Early‐Life Betaine Supplementation Drives Sex‐Specific Metabolic Programming in Rats, Affecting FGF21 Signaling and Energy Balance

ABSTRACT We aimed to evaluate the effects of maternal diet and betaine supplementation during the suckling period on Fgf21 expression and metabolic pathways related to FGF21 signaling and metabolic programming. Offspring of Wistar rats fed either a chow diet (CD) or a Western diet (WD) were studied at postnatal day 22 and at 7 months. During suckling, pups received betaine at a physiological dose corresponding to twice the average intake estimated from milk consumption, or a vehicle. After weaning onto a CD, all animals were switched to a WD from months four to seven. Biometric parameters, circulating markers, and gene expression in hypothalamus, retroperitoneal white adipose tissue (rWAT), and liver were analyzed, together with cecal Akkermansia muciniphila abundance. At day 22, a maternal WD reduced hepatic Fgf21 expression in both sexes; however, only males showed decreased Klb expression in rWAT, consistent with impaired FGF21 signaling. A maternal WD also reduced A. muciniphila abundance. Betaine increased Fgfr1 expression in rWAT of female offspring from control dams. By seven months, betaine supplementation in males born to WD dams increased adiposity, and insulin and leptin levels, whereas females exhibited an improved plasma lipid profile (lower NEFA and TG). Hypothalamic Drd2 and Fgfr1 expression further showed sex‐specific modulation by the maternal diet and betaine. In conclusion, betaine supplementation during suckling exerts sex‐specific long‐term effects on metabolic programming. Females showed an improved lipid profile, whereas males, particularly those exposed to a maternal WD, developed increased adiposity and altered endocrine profiles. The findings suggest that early‐life betaine supplementation can modulate long‐term metabolic outcomes through sex‐specific effects on FGF21‐related pathways.