Objectives Obesity and obesity-related disorders are reaching epidemic proportions worldwide. In this review, we summarize the accumulating studies that have emerged in the last few decades demonstrating that bioactives from different natural sources could potentially have anti-obesity effects. Methods We carried out an extensive search of relevant literature from Pubmed, Web of Knowledge, and other online databases for studies where anti-obesity effects were shown by compounds from natural sources. Results Appetite suppression, lipid metabolism regulation, and increase of energy expenditure are the main mechanisms by which anti-obesity effects are exerted. Plants represent the most studied natural source of anti-obesity bioactives. Camellia sinensis is the most representative species exerting several anti-obesity effects. Moreover, probiotics (bacteria which bestow health benefit), such as strains of Bifidobacteria and Lactobacillus families, and certain prebiotics (non-viable food components that confers a health benefit on the host associated with modulation of the microbiota effects), such as insulin-type fructans, have also shown capability to combat obesity. Finally, compounds from animal sources, in particular bioactive peptides derived from milk-derived whey and casein protein digestion, high dietary calcium, and omega-3s polyunsaturated fatty acids (n-3 PUFA) present in fish oils, have also shown potential anti-obesity effects. Discussion Several anti-obesity effects have been observed in different natural bioactives providing an interesting and potentially safer and more desirable treatment strategy for the development of anti-obesity functional or medical foods.