In the book Guide to Wild Foods and Useful Plants by Christopher Nyerges, the author states that he met a woman who said that she was "cured" of diabetes by eating prickly pear cactus pads, also known as nopales. The author also wrote that he has met people who have stopped insulin injections after eating prickly pear cactus pads.
Interestingly, prickly pear cactus, along with mesquite pods, were used to treat diabetes by Native Americans in the western United States.
Prickly pear cactus is also used to heal prostate infections.
Plants used to treat diabetes:
Avalanche Lily/Dogtooth Violet