An Introduction to Fat

Fat Avocado

This article provides an introduction to fat. Fat is one of the three macronutrients, a group that also includes protein and carbohydrates.

Fats, or lipids, play a crucial role in a healthy, balanced diet. For example, without fats we would not be able to utilize fat soluble vitamins, and would be deprived of a major source of energy. The important role of fats in the diet is often not well understood. This article is intended to support your discussions with parents to help their understanding of the health-promoting functions of this nutrient, along with other functions which may be considered harmful, particularly in excess.

Fats are a concentrated form of energy, and protect body tissues and organs and help maintain body temperature. Fats also help the body to use the four fat-soluble vitamins: A, D, E, and K. At about 9 calories per gram, fat provides more than double the energy per gram than that of carbohydrates and proteins (about 9 calories per gram for fat vs. about 4 calories per gram for protein and carbohydrates). The American Dietetic Association (ADA) recommends that fats should make up approximately 30–40% of daily total energy intake for children ages 1–3 years and 25-35% for ages 4–18 years. The ADA recommends that saturated fats should be as low as possible while maintaining a nutritionally adequate diet. Saturated fat intake for adults should be at the lowest level possible. Trans fatty acids, created during processing of unsaturated fatty acids, have been implicated in the development of atherosclerosis and should be present in the diet at the lowest levels possible in both adults and children. 

Normally, when discussing fats, we are referring to triglycerides. 95% of dietary fats are composed of triglycerides, which are made up of 3 fatty acids. Fatty acids are chains of carbon (C) atoms with hydrogen (H) atoms attached, and with an acid group (COOH) on one end. One example of a fatty acid is linoleic acid, shown below. Linoleic acid is "an unsaturated omega-6 fatty acid and is found in the lipids of cell membranes. It is abundant in many vegetable oils, including safflower, sunflower and corn oils.

Linoleic Acid

Three types of dietary fatty acids are known: saturatedmonounsaturated, and polyunsaturated. When a fatty acid's carbon chain is completely and evenly filled (or "saturated") with hydrogen atoms, it is considered a saturated fat. Fats made up of saturated fatty acids are solid at room temperature.

When a fatty acid's carbon chain is not completely and evenly filled with hydrogen atoms, it is known as an unsaturated or polyunsaturated fat. These fats are liquid at room temperature, and are known as oils. The partial hydrogenation of liquid vegetable oils to make margarine and shortening results in the formation of trans fatty acids. Trans fatty acids, like saturated fats, have been associated with increased levels of LDL cholesterol and therefore an increased risk of heart disease.

Some types of fats may promote health, while others have been associated with risks of certain chronic diseases such as cardiovascular disease. The 2010 Dietary Guidelines for Americans note that metabolic studies show that it is the type of fat, rather than total fat intake that affects common risk factors, such as serum lipid and lipoprotein levels, and that replacing saturated fat with unsaturated fats is more effective in decreasing cardiovascular risk than is reducing total fat intake.

Fat Associated with these effects on serum cholesterol values Food sources
Unsaturated fat
Monounsaturated fat (MUFA)
Lower total and LDL cholesterol, raise HDL cholesterol Nuts, avocado, canola and olive oils
Polyunsaturated fat (PUFA)
Omega-3 and omega-6 fatty acides are PUFAs
Lower total and LDL cholesterol Salmon, fish oil, corn, soy, safflower and sunflower oils
Saturated fat (SFA) Raise total and LDL cholesterol Meat, dairy, eggs, seafood, coconut and palm oils
Trans fatty acids Raise LDL cholesterol and lower HDL cholesterol Formed by hydrogenation in food production process; vegetable shortening, hard margarine, commercially prepared foods

Two other classes of lipids in the diet are phospholipids and sterols. Similar to triglycerides, phospholipids contain fatty acids and glycerol, but they also contain other substances. Phospholipids are key components in the membrane of cells and act as emulsifiers. Our bodies can make phospholipids, therefore they are not required in our diets and are not considered a dietary essential. We do consume phospholipids in certain foods, including egg yolks, liver, soybeans and peanuts. Typically, an adult would only consume 2 grams of phospholipids per day.

Sterols are also lipids, but most sterols do not contain fatty acids. Sterols have a multi-ring structure; the best known sterol is cholesterol. Cholesterol is one of the most widespread compounds in the body, with important functions. Because cholesterol is a key precursor compound involved in cell and hormone production, healthy cholesterol levels are essential for life. The body can actually make the cholesterol needed to support metabolic needs, so dietary cholesterol is not essential. About 85% of the blood cholesterol level is endogenous (produced by the body), and the balance is from dietary sources. High dietary intake of cholesterol is generally considered to be unhealthy due to its relation to cardiovascular disease. 

Essential and non-essential fatty acids

Fatty acids must be in sufficient supply in the body, either by creating them or by consuming them. 

Nonessential fatty acids are those that the body can make. Nonessential fatty acids are highly important despite the fact that we can manufacture them ourselves.

Essential fatty acids (EFAs) are those that the body cannot make, and therefore must come from food sources. The omega-3 and omega-6 classes are in this category and are characterized by double bonds in the omega-6 and omega-3 positions. They are essential to the diet particularly for skin integrity. People with deficient essential fatty acids will be more subject to skin infections and experience slower wound healing. 

A healthy diet contains a balance of omega-3 and omega-6 fatty acids. Omega-3 fatty acids and omega-6 fatty acids both play a role in healthy growth and development. The typical American diet, with a high intake of meat, tends to contain a much higher proportion of omega-6 fatty acids than omega-3 fatty acids, which are from fish and grain/seed sources.

Fatty Acid Description Food sources Applications in health
Omega-3: DHA (docosahexaenoic acid)
  • Helps support visual and cognitive development
  • DHA is the most abundant omega-3 fatty acid in the brain and retina
  • Regulates cell activity and healthy cardiovascular function
Cold water fatty fish (salmon, tuna), fish oil
  • Dietary DHA may reduce the risk of heart disease by lowering triglycerides
  • DHA-supplemented infant formula supports developmental outcomes in preterm infants
  • Being studied for potential role in reducing the risk of Alzheimer's disease and some forms of cancer
Omega-3: EPA (eicosapentaenoic acide)
  • Help support visual and cognitive development
  • Regulates cella ctivity and healthy cardiovascular function
  • May play a role in behavior and mood
Cold water fatty fish (salmon, tuna), fish oil, Human breastmilk
  • Anti-inflammatory; potential use in arthritis, asthma and other inflammatory conditions
Omega-3: ALA (alpha-linolenic acid)
  • Important support for cognitive and behavioral function and normal growth and development
Canola oil, walnuts, flaxseed, flax oil
  • ALA deficiency may occur in degenerative diseases including heart disease and cancer, arthritis, skin conditions, diabetic neuropathy, immune function and premenstrual syndrome
Omega-6 fatty acids
e.g., linoleic acid (LA)
  • Support brain development, stimulation of growth, maintenance of skin and hair growth
Vegetable oils such as soybean and corn; nuts and seeds
  • Lineleic acid is needed for the skin to keep the integrity of its epidermal water barrier


Fats are possibly the most misunderstood of all nutrients, and this misunderstanding has the potential to result in food choices that either restrict healthy sources of this important nutrient, or provide unhealthy forms in excess.

It is important for parents to understand the important role that fat plays in their child's healthy growth and development. By understanding which foods are nutritious sources of fats, and which foods should be avoided or eaten in small amounts, they will be able to provide their child with healthy sources of this critical nutrient. 

American Academy of Pediatrics Committee on Nutrition. Kleinman RE, ed. Pediatric Nutrition Handbook. 6th Edition. © 2009 American Academy of Pediatrics.

Dietary Reference Intakes (DRIs): Recommended Intakes for Individuals, Macronutrients
Food and Nutrition Board, Institute of Medicine, National Academies

U.S. Department of Health and Human Services and U.S. Department of Agriculture. Dietary Guidelines for Americans, 2010.

Shils ME et al., eds. Modern Nutrition in health and Disease. Philadelphia, PA: Lippincott Williams & Wilkins, 2006.
American Dietetic Association. Position of the American Dietetic Association: Nutrition Guidance for Healthy Children Ages 2 to 11 Years. JADA 2008;108(6):1038–47. 

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