APOB and metabolic syndrome: The relative abundance of the Christensenellaceae family has a negative relationship with BMI, LDL, and apolipoprotein B as well as features of metabolic syndrome such as obesity and hypertriglyceridemia (Waters and Ley, 2019; Li et al., 2020), and was positively associated with HDL (Fu et al., 2015; Hibberd et al., 2019).