Citrulline

An amino acid also found in watermelon: Does taking it before exercise make a difference?

Does taking citrulline before exercise improve endurance or recovery? In short, the evidence from human studies so far does not strongly support this. Because this amino acid, which is also found in watermelon, became a representative ingredient in pre-workout powders, single citrulline, citrulline malate, and products mixed with various ingredients are often discussed together. Since different forms and different exercise results are mixed under the same name, it is difficult to know what to expect based on the product label alone.

First, you must distinguish between food, single-ingredient, malate, and complex products, and then check the results of human studies by exercise type.

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Context of the Question: As watermelon's amino acid became an exercise amino acid

Citrulline is produced by the body, and watermelon is a well-known dietary source. The NIH Office of Dietary Supplements (ODS) also explains this. However, as this amino acid became a major ingredient in pre-workout supplements, L-citrulline alone, citrulline malate (citrulline combined with malic acid), and complex products mixed with ingredients like caffeine and arginine are all called 'citrulline.' Even if the name is the same, the content and research conditions differ.

This mixing of terms has increased expectations regarding exercise performance, but research results are inconsistent. Studies on exercise performance are few and vary in design, with mixed results showing they may help, hinder, or make no difference. The ODS summarizes that current evidence does not strongly support the improvement of exercise performance by citrulline or citrulline malate.

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Identity of the Ingredient: An amino acid produced by the body and found in watermelon

Citrulline is an amino acid synthesized by the body and obtainable through food. Watermelon is a well-known food source. However, the fact that it exists in food and the exercise effects of standardized supplements are two different questions.

When approaching it as a supplement, the form in which this amino acid is contained comes first. L-citrulline is citrulline itself. Citrulline malate is a form where citrulline is combined with malic acid. Even with the same weight, it cannot be read as the actual amount of citrulline. Even if 'citrulline malate' is written on the product label, the ratio of L-citrulline within it must be checked separately.

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Why Expectations Grew: Becoming a representative ingredient in pre-workout supplements

Expectations regarding endurance and recovery are attached to citrulline, but those expectations must be verified through exercise results in humans. This is because short-term high-intensity exercise and aerobic endurance do not use the same evaluation metrics.

As summarized by the ODS, current evidence does not strongly support the improvement of exercise performance. In a meta-analysis of 10 studies, there were no significant improvements in aerobic performance, rating of perceived exertion, oxygen uptake indicators, or lactate. This shows the gap between theory and actual evidence in humans.

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Differences in Product Form: Single, malate, or complex, same name, different contents

Citrulline supplements are mainly found in three forms.

Form	Characteristics	Points to Check
L-Citrulline	Contains only citrulline	Actual L-citrulline content
Citrulline malate	Combination of citrulline + malic acid	Ratio of citrulline in the total amount
Complex pre-workout	Citrulline + caffeine, arginine, etc.	Total amount of each ingredient and interactions

It is important to note that L-citrulline and citrulline malate cannot be read as having the same amount of actual citrulline for the same weight. For complex products, the total amount, interactions, and the possibility of banned substances for caffeine and other ingredients must be checked separately from citrulline.

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Foods and Supplements: Watermelon vs. Standardized Products

The fact that watermelon contains citrulline explains a food source. However, results from standardized single-ingredient studies or citrulline malate cannot be directly applied to watermelon consumption, nor can the image of a food be used as evidence for the efficacy and safety of a supplement.

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Different Research Questions for Each Type of Exercise

Expectations for citrulline vary by type of exercise. Short-duration high-intensity exercise, aerobic endurance, and blood pressure are different research questions. Some studies report the number of repetitions in strength training, some report endurance like marathons, and others look at vascular function. The reason results vary is that the research questions were different.

A meta-analysis of 10 studies showed no significant improvement in aerobic performance and related indicators, and a blood pressure meta-analysis combining 5 intervention studies showed no significant changes in brachial or aortic systolic and diastolic blood pressure. This demonstrates that citrulline does not work consistently across all areas of exercise.

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Combination Use and Individual Circumstances: Caution with Blood Pressure Medication and Complex Products

When considering citrulline, you should first check your current medications and other supplements. In particular, citrulline should not replace blood pressure treatment, and if you are taking blood pressure medication, you must inform your medical provider. The fact that there were no significant changes in a blood pressure meta-analysis does not mean it has absolutely no effect on an individual.

For complex pre-workout products, the total amount, interactions, and possibility of banned substances for caffeine and other ingredients must be checked separately. These complex ingredients can be a larger variable than citrulline itself.

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Safety Signals: Lack of Evaluation Beyond Short-Term Use

The safety of using citrulline in supplement form for several months has not been sufficiently evaluated. In one short-term weight training study, some participants reported gastrointestinal discomfort. Therefore, you must consider your exercise goals alongside any gastrointestinal discomfort or blood pressure management status.

If gastrointestinal discomfort occurs or if you are managing blood pressure, inform your medical provider or pharmacist about the product and your intake status rather than continuing use.

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Difference from similar ingredients: Arginine and Citrulline

Arginine and citrulline often appear together or side-by-side in exercise products, but they are different amino acids. Exercise results for one ingredient cannot be read as evidence for the other. You should also first distinguish between L-citrulline and citrulline malate.

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Final Decision Criteria: Check the Form and Evidence Before the Product Front

If you are choosing a citrulline product, it is practical to check in the following order:

• Whether it is single L-citrulline or citrulline malate
• Whether other ingredients such as caffeine or arginine are included in the product
• What your exercise goals are and your status regarding gastrointestinal discomfort or blood pressure management

And most importantly, it is necessary to acknowledge that human-based evidence is limited and conflicting. Studies on exercise performance are few and the results are inconsistent. The ODS does not provide strong support either. Meta-analyses have also shown no significant improvement in aerobic performance or blood pressure indicators.

Then, what should we look for? Rather than the front of the product packaging, checking the actual form and content of citrulline, the type of exercise, combined ingredients, and the human-based evidence available to date is a realistic starting point for evaluating this ingredient.

References

1. NIH ODS Dietary Supplements for Exercise and Athletic Performance.
2. Citrulline and aerobic exercise performance: systematic review and meta-analysis.
3. L-citrulline supplementation and blood pressure: systematic review and meta-analysis.

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This text explains the origin of the raw materials, the scope of research, and precautions before consumption. As this cannot replace individual diagnosis or treatment, please consult a medical professional if you are taking medication or if symptoms persist. If sudden and severe symptoms such as difficulty breathing or decreased consciousness occur after consumption, seek help from 119 or the emergency room.