L-Citrulline and Beetroot: What the Evidence Actually Shows

L-Citrulline and beetroot appear in almost every pre-workout on the UK market. Very few of those products explain what the ingredients are, and fewer still are honest about the regulatory position. Let us do both.

The Two Pathways

Nitric oxide is a short-lived signalling molecule the body produces continuously. It is generated by two broad routes.

The first is enzymatic, using the amino acid L-arginine as substrate. The second involves dietary nitrate: nitrate from food is reduced to nitrite by bacteria in the mouth, and subsequently to nitric oxide in the body. This second pathway is the reason nitrate-rich vegetables attract research attention at all.

L-Citrulline feeds the first pathway. It is converted to L-arginine in the body, and — perhaps counter-intuitively — supplemental citrulline raises circulating arginine more effectively than supplemental arginine does, because arginine is heavily metabolised on first pass through the gut and liver.

Beetroot feeds the second. It is among the more concentrated dietary nitrate sources.

Reading a Label Properly

Three things determine whether a nitric oxide product is serious or decorative.

1. Free-form citrulline or citrulline malate?

Citrulline malate is citrulline bound to malic acid, typically at a 2:1 ratio. A label stating 3000mg of citrulline malate delivers roughly 2000mg of actual citrulline. A label stating 3000mg of L-Citrulline delivers 3000mg. These are not equivalent, and the difference is rarely explained.

2. Is there a concentration ratio on the beetroot?

"Beetroot extract" with no ratio tells you almost nothing. A 10:1 extract means ten parts raw material concentrated into one part extract. Without that number, you cannot compare two products meaningfully.

3. Is the dose disclosed at all?

Proprietary blends list ingredients in descending order without individual amounts. This is legal and it is also, in my view, a way of avoiding scrutiny. If a brand will not tell you how much of something you are getting, assume there is a reason.

What the Research Has Examined

Both ingredients have been studied in exercise contexts, with outcomes ranging across measures of exercise performance, perceived exertion and recovery. The literature is mixed. Trials differ in dose, timing, training status of participants and the exercise protocols used, which makes direct comparison difficult and meta-analysis messy.

The pattern I would draw attention to is that effects, where reported, tend to be modest rather than transformative, and appear more consistently in some populations and protocols than others. Anyone presenting this literature as settled is overselling it.

Practical Considerations

• Beetroot can turn urine or stools pink or red. This is harmless and well documented, but it surprises people who were not warned.
• Antibacterial mouthwash interrupts the oral bacteria step in the nitrate pathway. If you are taking beetroot for nitrate, using strong mouthwash immediately afterwards works against you. This is a genuinely under-appreciated point.
• Speak to your GP before use if you take nitrates, blood-pressure medication, or medication for erectile dysfunction. The interaction potential here is real and worth taking seriously.
• Not intended for under-18s, or during pregnancy or breastfeeding.

Our Formula

Nitro Ox provides 3000mg of free-form L-Citrulline and 500mg of beetroot extract at 10:1 concentration per serving, in 150 capsules. Both amounts are disclosed on the label, and the citrulline is free-form rather than malate, so the number means what it says.