The study's seven participants, all men, were given 17 ounces (500 mL) of either natural watermelon juice, watermelon juice enriched with additional citrulline, or a placebo drink an hour before their workouts. Interestingly, the natural juice was just as effective as the enriched juice. The researchers also determined that intestinal cells can absorb more citrulline from watermelon juice than from citrulline supplements, especially when the juice is unpasteurized. 2. It helps heart health.