Exploring the relationship between soluble fiber intake and bone mineral density in endurance athletes

Background: Dietary recommendations to athletes are tailored to enhance performance and accelerate recovery. Recommendations focused on these parameters are rarely made in consideration of gut or bone health. Fermentable fibers may play a role in attenuating exercise-induced inflammation and in enhancing calcium absorption; thus, augmenting bone mineral density (BMD) in endurance athletes. Objective: The purpose of this study was to determine whether a relationship could be identified between: 1) soluble fiber and anterior-posterior (AP) lumbar spine BMD among a population of endurance athletes, and 2) total fiber intake and AP lumbar spine BMD among a population of endurance athletes. The study also aimed to assess whether calcium intake, sex, and physical activity levels would influence the relationship between soluble fiber intake and AP lumbar spine BMD. Design: This cross-sectional study included 95 athletes who self-defined their primary form of physical activity as an endurance sport. Dual-energy x-ray absorptiometry scans were employed to measure AP lumbar spine BMD and body composition. A self-administered 2005 Block Food Frequency Questionnaire was provided to assess average daily consumption of macronutrients and micronutrients. Reported energy intake was used to compute an individualized Adequate Intake (AI) for total fiber for each participant, based on the Food and Nutrition Board's AI recommendation that men and women consume 14 grams of fiber per 1,000 kilocalories of energy. Physical activity habits were measured by Actical(TM) accelerometers, which were worn by a subset of 55 participants for seven days. The accelerometers measured average number of minutes spent in sedentary behavior and light, moderate, and vigorous physical activity states. To determine whether physical activity influenced the relationship between soluble fiber intake and AP lumbar spine BMD, the median time spent in combined moderate and vigorous physical activity was used to divide the population into lower and upper quartile groups, and analyses were conducted in each group and compared. To determine whether sex, meeting fiber AI recommendations, or meeting calcium Recommended Dietary Allowances (RDAs), analyses were conducted in each group and compared. Results: Data were analyzed for 95 athletes (n = 47 male athletes, 48 female athletes; 38.15 ± 10.07 years of age). Twenty-one of the 95 participants met nutrient needs for total fiber (22%), 46 participants met nutrient needs for calcium (48%), and 11 participants met nutrient needs for vitamin D (12%). Fat-free mass, body mass index, and dietary vitamin D intake were significantly correlated with AP spine lumbar BMD (p = 0.008, p = 0.007, p = 0.015, respectively). No significant correlations were found between soluble fiber and AP lumbar spine BMD, or between total fiber intake and AP lumbar spine BMD in the overall sample or among any of the subgroups (p > 0.05). No significant between-group differences in regression slopes were found between men and women, between participants who met or did not meet fiber AI guidelines, between participants who met or did not meet calcium RDAs, or between participants in the lower versus the upper quartiles of combined time spent in moderate and vigorous physical activity. Conclusions A majority of participants in this cohort did not meet AI recommendation guidelines for fiber consumption. Nutrient recommendations to athletes may consider encouraging increased fiber consumption to help resolve this gap. The data presented here seem to indicate that fiber intake and bone mineral density are not related. A longitudinal study is required to assess if fiber intake plays a role in bone health in athletes.