What is HMB? HMB is a metabolite of leucine (a branched-chain amino acid), helps prevent protein breakdown. Hmb has been around in bodybuilding for years and used when cutting to prevent muscle breakdown and to recover faster. The amount of HMB needed to produce the benefits of muscle development is at least 3.0 grams each day witch you can get from tablets. HMB allows you to get the most from your workout, and helps you recover faster than ever. Hmb side effects what was found was only positive effects were found on muscle, body fat, blood pressure and cholesterol. Hmb reviews have been mixed but alot say it had benifts and is worth using on a cutting program.