,4ppctitf~. 199 I 16. 35-55
Dietary Restraint and Disinhibition: Is Restraint a Homogeneous Construct? JOACHIM
WESTENHOEFER
Department of Psychiatry, University of Goettingen ____._.The homogeneity of the restraint construct is Investigated in a study of 54.57 subjects participating in a weight reduction program. Using the German version of the TFEQ (Stunkard & Messick, 1985, Journal qf’Psycho.wmatic Research. 29.7 I 83; Pudel & Westenhoefer 1989a. Frayeboyen zum ~~vrrhalten: HandaweisunyL it is shown that different types of relations exist between the items measuring dietary restraint and the disinhibition scale. A discriminant analysis in a subgroup of moderately highly restrained eaters with either low or high disinhibition (n= 1759) reveals different sets of restraint behaviours and cognitions that differentiate between high and low disinhibition. These findings are replicated in an independent validation sample (n= 1693). Two restraint subscales are constructed, one associated with increasing disinhibition, the other with decreasing disinhibition. It is argued that different sets of restrained behaviours and cognitions should be differentiated when looking at the causal link between restraint and disturbances of eating behaviour. INTRODUCTION
Our understanding of human eating behaviour has been greatly advanced by the concept of restrained eating introduced by Herman and his colleagues (Herman & Mack, 1975; Herman & Polivy, 1975). Restrained eating is defined as the tendency to restrict food intake consciously in order to maintain body weight or to promote weight loss. Several investigations have shown that restrained eaters consistently show a tendency to overeat under several experimental conditions, including the preloads of food, ingestion of alcohol, and reaction to dysphoric moods (for review. see Ruderman, 1986). This phenomenon is related to the disinhibition of cognitive control of eating behaviour, and has been regarded as an experimental analogue of binge eating (Wardle & Beinart, 1981). Several studies have also shown a correlation between dietary restraint and binge eating, and there is substantial evidence for a causal link between restrained eating and binge eating (see Polivy & Herman, 1985; Wardle, 1987). The search for the mediating mechanisms has begun (Herman & Polivy, 1984; Tuschl, 1990). Restrained eating has been assessed with the restraint scale (Herman & Polivy, 1975, 1980), but it has been shown that this scale has several theoretical and psychometric problems (Stunkard & Messick, 1985; Ruderman, 1986). Particularly. dietary restraint and disinhibition are confounded within the restraint scale (Heatherton et al., 1988). Stunkard & Messick (1985) have developed a three-factor eating I am grateful to Volker Pudel and Kuni Becker for their helpful comments Address correspondence to: DipLPsych. Joachim Westenhoefer. Department of Goettingen, van-Siebold-Str. 5, D3400 Goettingen. F.R G. 0195~6663~91~010045+11
$03.00/O
on the manuscript. of Psychiatry. Univerwk
(‘ 1991 Academic
Press I-imilcd
46
J. WESTENHOEFER
questionnaire (TFEQ) to measure dietary restraint, the disinhibition of control, and perceived hunger. The restraint factor addresses the cognitive control of eating behaviour, and the disinhibition factor reflects dishinhibited eating due to situational components or emotional states. The validity of the TFEQ restraint scale is well substantiated with respect to eating behaviour (Laessle et al., 1989) and body weight (Pudel & Westenhoefer, 1989a). There is additional support for the validity of the disinhibition scale (Pudel & Westenhoefer, 1989a; Westenhoefer et al., 1990). Stunkard & Messick (1985) review several studies which show that the disinhibition factor, rather than the restraint factor, might explain the phenomenon of counter-regulation. Rossiter et al. (1989) found that bulimia nervosa patients have high restraint scores as well as high disinhibition scores. However. non-bulimic restrained eaters had still higher scores on the restraint scale, while the bulimia group had the highest scores on the disinhibition scale. These findings suggest that the disinhibition scale might be a more adequate measure of specific disturbances in eating behaviour. Nevertheless. disinhibition and restraint are not entirely independent constructs, since disinhibition by definition implies prior inhibition or restraint. Stunkard & Messick (I 985) suggest that behaviour reported on the disinhibition factor by unrestrained eaters may result from need satisfaction and not from disinhibition. Obviously, this is a problem of construct validity that remains to be solved. Despite the possible causal link between restrained eating and binge eating, there is some evidence that a subgroup of restrained eaters manages to be successful dieters without developing disturbances in eating behaviour. Lowe & Kleifield (1988) showed that there exists a subgroup of restrained eaters, designated as “successful dieters”, who maintain a body weight lower than their previous weights. In a laboratory experiment, these subjects did not show the classical phenomenon of counter-regulation. Westenhoefer & Pudel (1989) report that intermittent dieting behaviour is associated with problems and disturbances of eating behaviour, including exaggerated appetite for sweets, binge eating, and hyperphagic reactions under stress. People who diet more continuously experience such problems to a far lower degree. In several studies (Stunkard & Messick, 1985; Bjiirvell et al., 1986; Ganley, 1988; Pudel & Westenhoefer, 1989a), low to moderate correlations (r< /0.50/) were reported between the restraint factor and the disinhibition factor of the TFEQ; correlations were positive or negative in different samples. Pudel & Westenhoefer (1989a) found a substantial proportion of highly restrained subjects with very low disinhibition of control of eating behaviour, as well as others with very high disinhibition. Thus restrained eating as such does not seem to be a sufficient condition for the development of disturbances of eating behaviour, even if it is a necessary condition. One explanation might be that restraint has been defined as the intention to restrict food intake (Tuschl, 1990), and available data show that restrained eaters do actually restrict food intake. However, there might be several behavioural strategies for doing so. These strategies might vary in their effectiveness in establishing restrained eating behaviour as long-term behaviour, and in their potential for promoting disturbances of intake regulation (Westenhoefer et al., 1990). The aim of the present study is to examine this hypothesis. METHOD
The sample consisted of 54,525 participants in a computer-aided training programme for weight reduction (Pudel & Westenhoefer, 1989b) in F.R.G. supported
DIETARY
RESTRAINT
47
by the Federal Association of Local Health Insurances. This programme ran for 12 months, as a postal dialogue with the participants. The participation was voluntary and participants had to pay a small registration fee. As a part of the initial assessment, 2 months after the beginning of the programme. the German version of the threefactor eating questionnaire TFEQ (Stunkard & Messick, 1985; Pudel & Westenhoefer, 1989a) was filled out by the participants. In addition, they were asked about any major problems in eating behaviour, and whether they use vomiting as a deliberate means of weight control. All available data are self-reported. The majority of participants were overweight as might be expected in a weight reduction programme
(Table
1).
RESULTS
Table 1 also presents scores on the three TFEQ scales separately for men and women. The correlations in the whole sample were between restraint and disinhibition r= -0.37, between restraint and hunger r= -0.37, and between disinhibition and hunger r = 0.64. Restraint and disinhibition scores were distributed so that 2 1.3% of the participants had scores below the median of both scales, 31.1% had low restraint and high disinhibition scores, 32.4% high restraint and low disinhibition, and 15.2% had scores above the median on both scales. Thus, in contrast to the contention of Heatherton et al. (1988), restraint with high disinhibition was less common in the present sample than restraint and low disinhibition. As a first step of analysis, the sample was divided into 17 groups according to scores on the disinhibition scale, ranging from 0 to 16. The smallest subgroup consisted of subjects with a disinhibition score of 0 (n = 255); the largest subgroup had a disinhibition score of 8 (n= 5088). The mean scores for each question item on the restraint scale were computed for each of the subgroups and tested for linear relation to the disinhibition scores, and for deviations from linearity. Scores on the different restraint items ranged from negative to positive correlations with disinhibition. with or without deviations of linearity (Table 2). As might be expected from the overall correlation between restraint and disinhibition, most of the correlations were
TABLE 1 Age, weight and height of participants and scores on TFEQ scales
Women (n=46,132)
Age (years) Body weight (kg) Height (cm) Body mass index (kg/m’) TFEQ scale Dietary restraint Disinhibition Hunger
Men (n = 8.393)
mean
SD
mean
SD
43.6 73.5
12.7 Il.5
45.6
12.2
87.8
11.1
164.4
6.0
176.5
6.7
27.2
3.8
28.2
3.2
13.07 8.47 6.28
4.55 3.61 3.51
10.62 7.13 5.72
4% I.‘8 ;.;1
-
48
J. WESTENHOEFER
negative. However, there was variation in the shape of these relationships, with some highly significant deviations for linearity (Table 2 and Figure 1). Thus, it appears that the different restraint items are by no means homogeneous relative to the disinhibition of control. The second step of analysis was to examine whether there are distinctive types of restrained eating behaviour, one associated with high disinhibition, the other with low disinhibition of control. Only participants with a very low score (less than 5) or a very high score (more than 12) on the disinhibition scale were selected for this analysis. A discriminant analysis was computed, with low vs. high disinhibition as criterion variable, and the restraint items as discriminating variables. For participants scoring above zero on nearly every restraint item (high restraint) or scoring on almost none of these items (low restraint), discriminatory power cannot be expected. Thus, a moderately high score on the restraint scale (10-13 inclusive) was required for a participant to be included in this analysis. This restriction also made the sample homogeneous in degree of dietary restraint. Because discriminant analysis may easily find unreplicable discriminant functions, the selected 3,452 participants were randomly assigned either to an analysis sample for which the discriminant functions were computed or to a validation sample which was used to check the replicability of the discriminations.
TABLE 2
Relation of scores on restraint items to scores on the disinhibition scale TFEQ Item number
Disinhibition score = 0 group mean
4 6 10 14 18 21 23 28 30 32 33 35 37 38 40 42 43 44 46 48 50
0,78 0.68 0.93 0.81 0.79 0.95 0.45 0.74 0.79 0.55 0.78 0.75 0.12 0.54 0.61 0.89 0.55 0.79 0.71 0.70 0.81
*p
Dietary Restraint and Disinhibition: Is Restraint a Homogeneous Construct? JOACHIM
WESTENHOEFER
Department of Psychiatry, University of Goettingen ____._.The homogeneity of the restraint construct is Investigated in a study of 54.57 subjects participating in a weight reduction program. Using the German version of the TFEQ (Stunkard & Messick, 1985, Journal qf’Psycho.wmatic Research. 29.7 I 83; Pudel & Westenhoefer 1989a. Frayeboyen zum ~~vrrhalten: HandaweisunyL it is shown that different types of relations exist between the items measuring dietary restraint and the disinhibition scale. A discriminant analysis in a subgroup of moderately highly restrained eaters with either low or high disinhibition (n= 1759) reveals different sets of restraint behaviours and cognitions that differentiate between high and low disinhibition. These findings are replicated in an independent validation sample (n= 1693). Two restraint subscales are constructed, one associated with increasing disinhibition, the other with decreasing disinhibition. It is argued that different sets of restrained behaviours and cognitions should be differentiated when looking at the causal link between restraint and disturbances of eating behaviour. INTRODUCTION
Our understanding of human eating behaviour has been greatly advanced by the concept of restrained eating introduced by Herman and his colleagues (Herman & Mack, 1975; Herman & Polivy, 1975). Restrained eating is defined as the tendency to restrict food intake consciously in order to maintain body weight or to promote weight loss. Several investigations have shown that restrained eaters consistently show a tendency to overeat under several experimental conditions, including the preloads of food, ingestion of alcohol, and reaction to dysphoric moods (for review. see Ruderman, 1986). This phenomenon is related to the disinhibition of cognitive control of eating behaviour, and has been regarded as an experimental analogue of binge eating (Wardle & Beinart, 1981). Several studies have also shown a correlation between dietary restraint and binge eating, and there is substantial evidence for a causal link between restrained eating and binge eating (see Polivy & Herman, 1985; Wardle, 1987). The search for the mediating mechanisms has begun (Herman & Polivy, 1984; Tuschl, 1990). Restrained eating has been assessed with the restraint scale (Herman & Polivy, 1975, 1980), but it has been shown that this scale has several theoretical and psychometric problems (Stunkard & Messick, 1985; Ruderman, 1986). Particularly. dietary restraint and disinhibition are confounded within the restraint scale (Heatherton et al., 1988). Stunkard & Messick (1985) have developed a three-factor eating I am grateful to Volker Pudel and Kuni Becker for their helpful comments Address correspondence to: DipLPsych. Joachim Westenhoefer. Department of Goettingen, van-Siebold-Str. 5, D3400 Goettingen. F.R G. 0195~6663~91~010045+11
$03.00/O
on the manuscript. of Psychiatry. Univerwk
(‘ 1991 Academic
Press I-imilcd
46
J. WESTENHOEFER
questionnaire (TFEQ) to measure dietary restraint, the disinhibition of control, and perceived hunger. The restraint factor addresses the cognitive control of eating behaviour, and the disinhibition factor reflects dishinhibited eating due to situational components or emotional states. The validity of the TFEQ restraint scale is well substantiated with respect to eating behaviour (Laessle et al., 1989) and body weight (Pudel & Westenhoefer, 1989a). There is additional support for the validity of the disinhibition scale (Pudel & Westenhoefer, 1989a; Westenhoefer et al., 1990). Stunkard & Messick (1985) review several studies which show that the disinhibition factor, rather than the restraint factor, might explain the phenomenon of counter-regulation. Rossiter et al. (1989) found that bulimia nervosa patients have high restraint scores as well as high disinhibition scores. However. non-bulimic restrained eaters had still higher scores on the restraint scale, while the bulimia group had the highest scores on the disinhibition scale. These findings suggest that the disinhibition scale might be a more adequate measure of specific disturbances in eating behaviour. Nevertheless. disinhibition and restraint are not entirely independent constructs, since disinhibition by definition implies prior inhibition or restraint. Stunkard & Messick (I 985) suggest that behaviour reported on the disinhibition factor by unrestrained eaters may result from need satisfaction and not from disinhibition. Obviously, this is a problem of construct validity that remains to be solved. Despite the possible causal link between restrained eating and binge eating, there is some evidence that a subgroup of restrained eaters manages to be successful dieters without developing disturbances in eating behaviour. Lowe & Kleifield (1988) showed that there exists a subgroup of restrained eaters, designated as “successful dieters”, who maintain a body weight lower than their previous weights. In a laboratory experiment, these subjects did not show the classical phenomenon of counter-regulation. Westenhoefer & Pudel (1989) report that intermittent dieting behaviour is associated with problems and disturbances of eating behaviour, including exaggerated appetite for sweets, binge eating, and hyperphagic reactions under stress. People who diet more continuously experience such problems to a far lower degree. In several studies (Stunkard & Messick, 1985; Bjiirvell et al., 1986; Ganley, 1988; Pudel & Westenhoefer, 1989a), low to moderate correlations (r< /0.50/) were reported between the restraint factor and the disinhibition factor of the TFEQ; correlations were positive or negative in different samples. Pudel & Westenhoefer (1989a) found a substantial proportion of highly restrained subjects with very low disinhibition of control of eating behaviour, as well as others with very high disinhibition. Thus restrained eating as such does not seem to be a sufficient condition for the development of disturbances of eating behaviour, even if it is a necessary condition. One explanation might be that restraint has been defined as the intention to restrict food intake (Tuschl, 1990), and available data show that restrained eaters do actually restrict food intake. However, there might be several behavioural strategies for doing so. These strategies might vary in their effectiveness in establishing restrained eating behaviour as long-term behaviour, and in their potential for promoting disturbances of intake regulation (Westenhoefer et al., 1990). The aim of the present study is to examine this hypothesis. METHOD
The sample consisted of 54,525 participants in a computer-aided training programme for weight reduction (Pudel & Westenhoefer, 1989b) in F.R.G. supported
DIETARY
RESTRAINT
47
by the Federal Association of Local Health Insurances. This programme ran for 12 months, as a postal dialogue with the participants. The participation was voluntary and participants had to pay a small registration fee. As a part of the initial assessment, 2 months after the beginning of the programme. the German version of the threefactor eating questionnaire TFEQ (Stunkard & Messick, 1985; Pudel & Westenhoefer, 1989a) was filled out by the participants. In addition, they were asked about any major problems in eating behaviour, and whether they use vomiting as a deliberate means of weight control. All available data are self-reported. The majority of participants were overweight as might be expected in a weight reduction programme
(Table
1).
RESULTS
Table 1 also presents scores on the three TFEQ scales separately for men and women. The correlations in the whole sample were between restraint and disinhibition r= -0.37, between restraint and hunger r= -0.37, and between disinhibition and hunger r = 0.64. Restraint and disinhibition scores were distributed so that 2 1.3% of the participants had scores below the median of both scales, 31.1% had low restraint and high disinhibition scores, 32.4% high restraint and low disinhibition, and 15.2% had scores above the median on both scales. Thus, in contrast to the contention of Heatherton et al. (1988), restraint with high disinhibition was less common in the present sample than restraint and low disinhibition. As a first step of analysis, the sample was divided into 17 groups according to scores on the disinhibition scale, ranging from 0 to 16. The smallest subgroup consisted of subjects with a disinhibition score of 0 (n = 255); the largest subgroup had a disinhibition score of 8 (n= 5088). The mean scores for each question item on the restraint scale were computed for each of the subgroups and tested for linear relation to the disinhibition scores, and for deviations from linearity. Scores on the different restraint items ranged from negative to positive correlations with disinhibition. with or without deviations of linearity (Table 2). As might be expected from the overall correlation between restraint and disinhibition, most of the correlations were
TABLE 1 Age, weight and height of participants and scores on TFEQ scales
Women (n=46,132)
Age (years) Body weight (kg) Height (cm) Body mass index (kg/m’) TFEQ scale Dietary restraint Disinhibition Hunger
Men (n = 8.393)
mean
SD
mean
SD
43.6 73.5
12.7 Il.5
45.6
12.2
87.8
11.1
164.4
6.0
176.5
6.7
27.2
3.8
28.2
3.2
13.07 8.47 6.28
4.55 3.61 3.51
10.62 7.13 5.72
4% I.‘8 ;.;1
-
48
J. WESTENHOEFER
negative. However, there was variation in the shape of these relationships, with some highly significant deviations for linearity (Table 2 and Figure 1). Thus, it appears that the different restraint items are by no means homogeneous relative to the disinhibition of control. The second step of analysis was to examine whether there are distinctive types of restrained eating behaviour, one associated with high disinhibition, the other with low disinhibition of control. Only participants with a very low score (less than 5) or a very high score (more than 12) on the disinhibition scale were selected for this analysis. A discriminant analysis was computed, with low vs. high disinhibition as criterion variable, and the restraint items as discriminating variables. For participants scoring above zero on nearly every restraint item (high restraint) or scoring on almost none of these items (low restraint), discriminatory power cannot be expected. Thus, a moderately high score on the restraint scale (10-13 inclusive) was required for a participant to be included in this analysis. This restriction also made the sample homogeneous in degree of dietary restraint. Because discriminant analysis may easily find unreplicable discriminant functions, the selected 3,452 participants were randomly assigned either to an analysis sample for which the discriminant functions were computed or to a validation sample which was used to check the replicability of the discriminations.
TABLE 2
Relation of scores on restraint items to scores on the disinhibition scale TFEQ Item number
Disinhibition score = 0 group mean
4 6 10 14 18 21 23 28 30 32 33 35 37 38 40 42 43 44 46 48 50
0,78 0.68 0.93 0.81 0.79 0.95 0.45 0.74 0.79 0.55 0.78 0.75 0.12 0.54 0.61 0.89 0.55 0.79 0.71 0.70 0.81
*p
