The present invention provides for microbial compositions and methods for reducing the concentration of short-chain fatty acids in the gut as a way to reduce energy uptake and manage obesity. More specifically, the invention provides for decreasing short-chain fatty acids available for absorption in the human gut, such as acetate, using one or more of: a probiotic including a homo-acetogenic, acetate oxidizing bacterium that converts acetate to H2; a probiotic including an acetoclastic methanogen; a microbial electrolysis cell comprising a homo-acetogenic bacterium and/or an acetoclastic methanogen; a prebiotic that enhances the growth or function of acetate-scavenging microbiota; or a highly selective antibiotic that targets H2-oxidizing methanogens.