Are the Initiation and Maintenance of a Resistance Training Program Associated with Changes to Dietary Intake and Non-Resistance Training Physical Activity in Adults with Prediabetes?

Prediabetes is associated with an elevated risk for developing type 2 diabetes (T2DM) and associated cardiovascular complications. Lifestyle factors such as physical activity (PA) and dietary intake are strongly implicated in the development of metabolic disease, yet few Americans meet PA and dietary recommendations. Middle-aged and older adults are at increased risk for developing prediabetes and T2DM due to age-related muscle loss, increased fat mass, and alterations in glucose handling. In addition, this segment of the population is least likely to meet PA guidelines, particularly the resistance training (RT) recommendation of completing a whole body routine 2x/week. Ideally, individuals would alter their lifestyle in order to meet PA guidelines and habitually consume a healthy diet, to decrease disease risk. However, behavior change is difficult and optimal strategies to promote and maintain changes have yet to be determined. Furthermore, behavior change interventions tend to be time-, cost-, and resource-intensive, limiting the ability for efficacious programs to be translated into community settings and broadly disseminated. Evidence suggests that health-related behaviors, particularly diet and exercise habits, tend to cluster together. Thus, intervening on one behavior (e.g. PA) may elicit a spillover effect, promoting alterations in other behaviors (e.g. diet), though findings to date are conflicting. The purpose of this dissertation was to determine if participation in a social cognitive theory-based RT program targeting the initiation and maintenance of RT exerts a spillover effect and is associated with alterations in dietary intake and/or non-RT PA in a population at risk for T2DM. Data from the 15-month Resist Diabetes study was analyzed to evaluate this possibility. Sedentary, overweight/obese (BMI 25-39.9 kg/m2 ), middle-aged and older (50 -69 years) adults with prediabetes (impaired fasting glucose and/or impaired glucose tolerance) completed a 3 month initiation phase where they RT 2x/week in a lab-gym with an ACSM-certified personal trainer. Participants then completed a 6-month faded contact maintenance phase, and a 6-month no-contact phase during which they were to continue RT on their own in a public facility. No advice or encouragement was given to participants to alter dietary intake or non-RT PA habits. At baseline, and months 3, 9, and 15, three non-consecutive 24-hour diet recalls were collected to evaluate dietary intake and quality, the Aerobics Institute Longitudinal Study Questionnaire was completed to evaluate non-RT PA, and body mass, body composition, and strength (3 repetition maximum on leg and chest press) were measured. At months 3, 9, and 15 social cognitive theory (SCT) constructs were assessed with a RT Health Beliefs Questionnaire. In the first study, dietary intake was assessed at baseline and after 3 months of RT. Using paired sample t-tests, reductions in intake of energy (1914 ± 40 kcal vs. 1834 ± 427 kcal, p = 0.010), carbohydrate (211.6 ± 4.9 g vs. 201.7 ± 5.2 g, p = 0.015), total sugar (87.4 ± 2.7 g vs. 81.5 ± 3.1 g, p = 0.030), glycemic load (113.4 ± 3.0 vs. 108.1 ±3.2, p= 0.031), fruits and vegetables (4.6±0.2 servings vs. 4.1±0.2 servings, p= 0.018), and sweets and desserts (1.1 ± 0.07 servings vs. 0.89 ± 0.07 servings, p = 0.023) were detected from baseline to month 3. No changes in other dietary intake variables were observed. These findings supported additional investigation in this area. The second study assessed changes in overall diet quality (Healthy Eating Index [HEI]-2010 scores) and non-RT PA over the initiation, maintenance, and no-contact phases using mixed effects models. Demographic, physiological, and psychosocial factors that may predict alterations to diet quality and non-RT PA were also explored. Energy and carbohydrate intake decreased with RT (β= -87.9, p=.015 and β= -16.3, p<.001, respectively). No change in overall dietary quality (HEI-2010 score: β= -0.13, p=.722) occurred, but alterations in HEI-2010 sub-scores were detected. Maintenance of RT was accompanied by an increase in MET-min/week of total non-RT PA (β=153.5, p=0.01), which was predicted by increased self-regulation for RT (β=78.1, p=0.03). RT may be a gateway behavior leading to improvements in other health-related behaviors among adults with prediabetes. These results support the use of singlecomponent vs. multi-component interventions. This may have broad translational potential for the development of time-, resource-, and cost-efficient lifestyle interventions which can improve multiple health-related behaviors and decrease disease risk.