Abstract
BACKGROUND: Evidence on the relationship between dietary fat intake and bone mineral density (BMD) remains inconsistent, particularly regarding sex- and site-specific differences in femoral bone health among older adults. METHODS: This cross-sectional study analyzed data from the 2017-2018 National Health and Nutrition Examination Survey (NHANES) to explore associations between dietary fat intake and femoral BMD in U.S. adults aged ≥ 50 years. Femoral BMD at four anatomical sites (total femur, neck, trochanter, intertrochanteric region) was measured using dual-energy X-ray absorptiometry (DXA). A high-fat diet was defined as > 35% of total energy intake from fat (%E). Sex-stratified, survey-weighted multivariable logistic regression models were applied to examine associations with osteopenia/osteoporosis after adjustment for relevant covariates. RESULTS: Among 1,127 adults aged ≥ 50 years (612 men; 515 women), high-fat diet consumption was more prevalent in men (59.5%) than in women (54.0%). Women showed a higher baseline prevalence of osteopenia/osteoporosis, approximately 1.7-2.0 times that of men across femoral sites. After multivariable adjustment, a high-fat diet was associated with lower odds of femoral neck osteopenia/osteoporosis in men (OR = 0.45, p = 0.03) and women (OR = 0.43, p = 0.04), with no significant associations observed at other sites. Sensitivity and substitution analyses yielded directionally similar results, suggesting a modest, potentially protective association when carbohydrates were replaced with dietary fat. Restricted cubic spline and exploratory dose-response analyses demonstrated a protective effect of moderate fat intake in both sexes, with distinct sex-specific patterns: a nonlinear trend in women-with maximal protection observed at 40-45%E (OR = 0.22, p = 0.02)-and a linear inverse association in men, with the lowest risk at 35-40%E (OR = 0.35, p = 0.01). CONCLUSIONS: These findings suggest a modest, sex- and site-specific association between dietary fat intake and femoral bone health in older adults. The observed relationships should be interpreted as exploratory and hypothesis-generating, emphasizing the need for longitudinal studies to confirm causality. Maintaining balanced macronutrient intake, rather than strict fat restriction, may be a reasonable dietary strategy for preserving bone health in aging populations.