Gender Differences in the Outcome of Obesity Treatments and Weight Loss Maintenance - A Systematic Review

Nanette Stroebele-Benschop; Antje Damms-Machado; Florence Marie P Milan; Carolin Hilzendegen; Stephan C Bischoff

doi:10.4172/2165-7904.1000176

ISSN: 2165-7904

Journal of Obesity & Weight Loss Therapy

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Gender Differences in the Outcome of Obesity Treatments and Weight Loss Maintenance - A Systematic Review

*Nanette Stroebele-Benschop^1, Antje Damms-Machado¹, Florence Marie P Milan², Carolin Hilzendegen¹, and Stephan C Bischoff¹**
¹Institute of Nutritional Medicine, University of Hohenheim, Stuttgart, Germany
²Institute of Agricultural Economics and Social Sciences in the Tropics and Subtropics, University of Hohenheim, Germany
Corresponding Author :	Nanette Stroebele Institute for Nutrition Medicine University of Hohenheim, Fruwirthstr. 12 D -70599 Stuttgart, Germany Tel: +49 (0)711-459-24620 Fax: +49-(0)711-459-24343 E-mail: N.Stroebele@uni-hohenheim.de
Received May 04, 2013; Accepted May 31, 2013; Published June 02, 2013
Citation: Stroebele-Benschop N, Machado AD, Milan FMP, Wössner C, Soz D, Bischoff S (2013) Gender Differences in the Outcome of Obesity Treatments and Weight Loss Maintenance - A Systematic Review. J Obes Weight Loss Ther 3:176. doi:10.4172/2165-7904.1000176
Copyright: © 2013 Stroebele-Benschop N, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract

Obesity is one of the major health concerns of today. The aim of the study was to review existing literature comparing gender differences in Weight Loss (WL) and Weight Loss Maintenance (WLM). A systematic review of published studies (to November 2009) examining WL and WLM and provided results separated by gender was conducted. Two reviewers selected studies for inclusion, assessed quality, and extracted data. The database search identified 1072 references for screening and 229 were selected for possible inclusion. A search update in August 2011 identified an additional 186 references and 62 were selected for possible inclusion. Fifty-four studies were included. Seventeen studies included surgical WL procedures and 37 studies examined nonsurgical WL treatments. For both types of WL treatment, about half of the studies reported higher absolute WL in men whereas the other half of the studies reported no gender differences. The majority of the 12 studies on WLM reported no gender differences. Meta-analysis revealed higher relative weight loss in men compared to women. WL treatment outcome appears to be in favour of WL in men. More research attention should be paid to gender specifics regarding WL treatment and WLM.

Keywords

Obesity; Gender; Therapy; Treatment; Weight loss

Abbreviation

BMI: Body Mass Index; LGBP: Laparoscopic Gastric Bypass; LSG: Laparoscopic Sleeve Gastrectomy; RYGB: Roux-en-Y Gastric Bypass; WL: Weight Loss; WLM: Weight Loss Maintenance; WMD: Weighted Mean Difference

Introduction

The prevalence of obesity is alarmingly high across the world [1] and affects both genders although it is higher in women than in men [2]. However, obese men are at a higher risk for obesity-related chronic diseases because of fat accumulation in mainly abdominal and visceral body regions.

The treatment of obesity can be mainly divided into two categories: conventional behavioural therapy focusing on dietary and physical activity changes or surgical therapy. The popularity of weight loss surgery has increased [3,4] and surgery for severe obesity appears to improve risk factors and decrease overall mortality [5]. Different types of surgery tend to report different levels of weight loss success [6] and more women than men tend to undergo weight loss surgery and enter any type of treatment in general [7]. However, given the diversity of patients including their starting weight or already existing co-morbidities, there has been no definite answer for the support of one surgical method over the other [8-10]. One systematic review, nonetheless, revealed results in favour of gastric bypass procedures compared to gastric banding to treat obesity in the U.S. [11]. One consistent factor for success in surgical patients appears to be younger age whereas divergent results on gender have been found [7]. Even less is known about factors for success in patients choosing conventional therapies. Pre-treatment weight loss and initial weight loss [12,13]. Psychological factors such as body satisfaction, mood or self-efficacy [14-16]. Or social support all appears to be factors that positively influence treatment outcome.

Consistent knowledge about successful long-term weight loss maintenance is lacking but the method of weight loss – surgical or conventional methods – appears to be unrelated to success. A metaanalysis of US studies revealed that 44% of the participants maintained their initial weight loss at two years and only 28% at four years [17]. Results from the National Weight Control Registry show the importance of dietary restraint and weight monitoring as well as eating breakfast, and adhering to a relatively intensive exercise regime [18-21]. Other mentioned factors for long-term success in weight loss maintenance seem to be certain medications, regular consultations with physicians and other support sources as well as social support [22,23].

Not many studies have further investigated subgroups and individual differences such as possible gender differences in the successful treatment and maintenance of weight loss.

The aim of this review was to look systematically at the differences in weight loss and weight maintenance after weight loss treatments between men and women including both surgical and conventional methods. The review’s objective is to determine whether men or women are more successful in either weight loss or weight loss maintenance and whether possible differences can be found between treatment types.

Materials and Methods

A systematic search for the published literature in the languages English and German was undertaken with Medline, Embase and Cochrane Database of Systematic Reviews (all dates starting with citations indexed 1980 to November 2009) [24]. An additional systematic search was conducted with citations indexed December 2009 to August 2011. Also, a hand search of reference lists identified by the systematic search of the literature was conducted. Search terms included obesity, overweight, surgery, weight loss program, weight maintenance, weight loss, psycho-education, dietetic counselling, diet, and caloric restriction. Eligible study types were cross-sectional, cohort and case-control studies, clinical trials, meta-analysis and systematic reviews with adult human subjects. Studies with subjects with preexisting medical conditions (e.g., diabetes, metabolic syndrome) were also included. Types of outcome measures were not specified but the article had to mention results on weight loss and maintenance of weight loss of both men and women. Excluded were studies addressing participants under the age of 18 years, participants with existing psychiatric disorders, studies without information on gender as well as case studies, abstracts, and editorials.

From a reading of the titles and abstracts, identified by the literature search, each eligible publication was selected if the inclusion criteria were met. The content was reviewed by two independent investigators to determine eligibility. When there were discrepancies, other investigators conducted additional evaluation of the study and discrepancies were resolved in conference. Assessment of methodology was made independently by both reviewers evaluating whether there was a clear research question with specific results, a clear description of inclusion and exclusion criteria, a sound methodology, generalizability and a mentioning of limitations. For each eligible study a checklist based on the PRISMA statement was filled out [24] and the following data was abstracted: Title, authors, publication year, journal title, country where the study was conducted, recruitment period, treatment indication, research question, setting, selection criteria, number of groups, study design, randomization, study length, primary study outcome, statistical methods, number of analysed subjects separated by gender and on gender reported results, weight related results (mean baseline weight in kg and/or BMI, mean weight change).

Hedges’ g statistics as a formulation for the Weighted Mean Difference (WMD) were used for the meta-analysis of studies with a continuous measure (comparison of relative mean weight loss between men and women) where data was available. The overall WMD with a 95% confidence interval was given. Based on the variability regarding participants and treatment within the included studies, the random effects model was considered. Heterogeneity was evaluated using the I²; statistic, which describes the percentage of variation as a result of heterogeneity rather than chance. For the analyses the statistical program STATA/IC 1² was used.

Results

General characteristics of included and excluded studies

The database search identified 1072 references for screening. Based on reading the title and the abstracts of all found references, 229 fulltext articles were reviewed for possible inclusion. Thirteen studies were selected mentioning weight loss separated by gender as outcome after weight loss surgery and 31 studies included results on weight loss separated by gender after other non-surgical treatments.

The additional more recent database search further identified 186 references for screening and 52 references were selected for full-text review. Ten studies were included, 4 studies reported results on weight loss separated by gender after weight loss surgery and 6 studies reported results on weight loss separated by gender after non-surgical treatments.

Taking together both systematic searches, the majority of the excluded 214 studies did not match the main criteria such as the analysis of weight loss (excluded studies examined e.g. complications during and after surgery, dietary habits without analyzing weight, hormonal changes after surgery, characteristics of people choosing surgery, psychological or behavioural variables affecting weight loss). The other excluded studies lacked comparison of men and women regarding weight (103 articles). An additional three studies had a sample population of less than 18 years of age and two studies investigated obese psychiatric patients (Figure 1). In the recent systematic search, one publication was identified that reported the same weight loss results separated by gender already mentioned in an earlier publication [25] and was therefore excluded [26].

Surgical studies

All except one [27] of the 17 included surgical weight loss studies [27-43] were cross-sectional prospective or retrospective studies (5 studies [31,37,41-43]). The follow-up years ranged from 0.5 up to 22.9 years. The majority of the studies ranged from 0.5-1 year follow- up (9 studies [28-30,32-38,40,42]) and the remaining studies ranged from 2 up to 5.7 years when leaving out the one retrospective analysis of 22.9 years of follow-up [31].

Of the 17 surgical weight loss studies, two studies were considered to have low quality due to either a small sample size with a weak methodology or missing inclusion criteria description [30,35].

Overall, of the 17 included studies, seven investigated the effects after some version of the gastric bypass (hand-assisted, open, stapled, transacted, laparoscopic RYGB) [28-33,41]. Seven studies published results using gastric banding [27,34,36,37,39,42,43]. Two studies used laparoscopic sleeve gastrectomy (LSG) [38,40] while one of the two included both LGBP and LSG (40). One publication did not specify the surgical procedure [39]. General study characteristics for the included surgical studies are presented in Table 1.

Results on gender differences in the surgical studies

Of the 17 studies that included surgical weight loss procedures, six studies reported higher absolute weight loss in men [28,29,33,38,39,43] whereas two studies reported greater absolute weight loss in women [32,35]. But one of the six studies that showed higher weight loss in men reported greater absolute weight loss in men but greater BMI loss in women [43]. One additional study revealed female gender as a significant predictor for percentage of excessive weight loss [42]. Six studies reported no gender differences [27,30,31,36,37,41]. One additional study examined changes in percentage of fat mass and fat free mass after bariatric surgery and found higher percentage loss of fat mass and higher percentage increases in fat free mass in men compared to women [34]. Further, one recent study only reported gender differences in fat free mass loss with a higher proportion of weight loss as fat free mass in men compared to women [40].

Five of the 17 included studies also looked at weight loss maintenance after surgery and four studies found no gender difference [27,31,34,37] whereas one study found better weight loss maintenance in men [39].

Non-surgical studies

Of the 37 included studies, 21 had a cross-sectional study design investigating the effect of behavioural interventions on weight loss [44-66]. Ten studies were randomized controlled trials or studies with at least two- group comparisons [25,30,65-73]. Three publications compared selected studies using meta-analytical techniques [17,73,74] and two publications were cross-sectional surveys (investigating weight loss strategies and other weight loss related variables) [75,76]. Further, one study looked at the effect of having different nutritionist as part of the intervention and its effect on weight loss [77]. Table 2 presents the study characteristics of the 37 included non-surgical studies.

The study quality was determined to be low in only three of the included studies with the main reason being missing information such as length of treatment, definition of program effectiveness or a small sample size [30,46,54].

The majority of the included non-surgical studies used behavioral modification as treatment choice including diet, exercise and psychological counselling treatment components (22 studies [30,45-50,54,66,68,52,53,55,57-59,63,64,68-71]). Only seven publications conducted studies with diet treatment only [25,44,56,60-62,70]. The meta-analysis by Ballor and Poehlman [74] included both diet only and diet and exercise interventions.

Results on gender differences in the non-surgical studies

Sixteen studies found no gender differences in weight loss treatments [30,45,48-54,58,59,63,65,66,69,74] whereas 16 study results showed better weight loss in men compared to women [25,44,46,47,55- 57,60-63,66,68,70,71,73]. Two of those 16 studies, however, showed either only better absolute weight loss in men using any type of fish supplement compared to a control intervention which was not the case in women [25], or better weight loss in men compared to women within one treatment group [70]. Furthermore, one cross-sectional survey of the Danish population found more men than women reporting to be successful in weight loss and weight loss maintenance [76]. One of the two meta-analysis using survey results showed that although women were twice as likely to attempt to lose weight, men were 40% more likely to have success in these attempts [73]. One of the other included metaanalysis investigated gender differences and the influence of exercise on diet induced weight loss but could not detect any gender differences [74].

Only one study found better weight loss in women across four different intervention groups varying in fish and fish oil content [25] but the significance disappeared when comparing the intervention groups separately.

Regarding weight loss maintenance, seven studies mentioned results on gender differences. Four studies revealed no gender difference [17,30,54,65], one of them a meta-analysis [17]. Two studies reported better weight loss maintenance in men [57,76] and two other studies revealed less regain in women than men [53,72]. One of these studies, however, compared Orlistat treatment with a placebo group [72].

Some studies, especially those with cross-sectional surveys did not include statistical results on weight loss or weight loss maintenance but rather asked participants about their weight loss strategies and practices [50,73]. One retrospective phone survey by Williamson et al. [75] revealed a self-reported average weight loss in men of 10-12lbs and an average weight loss in women of 8-9lbs but it was also reported that men started with a higher initial weight than women. The other study on predictors of adherence to diet and exercise programs revealed that men were more likely to complete a program than women [50].

A comprehensive meta-analysis separating surgical and nonsurgical studies and including the relatively large number of selected studies could not be conducted given the lack of available data in the publications. For a description of data available - Table 1 and 2. Most studies did not report mean changes in weight or changes in BMI including the standard deviation. Most studies’ focus were not on gender difference in WL or WLM but rather mentioned existing difference or the lack of in a brief paragraph or sentence in the result section without providing data, only four studies were suitable to compare relative weight loss between men and women providing means with standard variation and the number of participants (Figure 2). The weighted mean difference of the random effects model at -0.87 for relative weight loss indicated significant (p<0.001) but small effects with males losing more percentage weight than females. The meta-analysis revealed slight heterogeneity with I²; = 30.3% (p = 0.230). Post-hoc exploration identified one study to differ from the others by a considerably lower mean BMI [61]. Excluding this study from the meta-analysis, the overall effect size was lowered to -0.71 (95% confidence interval = -1.08 to -0.35, p<0.001) but removed heterogeneity completely (I²;= 0%).

Discussion

Given the small number of studies included in the meta-analysis, the results can not indicate a definite answer to the posed question of existing gender differences in weight loss and weight loss maintenance after weight loss treatments. For surgical procedures, six studies detected better results for men but six other studies detected no gender differences. Similar patterns could be observed for the included nonsurgical studies. Sixteen studies reported no gender differences whereas 16 studies found better weight loss in man compared to women. Where available, the difference in relative weight loss between men and women, as shown in figure 2, show results in favor of weight loss in men. The majority of extracted study results were reported in absolute weight loss although for the purpose of comparing men and women relative weight loss is a more accurate measure of detecting gender differences. Nevertheless, concluding from this systematic review, it seems apparent that women mostly do not achieve better weight loss than men.

The results looking at gender differences for weight loss maintenance are even less conclusive. The majority (8 studies) of all included studies mentioning weight loss maintenance reported no gender differences. Only three studies reported better weight loss maintenance in men and two studies reported better weight loss maintenance in women.

Some general limitations need to be mentioned. The research only included studies in English and German, which might cause underrepresentation of non-English and non-German reporting studies. In addition, the heterogeneity of the selected studies made it difficult to draw a convincing conclusion. Most of the included studies did not look at gender differences as their primary outcome and failed to report actual numbers separated by gender (such as age, weight, BMI, etc.). The studies not only varied widely in sample size but also in length and type of treatment as well as follow-up years. Given the heterogeneity of the studies found, and more specifically the outcome methodologies, and the lack of statistical results in some of the studies, the meta-analysis has only limited explanatory power of the results.

Overall, when generalizing the findings, it can be suggested that more attention should be paid when treating women for weight loss. In support of this conclusion is a recent systematic review of weight loss interventions comparing ethnic groups and gender which revealed that African-American women lose less weight than other subgroups [77]. The authors, however, could not explain the difference in weight loss outcome between African-American women and African-American men.

One necessary action step is to conduct further research with a focus on gender differences in weight loss and weight loss maintenance in particular to provide additional insight in possible underlying reasons and potential solutions for treatment outcome improvements.

Acknowledgements

This work was supported by the Competence Network of Obesity“research group Obesity and the GI tract“ funded by the Federal Ministry of Education and Research, Germany (No. FKZ 01GI0843) and by the “Competence Network: Gender and Nutrition”, funded by the University of Hohenheim, Germany.