Introduction

Obesity has been referred to as an “epidemic” due to its prevalence and related physical and mental health (e.g., depression) comorbidities [1, 2]. To address the obesity public health crisis, developing treatments that can be broadly disseminated is critically important [3]. To increase weight loss treatment dissemination, motivational interviewing (MI) for weight loss in primary care has garnered much clinical and research attention [4]. MI is an evidence-based, time limited, person-centered approach for strengthening a person’s motivation and commitment to change [5], and MI may be implemented effectively by general medical practitioners to treat health-related behavioral concerns [6].

Despite the clinical enthusiasm related to MI for weight loss in primary care, the empirical support is mixed and particularly lacking long-term follow-up data [4]. Of the numerous MI for weight loss trials in primary care, only three examined outcomes 12 months following treatment cessation [6,7,8,9]. These follow-up assessments suggest no significant average weight loss benefit for participants receiving MI when compared to usual care [8, 9] or attention control [7]. The data do suggest, however, at these longer-term follow-up assessments that the MI interventions were related to increased walking and decreased cholesterol [8]. Only one of these studies assessed depression symptoms, and treatment-related improvements reported at 3-month follow-up were not maintained at the 12-month follow-up assessment [7]. The latter study was the first to our knowledge to compare MI with a web-support component for weight loss in primary care to usual care and to a control intervention matched for attention also with a web-support component [7, 10]. This attention control intervention (nutrition psychoeducation) resulted in superior weight loss compared to usual care, whereas MI did not, at post-treatment and 3-month follow-up [10]. By 12-month follow-up assessment, weight loss for participants in nutrition psychoeducation trended towards significance compared to MI participants.

Based on the signal for longer-term MI benefits from Hardcastle and colleagues [8] and rather surprising positive results of the nutrition psychoeducation intervention [7, 10], a small weight-loss trial assessed if combining MI with nutrition psychoeducation (MINP) and a web-support component may bolster promising weight loss outcomes in primary care [11]. This trial also addressed important limitations of the MI for weight loss in primary care literature by utilizing clinicians typically available in primary care centers, testing intervention materials that are publically or easily accessible to primary care centers, and rigorously assessing MI fidelity. The MINP combination treatment resulted in significant weight loss and decreased depression symptoms at post-treatment and 3-month follow-up [11]. Longer-term durability of this intervention, however, still is unknown.

The current study aimed to assess the effects of the MINP with a web-support component weight loss intervention in primary care 12 months following treatment cessation. We hypothesized that the MINP trial in primary care would result in significant decreases in weight, and related physiological and psychological improvements, 12 months following treatment.

Methods

Participants

Participants were 31 adults (body mass index [BMI] between 25 and 55) with overweight or obesity receiving primary care services at an urban university-based medical healthcare center. They were recruited through primary care provider referrals and flyers placed in waiting/patient rooms. Recruitment was intended to enhance generalizability by utilizing relatively few exclusionary criteria which included: over 65 years old, severe psychiatric (e.g., schizophrenia) or medical problems (e.g., cardiac disease), pregnancy/breastfeeding, uncontrolled liver, thyroid disease, hypertension, or diabetes, or very irregular internet and telephone access.

Procedures

The study had University Human Investigation Committee (i.e., IRB) approval and all participants provided written informed consent. (See [11] for previously published procedures and results through 3-month follow-up). Treatment was provided by medical assistants. All participants were enrolled in MINP, a five-session, manualized, 3-month intervention. All participants received the same treatment, there was no randomization or control condition.

The first session included an initial 60-min in-person individual session. MINP included guidelines to help medical assistants flexibly apply MI focused on enhancing motivation for weight loss and treatment adherence and could include participants setting self-identified specific weight-related goals. Using MI (i.e., a nonjudgmental and collaborative approach, conveying respect, acceptance, and compassion with a stance toward evoking the participants’ motives for change using open-ended questions and focusing on change planning while avoiding the use of MI-inconsistent strategies such as confrontation or lecturing), the in-person session also included basic nutrition psychoeducation (e.g., portion sizes). Participants also received training in the use of (1) a free weight loss website (Livestrong.com; web-support component) and (2) a LEARN manual [13], a well-researched weight loss manual. Patients received four additional 20-min MINP sessions once every 3 weeks (i.e., two in person, two on phone). At subsequent appointments, if participants desired, each session started with a discussion of the participants’ specific and measurable behavioral weight-loss goals (e.g., walk 30 min 3 times a week, track food intake on Livestrong.com 4 days a week) from the previous session, personalized feedback on food journals, and ended with setting new goals, including problem-solving as necessary for when goals were not reached. Participants were contacted via phone, email, and postal mail to participate in the follow-up assessment and reimbursed $50 for completing the 12-month follow-up assessment.

Measures

The Beck Depression Inventory (BDI) [12] is a self-report measure of current depression symptoms with higher scores reflecting increased severity; the BDI has excellent reliability and validity. The BDI was completed via a secure online survey (i.e., Qualtrics) sent to the participants’ email address.

Physical measurements

Measurements were taken in person by master or doctoral level research assistants following standardized procedures. Height was measured at baseline using a wall measure. Weight was measured using a digital scale. Blood pressure and pulse were measured using automated blood pressure monitors, recorded readings were an average of two measurements. Participants were provided standardized instructions and a tape measure for measuring their own waist circumference using the umbilicus as a reference point at in-person assessments.

Statistical analyses

Power analysis was completed using Gpower and previous relevant literature. This was a one-sample within-subjects repeated design treatment trial. For each outcome, linear mixed models were used to model compound symmetry (CS) and unstructured (UN) covariance patterns across time (baseline and 12-month follow-up). The best-fitting model was chosen based on Schwartz-Bayesian Criterion (BIC). This approach allowed for incorporating all available data from each subject [14]. A one-sample t test was used to assess percent weight reduction. All tests were two-sided and considered significant at the alpha = 0.05 threshold. Analyses were completed using SAS, version 9.4 (Cary, NC, USA).

Results

Participants had a mean age of 48.4 years (SD = 10.6, range 24–63) and a mean BMI of 36.2 kg/m2 (SD = 6.1). The sample was primarily female (87.1%, n = 27). Participants identified as the following races and ethnicities: 41.9% (n = 13) as White, not Hispanic; 9.7% (n = 3) as White, Hispanic; 38.7% (n = 12) as Black, not Hispanic; 3.2% (n = 1) as bi/multiracial; and 6.5% (n = 2) as “other.” Retention was excellent, 83.9% (n = 26/31) of participants completed the 12-month follow-up (i.e., 15 months after treatment start). One participant’s data were excluded due to pregnancy before the 12-month follow-up assessment.

Overall, participants’ BMI was significantly lower at 12-month follow-up when compared to baseline (F(1, 22) = 6.19, p = 0.021). The percentage weight change at 12-month follow-up also was significant (t(22) = − 2.40, p = 0.025; d′ = 0.5), averaged − 3.0% (SD = 6.0), and ranged from − 15% lost to 7% gained. Approximately one-third of participants (34.8%) achieved or maintained 5% or more weight loss at 12-month follow-up.

Diastolic blood pressure (F(1, 22) = 8.33, p = 0.009) and pulse (F(1, 21) = 11.2, p = 0.003) decreased significantly from baseline to 12-month follow-up. Systolic blood pressure (F(1, 22) = 3.0, p = 0.097) and waist circumference (F(1, 22) = 3.24, p = 0.086) did not change significantly over time. Depression symptoms (BDI) decreased significantly across time (F(1, 23) = 9.91, p = 0.005). See Table 1.

Table 1 Assessment descriptive data
Full size table

Discussion

The current results preliminarily indicate that MI plus nutrition psychoeducation (MINP) weight loss treatment, delivered in primary care by medical assistants, was associated with improvements in weight (medium effect size based on d′), diastolic blood pressure, pulse, and depression symptoms 12 months following treatment cessation. Approximately one-third of participants also reached or maintained a 5% loss of initial body weight. There were no significant changes to systolic blood pressure or waist circumference.

To our knowledge, this is the first MI intervention for weight loss in primary care to report significant weight loss 12 months after treatment. On one hand, 34.8% of current participants reached or maintained 5% or more loss of initial body weight (~ 140 min total of intervention), a goal associated with attenuating harmful weight-related health consequences [15, 16]. Similar 12-month follow-up studies reported 4.8–7% [7, 9] and 17.4% [9] of participants achieving this 5% weight loss goal for those receiving MI-only or nutrition psychoeducation-only, respectively [7]. On the other hand, however, when the current combination MINP (− 3% average weight loss) results are descriptively compared to nutrition psychoeducation-only (− 1.7% average weight loss) and MI-only (+ 1.3% average weight gain) results at 12-month follow-up [6], the resources required for proper MI training, implementation, and supervision in primary care (which are likely to exceed that required for basic nutrition psychoeducation) may not be cost effective. Replication with a larger sample, control group, and cost effectiveness analyses may be warranted.

The observed improvements in depression symptoms, diastolic blood pressure, and pulse are inconsistent with previous literature. There were no significant physical measurement [7, 8] or depression [7] improvements by 12-month follow-up in previous MI for weight loss in primary care trials. The depressive symptom improvements are not surprising, however, given that depression and obesity often co-occur and treating one of the conditions is known to positively impact the other [2]. It is important to note that the average BDI scores, at both baseline and 12-month follow-up, fell within the minimal range. Future research with larger samples may wish to examine outcomes for individuals with elevated BDI scores. The potential improvements would need to be replicated and factored into future cost-effectiveness analyses.

It is important to consider the limitations of the current study. Most notably, this was a small, nonrandomized sample and the results may not generalize to nontreatment seeking populations. There was no direct comparison condition or overweight to obesity comparisons due to limited power. Based on other similar trials, participants enrolled in usual care, on average, do not experience significant weight loss [8,9,10] and in fact, this population tends to gain weight overtime [17]. Further, the waist circumference measurements were completed by the participants (and not trained assessors) which introduced more potential error for this data point.

To conclude, the MI plus nutrition psychoeducation (MINP) weight-loss trial in primary care resulted in statistically significant weight loss at post-treatment, 3-month follow-up [11], and 12 months following treatment cessation for individuals with overweight or obesity. The current trial provides preliminary and modest support for possible longer-term benefits of MI combined with nutrition psychoeducation. Future studies utilizing fidelity tested MI should include a cost effectiveness weight loss RCT within primary care to further clarify the current results, particularly in comparison to attention-control conditions, as comparable results may be achieved with nutrition psychoeducation only.

What is already known on this subject?

The motivational interviewing (MI) for weight loss in primary care data is lacking longer-term assessments, existing studies suggest MI resulted in no weight loss but increased walking and decreased cholesterol.

What does this study add?

Motivational interviewing plus nutrition psychoeducation treatment was associated with significant weight, physical, and psychological improvements 12 months following treatment cessation, and 1/3 of participants also reached a 5% weight loss.