XTend is “The first supplement ever proven to double your fat loss, double your muscle gain and double your strength when compared to whey protein! “At least that is what the XTend website says. I was intrigued and wanted to see if there was any proof of this claim and help others see if XTend was right for them.
Xtend Ingredients
Xtend is supplement made by Scivation (Scivation.com) and consists of various amino acids. Xtend consists of the following ingredients:
1. Branch chain amino acids – leucine, isoleucine and valine:
- Leucine (3.5 grams)
- Isoleucine (1.8 grams)
- Valine (1.8 grams)
2. Glutamine (2.5 grams)
3. Citrulline (1 gram)
4. Vitamin B 6 (10 mg)
The Xtend Research
On the Xtend website (Scivation.com) a study is quoted where it's said people lost 4.5 lb of body fat and gained 9 lbs of lean body mass over the course of an 8 weight strength training program. The research they quote is a study of branch chain amino acid supplementation vs. whey protein supplementation. It is not a study that compares Xtend to Whey protein.
This is an important distinction. In fact, in this study, people were given 14 grams of BCAAs. 2 scoops of Xtend contains 7.1 grams of BCAAs – so Xtend has only 1/2 the BCAAs used in the study.
While this study was supported by Scivation, the maker of Xtend, I did not see the word Xtend mentioned anywhere in the study. In other words, It does not appear to me that people used Xtend. Rather, they appear to have been given a supplement that contained branch chair amino acids (or whey protein). The study does not specifically say what BCAA supplement was used.
Also, while this appears to be a well designed study, it does not seem to be a published peer reviewed study. I see no citation where the study was published except that it was conducted by the Weider Research Group (Weider, as in Muscle & Fitness).
Since it appears that the study they quote is not on Xtend and not peer reviewed, let's instead review the ingredients in Xtend itself because there is indeed research on its ingredients.
Branch Chain Amino Acids
Branch chain amino acids are interesting because they appear to do several things. For example, BCAAs have been shown to reduce muscle breakdown that occurs with exercise. An amount of BCAAs that seems to work is about 77 mg per kilogram. So if you were 200 lbs (91 kg), you would take 7000 mg (7 grams). This is similar to the total amount of branch chain amino acids in Xtend.
BCAAs are theorized to reduce the entry of tryptophan into the brain, which limits production of serotonin. In theory, this means BCAAs may make an athlete more awake. That said, it is controversial whether BCAAs improve aerobic exercise performance.
Leucine appears to be one of the main branch chain amino acids responsible for enhancing muscle protein synthesis, which is likely the reason it is found in many protein supplements. Low levels of leucine may also result in a reduction in appetite. Research has noted that BCAA supplementation can increase appetite in older adults. Since muscle building requires extra calories, would BCAAs stimulate appetite in strength trainers as well? This is an interesting theory but one which has not been tested.
Glutamine
Many people use glutamine supplements because of a misunderstanding of the research which is propagated by fitness magazines. Glutamine is a non essential amino acid (and a conditionally essential amino acid) whose fitness reputation stems from the fact it helps some people recover faster from stressful events. Who are these people? They are not who you think…
As I told everyone in my book Nutritional Supplements: What Works and Why, the majority of the good glutamine research is conducted on very sick people like those who have cancer, AIDS or those who have undergone surgery. Often this research involved intravenous glutamine also – not glutamine supplements.
Why have you never seen this fact mentioned in fitness magazines or websites?
While there is some evidence that athletes (think Lance Armstrong) who do long duration aerobic exercise may have lower glutamine levels, the research on strength trainers is less well known. Still, for hard core bodybuilders (think Ronnie Colman), I think glutamine might be worthwhile until research proves otherwise. If you want to know more about glutamine read my review Glutamine The Dirty Little Secret that they don't want you to know about.
Citrulline Malate
This is a non-essential amino acid (watermelon is a good natural source of citrulline) that has some preliminary exercise research behind it. In one small citrulline study 17 men and women were given Citrulline while exercising on a treadmill to exhaustion.
People either received a placebo or citrulline (a total of 9 grams of citrulline over the course of testing). Ironically the people who received citrulline became exhausted faster than those who did not get citrulline. It is noteworthy that the people in this study received 9 grams of citrulline vs the 1 gram that is in the Xtend supplement. This was also a very small study, making it hard to draw definitive conclusions.
Conversely, other research has noted the citrulline enhances the utilization of branch chain amino acids. As such, incorporating both citrulline and BCAAs in Xtend does make some sense, at least in theory. This same study also noted slight elevations in growth hormone in response to intense exercise.
Another study published in the Journal of Strength and Conditioning research noted the citrulline supplementation reduced feelings of delayed onset muscle soreness (DOMS) after people performed 16 sets of weight lifting exercises. The amount of citrulline used in this study was 8 grams.
Vitamin B 6
Vitamin B 6 contributes little to muscle growth in healthy people. As a B vitamin it (along with other B vitamins) it helps the body convert food into fuel. But, B vitamins do not give people extra energy like, say, caffeine does.
Does Xtend Work?
Based on the evidence that I could find and what I know about supplements. I come to these conclusions about the Xtend amino acid supplement:
1. I could find no published peer reviewed studies on the Xtend product itself. As far as I can determine, everything that can be said about the Xtend supplement stems from what we know about the ingredients in Xtend.
2. Xtend is likely safe in most if not all healthy people.
3. In theory, the ingredients in Xtend – principally, BCAAs, glutamine and citrulline – may be of some benefit to those involved in very intense weight lifting or bodybuilding and perhaps aerobic exercise (e.g. running a marathon) . There is however no good proof for for recipe and I am basing this statement on simple logic and the preliminary evidence I could dig up on these ingredients.
4. People who are not “hard core” about their exercise regimen, do not need Xtend.
5. I could not locate any published peer reviewed study that compares Xtend to whey protein. The study quoted on the Xtend website is a comparison of BCAAs to whey protein – not Xtend to whey protein.
6. Contrary to what is stated on the Xtend website, I cannot find any published peer-reviewed proof for the statement that Xtend is “first supplement ever proven to double your fat loss, double your muscle gain and double your strength when compared to whey protein!” As such, this statement should be taken with a grain of salt until research proves otherwise.
What do you think?