BACKGROUND: Many firefighters have BMI above average and are considered overweight or obese. Considering that obesity is a risk factor for cardiovascular disease (CVD), one of the leading causes of death amongst firefighters, it is important that firefighters achieve and maintain a healthy body composition. Studies have shown that diets high in monounsaturated fatty acids, which are prevalent in peanut butter, can help prevent conditions such as CVD. Therefore, the purpose of this study was to determine if prolonged peanut butter consumption would alter body composition in full-time firefighters. METHODS: Forty firefighters participated in this randomized, controlled 8-week study that consisted of two groups: a peanut butter group (n=20) and a control group (n=20). After a one-week baseline period, the peanut butter group was provided peanut butter to consume five nights per week for seven weeks. The control group was to maintain their normal diet. Waist and hip circumference, BMI, and body fat percentage via bioelectrical impedance analysis (BIA) were measured at the beginning (PRE) and end (POST) of the 8-week period. Mixed-factorial ANOVAs were completed in SPSS version 29 to analyze the effects of group (peanut butter or control) and time (PRE and POST) on the following variables: waist circumference, hip circumference, body fat percentage, and BMI. Alpha level was set at .05 and Bonferroni adjustments were used for post-hoc tests when appropriate. The magnitude of Cohen’s d is reported as effect size. RESULTS: There was no significant effect of group or time, or interaction effect, on any of the variables analyzed. Favorable changes over time were observed in the peanut butter group for body fat percentage (-0.27%, CI95%: -0.69-0.15%, d = 0.33) and BMI (-0.30 kg/m2, CI95% = -0.72-0.13 kg/m2, d = 0.27), while non-significant increases were observed in the control group. CONCLUSION: Overall, within this subgroup of firefighters, there were no significant differences observed between groups over time. There was a small decrease in fat percentage and BMI in the peanut butter group, but the effect size was not significant. Consuming peanut butter 5 nights/week for 7 weeks did not negatively affect body composition and should be examined further as an affordable alternative for improving body composition.

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