OBJECTIVE: To assess the factors that could predict a successful completion of a weight loss program.
STUDY DESIGN: A single-centered, cross-sectional, prospective study conducted over 4 y.
SUBJECTS: Data were obtained on 1018 overweight subjects (788 women, 230 men) aged 14.8–76.3 y (mean 38.4) and body mass index (BMI) of 31.7 (range 25.03–57.1) seeking help to lose weight at a specialist obesity clinic.
MATERIALS AND METHODS: A program involving a hypocaloric, Mediterranean diet was prescribed plus recommendations for free-time exercise and day-to-day activity. Follow-up was weekly until the desired weight loss was achieved (‘successful completion’) or the patient dropped-out of the program (‘failure’). Cox's regression analysis was used to evaluate success and the variables included were compliance with the program, age, gender, initial BMI, physical activity, alcohol consumption, smoking habit, hypertension, diabetes, hypercholesterolemia, cardiovascular disease, previous dietary programs, cause of obesity, age at which excessive weight was first noted and parental obesity.
RESULTS: Factors predictive of completion were: gender (males responded better), previous dietary programs (predictive of dropout), initial BMI (higher index, lower completion), and age (younger age, poorer outcome). There was an interaction between parental obesity and offspring childhood obesity. Absence of parental obesity and adult-onset obesity had a higher probability of program completion.
CONCLUSIONS: In a standard weight reduction program the recommendations of dietary restriction and moderate exercise seems less effective for women, persons with high BMI, younger age groups and those who have had other attempts at weight loss. Poorest outcomes applied to those subjects with childhood obesity and who had obese parents.
Obesity has become an important public health problem involving many associated conditions, such as diabetes mellitus type II, hypertension and dyslipemia. After tobacco, obesity has become the second highest cause of preventable deaths that, in the USA, approach 280 000 per year among adults.1 More than 30% of the population of the United States can be considered obese; defined as a body mass index (BMI in kg/m2) ≥30 kg/m2. During the decade of the 1980s and the start of the 1990s the rate of obesity in the population increased at the annual rate of between 0.5 and 1 percentage points and with an accumulated increase of >50% over the last 10–15y.2 In Europe, 10–20% of the adult population is obese, and increments similar to those of the USA have been observed in England, Holland, Italy, Sweden, Germany and Spain.3,4,5 Several different explanations for this increase have been proposed such as a more sedentary lifestyle and an increased intake of calorie-rich foods.6
In the treatment of obesity there is a high rate of failure. From the earliest trials by Stunkard7 in the mid-1950s, the consensus has been that the majority of obese persons do not stay on dietary treatment programs and of those that remain, the majority do not lose weight, and of those that lose weight, the majority regain it. Owing to the chronic nature of obesity it is vital that there be continuous follow-up and tight control of the progress not only during the treatment stage but also during the subsequent weight maintenance stage. Unfortunately, patients tend to dropout from health-care weight-loss programs relatively quickly; usually on or around the sixth month of treatment.8
There have been extensive reviews of the effectiveness of different interventions designed to prevent and/or to treat obesity, as well as to maintain weight loss. Despite several serious problems of methodological differences making comparisons difficult, the main conclusions remain the same as that propounded by Stunkard in that the majority of patients relapse and regain the weight during the intervention, or soon after. Of considerable value would be a homogenization of the criteria used in studies of weight loss, including the use of an appropriate sample size, better randomization and a more extensive follow-up with appropriate supervision. Perhaps of more importance would be the identification of those factors such as ethnicity, sociocultural differences as well as genetic, psychological and environmental predisposition to weight fluctuations, which could provide an insight into the factors predictive of completing a weight loss program.9,10
These factors are attracting attention11 but, to-date, there are only a few such studies and the results are, frequently, contradictory. Some studies have focussed on the characteristics of patients who have achieved long-term solutions to their weight problems and, from the data, the investigators have attempted to establish methods for treatment together with profiling of individuals who would be ideally suited for weight reduction treatments.12
The proposal of the present study was to identify baseline characteristics of individuals who would most benefit from a conventional weight-loss program of decreased caloric intake combined with recommendations for physical exercise. This would help increase the possibilities of completing of the program. Similarly, those individuals may be identified for whom the strategy may have a much lower possibility for completion and/or who are likely to abandon the program prematurely. These individuals would then be offered other therapeutic strategies (drugs, physcotherapy, etc) that may offer a better probability of a successful program completion.
Materials and methods
All procedures were in accordance with good clinical practice and within the guidelines of the Helsinki Declaration for studies conducted using human subjects. The study principles were accepted by the Research Unit of the Las Palmas University Hospital of the Canary Islands. Patients' data were codified to guaranty anonymity.
Between September 1996 and May 2001, 1018 subjects agreed to a weight loss program. Included in this study were those randomly selected from among those attending our outpatient clinic specializing in obesity. The patients had a BMI >25 kg/m2 and were attending the clinic for the first time, were treatment naïve, or ex-patients who had long-abandoned their attendance at the clinic. The age range was between 14 and 76 y (mean=38.43; standard deviation s.d.=5.24) and the BMI between 25.03 and 57.16 kg/m2 (mean=31.79; s.d.=5.24).
Structure of the program
The patients agreed to a voluntary program of weight loss using dietary modifications and recommendations for physical exercise. In the first outpatient clinic visit lasting 30–45 min, a complete clinical history was obtained and a thorough physical examination was performed. Blood chemistry data, if available, were solicited and the nature of the program was explained. Initially, follow-up was weekly, in which evaluations were performed and solutions were proposed for difficulties that the patient may have been experiencing in complying with treatment. The treatment phase was deemed to have ended when the patient abandoned the treatment or, alternatively, the weight loss goal was achieved. The target was decided-upon in discussion with the patient before starting the treatment and was for a minimum weight-loss of 5–10% relative to baseline. When this was achieved the patient moved into the weight-maintenance stage, which was directed towards normalization of caloric intake and physical exercise over a period of 5 weeks. This stage was when the patient proceeded from ‘being on diet’ to ‘not being on diet’. The patient then proceeded to the follow-up stage of the treatment, which consisted of regular visits to the outpatient clinic every 15 days. Subsequently, the time-lapse between visits progressively lengthened to 2 or 3 months, depending on the patient's needs and/or choice. The objective was to instil, and maintain, good lifestyle habits. The initial blood chemistries were to diagnose possible diabetes and/or hyperlipidemia. Subsequent blood chemistries were routine follow-up to ensure that the patients’ biochemical profile was not adversely affected by the dietary program.
Characteristics of the diet
The body requirements and individual taste preferences were taken into account in designing hypocaloric diets. The energy requirements were calculated from the Harris–Benedict formula and, according to the type of physical activity, were decreased by about 2.6 MJ/day so as to induce an approximate loss of between 0.5 and 1 kg/week.
The intake in general was between 3.8 and 5.8 MJ for male and between 2.9 and 4.1 MJ for female subjects. This was higher in the more obese. The diet was the Mediterranean type in which the distributions of the principal components were as recommended by the Spanish Society of Community Nutrition,13 and comprised 35% fat (<10% saturated and 20% monounsaturated), 50% carbohydrates and 15% proteins.
General, spare-time, aerobic exercise was recommended such as walking, jogging, cycling, aerobics or swimming for a minimum of half an hour, three times a week. These recommendations were adjusted for the patient's capabilities. Other recommendations were to increase the physical activity in everyday patterns such as to walk instead of taking mechanized transport and to climb stairs rather than to use the elevator.
Determination of the effectiveness of the treatment
The duration of treatment varied depending on the individual characteristics of each patient. ‘Completion’ or ‘compliance’ with the program was defined as (1) a patient achieving the weight loss goal previously agreed; (2) the risk factors associated with obesity such as hypertension, dyslipidemia, hyperglycemia were brought under control and (3) the patient was able to proceed from the weight-maintenance stage on to the follow-up stage of the program. Individuals who did not fulfil the treatment phase or the maintenance stage requirements but who had achieved a substantial weigh loss were, for statistical purposes, not considered in the ‘completion’ group. The causes of abandoning the program were diverse and included being tired of dieting, pregnancy, lack of time to attend the clinic, having moved away from the area and economic pressures. In some cases, no motive or explanation was offered.
Variables collected in the study
The following variables were collected:
BMI calculated as weight height2 (in kg/m2). Weight was measured on a Roman balance, SECA model 712 with a capacity of 200 kg in 100 g increments. The patients were lightly clothed and without shoes. Height was measured at the same outpatient visit using a metered scale SECA 221 with a range of 6–230 cm in divisions of 1 mm. For statistical purposes the patients were segregated into the following groups based on the ‘Guidelines of the American Clinics for the Identification, Evaluation and treatment of Obesity and Overweight in Adults’ of the US Expert Committee on Obesity.6 These were: 1—overweight: BMI between 25 and 29.9 kg/m2; 2—obesity grade I: BMI between 30 and 34.9 kg/m2; 3—obesity grade II: BMI between 35 and 39.9 kg/m2; and 4—obesity grade III: BMI ≥40 kg/m2.
Age as a continuous variable and, as well, segregated into three groups: Group 1 <35 y, Group 2 between 35 and 50 y, Group 3 >50 y.
Physical activity in spare time and defined as adherence to moderate physical aerobic exercise regularly for at least half an hour/day at least three times a week as recommended by the US Expert Panel in their ‘Guide for the Identification, Evaluation and Treatment of the Overweight Adult’.6
Smoking habit classified as a function of the following standard criteria derived from the recodification of the WHO guidelines which define as: 1—never smoked, that is, those persons who have never smoked or who had not smoked for >6 months or more in the past; 2—ex-smoker, that is, those persons who do are nonsmokers at the time of attending the obesity clinic but who had done so for a period of 6 months or more in the past; 3—smoker of 1–4 cigarettes/day or occasionally at the time of the study; 4—smoker 4–20 cigarettes/day or occasionally at the time of the study; 5—smoker >20 cigarettes/day at the time of the study. For the purpose of the present study, this variable was simplified as: 1—smoker (comprising groups 3, 4, and 5, above) and 2—nonsmoker (comprising groups 1 and 2, above).
Alcohol: an amount >40 g/day is defined as excessive by the Spanish Society for Community Nutrition14 (Sociedad Española de Nutrición Comunitaria; SENC) and which would correspond to greater than two to three alcoholic beverages such as bottles of beer of 330 ml, glasses of wine of 80 ml, or the standard of spirits (anis, cognac, whisky, etc).14,15
Hypertension: for comparability with other studies, this variable of HT was defined according to the criteria of the WHO16 in which systolic blood pressure (BPS) ≥160 mmHg and diastolic blood pressure (BPD) of ≥95 mmHg. To be classified as hypertensive, the patient would need to fulfil the following definition of: HT overall=HT with treatment and/or BPS >160 mmHg and/or BPD >95 mmHg.
Diabetes mellitus type II was based on the patient's known status or, following a blood chemistry result indicating glycemia >6.9 mmol/l, according to the guidelines of the ‘Expert Committee on the diagnosis and classification of diabetes mellitus’.17 Measurement of glycemia was with the glucose-oxidase (hexokinase) method on fasting (>12 h) blood using the Hitachi 917 auto-analyzer.
Hypercholesterolemia defined as ≥6.2 mmol/l according to the criteria of the ‘Second Report of the Expert Panel on Detection, Evaluation and Treatment of High Blood Cholesterol in Adults’.18 Measurement was performed on fasting (>12 h) plasma using enzymatic methods in the Hitachi 917 auto-analyzer. To avoid excluding patients whose values corresponded to normal but were the result of hypolipemic therapy, the following criterion was used: total hypercholesterolemia (Tc) >6.2 mmol/l and/or hypercholesterolemia alone with treatment.
Cardiovascular disease: defined as previous diagnosis of ischemic heart disease.
Previous experience of diets for weight loss.
Cause of obesity as defined as having resulted from overeating, or from other causes such as cessation of smoking or sedentary lifestyle.
Age of commencement of obesity defined as infancy–adolescence or commencement in adulthood.
Parental obesity defined as one or both of the parents being, or having been, obese.
Duration of treatment defined as the length of time of patient compliance with the program, that is, up to the time the patient abandoned the treatment or, alternatively, successfully completed the weight-maintenance stage.
Attainment of ‘completion’.
The SPSS statistical package (version 10.0. for Windows) was used throughout. Descriptive analyses of the variables were using the test of proportions for qualitative variables and measurements of central tendency (mean or median), measures of dispersion (standard deviation; s.d.) for quantitative variables. Bivariate analyses of proportionality of distribution of categorical variables were estimated using the χ2 test. For continuous variables we used the Kolmogorov–Smirnov test to check that the variables were normally distributed. Normality was accepted at P>0.05. For comparisons of variables such as age, BMI, weight loss, percentage weight loss and treatment duration in which the distributions were non-normal, the comparisons of absolute means between groups were with nonparametric Wilcoxon test of sum of the ranges.
To evaluate the impact of the different variables associated with the obesity (BMI, age, gender, etc) across the treatment time (between the start and the end of the program whether due to having achieved target weight loss, that is, ‘completing’ or of having abandoned the program, that is, ‘failure’), we used the survival analysis of Cox stepwise forward regression with the Z statistic of Wald. This allows an evaluation of the impact of multiple covariables, whether categorical or continuous, in the same model. The steps followed were: Selection of the variable ‘duration’ for the time of survival as indicated by the amount of time the patient spent adhering to the program before achieving the objectives of the desired weight loss, or the period of follow-up until the patient abandoned the program without having achieved the target weight loss. We defined the status variable as an ‘event’ with the option ‘yes’ being the ‘completion’ variable. Covariables were age (continuous), BMI (continuous), gender, physical exercise, alcohol, cardiovascular disease, hypertension, hypercholesterolemia, diabetes type II, previous diets, smoking habit, cause of obesity, age of commencement of obesity and obesity of the parents. The statistic values generated were coefficient (B), standard error of B, Wald statistic, levels of significance, reason of the estimated advantages (exp(B)) and the 95% confidence interval (95% CI) of the value exp(B). Significance was set at P<0.05.
Of the 1018 subjects in the study sample (788 females and 230 males), 464 (45.6%) were classified as being overweight and 554 (54.4%) as being obese.
Table 1 summarizes the characteristics of the overall study sample of subjects who participated in the study, as well as segregated with respect to having satisfactorily completed the treatment, or not. Those patients who completed the treatment (29.6%) had done so in a mean period of adherence to the program of 5.71 months, with a mean weight loss of 11.82 kg and a percentage loss of 13.9% relative to baseline. The patients who abandoned the program without completion (70.4%) had a mean duration of compliance of 4.3 months, a mean weight loss of 6.57 kg, which represented a 7.37% loss relative to baseline.
Cox regression analysis
In the regression analysis placing weight-loss ‘completion’ as the outcome variable (as described, earlier), the variables in the stage of active weight loss in the overall study sample and which are highlighted by the analysis as the variables that influence an individual's completion of the program were age, gender, baseline BMI, prior participation in weight-loss programs, the period at which obesity was first noted, and antecedents of parental obesity (Table 2). For example, a male had 2.4 times the probability of successfully completing the program than the female counterpart (Figure 1). For each incremental year of age the possibility of completion increases by 1.6% (Figure 2). For each unit decrease in initial BMI the possibility of completion increases by 21% (Figure 3). To have tried a dietary program previously diminished the possibility of completion by 37% (Figure 4). The coinciding circumstances of adult-onset obesity and the absence of parental obesity increased the possibility of completion by 36%.
In our survey of the recent literature, the success of programs for the treatment of obesity vary between 10 and 80%19,20,21 and this high degree of variability is due, perhaps, to the differences in methodologies. There are not many studies published of results obtained in specialized obesity clinics and, in reviewing them, we observed a similar difficulty and variability in defining the criteria to describe the appropriate conclusion of a weight loss program. In general, a success of between 20 and 45% is considered satisfactory20,22,23 and, on this level, our results indicating that about 30% of study subjects could be defined as ‘completers’ are similar.
Our objective consisted, however, in identifying baseline characteristics that would allow us to predict the continued compliance with the weight loss program. Data from other studies addressing this issue are very difficult to compare because the strategies followed were different to that of the present study. Also, in some cases, the evaluations were made with artificial time-limit cutoff for outcome evaluation that was either too soon or too long after the conclusion of the program.
Similarly, the criteria of completion employed were very different and were defined as 5% weight loss with respect to initial weight, or 10%, or merely describes as ‘some’ weight loss and which continued throughout follow-up.22,23
The two fundamental aspects of the present study are that, firstly, the prediction is on the basis of ‘survival analysis’. This allows us to formulate a prediction for individuals who start and end the program over different timeframes. Also, we can evaluate the influence of the different variables over the whole period that the patient remains on the program and fulfils the objectives (or abandons the program, as the case may be). The second aspect of note is that we considered the patient as a ‘completer’ when a suitable weight loss had been achieved (a minimum weight-loss of 5–10% relative to baseline) and the patient had ended the weight-maintenance stage. At this point the patient is ‘discharged’ from the treatment and is introduced into the follow-up program, described above. Some investigators consider that achieving a BMI <25 kg/m2 or a weight loss of more-or-less 5–10% relative to baseline is sufficiently indicative of success; as do many patients, as well. However, we subscribe to the belief that success must include adherence to regular follow-up after an obesity-reduction program because without it the possibilities of maintaining the weight-loss are very low.24 Another consideration to bear in mind is that despite the terms ‘fulfilling’ the prescribe guidelines and ‘compliance’ with the treatment not being the same, the patients who continue attending the weekly outpatient clinic, do so while the outcomes are satisfactory (according to the weight being lost) and, conversely, others have abandoned the treatment or have started the maintenance stage. In this case, fulfilling is seen as compliance, and quitting the program is due to a variety of causes, as we have stated, above.
The modifiers of program effectiveness were identified as gender (males respond better), the participation in previous dietary programs (predictive of less completion), age (worse results in the young) and the combination of circumstances such as obesity commencing in adulthood and the absence of obese parents (predictive of greater completion).
Out results, despite the methodological differences mentioned earlier, coincide with those of Hoie and Bruusgard23and with those of Ogden et al25 who identified gender, baseline BMI and age as being predictive of weight loss. Unlike our study, Hoie and Bruusgaard23 did not observe any relationship between the participation in previous dietary programs and the low completion rate. Ogden et al25 as well Yass-Reed et al26 observed the opposite to ourselves in those individuals who had tried other dietary regimens were the ones who were more likely to fulfil a subsequent weight loss program. We observed that having participated in other dietary programs reduced the possibility of completion by 34%. This observation coincides with the recent studies of Kroke et al27 in which 18 001 individuals of a general population were assessed using a model of logistic regression. They observed that the best predictor of weight gain was a previous weight loss. The results of Colditz et al28 in a study of 31 940 women indicated that the important predictors of weight gain were a younger age and a previous weight loss. This factor of lower age being predictive of failure has been identified in other studies as well.29,30
Diabetes mellitus type II did not predict whether or not a subject would complete the program successfully despite some reports31 indicating that diabetic subjects lose less weight than do nondiabetic subjects. In our study BMI decrease was less in diabetic individuals, but diabetes per se had no influence on whether the subject fulfilled the ‘completion’ prediction.
We observed that factors such as the juvenile onset obesity and the presence of obesity in parents were strong indicators of lack-of-success in weight loss, especially if both circumstances coincided. Body fat distributions and obesity appear to be a result of polygenic interactions with a considerable genetic heterogeneity between individuals with similar proportions of body fat. Some studies propose a gene–-environment interaction with varying degrees of influence of one over the other. Bouchard et al32 proposed that the variability in the body fat phenotype is 25% due to genetic factors, 30% to cultural transmission and 45% nontransmissible environmental factors. Further, studies on families containing biological as well as adopted children have indicated that genetic and environmental factors exercise their effects independent of each other.33 The studies of Hainer et al34 in which basal metabolic index and body composition analyses were performed in monozygotic twins undergoing weight loss, suggest a strong genetic contribution to metabolic efficiency and several studies conclude that the body weight of the parents is a strong factor predictive of childhood obesity.35,36,37 From our own data we would extend this concept to include childhood obesity as a predictive factor of failure to respond to conventional weight loss programs.
Of special note is the study by Klem et al.38 This is one of the few studies that specifically examined the characteristics of individuals in minority groups who achieved weight stability over extended periods following substantial weight loss (minimum 13.6 kg after 5.5 y). The weight loss was achieved through different strategies (including 45% without reference to any specialist), but the most frequent strategy was that combining dietary reduction and moderate exercise not only during the period of active weight loss but also during the maintenance phase.
The development of strategies for the prevention and treatment of obesity is a current priority in health promotion. There appears to be no ideal method of weight loss that would be effective for all, and the criteria of success depend on different evaluation methods.39 Confronted with an obese individual, the immediate need is to perform a detailed evaluation of the etiological factors, family antecedents, previous attempts at weight loss together with an estimation of the grade and type of obesity and the associated pathology (cardiovascular disease risk factors included). Similarly, It would be of interest to determine, before initiating treatment for weight loss, the patient's history of dietary changes, states of anxiety or depression, etc since these can influence the degree of adherence to the treatment. It would be of considerable interest, as well, to evaluate the repercussion on compliance of other more general factors such as the motivations that underlie the patient's desire to undertake a weight-loss program.
From all of these variables, a prognosis of probable success and ‘completion’ can be derived and the different options of treatment may be considered (conventional treatment using diet and physical exercise, drug therapy, psychotherapy, surgery, etc). This has the advantage that false expectations on the part of the patient may be avoided and which, often, can be more of a prejudice than a benefit to the patient. The results of this study may not be appropriate to select high-risk groups of patients, but could be useful in understanding compliance probabilities with respect to obesity treatments in outpatient clinics.
In conclusion, in line with the proposals of some investigators,38,40 we believe in the importance of identifying individuals most likely to benefit from certain programs of weight loss and we are against the concept of a single type of program being effective for all. We strongly advocate change in lifestyle habits in young women with high BMI, who have had previous attempts at weight loss, who have had obesity since childhood and who have a family history of obesity. In dealing with treatments for obesity, only an appropriate change in lifestyle habits will achieve a long-term maintenance of the weight lost.
Future studies may need to focus on determining the success and completion rates of weight reduction in the obese, particularly in relation to environmental and genetic factors so that more effective individual-specific programs may be devised.
We thank Dr Sergio Martin-Correa for his help with the data collection. Editorial assistance was by Dr Peter R Turner of t-SciMed (Reus, Spain). The study was funded, in part, by Abbott Laboratories.