Alpha-keto-isovalerate as a biomarker of prebiotic efficacy for weight gain prevention

A method for predicting and/or quantifying the response of a subject to prebiotics in the prevention of diet induced weight gain, comprising:

• a) determining a level of alpha-keto-isovalerate in a urine sample obtained from a subject that has consumed prebiotics using 1H-NMR spectroscopy or mass spectroscopy, and
• b) comparing the subject's alpha-keto-isovalerate level to a predetermined reference value by mapping or graphing the urinary excretion of alpha-keto-isovalerate, wherein a decreased alpha-keto-isovalerate level, or an absence of change in the alpha-keto-isovalerate level, in the urine sample compared to the predetermined reference value indicates that the administration of prebiotics is effective in the prevention of diet induced weight gain in the subject,
• and wherein the predetermined reference value is based on an average alpha-keto-isovalerate level in a control population of subjects consuming a high fat diet and the change of alpha-keto-isovalerate level is determined relative to a cut-off value.