A literature search was performed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines for reporting systematic reviews and metaanalyses.

Of the 5,741 citations, 395 underwent full-text review. A flow diagram that outlines the systematic review process is provided in Figure 1. After the full inclusion and exclusion criteria were applied, bibliographies of existing systematic reviews reviewed, and adjudicated accordingly, 19 articles remained. The most common reasons for exclusion of articles were not English language, article type (abstract, review), treatment type (surgical, pharmacological), age younger than 60, not a RCT, BMI less than 30.0 kg/m² (WC <88 cm in women, <102 cm in men), duration less than 6 months, or weight maintenance study. The results of the methodological assessment are presented in Table 1. Of the 19 final selected articles, six were parent studies (Tables 2 and 3, Supplemental Appendix 1), and 13 were kin studies (Supplemental Appendix 2). Decisions were deliberately made about the relationships between publications to maximize high-quality information without counting participants twice. In Table 3, only the primary outcomes are presented because the baseline characteristics are the same as those reported in the kin studies (Table 2).

This review provides an evaluation of the literature on geriatric obesity interventions since 2005 using a two-tiered screening approach. Despite the importance of this public health concern, the number of published randomized trials is limited, highlighting a critical need to develop interventions to assess outcomes in this high-risk population. The geriatric obesity interventions assessed generally led to weight loss and improved quality of life and physical function, as measured using VO_2peak and muscle strength.

This review was deliberately focused on quality of life and physical function in addition to weight loss as important health indicators in older adults^30–32. The interventions generally emphasized weight loss as a common approach to obesity management. Only one study reported the proportion of subjects with clinically significant weight loss (≥5% of body weight)⁸, used as a surrogate for success in adult guidelines. Whether this threshold should be considered in older adults is unclear. Objective and subjective improvements in these domains were observed in the majority of the studies. The data demonstrate the general trends in achieving these outcomes. The current findings provide additional methodological data suggesting the importance of focusing on variables beyond weight loss in this population. Outcomes in older adults, such as functional status and self-reported health, may be useful to enhance geriatric obesity strategies and should be incorporated into daily practice.

The effect on physical function independent of weight loss should not be understated. Evidence of this phenomenon was observed particularly in subjects engaged in combined diet and exercise or exercise-only (aerobic or resistance) interventions. Although weight loss leads to improvements in function, the results suggest that functional improvements can be achieved with exercise alone. Even in the study consisting of less than 5% weight loss²⁵, improvements in function were observed, yet this was predominantly based on a healthy diet and an exercise program. Improvement of function promotes healthy aging and prevents ensuing disability, all of which can lead to better quality of life. Clinicians should be reluctant to consider weight loss with dietary measures alone if the desired outcome is improvement in physical performance, although combining weight loss and exercise results in maximum improvement in physical function and could mitigate the concern of potential sarcopenia and bone loss in older adults. In the studies with a diet-only or control arm that did not have any resistance exercise program, findings highlight the emergence of sarcopenia and bone loss, an important yet overlooked phenomenon of geriatric obesity interventions. Dietary weight loss leads to loss of fat mass and fat-free mass. These trials demonstrate the importance of unopposed weight loss in this population. Sarcopenia progresses with age, and older adults have lower compensatory capacity to offset the loss of muscle mass and strength that may hasten functional impairment and incident disability^{11, 33, 34}. Clinicians should evaluate each person individually and focus on wellness and prevention of sarcopenia and bone loss when recommending weight-loss therapy. The benefits of intentional weight loss observed might not apply to those whose weight loss is unintentional and should be monitored in the course of practice.

This review highlights critical concerns in examining and addressing obesity in older adults. First, high-quality RCTs are needed. Second, longer follow-up and effectiveness trials will clarify sustainability and outcomes of these interventions, which are related to geriatric life expectancy. Shared decision-making should be integrated into patient encounters. Third, pragmatic approaches are critically needed within a primary care infrastructure to manage this disorder. None of the studies tested interventions in primary care, arguably the most common setting for individuals to receive chronic disease management, although each study intervention was labor intensive, and participants engaged in behavioral change through nutritional and physical activity approaches. Hence, their implementation within a primary care or specialty setting may be challenging and face obstacles. Fourth, consensus is needed to standardize the structure of geriatric obesity interventions. Combined diet and exercise strategies, consisting of caloric reduction of at least 500 kcal/d, with appropriate protein and dietary supplementation and resistance exercise, may prevent sarcopenia and bone loss, which are associated with worse function⁹.

Pharmacological and surgical therapy were deliberately not assessed. Newer medications should be used with caution in older adults because they have considerable neuropsychiatric side effects, including memory impairment. These side effects may exacerbate underlying and compensated cognitive function in an age group already at risk of this condition. Bariatric surgery is an approved therapy for obesity, but the literature remains unclear as to its general benefits in adults aged 65 and older³⁵, although emerging long-term mortality benefits have been reported³⁶. Careful selection of older eligible adults undergoing an evaluation has been recommended³⁷. The definition of obesity in older adults is debated extensively³⁸. Measures that could be performed practically and economically in a clinical care setting such as BMI and WC were intentionally chosen. The specificity and sensitivity of these measures differ from those of body composition measures assessed using computed tomography, dual-energy X-ray absorptiometry, or magnetic resonance imaging, which cannot be reasonably performed on a population level. A BMI cutoff of 30.0 kg/m² is a well-established cutoff in defining obesity and is used to identify older adults eligible for the Medicare Intensive Behavioral Therapy benefit¹³. It is also associated with greater risk of death^{3, 15}. A number of subjects classified as overweight were eliminated from this review who would not only be eligible for treatment if they were younger⁸, but otherwise might have adiposity based on other assessment measures³⁸. Using WC may be reasonable and helpful in recognizing persons with normal central obesity who may have different underlying treatment and weight-loss strategies and provides a rationale for including such subjects in further study. There is also strong epidemiological evidence suggesting that a BMI of 25.0 to 29.9 kg/m² is associated with low mortality and functional impairment in older adults who otherwise would not be at high risk of death after weight-loss therapy^{39, 40}. BMI also incorporates fat and muscle mass, and relying solely on this measure ignores sarcopenia, sarcopenic obesity, and normal-weight obesity^{33, 41}.

Interventions focusing on obesity in the general population are often short in duration, and the current results suggest that this is not an exception in older adults. Most weight-loss studies, such as the Diabetes Prevention Program⁴² or Action for Health in Diabetes⁴³, have demonstrated initial weight loss within the first few months; the physiology and management actually differ in the weight maintenance phase. With the exception of one study identified in this review,⁹ all were of short duration. The shorter study duration raises considerable interest because it is likely that short-term outcomes improved, but whether they were sustained is unclear. Studies of 6 months or longer that concentrated specifically on sustained efficacy treatment trials, in accordance with the recommended weight loss guidelines,⁸ were deliberately focused on. Future studies need to examine long-term follow-up in this population.

The strengths of this review include the use of the PRISMA criteria, which reduces bias and error and improves the reproducibility and transparency of the process. The review emphasizes the importance of empirical evidence over preconceived knowledge by identifying knowledge gaps and highlighting methodological inconsistencies and weaknesses. A validated and systematic approach using validated PRISMA criteria with the assistance of an interdisciplinary team that includes experienced librarians increases the validity of the process. Screening was piloted to ensure consistency. The results were useful in identifying future research priorities. Availability of data and quality of the original reports inherently limit literature reviews. Incomplete reporting and negative trials are likely to be subject to reporting bias and may not be published. A priori, the authors were aware of the clinical heterogeneity observed in the known randomized trials and systematic reviews. The current results confirmed considerable methodological heterogeneity as well, so it was decided not to perform a metaanalysis. Although the data were diverse, in addition to weight loss, outcomes that were person-specific and meaningful in an aging population were focused on. Observational studies were deliberately not included to preserve validity. Considerable information can be concluded from well-conducted observational studies, although selection bias is unavoidable in this type of design. Therefore, results cannot be used to definitively support conclusions about obesity interventions based on the outcomes observed in this review. Individuals whose group mean age was 65 and older were included, and studies with subjects younger than 60, which have been included in previous systematic reviews, were omitted^{2, 17–20, 23}. Middle-aged individuals have different physiology and homeostasis and should be considered differently. Lastly, publication bias may affect the number of studies included in this study. Including studies with participants aged 60 to 64 also may be perceived as a limitation of this analysis.

Although there were a limited number of high-quality studies to support geriatric obesity interventions, current RCTs suggest that a reduction in weight can lead to improvements in physical function and quality of life. Body composition changes such as loss of fat mass and preservation of fat-free mass are favorable, particularly when resistance exercise programs are integrated into a program of caloric restriction. Well-designed RCTs are needed in this high-risk population to provide definitive guidance in a clinical care setting.