Monounsaturated fats are very popular now with the people who tell us what to eat. The reason for this is they do not raise blood cholesterol like saturated fats and they do not lower HDL, or good, cholesterol like polyunsaturated fats. Particularly good sources of monos are olive oil, canola oil, avocado oil, and walnut oil. Many studies have also found that polys oxidize quickly and suppress some parts of the immune system while monos do not. Oxidation of fats is a normal byproduct of metabolism in the presence of oxygen, just like iron rusting in the rain.
All fats oxidize but the more unsaturated, the faster the rate.
Oxidation has bad side effects, like damage to DNA and other molecules but one benefit is to kill bacteria that get into the body so there needs to be a balance here. This also implies that very high levels of antioxidants might not be the best for our health. A lot of the enthusiasm for high monounsaturated fat diets is based on observations that Greece and Italy have low rates of heart disease. Taking one factor out of context is not a good prescription for health. Now when nutrition news gets confusing, there IS a place to go to get the real story.