Fats are complex molecules composed of fatty acids and glycerol. The body needs fats for growth and energy. It also uses them to synthesize hormones and other substances needed for the body’s activities (such as prostaglandins). Fats are the slowest source of energy but the most energy-efficient form of food. Each gram of fat supplies the body with about 9 calories, more than twice that supplied by proteins or carbohydrates. Because fats are such an efficient form of energy, the body stores any excess energy as fat. The body deposits excess fat in the abdomen (omental fat) and under the skin (subcutaneous fat) to use when it needs more energy. The body may also deposit excess fat in blood vessels and within organs, where it can block blood flow and damage organs, often causing serious disorders.

Fatty Acids: When the body needs fatty acids, it can make (synthesize) certain ones. Others, called essential fatty acids, cannot be synthesized and must be consumed in the diet. The essential fatty acids make up about 7% of the fat consumed in a normal diet and about 3% of total calories (about 8 grams). They include linoleic acid and linolenic acid, which are present in certain vegetable oils. Eicosapentaenoic acid and docosahexaenoic acid, which are fatty acids essential for brain development, can be synthesized from linolenic acid. However, they also are present in certain marine fish oils, which are a more efficient source.







Where’s the Fat? 


Type of Fat Source
Monounsaturated Avocado, olive, and peanut oils 

Peanut butter


Polyunsaturated Canola, corn, soybean, sunflower, and many other liquid vegetable oils 


Saturated Meats, particularly beef 

Full-fat dairy products such as whole milk, butter, and cheese

Coconut and palm oils

Artificially hydrogenated vegetable oils


Omega-3 fatty acids Flaxseed 

Lake trout and certain deep-sea fish, such as mackerel, salmon, herring, and tuna

Green leafy vegetables



Omega-6 fatty acids Vegetable oils (including sunflower, safflower, corn, cottonseed, and soybean oils) 

Fish oils

Egg yolks

Trans fats Commercially baked foods, such as cookies, crackers, and doughnuts 

Some french fries and other fried foods



Potato chips