Ingredient Focus: Citrulline – What It Is, What It Does, How Much to Take (Part 1)

Since citrulline is one of the key ingredients in the Energy Drink of the Month for June 2016, it’s time to take a closer look. With the help of grapes and toothpicks, GreenEyedGuide answers your biggest citrulline questions.

Citrulline is an amino acid, but not an essential/non-essential amino acid our bodies use to build proteins. Citrulline is called “watermelon extract” and gets its name from watermelon’s Latin botanical name, (Citrullus vulgaris). So you’d think watermelon has a lot of citrulline, right?


One gram of fresh watermelon contains 2.1 milligrams (or 0.0021%) citrulline. That’s not much, but watermelon is the richest source. Other natural sources of citrulline include muskmelon, bitter melon, squash, gourd, cucumber, and pumpkin.

From Clever ways to cut a watermelon | The Organised Housewife
From Clever ways to cut a watermelon | The Organised Housewife

Citrulline isn’t just found in melons – the human body makes it too. The body can make it from the amino acid arginine or from the amino acid glutamine.

Allow me to demonstrate how similar they are, structurally, using my FAVORITE O-CHEM STUDY TOOL, EVER: grapes, toothpicks, and some other round edible props.


Like a watermelon seed, citrulline’s greatest value is not what it is, but what it becomes: citrulline becomes arginine. We’ll get more into this in PART II: What Does It Do, but arginine is an amino acid with several important jobs in the body. Citrulline is better absorbed than arginine, so the best way to get more arginine is to consume citrulline!

Citrulline may be misspelled as ‘citruline’ or sold as a citrulline malate supplement. When any ingredient has the letter “l” before it (l-citrulline v citrulline), the ‘l’ indicates a specific 3D orientation of the molecule. This orientation is as important as the orientation of the batteries you put in your TV remote. They only work a certain way. The opposite orientation of ‘l’ is ‘d’. The ‘l’ and ‘d’ come from Latin words that describe whether a light shined through a molecule would be rotated right or left, but that’s a nerdy-fact, and not the point.

When there is no ‘l’ or ‘d’ in front of a molecule, it’s a chemistry way to say “hey look, this is a mix of the ‘l’ and ‘d’ forms.” Putting a letter in front of the name implies all the molecules with the other orientation are weeded out. This is a good thing, because, like the batteries, only one orientation is active in the body, so weeding out the inactive forms means a purer product.

What about citrulline (or l-citrulline) versus citrulline malate? To explain the difference, I’ll turn it over to Dr. Jim Stoppani, one of my favorite biochemists on the planet.

STAY TUNED FOR PART TWO: What does Citrulline do?

References and Related Reading

Citrulline Part 2 (What It Does) and Part 3 (How Much)

WTRMLN WTR – Energy Drink of the Month – June 2016

Citrulline on (note – this site has HEAPS of information, but it may be a bit technical for some)



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