To encourage weight loss as a treatment approach for incontinence, it is important to estimate the magnitude of weight loss needed to improve urinary incontinence and produce satisfaction with urinary incontinence changes. Thus, this article extends our previous study by looking at the improvements in urinary incontinence that occurred with specific amounts of weight loss in PRIDE participants. A number of clinical guidelines stress that overweight and obese patients should be given the goal of losing 5–10% of their body weight, because these goals are feasible and likely to achieve health benefits. Modest weight losses of 5–10% of initial body weight have been shown to be effective in reducing blood pressure and prevention of noninsulin-dependent diabetes mellitus.^15–18 In this article, we examine the effects of losses of 5–10% of body weight on urinary incontinence among women in the PRIDE study.

Eligible participants were allocated randomly in a 2:1 ratio to an 18-month behavioral weight loss program (weight loss; n=226) or to a structured education program (control; n=112). Assessments were completed at 6, 12, and 18 months by staff members who were unaware of the participant's treatment assignment. The study was approved by the Institutional Review Board at each site and written consent was obtained from all participants before enrollment.

Participants randomized to standard education were offered seven 1-hour group education sessions over the 18 months. These sessions provided general information about weight loss, physical activity, and healthy eating habits.

Participants assigned to the weight loss program received an intervention modeled after those used in the Diabetes Prevention Program¹⁵ and Look AHEAD,^19,20 that was designed to produce an average loss of 7–9% of initial body weight by reducing calories and increasing physical activity. All participants were asked to attend weekly group meetings for months 1–6 and every other week for months 7–18. Participants were prescribed a calorie and fat restricted diet of 1,200–1,800 kcal/day, depending on initial weight, with less than 30% of calories from fat. Physical activity goals were gradually increased until participants were doing 200 minutes per week of activities similar in intensity to brisk walking. Behavior modification techniques, including self-monitoring of diet and exercise, were stressed throughout the program.¹⁴ After completion of the first 6 months of the program, each weight loss group was cluster-randomized to a maintenance program that focused on either refining skills or increasing motivation to improve longer-term weight loss maintenance. Women randomized to the two maintenance groups were similar to each other and to women in the control group on baseline characteristics. No differences in weight loss or urinary incontinence were observed between the two maintenance interventions over the 12-month maintenance period (West DS, Gorin AA, Subak LL, Foster G, Bragg C, Hecht J, et al. A motivation-focused weight loss maintenance program is an effective alternative to a skill-based approach. Int J Obes. in press).

At the beginning of intervention, participants in the weight loss and control groups were given a self-help incontinence behavioral treatment booklet with instructions for improving bladder control.²¹ No other information was provided pertaining to incontinence at the sessions or during follow-up visits.

Weight was measured with participants wearing street clothes, without shoes, using a calibrated digital scale (Tanita BWB 800, Tanita Corporation of America, Inc., Arlington Heights, IL) and recorded to the nearest 0.1 kg. Height was measured at baseline to the nearest centimeter using a calibrated, wall-mounted stadiometer and a horizontal measuring block. Physical activity was assessed with the Paffenbarger Activity Questionnaire.²²

Urinary incontinence was assessed with a 7-day voiding diary.²³ Participants were trained to record the time of each void and each incontinent episode and to identify each episode as stress (involuntary loss of urine associated with coughing, sneezing, straining, or exercise), urge (loss of urine associated with a strong need or urge to void), or other. These voiding diaries were reviewed by blinded assessment staff to reconcile any questions, inconsistencies, or omissions. As a secondary outcome, we assessed the quantity of urine lost involuntarily using a standardized pad test.²⁴ Participants collected and returned in sealed plastic bags preweighed urinary incontinence pads used during a 24-hour period, and the posttest weight of each pad was recorded in grams. At each 6-month assessment, participants were also asked to rate their overall satisfaction with the changes in their incontinence (5-point scale).²⁵ Subjective ratings of satisfaction have been shown to be valid and to correlate with changes in quality of life and urinary incontinence symptoms.²⁵

Demographic characteristics and medical, behavioral, and incontinence histories were ascertained using self-reported questionnaires.

To examine whether there was an association between the magnitude of weight loss and improvements in urinary incontinence, analyses were performed with participants grouped according to their weight loss from baseline to 6, 12, or 18 months. Log-rank tests were used to compare the proportion of participants with improvement in incontinence across four weight loss group categories. Generalized estimating equation negative binomial models were used to compare changes in mean incontinence frequency between women who gained weight and those who lost less than 5%, 5% to less than 10%, or 10% or greater of their initial body weight adjusting for potential confounders including treatment group, clinic, age, race, alcohol use, smoking status, number of live births, pelvic floor exercises, and self-reported kilocalories of physical activity.²⁶ Similarly, we compared the proportion of women achieving at least a 70% reduction in self-reported weekly incontinence frequency across weight loss categories using adjusted generalized estimating equation logistic models to account for clustering within treatment groups. A priori, we selected a reduction of at least 70% in incontinent episode frequency because this amount of change has been reported as a threshold for improvement in patient satisfaction.²⁵ The sample size provided 80% power in two-sided tests with a type I error of 5% to detect a 55% reduction in incontinence frequency among women who lost 0–5%, 5–10%, or more than 10% compared with those who gained weight.

For the generalized estimating equation analyses, we used multiple imputation of missing outcomes under the conservative assumption of nonignorable missingness. Specifically, we imputed missing weights assuming that dropouts in both groups returned on average to their baseline weight.¹⁴ We then imputed missing incontinence frequencies for both groups as if the participant had been assigned to the control group in which average weight losses were minimal but some reduction in incontinence frequency was observed. Summary effect estimates, standard errors, P values, and confidence intervals were computed using standard methods for multiply imputed data, which account for the additional uncertainty of imputed variables.²⁷

Participants were grouped into their category of weight loss at 6, 12, or 18 months without regard to randomized treatment assignment. The categories were gained weight, lost 0 to less than 5%, lost 5 to less than 10%, or lost 10% or greater of baseline body weight. Participants in the gained weight category gained on average 2.1 (±1.9) kg, 2.8 (±3.1) kg, and 3.5 (±3.2) kg at 6, 12, and 18 months, respectively. Table 1 shows the number and proportion of women in each of these categories at each time period. As expected, women in the weight loss intervention were overrepresented in the higher weight loss categories at 6, 12, and 18 months (all P<.001). Women in the various weight loss categories did not differ significantly from each other on baseline characteristics, including BMI and urinary incontinence measures (Table 2).

Among women who gained weight, lost 0 to less than 5%, lost 5% to less than 10%, and lost at least 10% at 6 months, 18.5%, 12.4%, 5.5%, and 9.5%, respectively, dropped out by 18 months. Participants who dropped out of the study had a greater number of incontinence episodes at baseline (P=.03) and were less likely to be married (P=.02).

We tested the interaction between randomization group and magnitude of weight loss and found that the effect of specific magnitudes of weight loss on urinary incontinence did not differ for women in the weight loss compared with the control group (Pvalues range from .12 to .93). Thus, the weight loss and control group were combined for all subsequent analyses.

Table 3 shows the adjusted changes in urinary incontinence in each of the weight loss categories. As shown, there was a strong association between magnitude of weight loss and absolute percent reductions in weekly frequency of total, stress, and urge urinary incontinence at 6, 12, and 18 months such that greater weight losses were associated with greater reductions in incontinent episodes frequency. There were no significant interactions between baseline BMI (BMI of less than 35 compared with more than 35) or baseline frequency of urinary incontinence and the weight change categories for any of the measures of urinary incontinence; thus, the relationship between weight change category and improvements in urinary incontinence was not modified by initial BMI or initial severity of incontinence. Similarly, women in the various weight loss categories did not differ in their reported use of the strategies described in the incontinence booklet.

Figure 1 shows the cumulative percentage of women who experienced 0% to 100% reductions in total urinary incontinence episodes at 6, 12, and 18 months, respectively, within each of the weight change categories. At 6 months, the proportion of women who achieved any given degree of improvement in urinary incontinence was lowest in the gained weight category followed by those who lost 0% to less than 5% and highest in those who lost 5% to less than 10% or 10% or greater. There was no further improvement for those who lost 10% or greater compared with those who lost 5 to less than 10% (P=.47). An identical pattern was seen at 12 months (P=.78); however, at 18 months, the gained weight category differed from all three of the weight loss categories with no difference between those who lost 0% to less than 5%, 5% to less than 10%, or 10% or greater (pairwise comparison P values from log-rank test ranged from .47 to .85).

As noted, we selected a 70% reduction in total, stress, or urge incontinent episodes per week as a clinically significant threshold. Table 4 shows the number and percentage of women in each weight loss category who achieved or failed to achieve this threshold. Using those who gained weight as the reference, we found (Table 5) that the adjusted odds of achieving at least a 70% reduction in total, stress, or urge incontinent episodes per week was significantly increased by greater weight losses (with the exception of stress incontinence at 6 months). Again, we found a strong association between weight losses of 5% to less than 10% of body weight and urinary incontinence improvement without further benefit among women with 10% or greater weight loss (P>.20 for all outcomes at 6, 12, and 18 months). Women who lost 5% to less than 10% of their body weight had 3.7 times the odds of achieving a 70% or greater reduction in total incontinent episodes compared with women who gained weight at 12 months and 2.4 times the odds at 18 months.

As seen in Table 3, the absolute changes in stress episodes were far greater than the absolute changes in urge episodes at each time point and in each category of weight loss. As a result of the large improvement in stress incontinent episodes in the weight gain group (which is used as the reference group), the relative changes in incontinent episodes and the odds of achieving a 70% reduction with greater weight loss appear smaller for stress incontinent episodes than for urge incontinent episodes.

Whereas weight losses of 5% to less than 10% were sufficient to produce improvements in frequency of incontinent episodes, changes on the pad test as a measure of 24-hour involuntary urine loss were seen only for those who lost 10 kg or greater relative to those who gained weight. Thus, a larger magnitude of weight loss may be needed to produce significant improvements on this measure of incontinence.

The women's subjective reports of satisfaction with their overall changes in urinary leakage were also strongly associated with weight loss. Approximately 75% of women who lost 5% to less than 10% of their body weight reported being moderately or very satisfied with the improvement in their leakage. Although satisfaction with urinary incontinence improvement does not always reflect the actual changes in urinary incontinence episodes,²⁸ these subjective assessments suggest a high benefit: risk ratio for a lifestyle approach to treating urinary incontinence.

It is of note that some of the women who gained weight reported improvements in their incontinence and approximately 40–50% of those who gained weight were moderately or very satisfied with these improvements. These findings may reflect the beneficial effects of joining a clinical trial with other women confronting similar issues, the provision of a booklet on behavioral approaches to incontinence, or fluctuations in the severity of incontinence over time.

These results are encouraging because weight losses of 5–10% can be achieved and largely maintained with current behavioral weight loss programs. For example, in the Diabetes Prevention Program,¹⁵ 49% of women lost at least 7% of their initial weight at 6 months and 37% were still 7% below baseline after an average of 2.8 years of intervention. Similarly, in a large cohort of overweight individuals with diabetes, 55.2% lost over 7% of their body weight at 1 year.²⁹

Whereas other treatments for incontinence, including both behavioral and pharmacologic approaches, are targeted to urinary incontinence alone, weight loss has a wide spectrum of benefits for overweight and obese women. Several studies show that modest weight losses of 5–10% of body weight are associated with improvements in a range of health outcomes, including reducing the risk of developing noninsulin-dependent diabetes mellitus and controlling and preventing hypertension.^15–18 A sustained decrease in urinary incontinence can now be added to the extensive list of health improvements associated with modest weight loss.

Strengths of this study include the large, diverse, well-characterized cohort of overweight and obese women, the use of a standardized lifestyle intervention program, the validated outcome measures collected by blinded assessors, and the excellent follow-up through 18 months. Participants in this trial reported levels of incontinence (mean of 24 episodes per week) that appear similar to cohorts of women undergoing surgery for incontinence³⁰ (mean of 22.4 episodes per week) and in trials of incontinence medication and a continence pessary.^31,32 However, in interpreting our findings, it is important to note that we are reporting associations between categories of weight change and urinary incontinence outcomes; participants were not randomly assigned to different categories of weight loss. Thus, the groups may not have differed only in weight loss. Most notably, our lifestyle intervention included both weight loss and physical activity; thus, changes in physical activity as well as weight loss may contribute to the urinary incontinence improvements reported here. However, to adjust for these possible confounders, we have added key variables to our multivariable statistical models, including demographic characteristics, use of pelvic floor exercises, and physical activity, in examining our results.