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I was a bit confused about the relationship between "omega-6" and
"omega-3" fatty acids, Linoleic Acid and Alpha-Linolenic acid, whether
they are good for you, and what the best sources are. This is what I
turned up:
Overview
- Humans require some fat in their diets, as they cannot create some essential kinds from other sources.
- Western diets generally contain too much fat, particularly saturated fat.
- We also eat the wrong ratio of polyunsaturated fats - we need to eat more omega 3 fatty acids. We also need to change the ratio of omega 3 to omega 6 in the favour of omega 3. The recommended omega 6 : omega 3 ratio is 2:1. Typical western diets are nearer 10:1!
- Particular fish, flax oil and some seeds and nuts are good sources of polyunsaturated fats with a good ratio of omega 3.
- Humans require some fat in their diets, as they cannot create some essential kinds from other sources.
- Western diets generally contain too much fat, particularly saturated fat.
- We also eat the wrong ratio of polyunsaturated fats - we need to eat more omega 3 fatty acids. We also need to change the ratio of omega 3 to omega 6 in the favour of omega 3. The recommended omega 6 : omega 3 ratio is 2:1. Typical western diets are nearer 10:1!
- Particular fish, flax oil and some seeds and nuts are good sources of polyunsaturated fats with a good ratio of omega 3.
Omega What?
Fats are classified by the length of their carbon chain backbone, the
number of C=C carbon double bonds, and the position of the first C=C
bond - the "omega number". For example, the omega-6 fatty acid
Linoleic Acid has a "18:2w6" structure - 18 carbon atoms, 2 double
bonds, the first of which is after position 6 in the chain.
There are two main types of polyunsaturated essential fatty acids,
commonly known as "omega-6" (W6) and "omega-3" (W3) fatty acids. They
differ in the the position of their first carbon-carbon double.
Essential Fatty Acids
The most commonly discussed W6 fatty acid is Linoleic Acid (LA). The
body can make gamma-linolenic acid (GLA), dihomo-gamma-linolenic acid
(DGLA), arachidonic acid (AA) from linoleic acid (LA,18:2w6).
There are at least 3 kinds of omega-3 fatty acids:
LNA (alpha-linolenic acid, 18:3w3),
EPA (eicosapentaenoic acid, 20:5w3) and
DHA (docosahexaenoic acid, 22:6w3).
EPA and DHA occur mostly in fish and seafood. LNA occurs mainly in
seeds and nuts. EPA and DHA can also be made by the body from
alpha-linolenic acid
Sources
For W3 generally, Flax seed is the best source. However, it only contains LNA, not EPA or DHA, so might not have the same health effects as eating fish.
Flax seed |
over 50% LNA |
Hemp seed oil |
about 20% LNA |
Pumpkin seed oil |
Between 1% and 15% LNA |
Canola oil |
up to 10% LNA |
Walnut oil |
between 3% and 11% LNA |
Name |
Fat Content of seed (%) |
LNA W3(%) |
LA W6(%) |
LA+LNA w3+w6(%) |
LNA:LA (Ratio) |
flax |
35 |
58 |
14 |
72 |
4:1 |
hemp |
35 |
20 |
60 |
80 |
1:3 |
pumpkin |
46.7 |
0-15 |
42-57 |
57 |
(0:60) - 1:4 |
soybean |
17.7 |
7 |
50 |
57 |
1:7 |
walnut |
60 |
5 |
51 |
56 |
1:10 |
Walnuts
I was particularly intrested in walnuts, so I did a bit of
investigation.
Walnut Oil:
Fat Type |
Percentage |
Saturated, total |
10% |
Monosaturated, Total |
14% |
Polyunsaturated, total |
76% |
- Linoleic |
61% |
- Linolenic |
15% |
Total Fatty Acids |
100% |
Further Reading
The text and table below this line came from the now defunct webpage
for the course "The Chemistry of Human Life" at
http://www.homepage.montana.edu/~bchem280/omega.html - this link
is now broken, so I've mirrored the information here.
BCHM 104N
The Chemistry of Human Life
Omega 6 and Omega 3 Fatty Acid Content of Common Foods (g/100 grams)
In the column below headed "omega-6," you will find the total omega-6 fatty acid content of each listing. The next three columns list the content of the individual omega-3 fatty acids: LNA (alpha-linolenic acid, 18:3w3), EPA (eicosapentaenoic acid, 20:5w3) and DHA (docosahexaenoic acid, 22:6w3). The quantities refer to grams per 100 grams of food. (100 grams is approximately one small serving.)
The information comes primarily from The Health Effects of Polyunsaturated Fatty Acids in Seafoods, Edited by Artemis P. Simopoulos, Robert R. Kifer, and Roy E. Martin, and published by Academic Press, Inc. in 1986.
Note: "Tr" signifies trace amounts "--" signifies lack of reliable data for a nutrient known to be present. The best sources of omega-3 fatty acids are highlighted.
SEAFOOD
Type of Food |
Omega-6 |
LNA |
EPA |
DHA |
Anchovies |
0.2 |
-- |
0.5 |
0.9 |
Bass, fresh water |
0.4 |
Tr |
0.1 |
0.2 |
Bass, striped |
-- |
Tr |
0.2 |
0.6 |
Bluefish |
0.4 |
-- |
0.4 |
0.8 |
Burbot |
0.1 |
-- |
0.1 |
0.1 |
Carp |
0.8 |
0.3 |
0.2 |
0.1 |
Catfish, channel |
0.7 |
Tr |
0.1 |
0.2 |
Cod, Atlantic |
Tr |
Tr |
0.1 |
0.2 |
Cod, Pacific |
Tr |
Tr |
0.1 |
0.1 |
Eel, European |
0.5 |
0.7 |
0.1 |
0.1 |
Flounder |
0.1 |
Tr |
0.1 |
0.1 |
Haddock |
Tr |
Tr |
0.1 |
0.1 |
Hake, Atlantic |
0.1 |
Tr |
Tr |
Tr |
Hake, Pacific |
0.2 |
Tr |
0.2 |
0.2 |
Halibut, Greenland |
0.5 |
Tr |
0.5 |
0.4 |
Halibut, Pacific |
0.2 |
0.1 |
0.1 |
0.3 |
Herring, Atlantic |
0.4 |
0.1 |
0.7 |
0.9 |
Herring, Pacific |
0.6 |
0.1 |
1.0 |
0.7 |
Mackerel, Atlantic |
1.1 |
0.1 |
0.9 |
1.6 |
Mackerel, King |
1.0 |
-- |
1.0 |
1.2 |
Ocean perch |
0.3 |
Tr |
0.2 |
0.1 |
Pike, northern |
0.1 |
Tr |
Tr |
0.1 |
Pike, walleye |
0.1 |
Tr |
0.1 |
0.2 |
Pollock |
Tr |
-- |
0.1 |
0.4 |
Rockfish, brown |
0.3 |
Tr |
0.3 |
0.4 |
Rockfish, canary |
0.1 |
Tr |
0.2 |
0.3 |
Sablefish |
0.5 |
0.1 |
0.7 |
0.7 |
Salmon, Atlantic |
0.7 |
0.2 |
0.3 |
0.9 |
Salmon, chinook |
0.6 |
0.1 |
0.8 |
0.6 |
Salmon, chum |
0.4 |
0.1 |
0.4 |
0.6 |
Salmon, coho |
0.7 |
0.2 |
0.3 |
0.5 |
Salmon, pink |
0.4 |
Tr |
0.4 |
0.6 |
Salmon, sockeye |
0.6 |
0.1 |
0.5 |
0.7 |
Sardines, canned |
-- |
0.5 |
0.4 |
0.6 |
Sea bass, Japanese |
0.1 |
Tr |
0.1 |
0.3 |
Shark, unspecified |
-- |
-- |
Tr |
0.5 |
Smelt, rainbow |
0.1 |
0.1 |
0.3 |
0.4 |
Snapper, red |
0.2 |
Tr |
Tr |
0.2 |
Sole |
0.1 |
Tr |
Tr |
0.1 |
Sprat |
0.2 |
-- |
0.5 |
0.8 |
Sturgeon, Atlantic |
0.6 |
Tr |
1.0 |
0.5 |
Sturgeon, common |
0.1 |
0.1 |
0.2 |
0.1 |
Swordfish |
-- |
-- |
0.1 |
0.1 |
Trout, brook |
0.3 |
0.2 |
0.2 |
0.2 |
Trout, lake |
1.4 |
0.4 |
0.5 |
1.1 |
Trout, rainbow |
0.6 |
0.1 |
0.1 |
0.4 |
Tuna, albacore |
0.3 |
0.2 |
0.3 |
1.0 |
Tuna, bluefin |
-- |
-- |
0.4 |
1.2 |
Tuna, skipjack |
-- |
-- |
0.4 |
1.2 |
Whitefish, lake |
0.7 |
0.2 |
0.3 |
1.0 |
Whiting, European |
-- |
Tr |
Tr |
0.1 |
Wolfish, Atlantic |
0.2 |
Tr |
O.3 |
0.3 |
Crustaceans
Type of Food |
Omega-6 |
LNA |
EPA |
DHA |
Crab, Alaska king |
Tr |
Tr |
0.2 |
0.1 |
Crab, blue |
0.1 |
Tr |
0.2 |
0.2 |
Crab, Dungeness |
Tr |
-- |
0.2 |
0.1 |
Crawfish |
0.2 |
Tr |
0.1 |
Tr |
Lobster, European |
Tr |
-- |
0.1 |
0.1 |
Lobster, northern |
Tr |
-- |
0.1 |
0.1 |
Shrimp, Atl brown |
0.2 |
Tr |
O.2 |
0.1 |
Shrimp, Japanese |
0.5 |
Tr |
O.3 |
0.2 |
Mollusks
Type of Food |
Omega-6 |
LNA |
EPA |
DHA |
Abalone |
-- |
Tr |
Tr |
-- |
Clam, littleneck |
-- |
Tr |
Tr |
Tr |
Clam, Japanese |
-- |
-- |
0.1 |
0.1 |
Clam, softshell |
0.2 |
Tr |
0.2 |
0.2 |
Conch |
0.1 |
Tr |
0.6 |
0.4 |
Mussel, Blue |
0.1 |
Tr |
0.2 |
0.3 |
Mussel, Mediterranean |
0.1 |
-- |
0.1 |
0.1 |
Octopus |
0.1 |
-- |
0.1 |
0.1 |
Oyster, eastern |
0.3 |
Tr |
0.2 |
0.2 |
Oyster, European |
0.1 |
0.1 |
0.3 |
0.2 |
Oyster, Pacific |
0.3 |
Tr |
O.4 |
0.2 |
Scallops |
0.1 |
Tr |
0.1 |
0.1 |
Squid, Atlantic |
0.1 |
Tr |
0.1 |
0.3 |
Squid, short-finned |
0.1 |
Tr |
O.2 |
0.4 |
Fats and Oils
Type of Food |
Omega-6 |
LNA |
EPA |
DHA |
Butter |
1.8 |
1.2 |
-- |
-- |
Canola oil(rape seed oil) |
22.2 |
11.2 |
-- |
-- |
Chicken fat |
19.9 |
1.0 |
-- |
-- |
Duck fat |
11.9 |
1.0 |
|
|
Flax seed oil (linseed oil) |
12.7 |
53.5 |
-- |
-- |
Margarine, hard, soybean |
19.4 |
1.5 |
-- |
-- |
Rice brain oil |
33.4 |
1.6 |
-- |
-- |
Safflower oil |
77 |
1 |
-- |
-- |
Mayonnaise, soybean |
37.1 |
4.2 |
-- |
-- |
Soybean oil |
51.1 |
6.8 |
-- |
-- |
Walnut oil |
52.9 |
10.4 |
-- |
-- |
Wheat germ oil |
54.8 |
6.9 |
-- |
-- |
Nuts and Seeds
Type of Food |
Omega-6 |
LNA |
EPA |
DHA |
Beechnuts, dried |
18.4 |
1.7 |
-- |
-- |
Butternuts, dried |
34.0 |
8.7 |
-- |
-- |
Chia seeds, dried |
3.4 |
3.9 |
-- |
-- |
Hickory nuts, dried |
20.9 |
1.0 |
-- |
-- |
Soybean kernels, roasted |
11.2 |
1.5 |
-- |
-- |
Walnuts, black |
34.2 |
3.3 |
-- |
-- |
Walnuts, English |
32.3 |
6 |
-- |
-- |