Are some kinds of fat good and some bad? The short answer is yes.
We need a certain amount of fat in our diet to be healthy. All of the fats found naturally in food are used by the body, including saturated, monounsaturated, polyunsaturated omega 6, and polyunsaturated omega 3 fats.
None of the fats found naturally in food can be called bad.
Unfortunately, because of industrial food processing, many of the fats we eat now are not natural fats!
The fats that are truly bad are those that are (1) industrially manufactured with heat and chemicals or (2) spoiled.
Unfortunately, those are the typical fats in processed food and restaurants.
For the details, continue!
All living things, both animals and plants, contain fat. So nearly all food contains fat:
Read more about Fat in Food
Saturated fats are healthy fats.
They are not the cause of heart disease and do not clog arteries. Older flawed studies lumped together saturated fats with trans fats and generated faulty conclusions, conclusions that are contradicted by newer research.
One advantage of saturated fats, such as beef fat and coconut oil, is that they do not spoil easily so do not easily turn into bad fats.
Like all fats, animal fats are a mix of saturated, monounsaturated, and polyunsaturated fatty acids. (See below for more on fatty acids).
Many animal fats are predominantly monounsaturated: chicken, duck, goose, turkey, and pork fat.
Some plant-origin fats are saturated: coconut oil, palm oil, and palm kernel oil.
There is no controversy about monounsaturated fats. Nearly all nutritionists agree that they are desirable fats!
Monounsaturated fats like olive oil are a major feature of the healthy Mediterranean Diet.
Canola oil, however, is a controversial monounsaturated fat. This site takes the view that canola oil is too questionable to use.
Polyunsaturated fats include the omega 6 and omega 3 fatty acids. Although Americans eat far too many omega 6 fatty acids and far too few omega 3 fatty acids, the body needs both. Additionally, the two essential fatty acids and many of the conditional fatty acids are polyunsaturated fatty acids.
Oils containing them are necessary, good, and healthy oils, when unrefined and kept from going rancid.
Polyunsaturated oils are very unstable and spoil quickly. Refining is an attempt to keep these oils from spoiling, yet the refining process also causes major damage to the oils.
Traditionally, people got polyunsaturated fats from whole foods – from seafood and fresh seeds and vegetables. They did not extract oil from vegetables like corn. They did not have the technology to do this extraction and if they had, the oil would have spoiled quickly.
Trans fats, such as partially hydrogenated oils used in processed food, are definitely bad. Trans fats are manufactured, unnatural fats. They interfere with many functions of the body, including fat metabolism. They contain malformed fatty acids that become incorporated into the body. As a result, trans fats consumption is associated with many diseases, including heart disease and cancer.
Trans fats are unsaturated. It is a myth that trans fats might be the "same" as saturated fats. The myth may stem from the way fat is used in the food processing industry, since it is not possible to make bakery, pastry, cookies, or fried foods without fat. Industry uses partially hydrogenated oils (trans fats) instead of butter and coconut oil (saturated fats) because the cheaper synthetic oils have a consistency similar to butter and coconut oil.
Fat is one of the three macronutrients. (The other two are protein and carbohydrates.) Your body can't survive without fat!
The body is unavoidably composed in part of fat. It also uses fat for fuel, to absorb fat-soluble vitamins and nutrients, and to create "messenger molecules" for the endocrine and immune systems.
Every cell of the body is contained by a cell membrane that is 50% fat. Not only do cell membranes hold the body together, they control the complex biochemistry of the cell (through ion channels and chemical receptors). Cell membranes are vital to cell function and thus to body function.
Our organs and tissues are made of a high percentage of fat. The brain is 60% fat. The entire central nervous system is largely composed of cell membrane. Other important membrane tissues include the lining of the lungs and the lining of the intestines. The eye and the inner ear are composed of a high percentage of specialized fats.
The good fats used in the cell membranes, the brain, the eye, and elsewhere aren't just any random fats. Fats in different parts of the body are composed of unique combinations of fatty acids.
Fatty acids are the building blocks of fats. There are hundreds of natural fatty acids, each with a different molecular structure and different characteristics and uses.
In the body, the right fatty acids need to be in the right place at the right time. And the source of these fatty acids is mostly the fat in food. Although the body can, technically, make for itself most (not all) of the needed fatty acids, it strongly prefers to use the fatty acids from the fats in the diet.
Because the body prefers to use the fats that it eats, it is important to eat a variety of healthy fats. Those are the good fats discussed on this site!
Although the body can, technically, synthesize many fatty acids, it cannot make the essential fatty acids (EFAs). EFAs are needed fats that the body can't make under any conditions and must get from the diet. There are only two: lineoleic acid (LA), which is an "omega 6" fatty acid, and alpha-linolenic acid (ALA), which is an "omega 3" fatty acid.
Some biochemists believe a few more fatty acids used in the body are conditional fatty acids (CFAs). These can't be made by the body in some/most people or under some/most conditions. In those cases, the diet would be the only possible source.
The body is able to store EFAs and other fatty acids for future use. In the course of metabolism, it will send the right fatty acid to the right place in the body.
However, and this is the key point for deciding which fats to eat, the body will substitute one fatty acid for another when it doesn't have enough of the preferred fatty acid. The consequence may be the Western diseases (heart disease, cancer, diabetes): traditional people eating a traditional variety of all-natural fats don't get Western diseases.
Different fats (such as olive oil, corn oil, butter) have different characteristics. Why? Each has a unique composition of fatty acids.
There are hundreds of different fatty acids, but a smaller number are important in human health. They fall into four classifications, according to characteristics of their molecular structure: saturated fatty acids, monounsaturated fatty acids, polyunsaturated fatty acids, and trans fatty acids.
Examples of fatty acids:
For more information about foods, good fats, and the four kinds of fatty acids:
Only one of these kinds of fatty acids can be thought of as "bad": synthetic trans fats. (There is a natural trans fatty acid that is beneficial, conjugated linoleic acid (CLA).)