Researchers from Purdue University in the US who carried out studies on mice fed a high-fat diet found the fruit halved the rate at which 'bad' low-density lipoprotein, or LDL, accumulated.
LDL is a form of cholesterol that leads to clogged arteries and heart disease.
The study found that the fruit also helped to control weight gain and resulted in fewer fatty deposits inside blood vessels, the Daily Mail reported.
Researchers believe the secret to watermelon's health-boosting properties lies in citrulline, a chemical found in the juice.
Previous studies have suggested citrulline has a role to play in heart disease prevention by lowering blood pressure.
Although the latest investigation showed no significant effects on blood pressure, it did find that watermelons had a powerful impact on other heart risk factors.
Researchers fed two groups of mice a high-fat diet but gave one water to drink and the other watermelon juice.
They tracked their health for several months and at the end of the experiment found the mice given watermelon juice had 50 per cent less LDL than those on water - despite eating the same diet.
They also weighed an average of 30 per cent less, but their blood pressure was no different.
"We didn't see a lowering of blood pressure. But these other changes are promising. We know that watermelon is good for health because it contains citrulline. We don't know yet at what molecular level it's working and that's the next step," research leader Dr Shubin Saha, said.
The study was published in the Journal of Nutritional Biochemistry.
