What it is: Glycine Propionyl L-Carnitine (GPLC) is a molecular-bonded form of propionyl-L-carnitine (PLC) and the amino acid glycine. "GPLC is categorized in the same family as carnitine and is very important in the formation of creatine," explains Marissa Lippert, RD and author of The Cheater's Diet.
What it'll do for you: GPLC acts as an antioxidant and leads a powerful fight against free radicals and protects against lipid peroxidation. It assists energy production by facilitating the transport of long-chain fatty acids into the mitochondria and the removal of waste substances. "Carnitine—and believably GPLC—helps protect against heart disease, type II diabetes and kidney disease," says Lippert. While experts are continuing to research its antioxidant properties, GPLC is most talked about for its role in stimulating muscle growth and increasing exercise performance.
A 2009 study performed at Florida Atlantic University examined the effects of GPLC on the performance of repeated high-intensity stationary bike sprints with limited recovery periods in male patients. In the double-blind study, 24 resistance-trained males participated in two test sessions with a week between each one. The men took oral supplements of either 4.5 grams of GPLC or 4.5 grams of cellulose 90 minutes before exercising. The men then performed five 10-second cycle sprints separated by one-minute active recovery periods. Heart rate and blood lactate levels (LAC) were measured prior to, during and following the five sprint bouts.
There was a significant effect: The men who took the GPLC had 16.2 percent less LAC, which is considered a good effect as LAC can increase muscle tension during a workout and lead to muscle damage down the road. The study suggests that short-term oral supplementation of GPLC can enhance peak power production in resistance trained males with significantly less LAC accumulation. Similar studies, including two performed at the University of Memphis agree that GPLC supplementation may increase the anaerobic threshold, maintain muscle carnitine content and increase resting nitric oxide production. The latter fact is key: By inducing nitric oxide release, the body optimizes the oxygen and nutrient delivery system to working muscles not only during but after workouts, which is ideal for recovery.
Suggested intake: Since GPLC is a novel nutrient, there is no official daily recommended intake but studies have shown that 4.5 grams is enough to have a positive effect on exercisers. One blogger mentioned he took a total of 9 grams and noticed less leg muscle fatigue during his workout.
While supplements seem to be the focus of GPLC studies, many food sources are naturally rich in carnitine and should always be considered first over supplements. Lippert suggests adding more beef, pork, chicken cheese, nuts and dark leafy greens to your diet.
Associated risks/scrutiny: Like with regular carnitine, GPLC may cause nausea and diarrhea. Other rare side effects include sleeplessness, increased appetite, body odor and rash. Additional research is needed.