Participating women were 21% nonwhite, including 8% black and 5% Hispanic; 76% had graduated from college. Mean (SD) age was 33.0 (4.7) years and pre-pregnancy BMI 24.3 (4.8) kg/m2. At 6 months postpartum, women reported a mean (SD) of 1.7 (1.3) hours of television viewing, 0.7 (0.7) hours of walking, 0.2 (0.3) hours of moderate physical activity, and 0.2 (0.3) hours of vigorous physical activity per day. Mean (SD) reported daily intake of total fat was 30.7% (7.2) of total energy, and intake of trans fat was 1.1% (0.5) of total energy.
Mean weight retention was 0.6 kg, with a range of −17.3 to 25.5 kg; 111 mothers (12%) retained at least 5 kg. Time between delivery and reporting of 1-year postpartum weight (mean 13.2 months) was not associated with the amount of weight retained. Mothers who retained at least 5 kg were younger, heavier before pregnancy, more likely to be nonwhite, unmarried, primiparous, and have lower income, and to have gained an excessive amount of weight during pregnancy. At 6 months postpartum they reported more hours viewing television and more intake of trans fat (). In these unadjusted results, postpartum walking, light/moderate activity, vigorous activity, return to work, breastfeeding, rates of depression, and smoking habits did not differ (). Compared with pre-pregnancy, television viewing did not change (mean [SD] difference 0.05 [1.23] hours/day).22
Demographic characteristics and associations with weight retention at 1 year postpartum among women in Project Viva.
For each daily hour of television viewing, the adjusted odds ratio (OR) for retaining at least 5kg was 1.24 (95% confidence interval [CI] 1.06–1.46). Trans fat intake similarly increased risk (adjusted OR 1.33, 95% CI = 1.09, 1.62 for each 0.5% of energy from trans fat; ). Adjustment for depression, light/moderate and vigorous physical activity did not alter the detrimental effects of television viewing or trans fat intake ().
Adjusted odds ratios of women retaining at least 5 kg at 1 year postpartum.
Trans fat intake was correlated with intake of both fiber (Spearman r = −0.55) and total fat (Spearman r = 0.77). Daily intake of fiber and total fat were each associated with postpartum weight retention ≥5 kg, although neither association remained after including both nutrients. For example, the adjusted odds ratio for fiber (0.72, 95% CI = 0.56, 0.94 per 3g/day), was reduced (0.87, 95% CI = 0.63, 1.20) after adjustment for total fat intake. Similarly, the effect of total fat (OR 1.64, 95% CI = 1.18, 2.30 per 10% of energy from fat) was reduced (OR 1.46, 95% CI = 0.96, 2.23) after adjustment for fiber intake. Additional adjustment for physical activity did not alter estimates for fiber or total fat (data not shown). After adjustment for fiber intake, trans fat remained associated with substantial weight retention (OR 1.26, 95% CI = 1.02, 1.56 per 0.5% of energy from trans fat). Because of the high correlation between trans and total fat, including both nutrients in the same model resulted in substantially wider confidence intervals for both.
Walking did not appear to be associated with weight retention on bivariate analysis and after adjustment for age (). An association of walking with weight retention was found after adjustment for participant characteristics and television viewing (OR 0.66, 95% CI = 0.46–0.95), with little additional change after inclusion of trans fat intake (). Walking appeared even more beneficial after adjustment for light/moderate and vigorous activity (Model 5, ). In this model neither light/moderate (OR 1.53, 95% CI = 0.77–3.03 per daily hour) nor vigorous activity (OR 1.06, 95% CI = 0.96–1.17 per daily hour) was associated with retaining ≥5kg, perhaps because only 353 (39%) women reported any light/moderate activity and 315 (35%) any vigorous activity. The effect of walking was also substantial when the analysis was restricted to the 441 participants who reported no postpartum light/moderate or vigorous activity (OR 0.47, 95% CI = 0.25–0.88 per daily hour of walking). There was no modification of the effects of television viewing, walking, and trans fat intake by race/ethnicity, parity, or pre-pregnancy BMI (all p values for interaction terms >0.15).
When additionally included, pre-pregnancy television viewing and physical activity were not associated with weight retention, and did not alter the observed significant effects of the three postpartum behaviors (data not shown). When postpartum behaviors were evaluated in categories rather than as continuous variables, associations with postpartum weight retention were generally linear. Adjusted odds ratios for the 4th through 2nd quartiles, each compared with the lowest quartile (OR 1.0) were 0.64 (95% CI = 0.35–1.17), 0.90 (95% CI = 0.47–1.73), and 1.02 (95% CI = 0.55–1.88) for walking; 2.21 (95% CI = 1.14–4.29), 1.57 (95% CI = 0.81–3.05), and 1.13 (95% CI = 0.50–2.52) for television viewing; and 1.92, (95% CI = 1.01–3.66), 1.25 (95% CI = 0.65–2.41), and 0.70 (95% CI = 0.34–1.43) for trans fat intake.
Beneficial categories of the three behaviors were defined as trans fat intake < median (1.06% of total energy), television viewing <2 hours/day (67% of participants), and walking ≥30 minutes/day (56% of participants). Sixty-one (7%) women reported none of the beneficial behaviors, 298 (33%) reported one, 368 (41%) reported two, and 175 (19%) reported all three. Compared with those who reported none, women reporting all three beneficial behaviors had a markedly reduced risk of retaining ≥5kg (OR 0.23, 95% CI = 0.08–0.66). Odds ratios decreased linearly across those reporting 0, 1, 2, or all 3 beneficial behaviors (p for trend <0.001, see ).
Figure 1 Odds ratios of retaigning at least 5 kg at 1 year postpartum according to the number of beneficial postpartum behaviors. Beneficial behaviors defined as (1) being below the median for trans fat intake, (2) watching less than 2 hours of television daily, (more ...)