Personally, I've found HMB useful, but only under certain conditions. It's fairly expensive, but when I'm on a CKD and severely restricting my carbs, it seems to work quite well as an anti-catabolic. I've done CKD's with and without HMB and I lose a significantly greater amount of muscle without it. I use 3gm a day and take it between meals. In any other situation, e.g. a traditional calorie restricted diet or bulking phase, I think it's pretty worthless.