux de mttabolisqe au repos ni au taux de restriction alimentaire. Nos rCsultats suggkent que le niveau d'entrafnement d9enduranee (c.-i-d. %/s, mix) et de restriction alimentaire, sams tenir compte des differences dans %amasse libre de graisse, contribue h la variation individuelle du taux de mttabolisrne au repos de sujets ftminins non sbbes. Ces rksultats ne semblemt pas Ctre relits h des concentrations plasmtiques h jeun d'homones thyroidiennes. AIors que les niveaux Clevts d9entrafnement d'endurance sont associCs h une augmentation des besoins Cwergttiques au r e p s , les taux plus Clevts de restriction dimentaire sont associCs h un taux de mttabolisme plus faible au repos et i une tendance h augmenter le taux de Ba graisse corporelle. Mots ~ 1 4 s: entrafnement d'endurance, restriction alimentaire, taux de mttabolisrne au repos, sujets Eminins, a p p r t tnergttique. [Traduit par la rCdaction]

'Author for correspondence. Printed in Canada ! Imprime au Canada

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PBEHLMAN ET AL.

Introductisn It is often noted that energy requirements of individuals with similar body weights and body composition are quite variable (Ravussin et al. 1986). Because resting metabolic rate (RMR) accounts for two-thirds or more of totd energy expenditure in ambulatory humans (Poehlman 1989), it is a major contributor to total energy requirements. A growing body of evidence suggests that the level of physical activity contributes to variation in RMR between individuals. Although still controversial, cross-sectional and exercise intervention studies support the notion that endurance training increases RMR (Lemon et al. 1984; Tremblay et al. 1985, 1986; Poehlman et al. 1988, 1989b, 1990), whereas other investigators have found no meaningful effect of endurance training on RMR (Davis et d. 1983; Binghm et al. 1989). The majority of these studies have been performed in males, whereas less information is available on females. Furthermore, of those studies that have examined the role of exercise training on RMR in females, equivocal results have been found (Eennon et al. 1984; LBlanc et al. 1984b; Tremblay et al. 1986; Lawson et A. 1987; Bingham et al. 1989; Owen 1988; ValliCres et d.1989). Whereas differences in experimental design, number of subjects considered, and state of energy balance may have contributed to divergent results among investigators, none of the previous studies have considered the possibility that dietary behavioral practices may influence metabolic rate. This is surprising since "normal" eating behavior of many young women in affluent societies is characterized by the attempt to restrict food intake to prevent weight gain or to promote weight loss (Polivy and Herman 1987) to comply with sociocultural standards for female beauty. Furthermore, alterations in resting metabolic rate have recently been shown to occur in a number of behavioral eating disorders (Bennett et al. 1989; Devlin et al. 19%). The purpose of this study was to examine the role of endurance training and dietary restraint as modifying factors on RMR in nonobese females characterized for body composition, maximal aerobic power, and energy intake. A second objective was to measure selected fasting hormones and substrates to identify possible relationships between the fasting hormonal milieu with variations in metabolic rate and dietary restraint. Methods Subjects Forty-four young nonobese females aged B 8 -39 volunteered for the experiment from the surrounding communities. Their physical characteristics are shown in Table 1. Ten subjects were taking oral contraceptives and one subject was amenorrheic. Because no significant differences in resting metabolic rate, plasma hormones, and substrates were noted between these subjects and regularly menstruating subjects taking no contraceptives, all subjects were pooled into one sample population. All volunteers were in good general health, determined by medical history and physical examination. None of the subjects had a history of a clinically significant eating disorder. All were nonsmokers and were weight stable by medical history (+2 kg within the past year). The nature, purpose, and possible risks of the study were carefully explained to each subject before she gave consent to participate. The experimental protocol was approved by the Committee on Human Research for the Medical Sciences of the University of Vermont. Resting metabolic rate R M R was determined by indirect calorimetry during the follicular phase of the menstrual cycle for 40 min after an overnight fast. All

TABLE1. Physical characteristics of young nonobese females -

Characteristic

Mean f SD

Range

Age (years) Weight (kg) Body fat (5%) Fat-free m s s (kg) YaistJhip ratio Vo, max L . min-' mL . kg-' * min-l

28f 5.9 59f 7.3 18f 5.2 48k5.8 8.77 f8.65

18-39.0 47-85 21 -34 35 -57 0.68 -8.92

2.86k0.55 48.5 f 8.67

1.6-4.8 29.5 -64.4

measures were performed at least 36 h after the last exercise bout, as vigorous exercise has not been shown to affect RMR after this period of time (Poehlman et al. 1989~).An introduction to all equipment and procedures familiarized the subjects with test conditions prior to actual measurements. RMR was established for each subject by indirect calorimetry for 45 min after an overnight fast in which volunteers slept at the Clinical Research Center. Subjects were awakened just prior to testing and were instructed to lie quietly and remain awake throughout the test. Briefly, a clear plastic ventilated hood was placed over the subject's head for the calorimetric testing. Room air was drawn through the hood and the flow rate measured by a pneumotachograph (Vertek, Burlington, VT). A constant fraction of expired air was withdrawn, dried, and delivered to a zirconium cell oxygen analyzer (Ametek, Pittsburgh, PA) and infrared carbon dioxide analyzer (Ametek). Energy expenditure (kcal * min- ') was calculated from the equation of Weir (1949). The intraclass correlation and coefficient of variation (CV) for WRaR determined using test -retest conditions in 17 volunteers is 8.90 and 4.3%, respectively, in our laboratory (Poehlman et al. B9W). Body composition and anthrspornetric measurements Each subject's body weight was determined on a metabolic scale to the nearest tenth of a gram while dressed in a previously weighed r o b . Body fat was estimated using the Siri equation (1956) from body density by underwater weighing and simultaneous measurement sf residual lung volume by helium dilution. Fat-free mass was estimated as total body weight minus fat weight. The reproducibility of percent body fat in 28 individuals was examined using test-retest conditions (within B week). The intraclass correlation for the estimation of percent body fat reached 0.98 and the CV was 4.9% (Poehlman et al. 1990). To estimate upper and lower body fat distribution, a plastic measuring tape was used to determine the waist to hip circumference ratio while subjects stood erect. Waist measurements were taken at the minimal circumference of the abdomen, while the hip circumference was measured at the maximal gluteal protuberance of the buttock. All measurements were performed by the same investigator. Daily energy intake Energy intake was determined from 3-day food diaries as previously described (PoeMman et al. 1988). Briefly, each subject was asked to weigh and record all food and beverages for 2 weekdays and 1 weekend day. Subjects were carefully instructed how to record dietary intake. Particular emphasis was placed on the importance of maintaining typical eating habits and describing foods and method of preparation in accurate detail. A 5-lb (1 lb = 0.453 kg) metabolic scale was sent home with each subject to aid in measurement. The Nutritionist I11 computer program (N-Squared Computing, 4.0 version) was used to analyze all diets for energy intake as well as relative and absolute quantities of macronutrients. Maxim1 aerobic power $Jo2 m)and physical activity Maximal aerobic power (vo2max) was assessed by a progressive and continuous exercise test to exhaustion on a treadmill as previ-


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CAN. J. BHYSIOL. PHARMACOL. VOL. 69, 1991

ously described (PoehBmn et al. 1990). Briefly, the initial running s p e d was selected as one h a was comfortable for the subject. After the first 3 min the incline was increased by 2.5 % every 2 min, while the speed remined constant. Vs, maw was recorded was the highest oxygen uptake for min during the test. Test-retest conditions (within 1 week) for r/o, max (n = 25) yielded an intraclass correlation of 0.94 and a CV of 3.8 % . (Poehlmn et al. 1990). The energy expended in leisure time physical activity within the past year was assessed in a structured interview with the use of the Minnesota Leisure Time Physical Activity Questionnaire (Taylor et al. 1978), as previously described (Poenlman et al. 1990). The mean daily energy expenditure during leisure time within the past year in this nonobese population was 487 f 287 kcallday (1 CaI = 4.1858 J) with a range of 50 - 1230 kcallday.

Dietary restmint The Three Factor Eating Questionnaire (Staenkard and Messick 2985) was used to assess the level of conscious restriction of food intake for each subject. This psychometric tool evaluates the state of chronic dietary concern that characterizes individuals who believe that they should regulate their body weight and body shape and basic d y refers to the intention to diet to achieve or maintain a desired body weight. Briefly, the questionnaire divides eating behavior into three different categories: cognitive restraint, hunger, and disinhibition. The cognitive restraint factor is generally regarded as the best too% available for psychometric assessment of restrained eating (Laessle et al. 1989). This factor consists of 21 items, with scores ranging from 0 to 21. A score of 0 represents no conscious restriction of food intake, whereas a score of 21 would signify the highest level of dietary restraint. All questionnaires were administered by the same investigator. Plasm deteminatia'sns Plasma glucose was determined using a YSI glucose analyzer (Yellow Springs Instrument Co., Yellow Springs, OW). Plasma imunoreactive insulin was determined by a modification of the radioimmunoassay technique of Stam et d.(1979). Plasma thyroxine (T4) , free T,, and 3,5,3 '-triiodsthyronine (T3) concentrations were measured using clinical assay kits maxter, Cambridge, MA) and free T3 was measured using an analog assay (Diagnostic Products, b s Angdes, CA). Statistics Pearson's correlation coefficient was used to assess the associations among the variables: RMR, body composition, maximal aerobic power, body fat distribution, dietary restraint, daily energy intake, and plasma hormones. Because of the association of RMR and VO, max with fat-free mass, partid correlation analysis was applied using RMR as the dependent variable and fat-free mass as the covariate (Snedecor and Cochran 1967) to estimate the relation between RMW and Vo, m x independent of fat-free mass. The partid correlation coefecient refers to the correlation between two variables (i.e., R M R and Vo, ma%)in which the third yariable is held constant (i.e., fatfree mass) so that only RMR and Vo2 max are involved in the correlation. All data are expressed as means f standard deviation.

Table 2 displays the mean and range of values for WMW, energy intake, diet composition, and dietary restraint in our population. Table 3 shows the univariate correlations among M R , body c o m p s i ~ o n ,Vo2 max, body fat distribution, energy intake, and dietary restraint in nonobese females. Of particular interest we the correlations of RMR with fat-free mass (r = 0.42; p < 0.01; Fig. 1) and lie, max (L.min-I) (r = 6.54; p < 0.0 1; Fig. 2). We also noted a trend for RMR to be lower in those individuals with the highest level of dietary restraint (r = -0.29; g = 0.07). Higher levels of dietary restraint were

TABLE2. Resting metabolic rate (RMR), daily energy intake, dietary cornpsition, and dietary restraint in young nonobese females Variable

Mean f SD

Range

-

W R (kcd - minsl) Energy intake (kcal Carbohydrate % g Protein % g

Fat % g Restraint score* *Restraint scores ranged from 0 to 21, where 0 was no conscious fd restraint. See Methods section for detailed description o f thee-factor eating questionnaire.

associated with higher levels of percent body fat (r = 0.3 1 ; p < 0.05; Fig. 3). To estimate the relation of RMR with the aforementioned variables, independent of fat-free mass, partial correlation analysis was performed using fat-free mass as the single covariate. Partial correlation coefficients are displayed in Table 4. The relation between RMR and Vs2 max was weaker than the univariate relation but still significant (partid r = 0.38; p < 0.05). Percent body fat (partial r = -0.38; p < 0.05) and dietary restraint (partial r = -0.36; p < 0.05) were also related to RMR, independent of fat-free mass. Table 5 shows the mean and ranges of plasma insulin, glucose, and thyroid hormones. All volunteers were euthyroid and exhibited normal ranges for plasma insulin and glucose. Other pertineat correlations Total and free concentrations of thyroid hormones (T3, FT3, T4, and FT4) were not related to RMR (range of r values from -0.24 to 0.12) or fat-free mass (range of r vdues from -0.21 to 0.07). Fasting insulin was positively related to percent body fat (r = 0.35; p < 0.05). Dietary restraint was not significantly related to fasting plasma insulin (r = -0.18), glucose (r = -0.OS), total Tg (r = --0.06), free T3 (r = 0.05), or total T4 (r = -0.261, but it was significantly related with free T4 (r = -0.42; p < 0.01). Dietary restraint was not significantly related to total energy intake (percent or absolute intake of macronutrients) (range of r vdues from -0.25 to 0.11; correlation data not shown in table form).2

This cross-sectional study examined the association of endurance training (Vo2 max) and dietary restraint on WMW in young mnobese females. The new fiqdings are (i) the significant association between WMR and Vo2 m x , independent of differences in fat-free mass, in nonobese females and (ii) the higher level of adiposity and lower RMR in those females exhibiting the highest degree of dietary restraint. This ,Raw data in tabular form may be purchased from the Depository of Unpublished Data, Document Delivery, CISTI, National Research Council of Canada, Ottawa, Ont., Canada KIA O S 2 .

POEHLMAN BT AL.

TABLE3. Univariate correlations among RMR, eo, max, body composition, fat distribution, dietary intake, and dietary restraint in nsnobese young females


WMR

to2 max ( L . min-I)

WT

FFM

% fat

W/H

DR

EH

whaR vo, m x (L min-I) WT FFM % fat W/H DR* EI NOTE:Significance levels: P = 0.31, p < 0.05; P = 0.40; p < 0.01. W R , resting metabolic rate; vo2 max, maximal aerobic power; PFM, fat-free mass; R fat, percent body fat; WIH, waist to hip ratio; DR, dietary restraint; BH, energy intake. *The score range was 0-21. A score of 0 signifies no conscious food restraint, whereas a score of 2 1 represents the highest levd of dietary restraint.

Fat-free mass (kg)

FIG.1. The relationship between resting metabolic rate ( W R ) and fat-free m s s in young nonobese females.

FIG.2. The relationship between resting metabolic rate (RMR) and

Po, m x in young nonobese females.

study differs from previous investigations in several aspects. First, we have considered the influence of a dietary behavior practice (i.e., dietary restraint) as a potential factor influencing metabolic rate and hormonal milieu while controlling for the influence of body composition. Second, we have studied a larger number of volunteers than previous investigators who have considered the effects of endurance training on metabolic rate.

v9

Resting metabolic rate and mar As expected, RMR was significantly related to fat-free mass (P = 0.42; p < 0.01). The magnitude of this association is lower than that reported by previous investigators (Ravussin et al. 1986; Owen 1988) but is similar to another study (FreyHewitt et al. 1990). Two possible reasons may contribute to the lower correlation in our study. First, the homogeneous nature of our nonobese population with respect to the range of fat-free mass is narrow and may attenuate the association between RMR and fat-free mass. Previous investigators who have reported higher correlations between RMR and fat-free mass have examined lean and obese individuals who exhibited a large range of body weight and fat-free mass (Ravussin et al. 1986). Second, it is interesting to consider the possibility that biological attributes such as high levels of dietary restraint and

% body f a t FIG.3. The relationship between percent body fat (by underwater weighing) and dietary restraint in young nonobese females.

(or) endurance training may actually "disturb9' the regression between RMR and fat-free mass. That is, these individuals may show higher or lower levels of energy expenditure per kilogram of the metabolically active tissue. To examine the association between RMR and Vo2 max, independent of fat-free mass, we employed partial correlation analysis using fat-free mass as the covariate. When this analy-

CAN. J. PHYSIOL. PWARMACOL. VOk. 69, 1991

TABLE4. Partial correlations between the dependent variable . I M W and the independent variables Vo, m x , body composition, and nutritional status, with fat-free mass as the covariate


Independent variables

Partial correlation

-

Qo2 max (I., ranin-') % body fat

Waistlhip ratio Dietary restraint Energy intake

8.38" -0.38* -0.16 -0.36" 0.16

TABLE5. Fasting plasma insulin, glucose, and thyroid hormones in young nonobese femdes Variable

Mean f SD

Range

Insulin @mol/L) Glucose (mg1dL) Thyroid hormones T4 @g/dL) FT, (ng/dL) T3 (ng/dL) FT, ( ~ g / d )

51.7a22.9 97.6 % 5.5

17.5 - 1211.0 $7.0- 109.0

8.11 f1.90 1.41$0.20 1.12f 0.33 1.92k0.39

4.80-12.80 1.02-2.08 0.65-2.23 1.20-2.92

sis was performed, the relationship between RMR and max was weaker but still significant (partial r = 0.38; p < 0.01). This finding suggests that females with a high lie, max have a higher WMR for their metabolic size (i.e., per kilogram of fat-free mass) and that energy requirements at rest are increased in endurance trained females. This finding confirms our previous observations in males (Poehlman et d. 1988, B989h7, 1990) and extends our findings to include young nonobese females. Previous studies that have examined the influence of endurance training or the "trained state" with RNIR have yielded discrepant results. Lennon et al. (1984) found a significant correlation between $10~max (predicted from a submaxipaad exercise test) and change in R M R (I- = 8.36) in obese females undergoing a program of aerobic exercise. Trernblay et d. (1986) found an = 11% increase in RMR in obese women after an 11-week program of exercise training. Lawson et al. (1987) reported an increase in RMR in six sedentary lean females that maintained body weight after a 10-week aerobic exercise program. These investigators suggested that the higher M R may result from a prolonged thermogenic effect of exercise and (or) increased energy intake, although the delay between the last exercise session and measurement of metabolic rate was not specified. In the present study, it is unlikely that the higher RMR in the trained females is due to the residual effects of the last exercise bout, since RMR was measured at least 36 h after the last exercise bout (Poehlman et al. 1989a). On the other hand, several investigators have found no exercise training effect on RMR. LeBlmc et al. (1984b) reported no difference in RMR between untrained, moderately trained, and highly trained females. However, upon closer inspection of their .data, a trend for a positive relation between training status (Vo2max) and RMR is noted. The fact that this finding

did not reach statistical significance suggests that a larger sample size may have been required to detect a training effect on RMR. ValliCres et al. (1989) found no changes in RMR of six elite female swimmers measured before and after a 30-day swimming cycle. In this study, however, RMR was measured at two different times in the r n e n s t d cycle. RMR has been shown to vary with menstrual cycle (Solomon et d. 1982; Webb 19861, which may have confounded the exercise training effect on RMR. Owen (1988) reported that regression lines for trained and untrained women were indistinguishable when adjusting RMR per kilogram of fat-free mass. It should be noted, however, that this conclusion was based on a small sample size of female athletes (n = 8) contained within a larger population of inactive femdes varying in age from 18 to 65 years. Finally, Bingham et al. (1989) examined the effects of a 9-week vigorous aerobic training program on RMR and found no mean change in three men and three women in slight energy deficit. A Barge variation in R M R response was noted, with three individuals showing an increase in RMR, whereas three others showed no change or a decrease in RMR. Collectively, the failure to detect small but biologically important differences in RMR between trained and untrained individuals in the aforementioned studies may relate to several factors that include (i) s d l sample sizes, (ii) a large variation in R M R response to exercise, (kbi) alterations in energy balance prior to the measurement of metabolic rate, and (kv) failure to take into account changes in energy expenditure with menstrual cycle function. It should be noted, however, that a cause and effect relationship between endurance training (Vo2 max) and a higher RMR cannot be established from this study. Indeed, RMR (Fontaine et al. 1985), max (Prud9hommeet al. 1984), as well as changes in RMR in response to exercise training (Boehlman et al. 1986) have been shown to be influenced by genetic endowment. Therefore, it is unclear whether endurance training was causative for the higher RMR or a higher RMR was already present in those individuals who selfselected to participate in exercise training. Resting metabolic rate and dietary restraint Previous studies that have examined the influence of exercise training on RMR in females have not considered the association of restrained eating behavior with alterations in resting energy metabolism. This is surprising given the fact that efforts to regdate body weight in young females in recent y e a s have intensified to a high degree in western societies (Zuckerrnan et d. 1986) and alterations in metabolic rate have been reported in women with eating disorders (Bennett et al. 1989; Devlin et al. 1990). In the present study we considered the potential role of dietary restraint as a modifier of metabolic rate, body composition, and hormsnal milieu. Restrained eating, as derived from a self-administered questionnaire, is a state of chronic dietary concern that characterizes people who believe that they should regulate their body weight and shape and has been linked to the development of binge eating and eating disorder syndromes such as bulimia nervosa (Polivy and Herman 1985; Wardle 1987). Although our subjects reported no clinically significant history of an eating disorder, we hypothesized that restrained dietary practices (as indicated by the volunteers) may be linked with an alteration in metabolic rate despite the maintenance of normal body weight.


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i q X 0 v d physical fitness on basal metabolic rate. Br. J. Nutr. 61: 155- 173. DAVIS,9. R., TAGLIAFERRO, A. R., KERTZER, R., GERARDO, T., NICHOLS, J., and WHEELER, J. 1983. Variations in dietary-induced themogenesis and body fatness with aerobic capacity. Eur. J. Appl. Physiol. 50: 3 19-329. DEVLIN,M. J., WALSH,B. T., KWAL,B. G., HEYMSFIELD, S. B., PI-SUNYER, E X.,and DANTZIC, S. 1990. Metabolic abnormalities in bulimia nervosa. Arch. Gen. Psychiatry, 47: 144- 148. FONTAPNE, E., SAVABEP, R., MMBLAY,A., Dm~aBs, J-P., WEHLMAN, E., and BOUCHARD, (1. 1985. Resting metabolic rate in monozygotic and dizygotic twins. Acta Genet. Med. Gemellsl. 34: 41 -47. FREY-HEWITT, B., VRANIZAN, K. M., DWEON, D. M., and WOOD, P. D. 1990. The effect of weight loss by dieting or exercise on resting metabolic rate in overweight men. Int. J. Bbes. 14: 327 -334. H. E., GEORGE, D. T., JIMEWSON, D. C., KAYE,W. H.,GWIRTSMAN, EBERT, M. H., and LAKE,C. R. 1990. Disturbances of noradrenergic systems in n o m l weight bulimia: relationship to diet and menses. Biol. Psychiatry, 27: 4 -2 1. , and PIRKE,K. M. LAESSLE, R. G., WSCHL,Pa. J., K ~ T W A UB.SC., 1989. A comparison of the validity of three scales for the assessment of dietary restraint. J. Abnorm. Psychol. 98: 504-507. LAWSON, S., WEBSTER, J. D., PA-, P. J., and GARROW, J. S. 1987. Effect of a 10-week aerobic exercise programme on metabolic rate, body composition and fitness in lean sedentary females. Br. J. Clin. Pract. 41: 684-688. LEBLANC, J., CABANAC, V., and SAMSON, P. 1984~.Reduced postprandial heat production with gavage as compared with meal feeding in human subjects. Am. J. Physisl. 246: E95 -E101. LEBLANC, J., MEWCIER, P., and SAMSON, P. 1984b. Diet-induced thermogenesis with relation to training state in female subjects. Can. J. Physisl. Pharmacol. 62: 334-337. E , SWWAGO, E., and DENNIS, LENNON, B., NAGLE,E, STRATMAN, S. 1984. Diet and exercise training effects on resting metabolic rate. Int. J. Obes. 9: 39-47. OWEN,0 . E. 1988. Resting metabolic requirements of men and women. Mayo Clin. Proc. 63: 503 -510. ~ E H L M AE.N9., 1989. A review: exercise and its influence on rest resting energy metabolism in man. Med. Sci. Sports Exercise, 21: 515-525. ~ E H L M AE. N ,T., T ~ M B L AA., Y , NADEAU, A., DUSSAULT, J., WBRIAULT, G., and BOUCHARD, C. 1986. Heredity and changes in homones and metabolic rates with short-term training. Am. J. Physiol. 250: ETI 1-E717. ~ E H L M AE.NT., , MELBY, C. L., and BADYLAK, S. F. 1988. Resting metabolic rate and postprandial themogenesis in highly trained and untrained males. Am. J. Clin. Nutr. 47: 793-798. POEHLMAN, E. T., LACHANCE, P., TREMBLAY, A., NABEAU,A., DUS~AULT, J., THBIPIAULT, G., DESPRES, S.-Po,and BBUCHARD, C. Acknowledgements 1989a. The effect of prior exercise and caffeine ingestion on mehbolic rate and homones in young adult males. Can. S. Physisl. Dr. Eric T. Poehlman is supported by grants from the Pharmacol. 67: 10- 16. United States National Institute of Aging (AG-07857) and the ~ E H L M AE.NT., , MELBY,C. L., BABYLAK, S. E, and CALLES, J. American Association of Retired Persons Andrus Foundation 1989b. Aerobic fitness and resting energy expenditure in young and The General Clinical Research Center at the University of adult males. Metab. Clin. Exp. 38: 85 -90. Vermont f RR- 109). The expert technical assistance of John POEHLMAN, E. T., MCAULIFFE, T. L., VANHBUTEN,D. R., and Hiser, Cathy Armstrong, and Chris Potter are gratehlly DANPORTH, E., Jw. 1990. Influence of age and endurance training on metabolic rate and hormones in healthy men. Am. J. Physisl. acknowledged. The insulin assays were kindly performed by 259: E66 -E72. Trish Mead in the laboratory of Dr. David Robbins at the PQLIVY, J., and HERMAN, C. Po 1985. Dieting and binging. A causal University of Vermont. We would like to thank Brs. Michael analysis. Am. Psychol. 40: I93 -20 1. Goran a d Harold Leitenberg for their constructive criticisms 1987. Diagnosis and treatment of normal eating. J. Consult. on the manuscript. Clin. Psychol. 55: 635 -644. PRUD'HBMME, D., BQUCHAWD, C., LEBLANC, C., LANDRY, E , and BENNETT, S. M., WILLIAMSON, D. A., and POWERS,S. K. 1989. FONTAINE, E. 1984. Sensitivity of maximal aerobic power to training is genotype-dependent. Med. Sci. Sprts Exercise, 16: 489 Bulimia nervosa and resting metabolic rate. Int. J. Eating Disord. 493. 8: 417-424. BINGHAM, S. A., GOLDBERG, G. R., COWARD, W. A., PWENTICE, RAVUSSIN, E., LILLIOJA, S., ANDERSON, T. E., CHRISTIN, L., and A. M., and CUMMINGS, S. H. 1989. The effect of exercise and BOGARDUS, C. 1986. Determinants of 24-hour energy expenditure

Two observations are worth noting in the present study. First, the positive relation between the level of dietary restraint and percent body fat (Fig. 4) suggests that individuals with restrained eating patterns have a higher level of body fat. Second, we noted a trend for restrained eaters to have a lower WMW (P = -0.29; p = 0.07). These results are consistent with those of others (Bennett et d o1989; Devlin et al. 1990) who found that normal weight subjects with bulimia nervosa were characterized by a lower RMR per kilogram of fat-free mass. Colleetively, it is interesting to consider the possibility that a restrained eating pattern may lower the resting energy requirements by its influence on WMR and contribute to the propensity to gain body fat. Furthermore, it is reasonable to speculate that the absence of a relation between RMR and level of endurance training (Vo2 max) in other studies examining young females may have been partially due to the inclusion of restrained eaters in their sample population. It cannot be determined from this study whether a restrained eating pattern was causative for the higher levels of adiposity and lower RMR, or that the higher level of body fat promoted a restrained eating pattern. The fasting hormone and substrate data in the present study do not provide further insight into metabolic disturbances that might accompany a restrained eating pattern and its influence on RMR and adiposity. Indeed, we noted no significant relation between fasting plasma hormone levels with dietary restraint or RMR. One could probably conclude that a chronic state of caloric deprivation or nutritional deficiency resulting in metabolic and endocrine dterations was probably not present in our population. It is possible that other hormonal systems may exhibit a greater sensitivity to alterations in eating behavior. A likely candidate may be the noradrenergic system, since this system has been shown to be sensitive to alterations in dietary intake and eating disorders (LeBlanc et al. 1984a; Welle et A. 1981; Kaye et al. 1990). In summary, our results support the eonclusions that the level of endurance training and degree of dietary restraint eontribute to individual variation in M R in nonobese young females.*High levels of endurance training, as reflected by a higher Va2 max, are associated with a higher RMR in nonobese females. On the other hand, dietary restraint may exert an opposing influence on resting energy requirements by decreasing RMR and thus contribute to the propensity to gain - - body fat.


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