"Instead of using a whopping dollop of mayonnaise on your sandwich, try using thin slices of avocado," suggests Megan Madden, a registered dietitian in New York, NY. A 1996 study done by researchers in Mexico found that people who ate avocado every day for one week experienced an average 17 percent drop in total blood cholesterol. What's more, their levels of LDL ("bad") cholesterol decreased and HDL ("good") cholesterol increased. Finding it tough to work avocado into your diet? Try drinking it in this delicious smoothie.