Methodology/Principal findingsTo investigate whether helminth-derived molecules have therapeutic effects on high-fat diet (HFD)-induced obesity, we isolated total lysates from Trichinella spiralis muscle larvae. We then checked the anti-obesity effect after intraperitoneal administration and intraoral administration of total lysate from T. spiralis muscle larvae in a diet-induced obesity model. T. spiralis total lysates protect against obesity by inhibiting the proinflammatory response and/or enhancing M2 macrophages. In addition, we determined the effects of total lysates from T. spiralis muscle larvae on anti-obesity activities in 3T3-L1 preadipocytes by investigating the expression levels of key adipogenic regulators, including peroxisome proliferator-activated receptor gamma (PPARγ), CCAAT-enhancer-binding protein alpha (C/EBPα) and adipocyte protein 2 (aP2). Oil Red O staining showed that the total lysates from T. spiralis muscle larvae decreased the differentiation of 3T3-L1 preadipocytes by decreasing the number of lipid droplets. In addition, the production levels of proinflammatory cytokines IL-1β, IL-6, IFN-γ and TNF-α were examined by enzyme-linked immunosorbent assay (ELISA). T. spiralis total lysates decreased intracellular lipid accumulation and suppressed the expression levels of PPARγ, C/EBPα and aP2.