Beta-hydroxy-beta-methyl butyrate (HMB) is a metabolite of the amino acid leucine. Since the first studies published by Steven Nissen and co-workers in the Journal of Applied Physiology showed that HMB prevented protein breakdown and promoted increased muscle growth in weight-training subjects, HMB has become a popular supplement in the strength training community. However, you can't adequately evaluate a supplement with only one study.
A study by K.L. Neighbors and co-workers from Armstrong Atlantic University, presented at the national meeting of the American College of Sports Medicine, showed that giving weight training football players three grams per day of HMB for 28 days increased lean muscle mass and decreased fat weight. The study provides more evidence that HMB is a viable supplement for bodybuilders, weight lifters and strength-speed athletes.
Medicine and Science in Sports and Exercise 32: S60, 2000.