Some supplement companies list L-Citrulline as an ingredient and others list Citrulline Malate.  So what's the difference?

By Dr. Adam M. Gonzalez
SHIFTED’s Chief Scientific Officer

Key Points:

• L-citrulline is a common ingredient found in pre workout due to its effects on increasing nitric oxide, improving blood flow, and delaying fatigue.  
• L-citrulline can be found as either “L-citrulline” or “citrulline malate” in pre workout supplements
• There are some issues with products using citrulline malate that should be considered.
• There is nothing wrong with using a product that has citrulline malate but using a product with L-citrulline allows for a better appreciation of how much you are actually getting. 

Citrulline is among the top ingredients found in pre workout supplements.  It is typically included in the form of L-citrulline or citrulline malate.  Let’s clear up the confusion and make sure you know what to look for on the label.

What is citrulline?

L-citrulline is a nonessential amino acid found primarily in watermelon.  It’s an ingredient that is worth including as a dietary supplement because you would need to consume approximately 2-3 pounds of fresh watermelon per day to achieve the minimum effective dose of L-citrulline [1]. 

L-citrulline has the potential to improve muscle function and decrease muscle fatigue during high-intensity exercise by serving as a nitric oxide precursor [2].  After ingestion, L-citrulline is well-absorbed into the bloodstream and is efficiently converted to L-arginine to support nitric oxide production. 

The evidence is clear that supplementing with L-citrulline is superior to supplementing directly with L-arginine because L-arginine is not well-tolerated and suffers significant breakdown in the gut which limits its bioavailability and efficacy [3]. 

In summary, supplementing with L-citrulline is one of the best dietary ways to promote the production of nitric oxide – a gaseous molecule that stimulates relaxation of smooth muscle in the blood vessels to promote vasodilation and better blood flow.  Thus, increasing nitric oxide may increase muscle performance, hypertrophy, and strength by facilitating oxygen and nutrient delivery to the working muscles, along with increasing “the pump” during training. 

What does the research show?

L-citrulline has gained much attention by researchers over the past decade due to the growing interest of weightlifters and athletes. The first study to ever show a benefit of L-citrulline was conducted in 2002 showing that citrulline (in the form of citrulline malate) increased the rate of oxidative ATP production and increased the rate of phosphocreatine recovery after exercise [4]. 

While this data is interesting, it must be noted that the study was conducted using a finger flexion exercise protocol in men complaining of fatigue.  Subsequently, as a result of this initial work, most of the future research investigating the potential performance-enhancing effects provided L-citrulline in the form of citrulline malate prior to strength training. 

In a review of the literature, my colleagues and I found that when performing ~5 sets of resistance training at ∼70% of one-repetition maximum, supplementing with 6 to 8 g of citrulline malate 40 to 60 minutes before exercise increased repetitions by ~3 compared with placebo [5].  Therefore, including citrulline malate in your pre workout appears to delay fatigue and enhance muscle endurance during high-intensity weightlifting.

What is the difference between a pre workout that uses L-citrulline vs. citrulline malate?

Malate is a tricarboxylic acid cycle intermediate that has been suggested to enhance energy pro- duction.  While there is a common claim that malate may offer a synergistic effect with L-citrulline, there is absolutely no evidence that malate offers any benefits on its own or in combination with citrulline [2]. 

No study has ever compared the effects of citrulline malate to L-citrulline, and no study has ever investigated the effects of malate in isolation.  Clearly, L-citrulline is the active ingredient that you should care about.

When citrulline malate is provided in a pre workout, it is typically either in a 2:1 ratio or 1:1 ratio. This means that an 8 gram dose of citrulline malate contains 4 to 5.3 grams of L-citrulline. However, many supplement companies fail to disclose the citrulline to malate ratio making it unknown how much citrulline is actually in the product. 

It’s also not uncommon to see a company highlight that they have 8 grams of L-citrulline in their product, when in fact they have 8 grams of citrulline malate.  Even worse, it has been shown that supplements containing citrulline malate are notorious for having significantly lower concentrations of L-citrulline as compared to the label claim [6]. 

What to look for on the label 

The minimum effective dose of L-citrulline seems to be ~3 grams, while the maximum effective dose is unknown but may be as high as 10-15 grams.  Higher doses of L-citrulline show to increase L-arginine concentrations in the bloodstream in a dose-dependent manner, without any adverse side effects [7]. 

Using a product with L-citrulline, as opposed to citrulline malate, allows for a better appreciation of how much you are actually getting. There is nothing wrong with using a product that has citrulline malate.  Just be sure that it is a reputable company, and you are getting an effective dose of L-citrulline.  SHIFTED takes out the guesswork and provides 8 grams of L-citrulline in its Maximum Pre Workout. 

 

About the Author

Adam M. Gonzalez is an associate professor in the Department of Allied Health and Kinesiology at Hofstra University. He earned a Ph.D. in Exercise Physiology from the University of Central Florida in 2015 and holds certifications as a Certified Strength and Conditioning Specialist (CSCS), along with a Certified Sports Nutritionist Certification (CISSN).

Adam's primary research interests include exercise and nutritional strategies to optimize body composition, maximize health, and enhance adaptations to exercise. He was also awarded the 2022 Nutritional Research Achievement Award by the National Strength and Conditioning Association.

References:

1.   Allerton, T.D., et al., L-Citrulline supplementation: impact on cardiometabolic health. Nutrients, 2018. 10(7): p. 921.  https://pubmed.ncbi.nlm.nih.gov/30029482/

2. Gonzalez, A.M. and E.T. Trexler, Effects of citrulline supplementation on exercise performance in humans: A review of the current literature. The Journal of Strength & Conditioning Research, 2020. 34(5): p. 1480-1495. https://pubmed.ncbi.nlm.nih.gov/31977835/

3. Bahadoran, Z., et al., Endogenous flux of nitric oxide: Citrulline is preferred to Arginine. Acta Physiologica, 2021. 231(3): p. e13572. https://pubmed.ncbi.nlm.nih.gov/33089645/

4. Bendahan, D., et al., Citrulline malate promotes aerobic energy production in human exercising muscle. British journal of sports medicine, 2002. 36(4): p. 282-289. https://pubmed.ncbi.nlm.nih.gov/12145119/

5. Vårvik, F.T., T. Bjørnsen, and A.M. Gonzalez. Acute Effect of Citrulline Malate on Repetition Performance During Strength Training: A Systematic Review and Meta-Analysis. International Journal of Sport Nutrition and Exercise Metabolism, 2021. 31(4): p. 350-358. https://pubmed.ncbi.nlm.nih.gov/34010809/

6. Chappell, A.J., et al., Citrulline malate supplementation does not improve German Volume Training performance or reduce muscle soreness in moderately trained males and females. Journal of the International Society of Sports Nutrition, 2018. 15(1): p. 1-10. https://pubmed.ncbi.nlm.nih.gov/30097067/

7. Moinard, C., et al., Dose-ranging effects of citrulline administration on plasma amino acids and hormonal patterns in healthy subjects: the Citrudose pharmacokinetic study. British journal of nutrition, 2008. 99(4): p. 855-862. https://pubmed.ncbi.nlm.nih.gov/17953788/