This is a repost from 2011. I should look up recent studies. In the meantime, I was reminded how compounds in watermelon affect blood flow.
For a food that’s 92% water by weight, it’s amazing it has any other benefit besides sweet hydration. But…
Effects Of Watermelon Supplementation On Aortic Blood Pressure And Wave Reflection In Individuals With Prehypertension: A Pilot Study, American Journal of Hypertension, 2011
In this study, participants (4 men/5 women, mid-fifties, with prehypertension: ~134/77 mmHg) had lower blood pressure after 6 weeks of watermelon:
“To the best of our knowledge, this is the first study demonstrating beneficial effects of L-citrulline/L-arginine from watermelon supplementation in arterial function in humans.”
Watermelon is rich in a substance called citrulline, which the body converts to the amino acid arginine, which can be used to make nitric oxide. (Another name for nitric oxide is nitrogen monoxide – like carbon monoxide except nitrogen instead of carbon.)
When blood vessels are exposed to nitric oxide, the muscles that make up the vessel relax, the vessel opening widens or dilates, and blood flow increases. The drug Viagra uses this same nitric oxide mechanism to increase blood flow through the penis causing erection.
This next study found not just better blood flow but better blood glucose, less body fat, and better serum lipids:
Rats were fed watermelon juice for 4 weeks. Compared to the control (fed water), and to groups fed lycopene and pectin, the melon drinkers had:
- Increased serum arginine (citrulline was converted to arginine)
- Improved insulin sensitivity
- Decreased fat mass (better/higher ratio of brown fat to white fat)
- Lower serum glucose
- Lower serum free fatty acids
- Lower triglycerides
- Lower cholesterol
- Lower serum homocysteine
- Improved blood flow
Supplementing with arginine has been shown to produce many of these benefits in humans (e.g. Effect of oral l-arginine supplementation on blood pressure: A meta-analysis of randomized, double-blind, placebo-controlled trials). However, not all arginine gets converted to nitric oxide. The body has other uses for arginine, notably making urea to get rid of nitrogenous waste! Supplementing with citrulline, however, is more likely to result in these benefits since the body breaks down up to half of oral arginine after we ingest it, then much of what’s left intact goes straight to the liver, not the vessels. Not so with citrulline, which doesn’t get degraded easily and bypasses the liver ending up in the blood stream. Gram-for-gram, less citrulline than arginine is needed for the same effect.
The gentleman holding the melon, Dr. Bhimu Patil from Texas A&M University, says:
“We’ve always known that watermelon is good for you, but the list of its very important healthful benefits grows longer with each study.”
In watermelons, these include lycopene, beta carotene and the rising star among its phyto-nutrients – citrulline – whose beneficial functions are now being unraveled. Among them is the ability to relax blood vessels, much like Viagra does.
“The citrulline-arginine relationship helps heart health, the immune system and may prove to be very helpful for those who suffer from obesity and type 2 diabetes. … Arginine boosts nitric oxide, which relaxes blood vessels, the same basic effect that Viagra has, to treat erectile dysfunction and maybe even prevent it. Watermelon may not be as organ specific as Viagra, but it’s a great way to relax blood vessels without any drug side-effects.”
Almost 92 percent of watermelon is water, but the remaining 8 percent is loaded with lycopene, an anti-oxidant that protects the human heart, prostate and skin health.
“Lycopene, which is also found in red grapefruit, was historically thought to exist only in tomatoes,” he said. “But now we know that it’s found in higher concentrations in red watermelon varieties.”
– Watermelon May Have Viagra-Effect, ScienceDaily, 2008