JAR life · 5 authors, 2 centres
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This one-year study of 52 midlife women (aged 40–60) found that greater age and increases in energy intake from summer to fall were the strongest predictors of increases in percentage body fat (%BF) by spring. Summer-to-winter %BF gains were not fully reversed by spring, especially in older women. The findings suggest that midlife women, particularly older women, should monitor their diet in the fall to prevent gradual body fat accumulation.
**Background:** Obesity affects 43.3% of US women aged 40 and older, and midlife women are at particular risk for weight gain and adverse changes in body composition. Age is positively correlated with weight gain, and seasonal changes in diet and physical activity may exacerbate this. The study aimed to determine whether age and seasonal changes in sedentary activity (sedAct), moderate-to-vigorous physical activity (MVPA), and energy intake (EI) predict changes in percentage body fat (%BF) in midlife women over one year.
**Methods:** This was a longitudinal, observational study of 52 midlife women (mean age 49.44 years, SD 5.82) from Grand Forks, North Dakota. Participants were observed across four seasons (summer, fall, winter, spring). %BF was measured via whole-body Dual Energy X-ray Absorptiometry (DXA) once per season. EI was assessed using the ASA24® (36 recalls per participant, ~10 days apart). Physical activity was measured with GTX3 accelerometers worn for 7 consecutive days, 12 hours/day each season. SedAct and MVPA were calculated using the Crouter algorithm and Freedson cut-points. Hierarchical multiple regression (MRC) models tested whether age and seasonal change scores (summer-to-fall, summer-to-winter, summer-to-spring) in sedAct, MVPA, and EI predicted summer-to-spring Δ%BF. Repeated measures ANCOVA (with age as covariate) assessed seasonal %BF changes.
**Key Results:** The season-by-age interaction for %BF was significant (F(1.93, 94.53) = 4.09, p = .021). Most participants (60%) experienced %BF increases from summer (M = 37.73%, 95% CI [35.84, 39.61]) to winter (M = 38.15%, 95% CI [36.20, 40.09]), and these increases were not reversed by spring (M = 37.88%, 95% CI [35.94, 39.82]). In the hierarchical MRC model 1 (summer-to-fall changes), age (β = 0.274, p = .040) and summer-to-fall increases in EI (β = 0.335, p = .012) were significant predictors of summer-to-spring Δ%BF (full model R² = .25, F(4, 47) = 3.89, p = .008). In model 2 (summer-to-winter changes), age was the only significant predictor (β = 0.332, p = .019; full model R² = .26, F(4, 46) = 3.93, p = .008). Model 3 (summer-to-spring changes) was not significant (R² = .18, F(4, 47) = 2.51, p = .054). Changes in MVPA and sedAct were not significant predictors in any model. Secondary analyses showed that sedAct increased in winter relative to summer (F(1, 50) = 9.56, p = .003) and MVPA was lower in winter than summer (F(1, 50) = 15.52, p < .001). Bivariate correlations showed that summer-to-fall increases in EI were associated with sustained %BF increases into both winter (r(50) = .37, p = .009) and spring (r(50) = .37, p = .007). No relationship was found between %BF and FSH levels.
**Clinical Implications:** The findings suggest that age-related increases in %BF in midlife women are exacerbated by increased energy intake during the fall. Summer-to-winter %BF gains are not fully reversed by spring, particularly in older women, contributing to gradual adiposity accumulation over time. Clinicians should counsel midlife women, especially those over 49, to monitor dietary intake during the fall months to mitigate seasonal %BF increases. Although MVPA and sedAct did not predict %BF changes, the study found that MVPA was far below recommended levels (37–44 min/week vs. 150 min/week recommended), and sedAct increased in winter, highlighting additional targets for health promotion. Limitations include the small, geographically specific sample (northern North Dakota) and the 9-month observation period (not covering a second summer).