Fat

All About Fat

Fat is one of the three main macro nutrients, along with carbohydrate and protein. Fat is an important foodstuff for many forms of life, and fats serve both structural and metabolic functions. They are a necessary part of the diet. Some fatty acids that are set free by the digestion of fats are called essential because they cannot be synthesized in the body from simpler constituents.

There are two essential fatty acids in human nutrition: alpha-linolenic acid (omega-3 fatty acid) and linoleic acid (omega-6 fatty acid). Other lipids needed by the body can be synthesized from these and other fats. Fats and other lipids are broken down in the body by enzymes called lipases produced in the pancreas.

Fats serve both as energy sources for the body, and as stores for energy in excess of what the body needs immediately. Each gram of fat when burned or metabolized releases about 9 calories. Fats are broken down in the body to release their constituents, glycerol and fatty acids. Glycerol itself can be converted to glucose by the liver and so become a source of energy.

Types of Fat

There are three major dietary fats in the foods we eat.

Unsaturated fats

These are found in plant foods and fish. These may be good for heart health. Unsaturated fats are found in salmon, avocados, olives, and walnuts, and vegetable oils like soybean, corn, canola, and olive oil.

Saturated fats

These fats are found in meat and other animal products, such as butter, cheese, and all milk except skim. Saturated fats are also in palm and coconut oils, which are often used in commercial baked goods. Eating too much saturated fat can raise blood cholesterol levels and increase the risk of heart disease.

Trans fats

These fats are found in stick margarine. Trans fats are also found in certain foods that you buy at the store or in a restaurant, such as snack foods, baked goods, and fried foods. When you see "hydrogenated" or "partially hydrogenated" oils on an ingredient list, the food contains trans fats. Trans fats are also listed on the food label. Like saturated fats, trans fats can raise cholesterol and increase the risk of heart disease.

Good Fats and Bad Fats

Good fats come mainly from vegetables, nuts, seeds, and fish. They differ from saturated fats by having fewer hydrogen atoms bonded to their carbon chains. Healthy fats are liquid at room temperature, not solid. There are two broad categories of beneficial fats: monounsaturated and polyunsaturated fats.

Monounsaturated fats

Monounsaturated fats have a single carbon to carbon double bond. The result is that it has two fewer hydrogen atoms than a saturated fat and a bend at the double bond. This structure keeps monounsaturated fats liquid at room temperature.

Good sources of monounsaturated fats are olive oil, peanut oil, canola oil, avocados, and most nuts, as well as high-oleic safflower and sunflower oils.

Although there's no recommended daily intake of monounsaturated fats, the Institute of Medicine recommends using them as much as possible along with polyunsaturated fats to replace saturated and trans fats.

Polyunsaturated fats

Polyunsaturated fats are essential fats. That means they're required for normal body functions but your body can't make them. So you must get them from food. Polyunsaturated fats are used to build cell membranes and the covering of nerves. They are needed for blood clotting, muscle movement, and inflammation.

A polyunsaturated fat has two or more double bonds in its carbon chain. There are two main types of polyunsaturated fats: omega-3 fatty acids and omega-6 fatty acids. The numbers refer to the distance between the beginning of the carbon chain and the first double bond. Both types offer health benefits.

Eating polyunsaturated fats in place of saturated fats or highly refined carbohydrates reduces harmful cholesterol and improves the cholesterol profile. It also lowers triglycerides.

Good sources of omega-3 fatty acids include fatty fish such as salmon, mackerel, and sardines, flaxseeds, walnuts, canola oil, and unhydrogenated soybean oil.

Omega-3 fatty acids may help prevent and even treat heart disease and stroke. In addition to reducing blood pressure, lowering triglycerides, polyunsaturated fats may help prevent lethal heart rhythms from arising.

Omega-6 fatty acids have also been linked to protection against heart disease. Foods rich in linoleic acid and other omega-6 fatty acids include vegetable oils such as safflower, soybean, sunflower, walnut, and corn oils.