What are Fats and Oils? Fats and Oils Definition

Healthy Fats - Olive Oil
Image by Steve Buissinne from Pixabay
  Last update November 11, 2021, article reviewed & updated multiple times since February 23, 2002.

  What You Need to Know

  • Fats and oils are one of the three kinds of substances known as lipids.
  • One molecule of fat is formed by the union of one unit of a substance called glycerol, with three units of substances called fatty acids.
  • In order for fats and oils to be able to be mixed with water, they must undergo a process known as emulsification.

Today we are starting our discussion of Fats and Oils as foods. In this article, we explore the definition of fats and oils, and we will talk about the characteristics of these substances. We talk about Fats Definition and the characteristics of these substances as Fats and Oils Definition.

Fats and Oils Definition

To make sure we are always on the same page, we have to make a differentiation between the words ‘fat,’ ‘dietary fat,’ and ‘body fat.’

  • I will use the phrase dietary fat whenever I am referring to fats that we eat.
  • I will use the phrase body fat whenever I mean the fat stored in our tissues, on our hips, or elsewhere in the body, including both the normal amounts and the excess.
  • And I will use the word fats, without any other descriptive word, when talking about the substances themselves.

The Composition Of Fats And Oils

Mushrooms With Garlic & Parsley Recipe - Heat the oil in a large frying pan

Fats and oils are one of the three kinds of substances known as lipids. In addition to fats, lipids include the compounds known as phospholipids (FOS-fo-lip-ids), and those known as steroids. We will talk about phospholipids and steroids as we go along, but for now, we are focusing
on fats.

Fats, like carbohydrates, are composed of the same basic elements: carbon, hydrogen, and oxygen. However, the smallest units of fats (called molecules of fat) are larger than molecules of carbohydrates, and the relative proportions of carbon, hydrogen and oxygen to each other in fats is different from those in carbohydrates.

One molecule of fat is formed by the union of one unit of a substance called glycerol, with three units of substances called fatty acids. There are a great many different types of fatty acids, but the dietary fats found in our foods and in our body fat are, for the most part, formed from only three kinds of fatty acids. (For those who are keeping notes, these are known as oleic acid, palmitic acid, and stearic acid, and they form fats known as olein, palmitin, and stearin.)

Glycerol (GLIS-er-all), sometimes called glycerin or glycerine, has three “arms.” Each of the three arms joins with one fatty acid to make a single molecule of fat. This explains why fats are referred to as tri-glycerides (usually spelled triglycerides, without the hyphen). These are the simplest fats.

The Composition Of Dietary Fats

Healthy Fats - Olive Oil
Image by congerdesign from Pixabay
Dietary fats are mixtures of the three fats mentioned above, olein, palmitin, and stearin. Differing amounts of each of the three result in the different characteristics of each type of dietary fat. For example, more olein and less of the other two lowers the melting point of the fat. When a fat has such a low melting point that it is liquid at room temperature, it is called an oil. Among these are olive oil, canola oil, and cod liver oil.

Human body fat contains from 70 to 80 percent olein, and therefore has a melting point below normal body temperature. As a result, simple body fats are found in the form of droplets of oil in body cells. In addition, nearly all body cells contain at least some body fat.

Pure fats are odorless and tasteless. The smell that we associate with fats, especially when cooking them, is due to foreign materials that have been absorbed into the fat. The smell of bacon cooking is due to the pork, not the fat. Rancid or spoiled fats smell bad because of bacteria action acting on the fats.

Fats are not soluble in either hot or cold water. Fats that are hard at room temperature can be melted, but they still don’t mix with water any more than oils do. You can shake oil and vinegar together in a jar, but as soon as you stop shaking, the water-soluble vinegar separates from the oil.

In order for fats and oils to be able to be mixed with water, they must undergo a process known as emulsification (E-mull-se-fa-KAY-shun). Emulsification is a process by which each droplet of fat is surrounded by a droplet of the emulsification agent. This holds the fat in solution long enough for it to be used.

The reason we can wash our dishes in water is that we use soap, which is an emulsifier. Soap holds the grease (the fats and oils) long enough for them to be washed away. We will talk more about emulsification when we talk about fat digestion.

Healthy Fats - Olive Oil
Image by Mareefe from Pixabay

The Difference Between Saturated And Unsaturated Fats

In large part because of the great Fat Versus Low Fat controversy that has been going on for half a century, many people tend to think that the only thing anyone needs to know about fats is whether they are saturated or unsaturated. The essential difference between saturated fats and unsaturated fats is that the one is hard at room temperature, and the other is liquid at room temperature.

The word ‘saturated’ means ‘filled to capacity.’ When talking about saturated and unsaturated fats, we are really talking about the amount of hydrogen in the chemical make up of the particular fat, compared with how much hydrogen that fat is capable of holding.

  • Unsaturated fats have fatty acids with less hydrogen than they can hold. These fats are liquids at room temperature and are called oils.
  • Saturated fats have fatty acids that are holding all the hydrogen possible, and they are hard at room temperature, like butter.

Once a fat is fully saturated, it cannot be made unsaturated, but unsaturated fat can be converted to saturated fat. This is done by heat, or by other chemical means, in a process known as hydrogenation (high-DROG-gen-nation).

What Are Partially Hydrogenated Oils?

The familiar phrase ‘partially hydrogenated oil,’ which appears on a great many labels, particularly fast-food labels, means that the unsaturated liquid oil was partially converted to a more solid fat. This is done to make the food item more substantial.

New studies appear to indicate that the partial-hydrogenation process is not good for health because it produces changes in the chemical structure of the fats that are unsafe.

Until Next Time…

Fats and Oils Definition: What are Fats and Oils?
In my next article, I will continue with our discussion of fats. We’ll look at the functions fats play in the body, and then begin talking about fat digestion.

Join me, won’t you?

The Science of Low-Carb & Keto Diets
    The Science of Low-Carb & Keto Diets

  • Presented by CarbSmart.com
  • This article is number 19 of 24 articles describing The Science of Low-Carb & Keto Diets. Visit this link or click the above image for all of the articles in the series.
Article History

  • Last Update November 11, 2021
  • Updated April 3, 2018
  • Updated August 19, 2010
  • Updated October 9, 2003
  • Original Article February 23, 2002
⬅️  Previous Article
Next Article  ➡️
About Dr. Beth Gruber
Dr. Gruber is a graduate of the Southern California University of Health Sciences and has been in private chiropractic practice in Long Beach, California since 1964. She also received both a Bachelor’s Degree and a Master’s Degree from California State University at Long Beach. She has written on health-related subjects for over 30 years, for several different publications. She lives in Southern California with her husband of 33 years. Both she and her husband follow and live the low-carb lifestyle full time.

Next Article:[contentcards url=”https://www.carbsmart.com/functions-of-dietary-fat.html” target=”_blank”]

More Vital Information articles by Dr. Beth Gruber.

Check Also

Dieting By “Blocking” Starch And “Blocking” Fat

The idea that starch or fat can be blocked from digestion appears to be an appealing idea. For the past thirty or more years, these products have come to the forefront periodically with promises for a new generation of overweight people. Each time they come on the market, they offer up suggestions that you can eat what you want so long as you take their product. The product, so goes the promise, will protect you from the consequences of eating the blocked food group.


  1. It was kind of confusing when i the article said Saturated fat can not be converted to unsaturated, but unsaturated can be converted to Saturated, by heat. So i was thinkin is it not Saturated like butter that can be heat for it to turn to oil?

    • saturated means that the fat has no double bond in its carbon-hydrogen+fatty acid chains (its structure), unsaturated fat has a double bond in its structure and can be broken down by hydrolysis (breaking down that double bond into single bond and turns to saturated acid)

  2. Sincerely speaking, Dr, Gruber did a great work in this piece. Simplicity and clarity of terms!
    Your piece satisfied my quest approprately.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.