What is Fat?

Different Kinds of Fat and How they Relate to Your Health

Olive oil is a form of healthy fat.
Olive oil is a form of healthy fat. Tim Boyle/Getty Images

What is fat and how does dietary fat fit into a healthy lifestyle? Let's look into the different kinds of dietary fat with their benefits and health effects. Then we'll explore how excess calories from fat might put fat our bodies.

Benefits of Dietary Fats

  • Slow digestion
  • Make you feel full
  • Slow absorption of carbohydrates in the intestine
  • Hormone production and balance
  • Improve mood
  • Absorb fat soluble vitamins - A, D, E, K
  • Keep you oiled -- hair, skin, joints, brain
  • Reduce inflammation
  • Emulsify (breakdown and move) fats
  • Brain health
  • Source of energy
  • These benefits do not apply to trans-fats, which have no benefits to health at all. More on them below.

There are different kinds of fats and some are more healthful than others. To understand that, let us do a very quick fat-science lesson. Don't worry, it's easy and you will be able to make better choices about the fats you buy and put in your mouth if you get a few key concepts.

What is Fat?

Dietary fats are divided into two categories, the generally unhealthy saturated fats and healthy unsaturated fats. Both are built with fatty acids. What makes them saturated or not has to do with whether or not all the places for a hydrogen atom in their structure are filled or not. Saturated are full. Unsaturated are not.

Before we get into the two kinds of dietary fat and which foods have them, there is another fat term you might be wondering about: essential fatty acids.

Essential Fatty Acids (EFAs) - the Building Blocks

Saturated and unsaturated fats are built with molecules that are made of 3 fatty acids (hence the term triglycerides) and a glycerol molecule. The fatty acids your body cannot make for itself are called essential fatty acids. The omega-3 fatty acids you may have heard are so healthful are in that category.

Those, along with omega-6 fatty acids, must be taken in through diet. The problem is that American diets are usually overly abundant in omega-6 and lacking in Omega-3 fatty acids, which is why people are currently urged to include omega-3 sources in their diets such as cold water fish, flax, green leafy vegetables, and nuts or use omega-3 supplements.

For details on fat structure, please see Saturated and Unsaturated - the Unhealthy and Healthy Fats

Healthy and Unhealthy - The Kinds of Fat

Saturated Fat

Saturation means that all the places for hydrogen bonds along the carbon chains that make the fatty acid chains in the fat are full. That makes the fat more stable. Saturated fats are hard at room temperature and doesn't breakdown as easily in cooking, which is one of its benefits.

  • Sources of saturated fat: Red meat, dairy products such as whole milk, cheese and butter; oils such as coconut oil, palm kernel oil and palm oil.

The conventional battle cry of dietary fitness has been to stay away from saturated fat. They raise LDL cholesterol levels and have been associated with heart disease, cancer and other diseases of inflammation. Everything, however, has its place and small amounts of saturated fat do have benefits to offer.

Saturated fats can provide vitamins and minerals. Studies show they help transport calcium to the bones, and they have a role in supporting the immune system. The brain also uses saturated fat, including cholesterol.

The saturated fats also help the body use and move unsaturated fat. The way different fats help breakdown and move other fats has implications for weight loss that are not fully understood but clearly put the need for balancing ones attitude toward fat in the forefront. Coconut oil, for example is a saturated fat that is gaining a reputation as a possibly healthful fat that may help stimulate the metabolism.

We don't need a lot of saturated fat. The U.S.D.A 2010 Dietary Guidelines suggest that for a healthful diet, saturated fat should be about 7% of the total calories you eat. That's not much.

Unsaturated Fat

Unsaturated fat is divided into two categories polyunsaturated and monounsaturated. Monounsaturated fats have one carbon bond that does not have a hydrogen molecule attached. Polyunsaturated fats have more than one bond for a hydrogen atom that is unfilled. Unsaturated fats are usually liquid, even when cool, so we call them oils, and they are less stable than saturated fats.

Both mono and polyunsaturated fats are generally considered healthy fats, with monounsaturated fat being the most healthy. Monounsaturated fat is associated with lowering bad cholesterol (LDL) and raising good (HDL).

  • Sources of monounsaturated fats: olive oil, high-oleic sunflower oil and safflower oil, canola oil avocado, almond, peanut corn, sesame soy and cod liver oil
  • Sources of polyunsaturated fats: cold water fish like salmon, walnuts, seeds, dark leafy greens, and flax oil.

Trans Fats

Technically, trans fats are unsaturated fats, but they have been chemically altered by industry to have an extra hydrogen atom attached to them. Thus they are "partially hydrogenated". Unsaturated fats tend to be unstable, partial hydrogenation makes them more stable and that means they have a longer shelf life. That is good for the packaged food maker or a grocery store, but it's bad for you. Trans fats raise bad cholesterol, which clogs arteries and lower good cholesterol, which helps our bodies make sex and steroid hormones and contributes to cell flexibility. The F.D.A requires that trans fats be labeled in foods. Read the labels. If says trans fats, stay away. Remember, a partially hydrogenated fat is a trans fat.

Calories, Fat, and Your Body

Remember the last point on my list of benefits of fat? It was one of the most important. Fats are a source of energy. Dietary fats are the most dense source of calories we have. They provide approximately twice as many calories per gram as carbohydrates or protein. If we eat more calories than we need to burn, whether from fat or other nutrients, our bodies are very efficient and store those calories as body fat. Body fat does have an important role to play in our health.

Benefits of body fat include:

  • Source of energy
  • Pads organs and bones
  • Insulates
  • Helps regulate body temperature
  • Used to make hormones
  • Helps transport nutrients
  • Protects nerves
  • Helps make up our cell membranes

The problem is that we tend to eat too many calories, far more than we need, and then our body stores them as fat and we gain weight. So there are two main dangers associated with fat: One, we eat too many unhealthy saturated fats which make our arteries hard and lead to problems like heart disease and stroke. And two, we eat too many fat calories overall which are then stored in our bodies as excess fat.

How Much Fat to Eat

Clearly there are benefits to fats, and there are benefits to having some stored fat. What we need to do is eat the right amount of fat. According to the USDA, approximately 30% of our daily calories can be from fat and at least 23% of those need to be from the healthy unsaturated fats, so that less than 10 percent of our calories are from saturated fatty acids. And, our fat consumption needs to take place in the context of an overall healthy diet and lifestyle.

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U.S.D.A. Dietary Guidelines 2010

Erasmus, U. (1999). Fats that Heal Fats that Kill

NIH, Weighing in on Dietary Fats