Length of Overnight Fasting and 6-year Weight Change in the Cancer Prevention Study-3

Longer overnight fasting (ONF) is a potential strategy for weight control. Although promising, the evidence from large population-based studies is limited. To examine the association of self-reported ONF duration with 3- and 6-y weight change in the American Cancer Society’s Cancer Prevention Study-3 prospective cohort. United States adult Cancer Prevention Study-3 participants completed a 24-h validated meal and snack timing and frequency grid (weekday and weekend) in 2015, from which weighted ONF hours were calculated. Participants reported body weight in 2015, 2018, and 2021. Three- and 6-y weight change (kg, and % body weight) were assessed. Among 104,420 mostly female (78.5%) participants aged 52.7 ± 9.5 (standard deviation) y followed for 6 y, a 1-h increase in ONF length was associated with a small but statistically significant reduction in weight gain over 3- and 6-y periods [multivariable-adjusted mean difference in % body weight = −0.02, 95% confidence interval (CI): −0.05, −0.00, P = 0.03 and −0.04, 95% CI: −0.07, −0.01, P < 0.01, respectively]. The mean difference of 6-y % reduction in weight gain was slightly greater among individuals with overweight (−0.05, 95% CI: −0.10, 0.00, P = 0.05) and obesity (−0.06, 95% CI: −0.12, 0.01, P = 0.08) compared with those with healthy body mass index (−0.03, 95% CI:−0.07, 0.01, P = 0.13) or underweight (0.16, 95% CI: −0.04, 0.36, P = 0.13, Pinteraction < 0.0001). Stronger associations were observed among those ≤55 y than 56+ (P < 0.001), and those with higher waist circumference (Pinteraction < 0.0001) but not by sex or earlier/later fasting period. Longer ONF was associated with slightly lower body weight in adult males and females over 6 y that was stronger among those with overweight or obesity, higher waist circumference, and those aged ≤55 y. The magnitude of weight change, although in the hypothesized direction, suggests that prolonged ONF may have modest impact on weight control over time.