A single-centre, retrospective chart review. Data were collected for a five year period.

All procedures were in accordance with good clinical practices and were within the guidelines of the Helsinki Declaration for studies conducted using human subjects ¹². The Ethical Committee of Las Palmas de Gran Canaria University accepted the study principles. Patients' data were codified to guaranty anonymity.

Between February 2009 and January 2013, 500 subjects agreed to a weight loss programme. The data was collected in consecutively enrolled participants attending our clinic specialising in obesity. The patients had a BMI >25 kg/m² and were attending the clinic for the first time. The age range was between 18 and 81 y (mean= 41.7; standard deviation s.d.= 11.47) and the BMI was between 25.09 and 51.33 kg/m² (mean=31.44; s.d.=4.41). The study finished in January 2014, when the last of the 500 subjects concluded the intervention.

The patients agreed to a self-paying programme for weight loss through modification of diet and physical exercise recommendations. A complete clinical history was obtained and a complete physical examination was carried out in the first outpatient clinic visit, lasting 30–45 min. The blood chemistry data were solicited, when available, and nature of the programme was explained. Initially, through weekly follow up, evaluations were performed and solutions were suggested for problems that the patient might have been experiencing in adhering to treatment. When the patient discontinued treatment or, alternatively, the weight loss goal was reached, the treatment phase was considered to have ended. From there, the patient went on to the stage of weight maintenance, which focused on normalising caloric intake and physical exercise throughout a five-period week. The patient proceeded on to the follow-up stage of treatment, consisting of regular visits to the outpatient clinic every 15 days. Depending on the patient's needs and/or choice, the time-lapse between visits progressively lengthened to two or three months, with the objective to establish, and keep up, good lifestyle habits ¹³.

In designing hypocaloric diets, body requirements and individual taste preferences were considered. The energy requirements, derived via the Harris–Benedict formula, were decreased by about 2.6 MJ/day according to the type of physical activity in order to induce an estimated loss ranging from 0.5 to 1 kg/week.

The general intake ranged from 3.8 to 5.8 MJ for male and 2.9 to 4.1 MJ for female subjects. For more obese individuals, this ran higher. The Mediterranean diet was used, which follows distributions of the principal components recommended by the Spanish Society of Community Nutrition (14]. The diet was comprised of 35% fat (<10% saturated and 20% of monounsaturated), 50% carbohydrates and 15% protein.

Regular moderate aerobic exercise at least three times a week for a minimum of half an hour/day was implemented in accordance with the US Expert Panel’s ‘Guide for the Identification, Evaluation and Treatment of the Overweight Adult’ ¹⁵. Adjustments were, of course, made given the patient’s capabilities. The increase of physical activity in daily habits were among other recommendations.

'Completion' of the programme was defined as the patient reaching the previously agreed upon weight loss goal and the viability to proceed from weight maintenance to the follow-up stage of the programme. For statistical purposes, individuals unable to fulfil the treatment or maintenance requirements but had achieved a substantial weight loss were not considered in the 'completion' group.

The treatment duration varied as the individual goals and profile of each patient are different. The goal was agreed upon with the patient before intiating treatment and at an established minimum weight loss of 5% was set relative to baseline. When the desired weight loss goal was attained, the patient transitioned to the weight maintenance stage, which focused on normalising caloric intake and physical exercise throughout a five-period week. This was the point when the patient moved from ‘dieting’ to ‘not dieting’.

The SPSS statistical package (version 15.0. for Windows) was used throughout the data analysis. The qualitative variables and measurements of central tendency (mean or median) and measures of dispersion (standard deviation; s.d.) for quantitative variables were tested by the descriptive analyses of the variables. Using the ϰ² test, bivariate analyses for the proportionality of distribution of categorical variables were calculated. We used the Kolmogorov–Smirnov test to verify that the variables were distributed in a normal fashion for continuous variables. P>0.05 was considered normal. In comparing variables, durations in which the distributions were not normal, like BMI, age, weight loss, percentage weight loss and treatment, the comparisons of absolute means among groups were measured using Wilcoxon test, a nonparametric, for the sum of the ranges.

The evaluation of the impact of the differing variables linked with obesity (age, gender, BMI, etc.) across the time of treatment (from start to finish of the programme, whether due to having lost the desired weight, in other words, 'completion' of the programme, or having discontinued the programme, in other words, 'dropout'), we used the survival analysis of the Cox step-by-step towards regression with the Z statistic of Wald. Whether categorical or continuous, this permitted the impact of multiple covariables in the same model to be assessed. The measures taken were: to select the variable 'duration' of time of survival, as indicated by the amount of time it took the patient to follow the programme in order to lose the desired weight, or the follow-up period until the patient discontinued the programme without having last the desired weight. The status variable was defined as an 'event' with the option of 'yes' for the 'completion' variable. Covariables were body fat percentage, age (continuous), BMI (continuous), alcohol, smoking habit, gender, hypothyroidism, previous diets, physical exercise, and age of commencement of obesity. The statistic values standard error of B, generated were coefficient (B), levels of significance, Wald statistic, the 95% confidence interval (95% CI) of the value exp(B) and reason of the estimated advantages (exp(B)). Significance was set at P<0.05 (13).

The present study has several limitations. The selection of subjects was not randomly performed. The data were gathered in consecutively enrolled participants in real-life settings, as opposed to data gathered in controlled research settings, where a more rigorous inclusion criteria has the possibility to limit external validity. However we consider that this kind of studies could also be useful to understand the problem of obesity in real life. We enrolled few men (14.6 %). This must be taken into account in the comparative results between sexes. However this fact is repeatedly observed in other studies on weight reduction treatments (13,20,21] probably because men are less likely to perform this type of treatment.

The strengths of the study include that all data were collected by a single observer, in the same place and with the same measurement instruments which implies a reduced measurement error both intra - observer and between instruments. Also, all data were treated and analyzed by the same investigator. Several studies have indicated that the differences between observers are significantly greater than the intra-observer differences ²². We have not found survival studies that had considered the percentage of fat mass as an adherence predictor to treatment.

Finally, we would highlight that all subjects were part of a real population, taking weight loss treatment voluntary in an obesity clinic.

Our data suggest that both HMD plus the recommendations of physical activity were effective at reducing weight and fat mass of overweight and obese adults, as hypothesised.

Attrition rates in obesity trials range from 10% to 80% ^{23, 24, 25, 26}. This elevated percentage of variability may be due to differing methodologies. Not many published studies report the results found in specialised obesity clinics and, in reviewing, we noted similar difficulty and variability in attempting to define the precise criteria that would outline a sufficient conclusion of a weight loss programme.

In this study, 51.8% of patients experienced more than a 5% reduction of baseline body weight. Numerous reports have concluded that modest weight losses of 5–10% were associated with significant improvements in related comorbidities (hypertension, diabetes, hyperlipidemia, cardiovascular disease, osteoarthritis, sleep apnea, etc.) in obese subjects ^{27, 28, 29, 30, 31, 32}. Moreover, a Mediterranean type diet appears to be more effective in inducing clinically significant long-term improvements in cardiovascular risk factors and inflammatory markers than a low fat diet ³³.

Just 21.4% of the patients achieved the weight loss goal previously agreed upon and successfully completed the weight maintenance stage. Despite the high attrition rate, the completers resulted in a mean weight loss of 10.6 kg (12.9%) from the starting weight during the first six months.

In a recent systematic review of randomised clinical trials focused on weight loss, having at least a one-year follow-up, Franz and colleagues ³⁴ reported that a mean weight loss of 5 to 8.5 kg (5% to 9%) was noted during the initial six months due to interventions involving a reduced-energy diet and/or weight loss medications, with weight plateaus occurring at approximately six months. The magnitudes of the loss of weight noted in the present study suggest that a hypocaloric Mediterranean diet plus physical activity could be an effective way to improve weight loss in obesity treatments.

In 2015, Clark and colleagues ³⁵, in a systematic review and meta-analysis, focused on comparing changes from treatment programmes for adults who were overfat. They observed that when exercise and diet is combined you obtained better results than diets alone in reducing body mass and fat mass and at the same time maintaining lean body mass following treatment.

The results of the current study indicate that the combination of a hypocaloric MD and regular moderate physical aerobic exercise may be effective at reducing weight, as well as body fat percentage (-26.8% from baseline), in patients complying with the treatment.

The second objective was to identify baseline characteristics that can help us predict further compliance with the weight loss programme. A number of factors might influence adherence to a diet, for example the length of intervention, disease state, patient support, and restrictiveness ³⁶. It is very difficult to compare from other studies because the strategies involved in the studies are different than that of the present study. In the present study, the results are based on the 'survival analysis'. Which permits a prediction for individuals who initiate and follow through with the programme over different timeframes to be formulated. We can estimate, as well, the importance of the differing variables druing the entire period that the patient stays on the programme and achieves the objectives.

The factors associated with the completion of the treatment were gender (males higher completion), baseline fat mass percentage (higher percentage, lower completion), attending to previous dietary programmes (predictive of less completion), age (worse results in the young) and hypothyroid disease (predictive of dropout). Initially, the survival study was performed excluding the variable fat mass percentage, and here, BMI appeared as predictor of successful completion. By including fat mass percentage in the Cox regression analysis, the influence of BMI was nullified.

In a 2014 systematic review of randomised trials of weight loss interventions using traditional diet and/or exercise interventions, Kaiser and colleagues found that the possibility of dropout was significantly higher for females than for males, as well as in those subjects with a higher BMI ¹⁰. In 2015, another study also suggested that a higher level of obesity were more likely to drop-out ³⁷.

Conflicting results have been observed between age and attrition ³⁸. Weight loss programmes conducted in research settings showed no association between relatively young age and treatment discontinuation ^{39, 40, 41, 10}, while the present study and other studies found that relatively young age was an important predictor of dropout ^{19, 20, 21, 37, 42, 43}. Some authors hypothesised that older patients were aware of the health benefits of weight loss ⁴⁴.

Our findings suggest that having experienced previous diet programmes significantly reduced the probability of completion. Bautista and colleagues ¹⁹ also reported similar results. However, previous experience of weight loss predicts attrition only in selected reports. In our review of the literature, we did not find studies related to predicting the role of fat mass percentage on attrition.

Desertion is lower in patients treated with cognitive behavioural therapy ^{45, 46, 47}, and the expected rates outside the controlled studies are even higher ⁴⁸. In several studies, it was observed that the total stress level differentiates patients who do not continue treatment from those who finish the programme ^{37, 49, 50}. Dietary programme alone is not the sufficient to treat overweight and obese patients who suffer psychological distress because they are unable to control anxiety that nutritional strictness produces ³⁷.

We subscribe to the belief that, in the short term, diet programmes may produce weight loss ^{51, 52}, however the maintenance of this weight loss is often difficult and often requires doing exercise and following a lower-energy diets as a long term habit in a person’s lifestyle ⁵³. A comprehensive programme of lifestyle modification is considered the first option for losing weight and maintaining this weight loss (National Institute, 98) ⁵⁴. Lifestyle modification, i.e. behavioural weight control, is comprised of three primary components: exercise, diet, and behaviour therapy ⁵⁵.

There is not enough consistency between the results of different studies regarding predictors of successful treatment for weight reduction. The results of this study may not be suitable for select high-risk groups of patients, but could be useful in understanding compliance probabilities with respect to obesity treatments in outpatient clinics.