The Association between Poor Diet Quality, Physical Fatigability and Physical Function in the Oldest-Old from the Geisinger Rural Aging Study.

More perceived physical fatigability and poor diet quality are associated with impairments in physical function in older adults. However, the degree to which more perceived fatigability explains the association between poor diet quality and low physical function is unknown. We examined this relationship in 122 (66F, 56M) of the oldest-old participants from the Geisinger Rural Aging Study (GRAS). We used 24-h dietary recalls to assess the Healthy Eating Index (HEI), the Pittsburgh Fatigability Scale (PFS, 0-50) to assess perceived physical fatigability, and the PROMIS Physical Function 20a* to assess physical function. We grouped participants into three age categories: 80-84 (n = 51), 85-89 (n = 51), and 90+ (n = 20) years. Multiple linear regression revealed that a lower HEI was associated with higher PFS Physical score after adjusting for age group, sex, body mass index, and the number of medical conditions (p = 0.001). Several macro- and micro-nutrient intakes were also lower in those reporting more (≥15) compared to less (<15) perceived physical fatigability. Mediation analysis revealed that PFS Physical scores explained ~65% (p = 0.001) of the association between HEI total score and PROMIS19 Physical Function score. Poor diet quality may contribute to more perceived physical fatigability, which could exacerbate impairments in the oldest-old's physical function.