Fat

The fat found in the food you eat is known as dietary fat. Dietary fats are triglycerides, compounds made up of three fatty acids and a glycerol molecule. After fats are digested, they are either used for energy or stored as body fat.¹ Fat in the diet is necessary for the absorption of some vitamins and is generally vital to proper body function.

Both plant- and animal-derived foods contain fat. The four main types of fat are saturated fat, monounsaturated fat, polyunsaturated fat, and trans fat. These fats are composed of different fatty acids. Because of their different chemical structures, they have different effects on the body. Most dietary recommendations suggest limiting saturated fats (though these recommendations have been called into question) and eating unsaturated fats in moderation. 

Saturated fats are solid at room temperature and are found in meat, dairy, and coconut oil. Unsaturated fats are liquid at room temperature and are found in vegetable oils, nuts, avocados, fish, etc. For a typical 2,000 calorie diet, the Dietary Guidelines for Americans recommends eating between 44 and 78 grams of fat per day.² 

Omega-3 fatty acids and omega-6 fatty acids are two types of fatty acids that get a lot of attention. They are essential fatty acids, which means the body cannot produce them itself and must instead get them from food sources.³ Both are necessary for a healthy diet, but some research suggests that the Western diet is too high in omega-6 fatty acids and too low in omega-3 fatty acids, and this unfavorable ratio might cause health problems.⁴ 

Dietary sources of omega-3 fatty acids include flax seed and fatty fish like salmon, anchovies, herring, and sardines. Omega-6 fatty acids are primarily found in vegetable oils, including corn, sunflower, and safflower oils, which are commonly used in processed foods.

Because fat has more calories per gram than protein or carbohydrates ( 9 calories per gram vs. 4 per gram), some suggest that a diet high in fat might lead to weight gain.⁵ Nonetheless, it is not a good idea to follow a low-fat diet, because restricting fat consumption also restricts the consumption of fats that are good and even necessary for your health.⁶ 

Though it is unclear whether it is necessary to avoid saturated fat in the diet, there is no question that you should avoid artificial trans fat. These are the trans fats made during food processing. Trans fans have been found to increase LDL cholesterol (the "bad" cholesterol) while decreasing HDL cholesterol (the "good" cholesterol).⁷ Read packaging to avoid synthetic trans fats, which are found in hydrogenated oils, margarine, and many snack foods.

Fatty Foods

Sources

1. Encyclopedia Britannica - Fat
2. Mayo Clinic - Dietary fats: Know which types to choose
3. Harvard School of Public Health Nutrition Source - Ask the Expert: Omega-3 Fatty Acids
4. Biomedicine & Pharmacotherapy - The importance of the ratio of omega-6/omega-3 essential fatty acids.
5. Mayo Clinic - Healthy diet: Do you follow dietary guidelines?
6. Harvard School of Public Health Nutrition Source - Fats and Cholesterol
7. PLOS ONE - Effect of animal and industrial trans fatty acids on HDL and LDL cholesterol levels in humans--a quantitative review.