Those who seek a well-chiselled body can start clearing out their medicine cabinets. A US study reveals that of the more than 250 dietary products available, only HMB and creatine supplements have sufficient scientific evidence to show that their use increases lean body mass and strength gains when accompanying resistance training.
The researchers have warned of the significant impact these results could have on future purchases of body-enhancing supplements.
Although scientific support for specific 'hyper' nutrition to aid muscle growth has been periodically claimed, the scientists said that any support for the use of these nutrients is usually non-quantitative and often unsystematic, and conclusions are often open to subjectivity.
The team from Iowa State University in the US carried out a meta-analysis of available data to determine whether supplementation of dietary components, above normal intakes or above the requirement, can increase lean mass gains associated with resistance training. They also looked for evidence of strength gains.
About 250 supplements were gathered from the product lists of eight dietary-supplement marketing companies, as well as a review of six magazines targeted specifically at the body-building community, and five published scientific reviews on dietary supplements.
The review revealed that of the approximately 250 candidate supplements, only 48 studies met all the inclusion criteria. Of these, six supplements were supported by greater than one citation each: creatine, HMB, chromium, DHEA, rostenedione and protein.
The search was confined to randomised, placebo-controlled studies published in peer review journals only, but studies were rejected if they did not involve any form of resistance exercise, or the subjects suffered from an abnormal health condition. Gender was measured equally and no restrictions placed on the exercise history of the subjects, although training was recorded as a variable.
The studies also had to be at least three weeks in duration and had to involve subjects carrying out a full body - all major muscle groups - resistance-training regimen two or more times per week.
Of the original list of 250 substances marketed as dietary supplements, creatine and HMB - which is produced in the body and in certain foods such as catfish and alfalfa - were the only supplements found to be effective in increasing lean tissue gain with resistance training.
Finally, with regard to lean mass gain, the scientists found that creatine and HMB have similar effects, with lean gain approximately doubling over the placebo group. They also revealed that although this could suggest a similar mechanism of action, the literature would suggest the work of independent mechanisms.
Full details of the study can be found in the February edition of the Journal of Applied Physiology.