Genetic Variants, Lifestyle Factors and Changes in Body Fat Percentage in Young Adults: An Exploratory Prospective Study

Background/Objectives: We examined whether eight obesity-associated polymorphisms and four lifestyle exposures were associated with changes in body fat percentage (BF%) in young adults. Methods: Eighty-four young adults of European ancestry (82% women; age, 20.5 ± 2.6 years) from Kazan, Russia, underwent bioelectrical impedance analysis at baseline and follow-up, 1.9 ± 0.8 years apart. A subsample was genotyped for eight obesity-associated polymorphisms (ADCY3 rs11676272, RERE rs301806, FTO rs1421085, TNRC6B rs4821940, PATJ rs12140153, TFAP2B rs734597, MMS22L rs9385223, and SLC22A3 rs9364554). Dietary intake and sleep characteristics were assessed using questionnaires, including the Pittsburgh Sleep Quality Index (PSQI). Follow-up BF% was analyzed using ANCOVA adjusted for baseline BF%, follow-up duration, age and sex, with false discovery rate (FDR) correction for multiple testing. Results: Mean BF% increased by 1.61 ± 3.97 percentage points (pp) in men (p = 0.14) and by 0.25 ± 4.43 pp in women (p = 0.65), with wide inter-individual variation. Compared with participants in the bottom quartile (BF% change ≤ −2.45 pp), those in the top quartile (BF% gain ≥ 3.38 pp), i.e., those who gained more body fat, were more likely to carry the FTO rs1421085 T allele (p = 0.02; FDR q = 0.157), consumed fewer vegetables (p = 0.004; FDR q = 0.036), and had longer sleep duration (p = 0.028; FDR q = 0.126). Furthermore, poorer subjective sleep quality was associated with higher follow-up BF% in the whole cohort (β = 1.96 pp per PSQI point; 95% CI, 0.23–3.68; p = 0.027; FDR q = 0.11). Conclusions: Given the modest sample size and relatively short follow-up, few associations were detected, most of which did not remain significant after correction for multiple comparisons. Nevertheless, vegetable intake and sleep characteristics may be relevant to changes in adiposity during young adulthood.