The association between a healthy and sustainable diet based on the planetary health diet index (PHDI) and the odds of postmenopausal osteoporosis.

Abstract

Background: Osteoporosis is a widespread metabolic bone disorder among postmenopausal women and is characterized by reduced bone mineral density and an elevated risk of fractures. Beyond the role of individual nutrients in bone health, increasing attention has been paid to the broader implications of dietary patterns for environmental sustainability. Food production systems, particularly those heavily dependent on animal-based foods, are among the main contributors to greenhouse gas emissions, highlighting the need for dietary approaches that support both human health and environmental protection. In this context, the Planetary Health Diet Index (PHDI) has been developed as an integrated measure of diet quality and sustainability, promoting plant-based foods and limiting environmentally intensive food sources. Accordingly, this study examined the association between adherence to the PHDI and the risk of osteoporosis among postmenopausal women in Tehran.

Methods: In this hospital-based case-control study, 440 postmenopausal women (220 cases and 220 controls) were recruited. Bone mineral density was determined using dual-energy X-ray absorptiometry (DEXA). Dietary intake, demographic variables, and physical activity were assessed through validated questionnaires. Independent t-tests and multivariable logistic regression analyses adjusted for age, body mass index (BMI), and total energy intake were conducted using SPSS version 27. Statistical significance was set at p < 0.05.

Results: A total of 440 postmenopausal women (220 cases and 220 controls) were included in the study. Compared with controls, women with osteoporosis had significantly higher body weight (74.81 ± 11.92 vs. 71.01 ± 9.85 kg; p < 0.001) and body mass index (29.09 ± 4.13 vs. 27.91 ± 5.47 kg/m²; p = 0.011), and lower physical activity levels (1531.86 ± 830.59 vs. 1967.24 ± 866.34 MET-min/week; p < 0.001). In multivariable logistic regression analyses adjusted for age, BMI, total energy intake, alcohol consumption, and physical activity, higher PHDI scores were independently associated with lower odds of osteoporosis (adjusted OR = 0.923; 95% CI 0.905-0.941; p < 0.001), corresponding to a 7.7% reduction in the odds of osteoporosis per one-unit increase in PHDI score. When PHDI was categorized into tertiles, and using the highest tertile as the reference group, women in the lowest and middle tertiles had significantly higher odds of osteoporosis after adjustment for confounders (adjusted OR = 12.42; 95% CI 6.70-23.04; P < 0.001 and adjusted OR = 2.02; 95% CI 1.18-3.45; P = 0.011, respectively). The crude ORs for the lowest and middle tertiles were 12.66 (95% CI 12.10-13.22; P < 0.001) and 1.92 (95% CI 1.43-2.41; P = 0.009), respectively, indicating that adjustment for confounders did not materially change the estimates.

Conclusion: In this case-control study, greater adherence to the PHDI was associated with lower odds of postmenopausal osteoporosis. However, given the observational design, these findings should be interpreted as an association rather than a causal effect. Prospective cohort studies and randomized controlled trials are warranted to confirm these results and to establish the temporal relationship between sustainable dietary patterns and bone health.