Objective: Noncommunicable diseases such as obesity have become a serious global public health epidemic. This study aimed to examine whether there was an association between early life factors (with a special focus on breastfeeding) BMI, waist circumference, and the metabolome in offspring at 20 years. Methods: Data from the Western Australian Pregnancy Cohort (Raine) Study were analyzed using 1,024 plasma samples from the 20-year follow-up. A liquid chromatography, tandem mass spectrometry metabolomics approach was used to measure metabolites. Multiple linear regression models were performed and adjusted for relevant confounders. Inverse probability weighting was used to adjust the 20-year data for differences in socioeconomic variables between participants and nonparticipants since the commencement of the study. Results: An inverse association between breastfeeding and BMI or waist circumference at 20 years was lost after adjusting for parental prepregnancy BMI and maternal smoking during pregnancy. There was no significant effect of breastfeeding on metabolite concentrations at 20 years. Conclusions: Although other studies have shown associations between breastfeeding, obesity, and metabolite concentrations at younger ages, this was not evident in our study in young adults. We found no association of metabolites previously associated with waist circumference at 20 years and breastfeeding in early life.