OIL AND FAT: ESSENTIAL FATTY ACIDS
Diagram
Two families of essential fats
Omega-3 fatty acids
Polyunsaturated fats with the first double bond three carbons from the methyl end. ALA from plants, EPA and DHA from fish.
↓
Omega-6 fatty acids
Polyunsaturated fats with the first double bond six carbons from the methyl end. Linoleic acid from vegetable oils is the main one.
Figure 1: Omega-3 and omega-6 are both essential polyunsaturated fats, but their first double bond sits in a different place and they come from different foods. Drawn in our own style from the unsaturated fatty acid discussion in Akoh and Min, Food Lipids, and in Leray, Lipids: Nutrition and Health.
Introduction
Omega-3 and omega-6 fatty acids are both essential polyunsaturated fats, which means the body needs them but cannot make them, so they must come from food. The difference is the position of the first double bond: in omega-3 fatty acids it is three carbons from the methyl end of the chain, and in omega-6 fatty acids it is six carbons from the methyl end. That small difference in structure gives them different food sources and different roles in the body. Omega-3 fatty acids come mainly from oily fish and from some plant seeds, while omega-6 fatty acids come mainly from vegetable oils.
Quick comparison
Table 1: Omega-3 Fatty Acids compared with Omega-6 Fatty Acids
| Aspect | Omega-3 Fatty Acids | Omega-6 Fatty Acids |
|---|---|---|
| First double bond | Three carbons from the methyl end | Six carbons from the methyl end |
| Main fatty acids | ALA, EPA and DHA | Linoleic acid and arachidonic acid |
| ALA and linoleic acid | ALA is the plant omega-3, and the body can lengthen it to EPA and DHA | Linoleic acid is the main omega-6, and the body can lengthen it to arachidonic acid |
| Main food sources | Oily fish, flaxseed, chia and walnuts | Soybean, sunflower, corn and safflower oils, nuts and seeds |
| Made by the body | No, they are essential and must come from food | No, they are essential and must come from food |
| Role | Part of cell membranes, especially in the brain and eyes, and the source of signalling compounds | Part of cell membranes and the source of signalling compounds |
| In the diet | Eaten in smaller amounts in most diets | Eaten in larger amounts, because vegetable oils are widely used |
| Form in food | EPA and DHA in fish, ALA in plant seeds | Linoleic acid in vegetable oils and seeds |
| Stability | Very unsaturated, so they oxidise readily | Unsaturated, so they oxidise, but less readily than the long chain omega-3 fats |
| Deficiency | The books used here describe both as essential, so a diet with neither cannot meet the need | The books used here describe both as essential, so a diet with neither cannot meet the need |
Scientific explanation
Definition
Omega-3 fatty acids are polyunsaturated fatty acids whose first double bond is three carbons from the methyl end of the chain, including alpha-linolenic acid (ALA) from plants and eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from fish. Omega-6 fatty acids are polyunsaturated fatty acids whose first double bond is six carbons from the methyl end, including linoleic acid from vegetable oils and arachidonic acid made from it in the body.
Working principle
Both families are built from the same starting chemistry: the body lengthens and desaturates the parent fatty acid, ALA for omega-3 and linoleic acid for omega-6, to make longer chain fatty acids. Because the body cannot make the parent fatty acids, both are essential and must be eaten. The position of the first double bond decides the shape of the chain and which enzymes act on it, so the two families give different signalling compounds in the body. The same enzymes work on both families, so the two compete for them, which is why the balance of omega-3 and omega-6 in the diet matters.
Apparatus
The books used here name no laboratory apparatus for measuring or comparing either term, so no apparatus list is given.
Measurement procedure
The books used here give no standard laboratory procedure with volumes and steps for either term, so no procedure is invented here.
Factors affecting readings
For both families, the food source decides which fatty acids are eaten: fish gives EPA and DHA directly, while plant seeds give ALA, which the body must lengthen. Cooking and storage matter for both: heat, light and air oxidise these very unsaturated fats, so oils rich in them are kept dark, cool and closed. The books used here give no numeric intake values, so none are stated.
Formulas and calculations
The books used here give no formula for either term, so no formula is given here.
Industrial applications
- Omega-3 fatty acids: oily fish and fish oils, eaten as food and used in supplements.
- Omega-3 fatty acids: flaxseed, chia and walnut oils, used as plant sources of ALA.
- Omega-6 fatty acids: soybean, sunflower and corn oils, used as general cooking oils.
- Omega-6 fatty acids: nuts, seeds and their oils, used in spreads, dressings and baking.
- Both families: infant and food products where essential fatty acids must be present.
Advantages and limitations
- Omega-3 fatty acids, advantage: EPA and DHA come ready made from fish, and ALA comes from plant seeds.
- Omega-3 fatty acids, limitation: the long chain forms oxidise readily, so fish oils need dark, cool, closed storage.
- Omega-6 fatty acids, advantage: linoleic acid is plentiful in common vegetable oils, so it is easy to eat enough.
- Omega-6 fatty acids, limitation: because vegetable oils are used so widely, omega-6 is often eaten in much larger amounts than omega-3.
FAQ
What is the difference between omega-3 and omega-6 fatty acids?
The first double bond sits three carbons from the methyl end in omega-3 and six carbons from the methyl end in omega-6, and they come from different foods.
Which foods give omega-3?
Oily fish gives EPA and DHA, and flaxseed, chia and walnuts give ALA.
Which foods give omega-6?
Vegetable oils such as soybean, sunflower and corn oil, and nuts and seeds, give linoleic acid.
Can the body make them?
No. Both are essential, so they must come from food.
Why does the balance matter?
Both families use the same enzymes, so they compete, and the mix eaten decides which signalling compounds the body makes.
References and further reading
- FTN books on disk: Technology of Fats and Oils.
- Leray, Claude. Lipids: Nutrition and Health. CRC Press, 2014.
- Akoh, Casimir C. and David B. Min (eds). Food Lipids: Chemistry, Nutrition, and Biotechnology. 2nd ed., CRC Press, 2002 (Google Books page read)
- Google Books pages read for this article:
- Akoh, Casimir C. and David B. Min (eds). Food Lipids: Chemistry, Nutrition, and Biotechnology. 2nd ed., CRC Press, 2002 (Google Books page read)
