Introduction
Morbid obesity is a major contributor to a wide variety of disease states including diabetes mellitus, coronary artery disease, and sleep apnea. Obesity, generally defined as a body mass index (BMI) greater than 30 kg/m
2, increases the risk of all-cause death [
1]. Due to the high prevalence of overweight (BMI between 25 and 30 kg/m
2) and obesity, interventions such as diet and exercise to promote weight loss have become increasingly important to reduce morbidity in the general population. The benefits of exercise include increasing energy expenditure and lean body mass while contributing to fat loss, reducing obesity-related complications, and improving self-esteem and depression [
2]. Exercise also improves cardiopulmonary fitness, which may reduce mortality from cardiovascular disease [
3].
The literature varies on the magnitude of weight loss that can be achieved by exercise and the level of activity necessary to achieve it. A negative energy balance of 500 calories per day results in 1 pound of weight loss per week [
4]. To achieve this with exercise requires the equivalent of 1 h/day of aerobic exercise. Walking is one of the easiest and safest ways to establish an exercise program for overweight patients, with 70,000 to 100,000 steps per week necessary to help weight loss. Over a 12-week period, studies have found that overweight patients lose 2.5% to 8% of their body weight through exercise alone [
5,
6]. Long-term maintenance of physical activity (contributing to energy expenditure of 1,500 to 2,000 kilocalories (kcal) per week) has been found to decrease weight gain [
7]. The NHLBI Obesity Education Initiative Expert and the US Preventive Services Task Force developed guidelines establishing the amount of physical activity necessary to promote weight loss and reduce comorbidities. They generally consist of at least 30 min of aerobic activity daily, amounting to an energy expenditure of 2,500 to 3,500 kcal per week [
8].
Exercise has been postulated to improve weight loss after bariatric surgery. However, even moderate physical activity is often difficult for morbidly obese patients due to comorbidities such as osteoarthritis and asthma. Patients who have undergone bariatric surgery are forced to make dietary changes due to the restrictive and/or malabsorptive changes of the operation. The role of physical activity in contributing to weight loss is less clear, as patients are already forced to significantly decrease their caloric intake. Recommendations regarding physical activity are more difficult to enforce. It is critical to evaluate whether exercise improves weight loss outcomes to determine if this modality should be mandated as part of the standard postoperative guidelines.
This systematic review analyzes the evidence regarding physical activity following bariatric surgery. The main outcome of interest is postoperative weight loss, but additional information regarding the instruments used to measure exercise and the definition of physical activity is also assessed.
Materials and Methods
Identification and Selection of Studies
This study is part of a larger systematic review examining patient factors related to postoperative weight loss after bariatric surgery. Relevant studies evaluating exercise were identified by searching MEDLINE (1/1/1988 to 3/4/2009) under the search words ((“Bariatric Surgery”[Mesh/NoExp] OR “weight loss surgery” OR “obesity surgery” OR “weight reduction surgery” OR “Biliopancreatic Diversion”[Mesh] OR “Duodenal switch”OR "laparoscopic band" OR “lap band” OR “gastric band” OR “Gastric Bypass”[Mesh] OR “Gastroplasty”[Mesh] OR “gastric sleeve” OR “sleeve gastrectomy”) AND “Obesity”[Mesh]) AND (“Physical Therapy Modalities”[Mesh] OR “Physical Therapy (Specialty)”[Mesh] OR “Exercise Movement Techniques”[Mesh] OR “Complementary Therapies”[Mesh] OR “physiotherapy” OR “physio therapy” OR “therapeutic exercise” OR “Occupational Therapy”[Mesh] OR “Exercise”[Mesh] OR “Exercise therapy”[Mesh]). We manually mined reference lists of the retrieved studies to identify additional relevant publications.
The full text of the articles was evaluated with a standardized article screener by two of the researchers. The selection criteria included studies published in English with patients over the age of 18 years (studies with patients both over and under 18 years old were accepted) who underwent bariatric surgery (open or laparoscopic gastric bypass, laparoscopic gastric banding, biliopancreatic diversion, vertical-banded gastroplasty, or gastric sleeve; other bariatric procedures or not bariatric surgery were excluded). Accepted study designs included case series/cohort, case control, and randomized control trials; studies with a sample size of less than ten were excluded. Studies that did not report on exercise and postoperative weight loss were excluded.
Data were abstracted from each study by two physicians. The following relevant information was recorded: study design, type of operation, baseline patient demographics, number of patients and definition of physical activity or exercise, and degree of postoperative weight loss.
A meta-analysis was performed to assess the combined association of postoperative exercise on 12-month postoperative weight loss, calculated as percent total BMI loss. Studies were included if they reported 12-month weight loss for patients who exercised versus patients who did not exercise as % BMI change or BMI points lost, resulting in three studies included in the meta-analysis. Patients in the exercise group were defined as meeting a certain threshold of activity, which differed per study. The mean difference method in REVMAN (version 5.0.22) was used [
9]. A random effects model was used to calculate mean differences, 95% confidence intervals (CIs), a combined overall association with
P value, and the
P value for testing heterogeneity (
P < 0.1 was considered significant). When the standard deviation (SD) was not available, as was the case for two studies, it was estimated using the mean SD from other studies.
Discussion
Eleven of the thirteen studies reported that exercise and physical activity correlate with greater postoperative weight loss following bariatric surgery. Meta-analysis suggests 4.2% greater degree of weight loss (total BMI) at 12 months, and greater weight loss persists out to 24 months. There is significant variation in how exercise is defined, with few studies using validated surveys and none that are specific to bariatric surgery patients. Standard guidelines for appropriate amount of exercise for bariatric patients still need to be developed.
There is great variation in how exercise is measured and the minimal threshold to define a physically active patient. Of the two studies that found inconclusive results, Larsen et al. used the Sport Index of the Baecke Questionnaire and report that exercise levels may be too low after gastric bypass to contribute to weight loss. The Sport Index may not be appropriate to measure physical activity in this population. Metcalf et al. found no association between physical activity and EWL but there is a benefit in lean body mass.
The definition of an active patient differs among studies, but four studies require at least 30 minutes of exercise on 3 or more days per week. Three studies require from 20 to 200 minutes per week. However, only Bueter et al. and Hernandez-Estefania et al. specify the type of activity to be endurance sports and walking, respectively, while the remainder do not state a lower limit of what is accepted as exercise.
An appropriate definition of exercise should include the weekly duration as well as the type of activities performed. There are few validated instruments used in the bariatric literature to measure activity levels, and all are based on self-reporting. The two most relevant surveys reported in this review are the Baecke Physical Activity Questionnaire and the International Physical Activity Questionnaire. In a recent review of studies assessing physical activity in cardiac patients, the two most frequently used instruments are the Baecke Questionnaire and the Stanford 7-Day Physical Activity Recall [
27]. The latter has measures for sleep and moderate, hard, or very hard physical activity carried out in the past 7 days. Though it is the most commonly used survey in the cardiac population, it has low validity in women and was assessed to be not suitable for cardiac patients. There is no single instrument that is accepted as the gold standard for measuring exercise in bariatric patients. However, the use of a standardized and validated survey would allow for comparing and/or pooling between future studies.
There are no standardized guidelines for how much exercise is appropriate for the postoperative bariatric surgery patient. Some recommendations suggest that daily walking is adequate and pedometers are useful to help track activity [
28]. Others recommend a minimum accumulation of weekly activity points (200 to 300 points), based on what activities are performed (e.g. walking, bicycling, housekeeping, or sports) and for what duration [
29]. This method roughly correlates with the IPAQ score. Encouraging 30-45 minutes of physical activity of moderate intensity (e.g. walking) for 3 to 5 days per week has also been reported [
30]. This is the recommendation that is most commonly given in the studies included in this review. It also closely parallels the American Heart Association / American College of Sports Medicine guidelines on physical activity, which include 30 minutes of moderate-intensity aerobic activity on five days each week or 20 minutes of vigorous-intensity activity for three days each week [
31].
Motivating patients to exercise can be difficult, especially in the bariatric population. Counseling that begins preoperatively can help prepare patients for the physical activity that will be recommended after surgery. Instruction to walk, which is low-impact and already done to some degree by the majority of people, may increase compliance. Pedometers are a good motivational tool to encourage patients to fulfill set goals. Finally, barriers to exercise (e.g. health concerns, lack of proximity to a gym or park, feeling self-conscious) should be identified and minimized if possible. Screening patients for low physical activity can help to identify those who may need additional help and need targeted interventions to help them achieve optimal weight loss.
Though most studies report a positive association between physical activity and postoperative weight loss, this does not prove that exercise causes more weight loss after bariatric surgery. Patients who lose more weight may feel better physically and this can lead them to exercise more. A randomized trial or matched cohort would help demonstrate whether a causal relationship exists.
This review has some limitations mainly related to the heterogeneity of the studies. The variations in defining exercise and how it is measured made it difficult to compare the studies. Furthermore, the majority of studies did not report patient follow-up or actual compliance with exercise activities. This limits the validity of their findings and makes it challenging to identify the most successful exercise regiment for this patient population. Degree of weight loss is also reported in different ways, with some studies reporting kilograms or BMI points lost while others include the percentage of excess weight loss. In addition, little data is reported on the association of other patient factors, such as race, gender, or age, on the correlation between exercise and weight loss. The level of physical activity may differ according to baseline patient characteristics, with one study finding that women exercise more than men postoperatively [
32]. Targeting certain patients groups may be useful if they are found to benefit more from exercise.
In summary, postoperative exercise is associated with greater weight loss at 12 and 24 months after bariatric surgery. The long-term benefit of exercise in this patient population remains to be shown. Further studies are necessary to determine the appropriate recommendations for the minimum level of physical activity, as well as the best instruments for exercise in the bariatric population.
Acknowledgements
We would like to acknowledge the generous contribution of Paul G. Shekelle to the design of our project and critical review of the analysis. The VA Department of Surgery provided support for Dr. Livhits and Dr. Maggard. Dr. Maggard’s time was supported in part by a grant from the Robert Wood Johnson Physician Faculty Scholars program.