L-Arginine vs. L-Citrulline: What’s the Difference?

Difference Between l arginine and l citrulline

L-arginine and L-citrulline are two popular sports supplements touted to enhance nitric oxide levels and athletic performance. But what exactly are these compounds? How are L-arginine and L-citrulline different, and does one offer advantages over the other? Let’s break down the science behind these nitric oxide boosting supplements.

Difference Between l arginine and l citrulline

L-arginine and L-citrulline have both gained popularity as sports and workout supplements intended to enhance nitric oxide production, boost circulation, improve exercise performance, and aid muscle growth. However, L-citrulline has emerged as the superior nitric oxide booster over L-arginine. Thanks to differences in metabolism and activity, L-citrulline exhibits better bioavailability, prolonged effects, lower effective dosing, and fewer gastrointestinal side effects compared to L-arginine. Multiple studies now demonstrate that just 3-6 grams of L-citrulline taken before training can significantly increase strength, endurance, muscle recovery, and other athletic markers. Beyond boosting physical performance, L-citrulline also provides systemic benefits for cardiovascular health. As we’ll explore, L-citrulline has surpassed L-arginine as the go-to nitric oxide supplement with performance-enhancing effects across various sports and activities.

Defining L-Arginine

L-arginine is an amino acid that serves as a building block of proteins. It is considered a “conditionally essential” amino acid, meaning the body can usually synthesize sufficient amounts on its own, but supplementation may be needed in times of growth, injury, or stress.

Food sources of L-arginine include:

  • Turkey and chicken
  • Fish and seafood
  • Nuts and seeds
  • Soybeans
  • Dairy products
  • Whole grains
In supplement form, L-arginine is commonly taken by athletes and bodybuilders for purported benefits like:
  • Enhanced blood flow and circulation
  • Improved exercise performance
  • Increased muscle growth and strength
These effects are attributed to L-arginine’s role as a precursor for nitric oxide synthesis in the body.

Functions of L-Arginine

Here are the primary functions of L-arginine:
  1. Nitric Oxide Production: L-arginine is converted into nitric oxide in the body through the catalysis of the nitric oxide synthase (NOS) enzyme. Nitric oxide is a vasodilator that widens blood vessels to enhance circulation. Supplemental L-arginine aims to increase nitric oxide levels.
  2. Protein Building: As an amino acid, L-arginine is incorporated into proteins vital for muscle growth and tissue repair. This supports athletic recovery and exercise performance goals.
  3. Immune Support: L-arginine plays a role in immune cell function. Some research indicates L-arginine supplements may boost immunity and hasten recovery from infections.
  4. Hormone Secretion: L-arginine is involved in the synthesis of hormones like growth hormone, insulin, and testosterone. However, research is mixed on whether L-arginine increases levels of these hormones.
Through nitric oxide production, protein synthesis, and immune and endocrine effects, L-arginine is theorized to offer performance-enhancing and muscle-building benefits. But the hype may exceed the actual evidence...

Limitations of L-Arginine Supplements

Despite arginine’s theoretical mechanisms, research reveals limitations:
  1. Poor bioavailability - Most oral L-arginine is metabolized before reaching circulation. Only a small fraction makes it intact to act as a nitric oxide precursor.
  2. Short-lived spikes - Any rises in plasma L-arginine and nitric oxide are short-lasting, peaking at ~1 hour after ingestion. No prolonged benefits are derived.
  3. High doses needed - At least 3 grams of L-arginine are required to meaningfully affect nitric oxide levels, and 10+ grams for any enhancement of exercise performance or muscle growth.
  4. Intestinal side effects - Such high L-arginine doses frequently cause nausea, diarrhea, and abdominal pain.
Due to poor bioavailability, transient benefits, and GI issues with higher doses, L-arginine supplements fall short for many athletes despite sounding good in theory.

Introducing L-Citrulline

L-citrulline is another amino acid supplement that has surged in popularity in recent years. It is not incorporated into proteins, but rather metabolized into L-arginine in the kidneys.

L-citrulline is found in foods like:

  • Watermelon
  • Cucumbers
  • Garlic
  • Onions
  • Legumes
  • Seeds
  • Nuts
As a workout supplement, L-citrulline is also taken to increase nitric oxide production and enhance circulation and exercise performance. But due to differences in metabolism, L-citrulline may achieve these results more reliably than L-arginine.

Benefits of L-Citrulline Over L-Arginine

Here are some of the advantages L-citrulline exhibits over L-arginine supplements:
  1. Better Bioavailability:While much oral L-arginine is degraded and unable to increase nitric oxide, L-citrulline is efficiently absorbed intact and converted to arginine. For each 1 g of L-citrulline, up to 0.33 g of arginine is made available.
  2. Prolonged Effects: L-citrulline supplementation produces a slower, more sustained increase in circulating L-arginine and nitric oxide levels. Benefits are maintained for up to 6 hours versus only 1-2 hours with L-arginine.
  3. Lower Effective Dose: Just 3-6 grams of L-citrulline per dose sufficiently boosts nitric oxide compared to over 10 grams of L-arginine required for modest effects. The lower dose also minimizes GI side effects.
  4. Enhanced Performance: Due to better bioavailability and sustained nitric oxide elevation, studies consistently show 3-6 grams of L-citrulline enhances strength, endurance, and recovery metrics compared to L-arginine.
Researchers theorize the kidneys are better equipped than the intestines to metabolize amino acid precursors safely and efficiently into nitric oxide. This gives L-citrulline a clear edge.

L-Citrulline for Sports Performance

Multiple studies now demonstrate significant benefits of L-citrulline supplementation for athletic activities:
  • Increased strength and lean mass gains when combined with resistance training
  • Improved oxygen kinetics and power output during cycling
  • Enhanced resistance to fatigue during swimming endurance trials
  • Faster 5K and 10K running race times in recreational athletes
  • Improved number of bench press repetitions to failure
L-citrulline boosts performance by increasing nitric oxide production, augmenting blood flow, enhancing nutrient delivery, and clearing exercise-induced metabolic waste products like ammonia from muscles.

Additional Benefits of L-Citrulline

Along with boosting sports nutrition, L-citrulline exhibits other advantages as an amino acid precursor:
  1. Lowers blood pressure
  2. Reduces arterial stiffness
  3. Improves endothelial function
  4. Antioxidant activity to reduce oxidative stress
  5. May enhance erectile function in men
The collective benefits of L-citrulline on circulation and vascular health extend beyond just exercise effects to support overall wellness.

Conclusion of Difference Between l arginine and l citrulline

In summary, L-citrulline holds clear advantages over L-arginine for boosting nitric oxide levels and enhancing circulatory function and sports performance. Thanks to superior bioavailability, sustained activity, and lower effective dosing with fewer side effects, L-citrulline succeeds as a pre-workout supplement where L-arginine often falls short.
L-citrulline not only helps improve exercise training capacity and recovery in athletes across sports, but also provides cardiovascular and endothelial benefits for overall wellness. With a safe profile and abundance of evidence for efficacy, L-citrulline stands out among workout aids for natural nitric oxide boosting powers.