The Good Guys
Fats have gotten a bad reputation, but the truth is that unsaturated fats are excellent for you! Nuts, eggs, fish, flaxseed, and some plant oils are fantastic sources of omega-3 and omega-6 fatty acids, which are essential in the diet. 
Omega-3’s, in particular, help to reduce risk of heart disease, increase blood circulation, reduce joint pain, and reduce symptoms of depression. The American diet is typically low in essential omega-3 fatty acids, and we could definitely stand to increase our consumption of these powerful nutrients.
The Bad Boys
Saturated and trans fats, on the other hand, are very dangerous. Both types are major contributors to heart disease and strokes.
Saturated fats are usually associated with animal products: red meat, cheese, ice cream, etc. The nutrition label will always tell you the grams of saturated fat in the product you’re eating. Aim to keep saturated fats at 10% or less of your total fat consumption.
Trans fats are artificially-created saturated fats (naturally unsaturated fats that have been chemically altered to be solid at room temperature). Read more on trans fats. Trans fats can usually be found in packaged foods: Poptarts, crackers, chips, peanut butter, bread, and MANY common grocery store items. Aim to reduce your trans fat consumption to as little as possible. These fats are bad news, so if you can eliminate them from your diet, do so.
Did You Know?
If the Ingredients List says 
“partially hydrogenated”, then the item contains trans fats.
Often, the nutrition label will say 0 grams while the ingredient list will say partially hydrogenated soybean oil (or another trans fat). Companies can do this if the amount of trans fat is less than 0.5g per serving. Tricky, I know.
Thus your best plan of action is to read the ingredient lists thoroughly, and be fully informed about what you’re eating. Healthy unsaturated fats can (and should!) make up 25-30% of your daily diet. Limit saturated fats to 10% of total fat consumption (10% of the 25-30% you consumed that day), and eliminate trans fats if possible.
For more on weight loss, try “10 Ways to Make Weight Loss Work for You.”
For more on fats:
Fat-Free: Too Good To Be True?
Resources:
FDA, Office of Nutritional Products, Labeling, and Dietary Supplements
