This pilot study was a randomized clinical trial to assess the effectiveness of a SG high dietary fiber (≥30 g/day) intervention to prevent excessive GWG compared to the UC group. The intervention consisted of 12 weekly 60-minute lessons led by a Registered Dietitian aimed to increase fiber intake and was delivered using group-based phone counseling. The study was approved by the University of Kansas Medical Center Institutional Review Board (#00004032) and registered at ClinicalTrials.gov (NCT03984630). The trial was registered retrospectively. All subjects provided written informed consent prior to study participation.
Subjects and randomization
Women were recruited between 10-14 weeks in gestation in three waves between August 2016 and December 2016. Participants were block randomized in groups of 6-10 into either the intervention or the usual care group at a 2:1 ratio. Randomization was computer-generated using excel software by the study statistician. Participant blinding was not possible, but study staff taking assessments were blinded to group assignment. The inclusion criteria were maternal age 18-45 years, singleton pregnancy, and body mass index (BMI) ≥22 kg/m2- 40 kg/m2. We focused on women with a BMI ≥22 kg/m2 because they have a greater likelihood of gaining excessively, retaining weight postpartum, and shifting their BMI to an overweight or obese BMI category post-pregnancy1,33. Women were excluded if they had pre-gestational diabetes, gestational diabetes, pre-eclampsia, hypertension, other metabolic abnormalities, heart disease, smoking, and drug abuse. No women developed any of these medical conditions during the 12-week intervention. A CONSORT diagram is included in Figure 1.
Single goal intervention
The intervention group was instructed to consume ≥30 g fiber/day but was not given a calorie goal. This was intentional because we wanted to remove the driver of what is known to induce weight loss (calorie goal) and determine if a fiber goal alone can prevent excess GWG. The curriculum was developed based on the theoretical framework of the social cognitive theory (SCT)34 and focused on behavior shaping, goal setting, feedback and reinforcement, social/peer support, stimulus control, and relapse prevention. Participants received a binder with all lesson materials and were taught to track their daily total fiber intake using the LSTAtHome App (LifeScience Technologies, LLC, www.lifesciencetechnologies.com). In the App, only feedback on fiber intake was provided. No information was visible to the participants for kcals, other macronutrients than fiber, or micronutrients. The curriculum encouraged a balanced diet emphasizing fruits and vegetables, whole grains, low-fat dairy, and lean protein. Lessons focused on how to increase fiber intake with education on foods that contain fiber, high fiber recipes, and how to make over recipes to increase dietary fiber content. Sample weekly menu plans with grocery and shopping guides were provided. General physical activity recommendations during pregnancy were mentioned but no focus or reinforcement was provided (no pedometers).
Participants were given a phone number with a unique access code that allowed them to enter the group session. Maestro (Oakland, CA; www. maestroconference.com) phone conference system was used and each call was recorded. The session started with a review of the prior week’s goals, whether the goal was met, and a self-reflection of why the goal was or was not met with support and encouragement from group members and the Dietitian. Each week there was a structured lesson with an assignment to be completed after the session. The session ended with goal setting, discussion, questions, and wrap-up.
Snacks high in dietary fiber
To aid in increasing dietary fiber intake while skills to increase daily fiber intake were learned in weekly lessons, intervention participants received six weeks of high fiber snacks to consume two times per day. Each snack had ≥3 grams fiber/100 kcal. The daily fiber total for the two snacks was 10-12 grams of fiber ranging in kcal from 210 – 380 kcals. The snacks consisted of shelf stable foods that were given to the participant at the baseline visit. Examples include multiple flavors of Kind bars, chickpeas, chips made from beans and lentils, and snap peas. Additionally, they received whole grain cereals including whole wheat Puffins, Krave, and Chex.
Weekly body weight
Both groups were given body weight scales and standardized instructions with details on measuring body weight. Participants were instructed to measure body weight on the same day of the week at the same time of day while wearing minimal clothing and after voiding. Body weight was reported weekly either through the LST at home App for the intervention group or by text or email for the UC group.
Three multiple-pass 24-hour dietary recalls (two weekdays and one weekend day) were collected at baseline, six weeks, and 12 weeks, by trained research staff to characterize energy and nutrient intake. Multiple-pass 24-hour recalls accurately estimate dietary intake35,36 and contain less reporting bias than diet records35,37. The recalls were entered into the Nutrition Data System for Research (NDS-R, version 2016, Minneapolis, MN) for macro- and micronutrient analysis. For the baseline and 12 week visit, one diet recall occurred in person at the study visit. For the six week recalls, all occurred via the phone.
Height and weight
Height was measured without shoes to the nearest 0.1 cm using a wall mounted stadiometer (Health o meter®, Bradford, MA) at the baseline visit using standardized procedures. Body weight was measured while the participant was wearing minimal clothing (Seca 869, Chino, CA). Pre-pregnancy BMI was calculated using the measured height and the self-reported pre-pregnancy body weight.
Gestational weight gain calculation
Body weight was assessed in the laboratory at the baseline visit (week 0) and again after the intervention. These two values were used to calculate weight gain during the intervention. At study enrollment, women self-reported their pre-pregnancy body weight. Women were contacted following delivery and reported the highest body weight measured during their pregnancy. These values were used to calculate total GWG. The 2009 IOM GWG guidelines38 classifies excessive GWG as the following for each pre-pregnancy BMI group: normal weight women >16 kg, overweight women 11.5 kg, and obese women >9 kg. In addition, the IOM GWG guidelines lists expected GWG during each trimester. A personalized weight gain range was calculated based on the gestational week the participant started and ended the intervention. If the GWG during the intervention was above the calculated range, her weight gain was categorized as excessive using published ranges38.
Maternal body composition was assessed at baseline and at the completion of the study. The three-component model of Siri et al.39 was used to estimate body composition. The Siri et al. model uses total body water (TBW) measured by bioelectrical impedance, body volume (BV) measured by the Bod Pod® and body weight. Fat mass (kg) was determined by the following equation: FM (kg) = 2.057*BV (L) - 0.786*W (L) – 1.286*BW (kg); where BV is body volume in liters, W is TBW in liters, and BW is body weight in kilograms. Percentage of body fat (% fat) was calculated as (FM/BW)*100%. Body composition testing was completed following a standardized testing protocol uniform to our Body Composition Laboratory for all populations. Briefly, women reported to the laboratory for body composition assessment after a four hour fast and refraining from exercise for 12 hours. All tests were completed on the same day. For body volume testing, subjects wore minimal tight-fitting clothing (e.g. one-piece swimsuit) and a fitted hat (Allentown Scientific Associates, Inc., Allentown, PA). Body weight was measured to the nearest 0.01 kg using an integrated electronic scale. Body weight was assessed on a separate body weight scale (Seca, Inc., Chino, CA) in the laboratory and this value was used in the Siri equation to estimate body fat. Total body water was assessed by bioelectrical impedance (Tanita, Inc., TBF-310, Tokyo, Japan).
Women were sent a questionnaire via a RedCap40 link through email to report their body weight at one year postpartum. Postpartum weight retention was calculated by subtracting the pre-pregnancy body weight obtained during the study from the reported body weight at one year postpartum. In addition, questions were asked to assess if there were any residual behaviors from the intervention maintained postpartum and what information learned during intervention was still being used. Women were asked the following question: “Do you currently use information from the intervention to guide your eating” (response yes or no), “What information do you use from the intervention to guide your eating?” (open ended response), and “Do you currently try to eat high fiber foods as part of your diet?” (response yes or no).
The power calculation was based on a prior multiple goal (MG) pilot study performed by the study team where 78% gained excessively in the control and 29% gained excessively in the MG arm (unpublished data). Using this effect size, a sample size of n=13 women per arm (1:1) was estimated to have 83% statistical power with significance set a one-sided Type I error <0.05 using a Chi-squared test to detect a difference between the proportion of women gaining excessively in the SG intervention and the control. Though we lost no subjects in the prior pilot, we factored in 20% attrition, resulting in n=16 women being recruited for the SG arm. A 2 to 1 unequal allocation of women was employed, resulting in n=16 randomized to the SG arm and n=8 randomized to the control (UC) arm. Four (all in the SG group) were lost to follow-up, therefore, the final administered power for the primary aim only, was calculated to be 72%. No differences were found between the four lost to follow-up and those that completed the study.
Means and standard deviations were calculated for all continuous variables. To determine if the proportion of women gaining excessively differed between groups, a Chi-square test was completed at the end of the intervention (12 weeks) and at the end of pregnancy. An ANCOVA assessed if there was a between group difference for the change in body weight (during the intervention, total GWG, and up to one year postpartum) and body composition. The confounding variables included in the model were time between the baseline and 12 week visits, 6 week and 12 week total dietary fiber intake (grams/day), maternal age, and parity. A one-way ANOVA assessed between group (UC vs SG) differences at each study time point: week zero (baseline), week 6, and week 12. A paired t-test assessed within group differences between each study time point. Analyses are presented for all completers (intent to treat) and by using compliant subjects. Compliance was determined by attendance at the weekly GBPC sessions. To be considered compliant, participants must have attended ≥65% of the sessions (8 of 12 lessons). SPSS (IBM, version 24) was used for data analysis and significance was set at p≤0.05 for the primary analysis only. For all other comparisons, we calculated Cohen’s d to indicate effect size41. For this report, the values indicate how large of an effect was found in the intervention relative to the control group. Cohen’s d values are: ≤0.2=negligible effect, >0.2 to ≤0.5=small effect, >0.5 to ≤0.8=medium effect and >0.8 =large effect.