Monounsaturated fats are diet-friendly and heart-healthy fats found in foods such as olive oil, nuts and avocados. These fats may also help trim your waistline. A 2004 study in the “American Journal of Clinical Nutrition” reported that consuming 33 percent of daily calories from monounsaturated fats can assist with weight maintenance and loss, while also potentially reducing risks for cardiovascular disease.

Polyunsaturated fats are also “friendly” fats that can be found in fish, nuts and seeds. These fats can improve blood cholesterol levels and reduce the risks of developing cardiovascular disease and Type 2 Diabetes. Eating polyunsaturated fats will keep you feeling fuller longer, and less likely to blow your diet by overeating when hunger pangs hit.

Saturated fats come mainly from animal products. These unhealthy fats can raise total cholesterol and increase your risk for cardiovascular disease and Type 2 Diabetes. Foods high in saturated fats include high-fat cheese, meat, butter, cream, and whole milk. According to a 2010 study in “Nutrition Research,” a diet high in saturated fats is more likely to cause weight gain than a diet rich in unsaturated fats, making saturated fats both unhealthy and a bad choice for dieters.

Trans fats occur naturally in some animal products, but they’re most often produced during a process used to make unsaturated fats easier to cook with. Trans fats are “bad” fats that increase the risk of cardiovascular disease and raise unhealthy LDL cholesterol levels — and they’re also a dieter’s enemy. Research conducted at the Wake Forest Baptist Medical Center revealed that trans fats contribute to weight gain. During the 2006 study, monkeys that were fed trans fats gained weight, while those fed the same amount of calories in the form of monounsaturated fats did not. Avoid foods that have been cooked in partially hydrogenated oils, such as French fries and donuts, which are loaded with trans fats.