Compositions and methods useful for inducing an increase in fatty acid oxidation or mitochondrial biogenesis, reducing weight gain, inducing weight loss, or increasing Sirt1, Sirt3, or AMPK activity are provided herein. Such compositions can contain synergizing amounts of a sirtuin-pathway activators, including but not limited to resveratrol, in combination with beta-hydroxymethylbutyrate (HMB), keto isocaproic acid (KIC), leucine, or combinations of HMB, KIC and leucine.