International Journal of Obesity (1999) 23, 320±327 ß 1999 Stockton Press All rights reserved 0307±0565/99 $12.00 http://www.stockton-press.co.uk/ijo Is dieting good for you?: Prevalence, duration and associated weight and behaviour changes for speci®c weight loss strategies over four years in US adults

SA French1*, RW Jeffery1 and D Murray1

1Division of Epidemiology, School of Public Health, University of Minnesota, USA

OBJECTIVES: This present study describes weight control strategies used by a heterogeneous sample of US adults and their associations with weight and behaviour change over time. DESIGN: A prospective cohort study. PARTICIPANTS: Participants for this study were 1120 US adults recruited from the community who enrolled in a three- year intervention study to examine methods for preventing age-related weight gain. MEASURES: Measured body weight and self-reported behaviours related to body weight (dieting practices, dietary intake and physical activity) were completed annually for four years. RESULTS: Over 70% reported using each of the following dieting strategies at least once in four years: increase exercise (82.2%); decrease fat intake (78.7%); reduce food amount (78.2%); and reduce calories (73.2%). Cumulative duration of use of these behaviours was brief (for example, even the most common behaviours were used only 20% of the time). Global reports of dieting were not predictive of weight change over time. However, a dose±response relationship was observed between reported duration of use of several speci®c weight loss strategies over the four years and change in behaviours and weight gain. CONCLUSIONS: These ®ndings suggest that public health recommendations for weight control may need to place greater emphasis on persistence of weight control behaviours.

Keywords: dieting; weight loss; weight gain; obesity

Introduction tion-based surveys have restricted their inquiry to those who state that they are trying to lose weight at that present time, and have limited inquiry to general An estimated 44 million US adults were attempting to questions about exercising more or eating less to lose lose weight in 1990.1 Despite the fact that reports of weight.1,4 Data from the National Health Interview dieting for weight loss are common, weight gain in the Survey showed that among those trying to lose general population continues to be a major public weight, 61% reported doing so by increasing physical health issue.2 Interestingly, although reports of dieting activity and 79% by eating less.1 Data from the 1989 for weight control or loss are widespread, little is Behavioural Risk Factor Surveillance Survey showed known about the speci®c behaviours that are encom- that among those trying to lose weight, 10% used only passed by such reports and the extent to which these increased physical activity, 31% used only calorie behaviours are associated with weight change over reduction, 50% used both and 8% used neither for time.3 Such information is needed to better understand weight loss.4 Another community-based sample of US behavioural practices associated with successful adults currently trying to lose weight found that 71% weight control and for further development of public of women and 62% of men reported both changing health recommendations aimed at preventing weight their eating and exercise behaviours to lose weight.5 gain in the population. Available data comparing weight-related beha- Research on weight control practices to date have viours among current dieters and nondieters are had limited depth, both with respect to populations inconsistent. Some studies have found that dieters and behaviours assessed. Most cross-sectional popula- report lower intakes of high fat/high energy foods such as sweets, meat, french fries and soft drinks and higher frequency of high-intensity physical activity 6 *Correspondence: Dr SA French, Division of Epidemiology, compared to non-dieters. However, other studies School of Public Health, University of Minnesota, 1300 South have found weak or inconsistent associations between Second Street, Suite 300, Minneapolis, MN 55454-1015, USA. Received 3 June 1998; revised 1 October 1998; accepted 2 reports of dieting and behaviours associated with 3,7±9 November 1998 energy balance. Is dieting good for you? SA French et al 321 Data on the temporal stability of weight control recreational physical activity were associated with efforts in the general population and whether they two-fold increased risk in men and a seven-fold usually lead to weight loss have also been inconsis- increase in women of major weight gain (> 13 kg) tent.3,5,6,10,11 Williamson et al11 examined retrospec- over a ten year period.16 These ®ndings suggest that tive dieting efforts in a population-based sample of changes in speci®c eating and exercise behaviours are 21 673 adults. The median duration of dieters' most predictive of weight change over time. However, to recent weight loss attempts was four weeks among date, the speci®c eating behaviours assessed were women and six weeks among men. Reported weight limited (for example, total energy, percent fat and losses resulting from those attempts averaged 8 lb frequency of intake of speci®c foods). Importantly, (3.6 kg) in men and 10 lb (4.5 kg) in women. Reported intentional dieting efforts were not measured in the duration of weight loss attempt was not related to latter three studies. More information is needed about reported amount of weight loss. Levy & Heaton5 speci®c eating behaviour changes and their impact on found that among individuals trying to lose weight, body weight change, particularly as public health the average reported duration was 5±6 months. Over recommendations are directed toward targeting spe- the previous two years, they reported an average of ci®c behaviours (for example, increasing physical one weight loss attempt per year. These cross-sec- activity, fruit and vegetable intake and decreasing tional studies indicate that intentional dieting for meat consumption). weight loss is modestly successful over the short The purpose of this present study is to gain a better term. The only prospective study that we are aware understanding of the speci®c weight control practices of that has examined dieting and weight change also used by people in the general population and their suggests a modest, though much smaller, positive effect on body weight over time. The study obtained effect. Among a cohort of 1639 men and 1913 detailed assessment of behaviours people used to women, individuals who reported `current dieting' at control their weight, both type and duration of use, baseline but not two years later gained on average at annual intervals, in a cohort of adults followed over 4.4 lbs over that interval.6 Reports of current dieting at a 4 y period. Duration of use of weight control follow up but not at baseline were associated with an behaviours was examined in association with weight average weight loss of 71.0 lb (0.45 kg). Individuals and weight-related behaviour changes over this time who reported current dieting at both baseline and period. In addition, general reports of dieting status follow up gained an average of 0.99 lb over a two were examined in relation to these same outcomes. year period. This study did not have information on duration of dieting efforts. The extent to which dieting efforts, if sustained over time, would be associated with greater success in weight control (compared with Methods a single episode of dieting) is not clear from the studies done to date. Although dieters report making changes in eating Subject population and procedure and exercise behaviours, few studies have prospec- Subjects used in this study wee 1120 adults who tively examined changes in speci®c behaviours related volunteered to take part in a 4 y weight gain preven- to energy balance and their impact on body weight tion study, the Pound of Prevention study (POP). change. French et al12 examined changes in physical Recruitment and intervention methods and study out- activity and intake of speci®c foods as predictors of comes are described in detail elsewhere.17,18 Subjects weight change over a period of two years in a cohort were recruited by direct telephone solicitation, news- of 1639 men and 1913 women. In women, increases in paper advertisements, and a direct mailing to employ- frequency of french fry, dairy products, sweets and ees of a large educational institution. In addition, low- meat consumption were associated with weight income women (  $25 000 annual household income) increases, while increases in physical activity were were speci®cally targeted for recruitment at health associated with decreases in weight over two years. In clinics administering the Supplemental Nutrition Pro- men, increases in intake of sweets and eggs were gram for Women, Infants and Children (WIC). Elig- associated with weight increases, while increases in ibility criteria for study enrollment were: (1) age 20± physical activity were associated with weight 45 y; (2) not currently pregnant or having given birth decreases. Colditz et al13 found that neither total in the past 12 months; (3) not currently in treatment energy nor dietary fat intakes were associated with for a serious medical or psychological disorder; (4) weight change over 8 y among 31 940 nonsmoking willingness to participate in the study for three years. women. However, Klesges et al,14 found that dietary Participants were randomized to treatment or control fat was a consistent positive predictor of weight and completed four assessments (baseline and change over two years in 142 men and 152 women. annually for three years). Treatment considered of Rissanen et al,15 found that low levels of physical monthly mailed newsletters emphasizing one or more activity predicted weight gain over ®ve years among a of the following behaviours: regular self-weighing, cohort of 12 000 men and women. Data from increased physical activity, increased intake of fruits NHANES I showed that consistently low levels of and vegetables, and decreased intake of high fat foods. Is dieting good for you? SA French et al 322 Reduction in energy intake was not speci®cally summed across 4 y. Prevalence for the three dieting recommended. measures is reported as the proportion of the total sample that reported dieting zero, one, two, three or four years. Measures Each of the following measures was completed annually. Dietary intake. Dietary intake during the past year was assessed using the 60-item Block Food Frequency (BFF) recall.19 Dietary variables used in the present Body weight. Weight was measured in light clothing report include total energy intake, percent energy without shoes on a calibrated balance-beam scale. from fat, percent energy from sweets, number of Height was measured at baseline with a wall-mounted servings of vegetables eaten per day, number of ruler. Body mass index was computed (BMI: weight servings of fruits eaten per day. (kg)/height (m)2). Physical activity. Physical activity was measured Speci®c weight control behaviours. Speci®c beha- using a self-administered version of the Physical viours related to weight control were assessed using a Activity History (PAH).20 The PAH has been used 23-item checklist developed by the researchers. At to assess physical activity in several large epidemio- each assessment point, participants were asked to logical studies. Respondents indicate the average report whether they had engaged in each of 23 frequency per week of engaging in each of 13 differ- behaviours related to weight control during the past ent groups of physical activities for 20 or more year. For each behaviour reported in the past year, minutes at a time during the past year. Activities participants were asked the total duration in weeks. To include high intensity and low intensity leisure time express the extent to which each of these speci®c activities, home maintenance/household activities, weight control behaviours were practised over the and vigorous job activities. The frequency of each course of the study, the duration measures were activity was multiplied by an estimated intensity score summed over four years. Prevalence for the speci®c for that activity in metabolic units and those products weight control behaviours is reported as the propor- were summed across 13 activities to yield a total tion of the total sample that reported doing the speci®c physical activity score. behaviour at least once during the 4 y period. Cumu- lative duration of each practice was calculated by summing the number of weeks each behaviour was Demographic variables. Demographic information engaged in across the 4 y study period. Those who did was self-reported and included: (1) age in years; (2) not report doing the speci®c behaviour were assigned current marital status (currently married vs other); (3) a zero value for the duration variable. Several ques- education (less than college; college or greater); (4) tions were asked about purging behaviours and diet ethnicity/race (white vs other); and (5) income pill use. To simplify data analysis, a summary purging (> $25 000/y;  $25 000/y). measure was created by summing the prevalence of reported vomiting, laxative, diuretic, appetite suppres- Smoking status. Smoking status was self-reported sant and diet pill use. Two questions were asked about (current vs nonsmokers). participation in formal weight loss programs (with and without food provided), these were also summed. Statistical analysis Therefore, 17 speci®c weight control strategies were All analyses were conducted using the SAS 6.12 examined. software package.21 Analyses included men and women who completed the annual questionnaire at General dieting status. General dieting status was baseline and year four (n ˆ 1120). Women who assessed using three different questions. Firstly, cur- became pregnant during the study were excluded rent dieting was assessed with the question `Please from analyses (n ˆ 106). check the ONE answer that describes you now: I am Several approaches were used to examine associa- not currently dieting; I am currently dieting to lose tions between duration of use of weight control weight; I am currently dieting to keep my weight practices and changes in weight and behaviour. where it is right now.' Current dieters were de®ned as Firstly, linear regressions were run in which changes those who checked either dieting for weight loss or in behaviour or weight was the dependent variable, maintenance. Secondly, regular dieting was assessed baseline value of the dependent variable was a cov- with the question `Have you been dieting regularly ariate, and the cumulative duration of each weight doing the past year?' (yes or no). Thirdly, trying to control strategy was the independent variable. Models lose weight (no time frame speci®ed) was assessed which included other covariates (treatment group with the question `Do you do anything to try to lose assignment, body mass index, education, smoking, weight?' (yes or no). To assess the overall prevalence marital status, income and ethnicity) were also exam- of dieting over 4 y, each of these measures were ined, but are not presented because they did not Is dieting good for you? SA French et al 323 materially alter the pattern of ®ndings. Examination of family incomes of $40 000 or more, and only about the residuals showed the distributions to be normal, 18% were current smokers. Body mass index was therefore the linear models were deemed appropriate. slightly higher than population averages, with the Each strategy duration variable was examined in mean body mass index just at the cutpoint for standard separate equations because the duration variables de®nitions of overweight.2 were highly intercorrelated (median r ˆ 0.51; Table 2 shows the overall prevalence of reporting range ˆ 0.33±0.72). Because of the multiple testing each speci®c weight control behaviour at any time in involved, a Bonferoni-adjusted P-value of P < 0.001 4 y. Cumulative duration of each practice over 4 y was used to assess statistical signi®cance, providing a (mean and median) for the prevalent cases is also report-wide Type I error rate of 5%. shown. The most common weight control behaviours Categorical analyses were also run to examine their reported in this sample were increasing exercise consistency with the linear models. Categories of levels, reducing calorie intake, reducing fat intake, duration were created that were speci®c to each reducing the amount of food eaten, and eliminating behaviour. The duration was ordered from least to sweets. Over 70% of the sample reported doing each most frequent (for example, where 0 re¯ected those of these behaviours at least once over the 4 y period. who did not do the behaviour at all during four years, The prevalence of the summary measure of the pur- and 4 re¯ected those who did the behaviour the most ging behaviours was 15.8%. The least reported pur- frequently). Categorical analyses were consistent with ging behaviours were vomiting, laxative or diuretic linear models and are reported only selectively for use, with less than 3% of the sample ever reporting illustrative purposes. each of these over the 4 y period (data not shown). Nine dependent variables were examined: change The most reported purging behaviour was appetite (year 4±year 1) in: (1) body weight; (2) total energy; suppressant use (11%). In general, more healthful (3) percent fat energy; (4) percent carbohydrate weight control behaviours were reportedly engaged energy; (5) percent alcohol energy; (6) percent in for longer durations than less healthful behaviours. energy from sweets; (7) physical activity score; (8) For example, the median duration reported for vegetable servings; and (9) fruit servings. All 17 decreasing fat intake was 40 weeks, out of a possible weight control behaviours (independent variables) 208 weeks (that is, 10 months over a 4 y period). The were examined in relation to weight change and median duration for increasing physical activity y was total energy change. Additional pairs of dependent 27.5 weeks, or seven moths over a 4 y period. By and independent variables were examined based on contrast, the median duration reported for the their expected association. For example, the strategy unhealthy weight control behaviours was zero weeks `increase fruit and vegetable intake' was examined in for fasting, two weeks for any purging, and one week relation to change in percent energy from fat, vege- for skipping meals. Over the 4 y period, 18.2% of the table intake and fruit intake, but not in relation to sample reported ever participating in a formal weight change in physical activity score. loss program for a median duration of 14 weeks. Table 3 shows univariate associations between cumulative duration (in weeks) of speci®c weight control behaviours over the 4 y period, and changes Results in weight and weight-related behaviours during the same time interval. Blank entries re¯ect associations that were not examined (for example, duration of Table 1 shows demographic characteristics of the reported increase in fruit and vegetable intake and study sample. Participants were on average 35 y old, change in physical activity score). Overall, duration of 80% were female, about half had completed college, use of the speci®c behaviours was inversely associated half were currently married, about half had annual with weight change. Associations were statistically signi®cant for 5 of the 17 strategies. Participants who Table 1 Demographic characteristics of study participants reported engaging in speci®c weight control beha- (n ˆ 1120) viours for longer durations gained less weight than Age (y) 35.0 (6.4) those who reported engaging in the behaviours for a Sex (% female) 79.6 shorter duration or not at all. For example, the linear Weight (lbs) 168.2 (38.8) Body mass index (kgm2) 27.2 (5.8) regression analysis showed that each week of reported Education (%) calorie reduction was associated with 0.059 lb less  High school 12.6 weight gain over the 4 y study period. The categorical Vocational/some college 37.0  College degree 50.4 analysis indicated that those who reported not enga- Race/ethnicity (% caucasian) 87.6 ging in calorie reduction at all gained 5.04 lb on Income (annual family; %) average over the 4 y period whereas those who  $25 000 35.4 $25 001±$40 000 24.5 reported engaging in calorie reduction for 49 or > $40 000 40.0 more weeks (49±208 weeks) gained 0.59 lb on aver- Currently married (%) 48.4 age (data not shown). Strategies whose cumulative Current smoker (%) 18.4 duration of use was signi®cantly associated with less Is dieting good for you? SA French et al 324 Table 2 Percent of adults (N ˆ 1120) reporting speci®c weight control behaviours and cumulative duration of those behaviours over four years

Durationb (weeks)

Prevalence (%) Mean (s.d.) Median

Increase exercise 82.2 38.8 (38.1) 27.5 Decrease fat intake 78.7 50.0 (46.8) 40 Reduce food amount 78.2 34.9 (35.8) 24 Eliminate sweets 73.3 29.7 (32.1) 18 Reduce calories 73.2 32.2 (34.2) 20 Change food type 66.8 34.3 (36.6) 23 Increase fruit and vegetable intake 66.5 33.9 (38.0) 21 Eliminate snacking 66.1 28.9 (32.2) 18 Eat low calorie diet foods 47.6 40.7 (43.9) 25 Eat less meat 46.7 32.2 (39.2) 16 Skip meals 35.6 13.7 (25.3) 1 Eat less carbohydrates 24.2 20.1 (24.2) 12 Decrease alcohol intake 23.9 20.4 (27.9) 8 Weight loss groups (with or without 18.2 21.1 (21.0) 14 food provided) Purginga 15.8 11.9 (26.7) 2 Fast 13.7 4.1 (10.5) 0 Liquid diet supplements 11.1 13.5 (22.2) 5

Note: s.d. ˆ standard deviation. a Purging includes laxatives, diuretics, appetite suppressants, diet pills, vomiting. b Among those who reported engaging in the behaviour at one or more assessments. Duration ranges from 0±208 weeks.

Table 3 Regression coef®cients (standard errors) of seven dependent variables (change) in relation to cumulative duration (in weeks) of weight control practices over four years

Change in

Percent Weight Total energy Percent fat Physical Vegetable Fruit energy Strategy (lbs) (kcal) energy activity intake intake sweets

Increase exercise 70.035 (0.012) 71.747 (0.594) 0.126 (0.021)** Decrease fat intake 70.031 (0.010)* 70.940 (0.482) 70.024 (0.005)** Reduce food 70.045 (0.013)* 71.421 (0.640) amount Eliminate sweets 70.059 (0.015)** 71.414 (0.741) 70.033 (0.007)** 70.012 (0.009) Reduce calories 70.059 (0.014)** 71.566 (0.684) Change food type 70.039 (0.013) 71.054 (0.644) 70.024 (0.006)** 0.002 (0.001) 0.0002 (0.001) Increase fruit and 70.050 (0.012)** 70.964 (0.614) 70.023 (0.006)** 0.003 (0.001)** 0.002 (0.001) vegetable intake Eliminate snacks 70.050 (0.016) 70.257 (0.753) 70.016 (0.007) 70.012 (0.009) Eat low-calorie diet 70.005 (0.012) 70.314 (0.605) 70.018 (0.006) 70.009 (0.007) foods Eat less meat 70.041 (0.013) 71.699 (0.645) 70.027 (0.006)** Skip meals 70.046 (0.022) 0.199 (1.093) 70.006 (0.011) Eat less 70.066 (0.030) 72.639 (1.427) 70.033 (0.014) carbohydrates Drink less alcohol 70.030 (0.024) 72.620 (1.164) Weight loss groups 70.0002 (0.037) 71.158 (1.852) 70.039 (0.018) 70.140 (0.065) Purging 70.015 (0.035) 71.635 (1.637) Fast 70.213 (0.082) 75.675 (4.104) 70.030 (0.040) Liquid diet 70.074 (0.052) 2.348 (2.426) supplements

Note: Adjusted for baseline values of the change (dependent) variable (Year 4±Year 1). Empty cells re¯ect associations that were not examined. Purging methods include laxatives, diuretics, appetite suppressants, diet pills, vomiting. Weight loss groups includes with or without food provided. * P < 0.001; ** P < 0.0001.

weight gain over the four year study period included alcohol, liquid diet supplements, eating low calorie the following: calorie reduction (B ˆ 70.059), diet foods, and weight loss groups were not signi®- increased fruit and vegetable intake (B ˆ 70.050), cantly associated with weight change over 4 y. fat reduction (B ˆ 70.031), elimination of sweets In addition to their associations with weight change, (B ˆ 70.059), and reducing food amount eaten durations of weight control strategy use were asso- (B ˆ 70.045). Durations of increased physical activ- ciated with changes in the behaviours associated with ity, elimination of snacks, fasting, skipping meals, use of the strategy. For example, cumulative duration eating less meat, purging behaviours, drinking less of increasing physical activity was associated with Is dieting good for you? SA French et al 325 increases in physical activity score, as measured by spent practicing the behaviour. Durations were longest the PAH. One week of increasing physical activity for the healthful strategies listed above, ranging from was associated with a 0.126 unit increase in physical a median of 18 weeks for eliminating snacking to 40 activity score. Those who reported the longest dura- weeks for decreasing fat intake. Unhealthy weight tion for increasing physical activity reported an control strategies were both less prevalent and sus- increase in physical activity score of 3.39 units over tained for a shorter duration. 3 y, while those who did not report using this strategy Previous studies of weight control efforts in the reported a decrease in physical activity score of general population have used global measures of 75.48 units (data not shown). Similarly, duration of dieting and have found inconsistent associations increasing fruit and vegetable intake was associated between reports of dieting and weight control. The with greater increase in fruit and vegetable intake on present ®ndings suggest that a more informative way the food frequency measure. to examine weight control efforts in the general Several weight control strategies were associated population is to ask people to describe the speci®c with decreases in percent energy from fat (decreasing behaviours they engage in rather than to label them- fat intake, eliminating sweets, changing food type, selves globally as dieting or not. While a small increasing fruit and vegetable intake, and eating less percent of the sample described themselves as `diet- meat). None of these strategies were signi®cantly ing' (about 17±28%), many more engaged in beha- associated with decreases in total energy intake. viours intentionally for the purpose of weight control Reports of decreasing carbohydrate intake were not (about 82%). Global reports of dieting for weight loss associated with changes in carbohydrate intake as were not associated with changes in body weight or estimated by the food frequency questionnaire, nor behaviours related to energy balance. By contrast, were reports of decreasing alcohol intake associated reported duration of engaging in speci®c behaviours with changes in alcohol intake estimated by the food related to energy balance and weight control were frequency questionnaire (data not shown). consistently associated with weight change. These Although most individuals reported that they gen- ®ndings are important as they raise questions about erally do something to try to lose weight, only a small the interpretation of population-based surveys on minority reported regularly dieting or that they were dieting prevalence. On the one hand, the fact that 44 currently dieting for weight loss on any given day million people in the US are trying to lose weight across a 4 y period. The cumulative prevalence of might be interpreted as a positive response to the high `currently dieting' was 47.4%, 24.3%, 13.9%, 9.2% prevalence of overweight.1 On the other hand, the fact and 5.2%, for zero, 1, 2, 3 and 4 y, respectively. The that reports of intentional weight loss efforts are not cumulative prevalence of `regular dieting in the past associated with changes in behaviours related to year' was 63.8%, 18.8%, 9.6%, 4.9%, and 2.8%, for 0, weight control suggests that these reports re¯ect a 1, 2, 3 and 4 y, respectively. The cumulative preva- desire or intention to lose weight rather than actual lence of `doing something to try to lose weight' (no changes in behaviour that would impact body weight.3 time frame speci®ed) was 9.5%, 8.1%, 12.0%, 19.6%, Furthermore, data from this present study suggest that and 50.7%, for 0, 1, 2, 3 and 4 y, respectively. These many people who do not label themselves as `dieting' cumulative global dieting measures were not signi®- nevertheless engage in behaviours to control body cantly associated with weight or behaviour changes weight. Population-based surveys that focus only on (data not shown). individuals who state that they are currently trying to lose weight may omit a substantial portion of the population that is actively engaging in weight man- Discussion agement behaviour. If a thorough understanding of behaviours associated with successful weight control in the population is to be gained, a more inclusive This study is the ®rst to report information about the approach to identifying the target population must be duration of use of speci®c weight control behaviours utilized. A ®rst step would be to broaden inquiry to in a nonclinical sample and their associations with speci®c weight-related behaviours among the general weight and behaviour changes over time. The majority population, rather than inquiring about vaguely of the sample reported engaging in each of the de®ned dieting efforts and narrowly de®ning the following weight control behaviours at least once target population to those who report dieting or during the 4 y study period: calorie reduction, trying to lose weight. In addition, asking for reports increased exercise, increased fruit and vegetable about speci®c weight control practices rather than intake, elimination of sweets, elimination of snacks, global reports of dieting may reduce measurement decreased fat intake, decrease food amount, and error because the information requested is more spe- changing food type. Most of these behaviours would ci®c, and because social desirability in¯uences may be considered healthful and reasonable to continue for exert less strong an in¯uence on reports of speci®c long periods of time. However, even the longest behaviour vs global dieting reports. cumulative durations reported were only about 8.7± The ®ndings from the present study also suggest 19.2% of the total possible time that could have been that most adults choose weight control strategies that Is dieting good for you? SA French et al 326 are reasonable (namely, healthy), potentially sustain- might be expected given that change in energy able, and when sustained, are effective in controlling intake during short-term weight loss efforts of less weight gain over time. A major issue is to identify than one week duration would not be captured by a strategies to promote lengthier durations for sustain- measure of habitual energy intake that re¯ects intake ing these behaviours so that they can exert desired across the entire year. weight control effects. This present study found that Strengths of this present study included information the median duration for some of the most healthful about a wide variety of weight control behaviours and and prevalent weight control practices was actually the duration of use over a lengthy time period among a quite short. For example, decreasing fat intake was heterogeneous nonclinical sample of adults. This sustained for only 40 weeks (10 months) over the study is also the ®rst to prospectively relate informa- course of 4 y; physical activity increases were sus- tion on duration of weight control behaviours to tained only 7 months over 4 y. These ®ndings are weight change and behaviour change outcomes. Cor- comparable with other community-based surveys relations between reports of weight control beha- among adults trying to lose weight.5,11 Current viours, reported behaviour changes and weight weight loss efforts were sustained about 5±6 months changes provide indirect evidence of the validity of in one study.5 In another study, the most recent weight these weight control strategy reports. Limitations of loss attempt was sustained only six weeks among men the present study include lack of information on (1) and four weeks among women.11 The ®ndings from whether the duration was continuous or intermittent; the present study are dif®cult to compare with the (2) the magnitude of the changes (for example, how latter studies, however, because in the present study, much of an increase in physical activity, or how much durations were summed across years and were not of a decrease in fat intake was made); and (3) whether speci®cally linked to a particular weight loss episode. speci®c practices were done alone or on combination However, the ®ndings are consistent in showing that with others. Detailed qualitative information on the weight loss efforts or duration of engaging in speci®c behaviour changes was also lacking (for example, weight-control behaviours, are typically of short dura- what types of food changes were made when people tion. reported changing food type?). In addition, the out- Are weight loss efforts successful in the general come behaviour changes assessed were cumulative population? In the present study, the answer appears measures that re¯ected behaviour for the entire year to be a quali®ed af®rmative; that is, efforts are (for example, the food frequency measure assessed successful if sustained long enough. For example, past year's intake). Therefore, it was not possible to from the linear regression analysis, we saw that temporally link reported episodes of calorie or fat engaging in calorie reduction for 48 weeks over a reduction to speci®c dietary changes. Finally, 4 y period (or 3 months per year) was associated with although the sample in this present study was a cumulative weight loss of 72.8 lbs. Single or recruited from the community and included a sizeable combined strategies sustained over longer time peri- number of lower-income women, it is possible that ods could result in larger weight control effects. weight control practices differed from a random or However, durations of strategy use were highly inter- representative community-based sample. People who correlated in the present study and inferences about enrolled in a weight gain prevention study may be additive effects, or comparisons between strategies more likely than others to engage in weight control must be made with caution. Although the weight practices, or may differ in the type, number or dura- changes are small by clinical standards, they are tion of weight control practices adopted. However, meaningful from a population perspective. The only even if the prevalence or duration of certain weight other population-based data on success of weight loss control practices differed in the present sample, the attempts showed that men and women reported losing effects of a given weight control practice on weight about 8±10 lb during their most recent weight loss changes over time presumably would be similar, given attempt.11 Duration of dieting was not associated with a similar duration of use. amount of weight loss, again, perhaps due to the global nature of the dieting reports. Overall, the ®ndings from the present study provide support for speci®c behavioural recommendations for weight con- Conclusions trol at the population level. Interestingly, behaviours commonly thought to involve more drastic changes in energy intake, These ®ndings from the present study are consistent which would theoretically produce larger weight with the idea that many speci®c weight control stra- changes, were not associated with weight change or tegies are effective and produce weight control effects change in total energy intake (for example, purging, in a dose-response fashion with duration. Inquiry liquid diet supplements, low-calorie diet foods, and about speci®c weight-related behaviours appears to participation in formal weight loss programs). Fasting be more informative than global reports of dieting. A and skipping meals were associated with weight major barrier to weight control may be that behaviours changes but not energy changes. These ®ndings are not sustained for lengthy enough durations to have Is dieting good for you? SA French et al 327 maximal weight control impact. Further research is 9 Tuschl RJ, Laessle RG, Platte P, Pirke KM. Differences in needed to (1) de®ne the magnitude, frequency and food choice frequencies between restrained and unrestrained eaters. Appetite 1990; 14: 9±13. duration of behaviour changes needed to control 10 Heatherton TF, Polivy J, Herman CP. Restraint, weight loss weight; (2) temporally link reports of speci®c beha- and variability of body weight. J Abnorm Psychol 1991; 100: viour changes to measured behaviour and body weight 78±83. changes; and (3) identify methods that will enhance 11 Williamson DF, Serdula MK, Anda RF, Levy A, Byers the duration that speci®c weight control practices are T. Weight loss attempts in adults: Goals, duration, and rate of weight loss. Am J Public Health 1992; 82: 1251± sustained. 1257. 12 French SA, Jeffery RW, Forster JL, McGovern PG, Kelder Acknowledgements SH, Baxter JE. Predictors of weight change over two years This research was supported by grant DK45361 from among a population of working adults: the Healthy Worker the National Institute of Diabetes and Digestive and Project. Int J Obes 1994; 18: 145±154. Kidney Diseases with additional funding from the 13 Colditz GA, Willett WC, Stampfer MJ, London SJ, Segal MR, Speizer FE. Patterns of weight change and their relation to diet Centers for Disease Control and Prevention. in a cohort of healthy women. Am J Clin Nutr 1990; 51: 1100± 1105. References 14 Klesges RC, Klesges LM, Haddock CK, Eck LH. A long- 1 Horm J, Anderson K. Who in America is trying to lose itudinal analysis of the impact of dietary intake and physical weight? Ann Intern Med 1993; 119: 672±676. activity on weight change in adults. Am J Clin Nutr 1992; 55: 2 Kuczmarski RJ, Flegal KM, Campbell SM, Johnson CL. 818±822. Increasing prevalence of overweight among US adults: the 15 Rissanen AM, Heliovaara M, Kneckt P, Reunanen A, Aromaa National Health and Nutrition Examination Surveys, 1960 to A. Determinants of weight gain and over-weight in adult 1991. JAMA 1994; 272: 205±211. Finns. Eur J Clin Nutr 1991; 45: 419±430. 3 French SA, Jeffery RW. Consequences of dieting to lose 16 Williamson DF, Madans J, Anda RF, Kleinman JC, Kahn weight: Effects on physical and mental health. Health Psychol HS, Byers T. Recreational physical activity and ten-year 1994; 13: 195±212. weight change in a US national cohort. Int J Obes 1993; 17: 4 DiPietro L, Williamson DF, Caspersen CJ, Eaker E. The 279±286. descriptive epidemiology of selected physical activities and 17 Jeffery RW, French SA. Preventing weight gain in adults: body weight among adults trying to lose weight: the Beha- Design, methods and one year results from the Pound of vioral Risk Factor Surveillance System survey, 1989. Int J Prevention study. Int J Obes 1997; 21: 457±464. Obes 1993; 17: 69±76. 18 Jeffery RW, French SA. Prevention of weight gain in 5 Levy AS, Heaton AW. Weight control practices of US adults adults: The Pound of Prevention study. Am J Public Health trying to lose weight. Ann Intern Med 1993; 119: 661±666. (in press). 6 French SA, Jeffery RW, Forster JL. Dieting status and its 19 Block G, Hartman AM, Dresser CM, Carroll MD, Gannon J, relationship to weight, dietary intake, and physical activity Gardner L. A data-based approach to diet questionnaire design changes over two years in a working population. Obesity Res and testing. Am J Epidemiol 1986; 124: 453±469. 1994; 2: 135±144. 20 Jacobs DR, Hahn LP, Haskell WI, Pirie P, Signey S. Validity 7 French SA, Jeffery RW, Wing RR. Food intake and physical and reliability of short physical activity history: CARDIA and activity: A comparison of three measures of dieting. Addict the Minnesota Heart Health Program. J Cardiopulmonary Behav 1994; 19: 401±409. Rehabil 1989; 9: 448±459. 8 Tuschl RJ, Platte P, Laessle RG, Stichler W, Pirke KM. 21 SAS Institute, Inc. SAS/STAT Software: Changes and Energy expenditure and everyday eating behavior in healthy Enhancements through Release 6.12. Cary NC: SAS Institute; young women. Am J Clin Nutr 1990; 52: 81±86. 1997.