I consume watermelon on a regular basis, using watermelon for myself and the athletes that I train before, during and after competitions. I have urged them to incorporate watermelon consumption as part of their regular diet, not knowing how much good was coming from eating the fruit. Not only is watermelon an extremely tasty whole food, but it has a positive effect upon the functions of the human body.
The research article, Watermelon Consumption Increases Plasma Arginine Concentrations in Adults was a 19 week study including 12 males and 11 females between the ages of 36-69 was approved by the committee on human research of the Johns Hopkins School of Public Health and Hygiene in Baltimore, MD. The purpose of the study was to determine the level of effectiveness of consuming specific amounts of watermelon over the three week period and measure the results. Watermelon contains a large amount of citrulline which the body converts to arginine. The amino acid arginine is required to produce proteins and other molecules, including nitric oxide, proline and creatine. Nitric oxide (NO), is responsible for regulation of vascular tone and aids in the prevention of pathogens and tumor cells as an important part in boosting immunity. Proline is essential part of collagen and is critical to joint function and wound healing. Creatine is a major energy storing substance for and critical to the function of skeletal muscle and neuronal cells. Taking an oral form of arginine has been used to aid the bodily functions, but 40% is catabolized by the intestinal tissues and another 10 to 15% of the amino acid is processed by the liver. Whereas citrulline by passes the liver completely with minimal intestinal absorption, therefore leaving the body free to access the full amount of converted arginine.
The subjects were given either 3 cups (780 grams) or 6 cups (1560 grams) of watermelon juice. There was no control group for this experiment. There were several periods prior, during and upon completion of the watermelon juice consumption that fasting measurements taken revealed that plasma levels of arginine and ornithine and stable amounts of plasma citrulline were present. The rates were up to 22% greater than prior to ingestion of the watermelon juice.
I do believe that the experiment has validity. Though the group was not large a one, the data provided significant proof that watermelon ingestion does increase the levels of arginine and other amino acids that are essential to maintaining and achieving good health.
The whole premise of the study was to determine the effects of ingesting watermelon juice enriched in L-citrulline (CWJ) (3.45 g per 500 mL) on athletes competing in half marathon running events. The study consisted of 21 healthy, amatuer runners in a double blind test. Each of the runner’s ages 18-45 years had at least four years of experience in distance running. The subjects were either given the watermelon infused with additional L-citrulline or a placebo, the runners were directed to run the half marathon and then were administered jump tests and interviewed to assess their rate of perceived exertion. Later on, they were again interviewed on levels of soreness at 24 and 72 hours. Plasma tests were also conducted to evaluate potential muscle damage.The study was approved by the University’s Institutional Review Board and in accordance with the Declaration of Helsinki.
The results demonstrated that the groups with the CWJ had lower perceived exhaustion levels than that of the placebo group, maintained their jump test levels after running and had lower levels of lactate present in their blood. After the race, the blood tests revealed that the group that had taken the CWJ had actually increased the levels of arginine (27%) and increased the basal levels (14%). The placebo group lowered the basal levels b 13%. However, these differences were only noted after the testing. The results demonstrated that the intake of L-citrulline has the potential to reduce muscle fatigue. The effect of nitric oxide production also helps to maintain muscle contractility for a longer period of time and improve the exercise performance due to increased blood flow.
In regard to the percentage amounts of citrulline that is converted to arginine and then nitrate, I was unable to find that information in any of the 4 articles that I read. I was able to find this on the Examine.com website: “L-arginine and L-ornithine are subject to reduced absorption when supplemented in doses of 10g or more, which can result in diarrhea. L-Citrulline does not have this side-effect, and since it increases plasma levels of all three amino acids, it is generally preferred as a supplement over L-arginine. Though L-citrulline doubles ornithine plasma content, L-ornithine supplementation can increase ornithine plasma content even more, by 300 – 500 percent.” The side effect being referenced is diarrhea caused by ingesting more than 10 mg of arginine. But I am not able to answer your question directly regarding actual conversion percentages, though I did find that the arginine supplementation lost 40% in the intestines and another 10 to 15% in the liver, as noted previously.
Citrulline - Scientific Review on Usage, Dosage, Side Effects. Examine.com
Collins, J K., Wu, G., Perkins-Veazie, P., Spears, K., Claypool, P. L. et al. (Mar, 2007) Watermelon consumption increases plasma arginine concentrations in adults. Nutrition; Kidlington Vol. 23, Iss. 3. Doi_10.1016_j.nut.2007.01
Marini, J. C., Didelija, I. C., Castillo, L., & Lee, B. (Aug, 2010). Plasma arginine and ornithine are the main citrulline Precursors in mice infused with arginine-free diets. Journal of Nutrition.
Martinez-Sanchez, A., Ramos-Campo, D., Fernandez-Lobato, B., Rubio-Arias, J. A., Alacid, F., & Aguayo, E. (Jun 13, 2017).Biochemical, physiological, and performance response of a functional watermelon juice enriched in L-citrulline during a half-marathon race. Food Nutr Res. 2017; 61(1): 1330098. doi: 10.1080/16546628.2017.1330098
Phil Ross, AKA Master Phil and The Kettlebell King is a Master Kettlebell Instructor, College Professor in Wellness and Exercise, holder of a Masters Degree in Sports and Health Sciences, Author, 9th Degree Black Belt, and Master Bladewielder & Bodyweight Specialist. Master Phil has also launched a certification course: BodyBell Method, which is recognized by the highly regarded ACE (American Council of Exercise). Read a more in-depth description of Master Phil’s qualifications and accomplishments here. Have a question for Master Phil? Click here and send it in! View Phil's collection of Fitness DVD's here.