Liquid at room temperature, these plant-based fats can lower cholesterol when used in place of saturated fat in the diet.
Credit: Randy Mayor; Leigh Ann Ross

Sources: Canola, olive, and peanut oils, as well as peanuts, pecans, and avocados

What you need to know: Studies show that healthful fats like olive oil and peanuts, in particular, are good for the heart, weight loss, and health in general, possibly because they are rich and satisfying even in small amounts. An article published in the July 2007 Diabetes Care finds monounsaturated fats might help trim weight around the waist. Volunteers with a family history of abdominal fat and diabetes were asked to eat three different diet plans. Calories were held constant, but the changing factors were the amount and type of fat and the amount of carbohydrates. For the first 28 days, diets were ­enriched with saturated fat. Next, each person followed a 28-day diet plan with a higher amount of monounsaturated fat. In the third phase, carbohydrates were emphasized. Weight and body composition held constant on all three plans, but body fat shifted out of the belly area when volunteers were ­eating higher levels of monounsaturated fats. Fat migration is important because fat stored deep around the belly is a greater risk factor for heart disease, diabetes, breast cancer, and high blood pressure than fat stored in the hips and thighs.

Cooking strategies: While olive oil attracts the most attention, other liquid oils are healthful and versatile, too. Canola and peanut oils are both good sources of monounsaturated fat with high smoke points (the temperature where oil begins to burn); canola has a mild flavor great for baking or sautéing, while peanut oil delivers nutty flavor to stir-fries or Asian-inspired vinaigrettes. There's no reason to use a single type of oil exclusively (we tend to use olive or canola, depending on the dish), but use these healthful oils sparingly. When experts talk about healthful fats, Jennifer Nelson, RD, director of nutrition therapy at the Mayo Clinic, says they aren't giving you carte blanche to eat as much as you want. The idea is to enjoy moderate amounts and to use unsaturated fats most often