This metabolite of leucine has been shown to benefit muscle recovery and growth in as little as 3 grams per day. The dosage and price go up however if you take it for fat loss.
For fat loss, take 1.5--3g of HMB three or four times per day, preferably on an empty stomach(between meals) or prior to exercise. Combining this supplement with carnitine can help to further improve fat loss, especially when used with low-carb diets, by promoting the transport of fat into mitochondria, where it is burned as fuel.
For muscle growth and strength gains, beginning lifters can take 3g per day; experienced lifters need up to 12g daily in two or three divided doses.
Research studies in trained lifters taking HMB showed far less impressive results than in untrained subjects. For that reason, bodybuilders with more training experience will need to boost the dose to experience similar results.
Some have said that experienced lifters may not need to go to the expense of a product like HMB. Leucine may do the trick just as well.
Studies from ergo-log:
Give volleyball players HMB for seven weeks… 29.10.2012
How HMB works 23.10.2012
HMB only works well after a loading period 08.10.2012
HMB keeps aging body muscular and trim 25.09.2012
Creatine plus HMB 01.09.2012
HMB needs vitamin D 11.06.2012
The joint anabolic effect of EPA and HMB 27.10.2010
HMB's successor is called HICA 25.01.2010
HMB has virtually no effect, says meta study 06.08.2009
The Encyclopedia of Supplements A-F. Jim Stoppani. Flex. 29.10 (Dec. 2011): p196.
Leucine is King (Part 1) For Muscle Building and Fat Burning
Leucine is King. Part 2 This is the Whey.
Leucine is King: (Part 3) How Do You Get the Amount You Need? Whey Plus Leucine
Leucine is King (Part 5): Leucine metabolites - HMB (beta-hydroxy beta-methylbutyrate) and HICA (leucic acid or alpha-hydroxy-isocaproic acid)