Love it or hate it, grapefruit contains a compound that lowers insulin, which is a fat storage hormone. A study found that eating one half of a grapefruit before every meal resulted in weight loss without making any other dietary changes. Grapefruits are also around 90% water, which means they hydrate you while simultaneously making you feel full.
An important note: grapefruit contains medically active compounds that can seriously interfere with a wide variety of medications, including common drugs like some allergy and blood pressure medications. People with diabetes should also consult their doctor before incorporating grapefruit extensively into their diets.