The dietary supplement industry is estimated to be a $17 billion/year industry and new supplements appear as often as new versions of the Georgia State flag. In this presentation, three dietary supplements will be evaluated: 1) an energy bar containing conjugated linoleic acid (CLA), 2) an agent purported to block the Myostatin protein, and 3) a phytochemical version of human growth hormone. Ads for all three supplements claim to induce weight and fat loss, increase lean mass, and enhance metabolic rate.
Conjugated Linoleic Acid. Energy bars have long been a staple of nutritional foods for athletes, but recently manufacturers have added ingredients other than macro or micronutrients. The energy bar reviewed in this presentation contains conjugated linoleic acid (CLA). With 220 calories and 1.5 grams of CLA per bar, the manufacturer recommends one bar daily as a meal replacement. CLA was discovered in 1978 when researchers found a substance in fried ground beef that appeared to inhibit mutagenesis in laboratory animals. CLA is a naturally occurring fatty acid found in the fat of ruminant animals and dairy products and is an isomer of linoleic acid. CLA has been shown to lower adiposity in animals and sometimes in humans, but the human studies did not have rigorous controls for diet and exercise. The mechanism of action is unknown, but CLA is theorized to reduce lipoprotein lipase activity, reduce intracellular triglycerides, and enhance glycerol release from adipose tissue. The benefits of CLA on body composition are documented in animals, but scant support for such effects exists for humans. More promising is the research on CLA and cancer prevention.
Myostatin Inhibitor. "Double-muscled" animals have been of great interest to the livestock industry for hundreds of years. The "Belgian Blue" and "Piedmontese" cattle exhibit muscular hypertrophy producing greater meat yields with lower fat. In 1997, researchers at Johns Hopkins discovered and named a protein, Myostatin, as a specific inhibitor of muscle cell growth. Moreover, they determined that a genetic mutation resulting in the absence of Myostatin was responsible for "double-muscled" cattle. The supplement industry was quick to develop products that purportedly neutralized Myostatin, allowing supplement users to "grow new muscles." Preliminary human studies suggest that Myostatin may play a role in AIDS-associated muscle wasting and in age-related sarcopenia, but no dietary supplement can alter gene expression.
Phytochemical HGH. Ever since 1990, when a study revealed that older men who were given weekly injections of growth hormone for 6 months increased lean body mass and decreased fat mass, growth hormone has been viewed as the anti-aging drug. Subsequent studies have shown that growth hormone can alter body composition, but not improve muscle strength. Growth hormone has some negative side effects, including increases in blood pressure and blood glucose levels. Other potential problems include faster growth of cancers. Recently, supplement manufacturers have been touting a phytochemical or nutraceutical version of growth hormone, called Symbiotropin. The claims for the "all natural" supplement say it has all of the benefit of human growth hormone with none of the side effects. It claims to be the answer to "andropause." No published research exists about the effects of the dietary supplements claiming to be substitutes for human growth hormone, although websites selling the product provide papers that were presented at "scientific" meetings.
