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Objective: To investigate whether the paradoxical weight gain associated with dieting is better related to genetic propensity to weight gain than to the weight loss episodes themselves., Subjects: Subjects included 4129 individual twins from the population-based FinnTwin16 study (90% of twins born in Finland 1975-1979). Weight and height were obtained from longitudinal surveys at 16, 17, 18 and 25 years, and number of lifetime intentional weight loss (IWL) episodes of more than 5 kg at 25 years., Results: IWLs predicted accelerated weight gain and risk of overweight. The odds of becoming overweight (body mass index (BMI)≥ 25 kg m(-2)) by 25 years were significantly greater in subjects with one (OR 1.8, 95% CI 1.3-2.6, and OR 2.7, 1.7-4.3 in males and females, respectively), or two or more (OR 2.0, 1.3-3.3, and OR 5.2, 3.2-8.6, in males and females, respectively), IWLs compared with subjects with no IWL. In MZ pairs discordant for IWL, co-twins with at least one IWL were 0.4 kg m(-2) (P=0.041) heavier at 25 years than their non-dieting co-twins (no differences in baseline BMIs). In DZ pairs, co-twins with IWLs gained progressively more weight than non-dieting co-twins (BMI difference 1.7 kg m(-2) at 16 years and 2.2 kg m(-2) at 25 years, P<0.001)., Conclusion: Our results suggest that frequent IWLs reflect susceptibility to weight gain, rendering dieters prone to future weight gain. The results from the MZ pairs discordant for IWLs suggest that dieting itself may induce a small subsequent weight gain, independent of genetic factors.

Background: The effects of weight-loss attempts on long-term weight gain remain unclear., Objective: The objective was to study prospectively how attempts to lose weight relate to future risk of major weight gain (>10 kg) and whether familial factors affect this relation., Design: Participants in the Finnish Twin Cohort (3536 men and 4193 women aged 18-54 y at baseline) were followed up for 6-15 y. The role of familial factors was studied in 1705 twin pairs in this cohort who were discordant for weight-loss attempts at baseline. Baseline (1975) and follow-up (1981 and 1990) data-including weight, weight-loss attempts (dieting), and selected confounders-were obtained via mailed questionnaires., Results: Average weight gain was at most weakly associated with weight-loss attempts. The risk of major weight gain for subjects attempting to lose weight at baseline was greatest among initially young (18-29 y) men (over 6 and 15 y, respectively-odds ratios: 2.01 and 1.74; 95% CI: 1.13, 3.57 and 1.11, 2.75) and middle-aged (30-54 y) women (over 6 and 15 y, respectively-2.43 and 1.52; 1.33, 4.42 and 1.06, 2.22) and persisted after potential confounders were controlled for. These risks decreased and became nonsignificant in the pairwise twin analysis, suggesting that the relation between dieting and subsequent major weight gain may also have a familial component., Conclusions: Weight-loss attempts may be associated with subsequent major weight gain, even when several potential confounders are controlled for. Genetic and familial factors may contribute to this association.