The invention relates to a strain of Bacteroides uniformes with registration number CECT 7771, and to the cellular constituents, metabolites and/or secreted molecules thereof. The invention also relates to a composition (nutritional or pharmaceutical) comprising at least one of the previous products. The invention further relates to the use of a strain of Bacteroides uniforms, preferably CECT 7771, or of the cellular constituents, metabolites and/or secreted molecules of said strain, or of a composition comprising same, for the prevention and/or treatment of alterations such as excess weight, obesity, adipocyte hypertrophy, hepatic steatosis or fatty liver, dyslipidemia, hyperglycemia, insulin resistance and diabetes, metabolic syndrome, hypertension, cardiovascular diseases, dysfunction of the immune system, reduced defenses against infections, and imbalance in the composition of the intestinal microbiota.