THE RESULT: You may gain trans fat.THE FIX: Margarine is made by forcing hydrogen through vegetable oils, which makes it solid at room temperature and also produces trans fat, a type of fat that raises “bad” LDL cholesterol and lowers “good” HDL cholesterol. Check ingredients; many margarines still use these partially hydrogenated oils and can contain up to 2.5g of trans fat per tablespoon. (The American Heart Association recommends limiting trans fat to less than 1% of your daily calories—about 2g for the average person on a 2,000-calorie- per-day diet.) Other margarines now blend trans-fat-free palm oils with emulsified vegetable oils and are trans fat free. Butter is made from cream (the fatty top layer of whole milk) that’s churned until the fat solids separate. By law, it must contain at least 80% milk fat—artisanal varieties may have more. You can’t hide it: Butter contains fat and a good bit of it—7g of sat fat per tablespoon. But in moderate amounts, butter can be part of a healthy diet. There’s really no substitute—it produces rich flavors, helps create tender baked goods, and is key for browning.