Even if you're not a weight lifter, you've undoubtedly heard of creatine, one of the most researched supplements in history.



It's a combination of amino acids produced by the liver, kidney and pancreas. Creatine is not a steroid -- it's naturally found in muscle and in red meat and fish, though at far lower levels than in the powder form sold on bodybuilding websites and at your local GNC. 



How does it work? Creatine reduces fatigue by transporting extra energy into your cells, says Ari Levy, M.D., who works with patients at the Program for Personalized Health and Prevention at the University of Chicago Medical Center. Adenosine triphosphate, or ATP, is the compound your body uses for energy. For a muscle to contract, it breaks off a phosphate molecule from ATP. As a result, ATP becomes ADP (adenosine diphosphate). The problem: You can't use ADP for energy, and your body only has so much stored ATP. The fix: ADP takes a phosphate molecule from your body's stores of creatine phosphate, forming more ATP. 



If you have more creatine phosphate -- which you do if you take a creatine supplement -- you can work out longer and do sets of, say, eight reps instead of six. Over weeks and months, that added workload allows you to add lean muscle mass, lift heavier weights, and become stronger. (To build muscle and blast fat at the same time, check out The Incredible 82-Day Speed Shred.)



But should you worry about side effects? Does creatine cause you to lose weight when you stop it, or does it hurt your kidneys, like you may have heard? Here are the key myths and facts you need to know.



Creatine is similar to anabolic steroids. Myth. Steroids mimic testosterone and are banned in the Olympics and in professional sports. By contrast, the International Olympic Committee, professional sports leagues, and the National Collegiate Athletic Association do not prohibit creatine. (The NCAA won't let colleges give it to athletes, though.) 



Creatine can help you build muscle mass without hitting the gym. Myth. It shows some improvement in kids with muscular dystrophy, even if they're not exercising, says Mark Tarnopolsky, M.D., Ph.D., professor of pediatrics and medicine and director of the neuromuscular and neurometabolic clinic at McMaster University Medical Center in Ontario. “[But] the best effect in healthy humans is seen when creatine is combined with resistance exercise training.” If you're trying to build muscle, make sure you're doing common exercises like pushups correctly. (You probably aren't!) Click here to find out the 5 Exercises That Make Trainers Cringe -- and the right ways to do them.



Creatine causes gastrointestinal upset. True -- but it's rare. Tarnopolsky says his studies show 5 percent to 7 percent of people experience either stomach aches, diarrhea or both.



Creatine will help you run a faster 5K. Myth. Creatine helps athletes with more fast-twitch muscle fibers (used to swing a baseball bat) more than athletes with more slow-twitch ones (used by marathon runners). "If you're an endurance athlete, if you're not doing something that involves the fast-twitch muscle fibers, you don't need to be on creatine," says orthopedic surgeon Tony Wanich, M.D., a sports medicine specialist at Montefiore Medical Center in New York. 



Creatine causes weight gain. Fact. (But that's kind of the point.) It pulls H2O into your muscles, which causes water-weight gain and makes muscles look bigger initially. (You don't actually gain muscle fibers until you work out.) "Creatine is a molecule that has a very strong attraction for water," says Gordon Purser, Ph.D., a professor of chemistry at the University of Tulsa who studies creatine and has used it himself for the past decade. No two people will have the same results. "Weight gain of about 0.8 to 2.9 percent of body weight in the first few days of creatine supplementation occurs in about two-thirds of users," says Christine Rosenbloom, Ph.D., R.D., sports dietitian for Georgia State University Athletics and editor in chief of Sports Nutrition: A Practice Manual for Professionals. What can you expect after the water weight gain? In a study of 20-year-olds taking creatine and doing weight training, Tarnopolsky found some gained two pounds of muscle but one even gained 17 pounds of it -- with the same amount of supplement and the same training. 



Creatine doesn't work well for everyone. True. "One major factor with creatine is that some people have high levels in muscle naturally," says Tarnopolsky. Meat and fish eaters are less likely to respond than vegans, who have low levels in their diet. Your muscle makeup matters, too. Most people have about 50 percent fast-twitch fibers (responsible for sprinting and jumping) and 50 percent slow-twitch fibers (responsible for endurance exercise), says Peter Adhihetty, Ph.D., assistant professor in the department of applied physiology and kinesiology at the University of Florida in Gainesville. Those guys should respond well. But people with 70 percent fast-twitch and 30 percent slow-twitch muscle will see even more results, he says. 


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Creatine makes you look softer. True. There's a reason bodybuilders stop using creatine a month or so before a competition. "As the creatine hydrates itself, it causes water to flow into the muscle. That extra water may increase the volume of the muscles, but it also makes them look mushy rather than defined," says Purser. Your move: Take it during the fall, winter and spring to build muscle. Go off it during the summer to show off your beach abs. 

(And for a great workout that'll get you beach-ready, try The NFL Workout.)

Creatine users will lose muscle when they stop taking the supplement. Myth. Your muscles may look smaller because creatine adds water volume. "The real question is, 'Will you maintain your strength and muscle mass, dry muscle mass, when you discontinue the use of creatine?" says Purser. "The answer to that is absolutely yes. Once you have built the muscle, as long as you continue to lift, you will maintain it." 


You shouldn’t take too much creatine. Fact. “It is illogical to take more than 20 grams a day for a week max or seven grams a day for months,” says Tarnopolsky. “[There is] no evidence that this would do anything more in terms of loading the muscle, so why on earth would someone waste money and time and effort for unknown risks and zippo added benefit. Anything in the world -- sugar, coffee, fat, protein, salt -- taken in excess can lead to health issues.” 



SO, YOU WANT TO TAKE CREATINE? HERE'S HOW.


You'll see a bunch of different forms of creatine on your supplement store's shelves. The one you want is creatine monohydrate. "Creatine monohydrate is the exact compound that more than 95 percent of the studies used, so why take a chance on another compound from a safety and effectiveness perspective?" Tarnopolsky says.



The first week you go on creatine, some experts recommend a "loading phase" of 20 grams a day for five to seven days. Afterward, go to 5 grams per day.

The fine print: See your doctor first if you have high blood pressure or diabetes, if you regularly take any prescription meds or non-steroidal anti-inflammatory drugs like ibuprofen (which can tax the kidneys), if you're over age 40 (since kidney function slowly declines after age 30), or if you have a history of kidney or liver disease.

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