|How to Calculate Essential Fatty Acid Requirements|
|Written by walquis|
|Monday, 29 November 2010 14:47|
How much of the essential fatty acids do I need, and how do I know I'm getting enough?
(The class notes on fat metabolism may be helpful for understanding of this article).
"...people need to take in at least 2 to 3 percent of their calories in the form of [essential] omega-6 fatty acids and at least 1 to 1.5 percent of their calories as fat in the form of [essential] omega-3 fatty acids." --"Know Your Fats", p. 105
There are only two essential fatty acids; one is an omega-3 fatty acid, and one is an omega-6 fatty acid. The omega-3 fatty acid is alpha-linolenic acid (abbreviated as ALA), and the omega-6 fatty acid is linoleic acid.
How do I convert the minimum essential fatty acid (EFA) recommendations from percent-of-total-calories into a kitchen measurement?
Let's assume a 2000-calorie-per-day diet, and start with the omega-3 EFA recommendation: If I use flax oil to meet my minimum omega-3 EFA levels of 1.5% of calories, then how much flax oil do I need to eat?
1.5% of 2000 calories is 60 calories.
As a rule of thumb, fat has 9 calories per gram. To convert calories to grams, divide 60 calories by 9 calories/gram. 60/9 = 6.67 grams alpha-linolenic acid (ALA).
How much flax oil contains 6.67 grams of ALA?
Reading from the fatty acid composition chart, flax oil is 60% alpha-linolenic acid. Another way to say it: 1 gram flax oil per 0.6 gram of ALA.
6.67 grams ALA, multiplied by 1 gram flax oil per 0.6 grams ALA = 6.67 x 1/0.6 = 11.12 grams flax oil.
A tablespoon of oil is 13.62 grams. So, slightly less than 1 tablespoon of flax oil per day would provide the minimum recommended allowance of the omega-3 essential fatty acid. (NOTE: this is a minimum. Our bodies could stand to have a lot more.)
How much of the omega-6 EFA do I need?
The other essential fatty acid, linoleic acid, is an omega-6 acid. The minimum recommended amount is 3% of total calories, about twice the recommendation for alpha-linolenic acid.
3% of 2000 total calories/day = 120 calories per day.
Flax oil is about 14% linoleic acid (from the fatty acid composition chart), so if I take 1 tablespoon flax oil per day for omega-3 requirements, I'm also getting some linoleic acid.
How much more linoleic acid do I need?
Let's see how much linoleic acid is in a tablespoon of flax oil. 14% x 13.62 = 1.9 grams. At 9 calories per gram, that's 1.9 x 9 = 17.2 calories linoleic acid in a tablespoon of flax oil, which is not very much. I need another 103 calories or so of the omega-6 EFA. 103 calories, divided by 9 calories/gram = 11.44 grams of linoleic acid still needed.
Not to worry; many oils are loaded with the omega-6 EFA. In fact, the worry is getting too much linoleic acid relative to alpha-linolenic acid. The ratio of omega-6 to omega-3 EFAs should be as close to 1:1 as possible. Up to 4:1 is OK. (The typical American diet comes in at about 20:1 or 30:1).
Can I get the omega-6 EFA from butter? According to the fatty acid composition chart, butter has lots of saturated and mono-unsaturated fat in the form of palmitic and oleic acid, but not much EFAs (although the EFA ratio is not bad). I'll have to look somewhere else to get my remaining 11.44 grams of linoleic acid.
The fatty acid composition chart shows that both corn oil and soybean oil are more than 50% linoleic acid. Sesame oil and peanut oil are also good sources.
Soybean oil being about 53% linoleic acid, all I need to do to fulfill my omega-3 EFA minimum is find a food that has at least 11.44 grams linoleic acid, divided by .53 grams linoleic acid per gram soybean oil = 21.58 grams of soybean oil.
If all of a food's fat comes from soybean oil, then I look for 21.58 grams of fat on the label. However, with respect to processed foods it's hard to find one with soybean oil as its only fat--and it would likely be partially hydrogenated soybean oil anyway.
Fresh, whole foods such as walnuts make the job easier. For instance, based on nutrition information downloadable from walnuts.org, 1 ounce of California walnuts = 28.35 grams (or 14 walnut halves).
This nutrition information shows that 14 walnut halves supply 11 grams of linoleic acid (and 2.5 grams alpha-linolenic acid as a bonus).
So, by eating 15 or 16 walnut halves in addition to a tablespoon of flax oil, I've satisfied my EFA requirements for one day. And, since an ounce of walnuts has 2.5 grams of alpha-linolenic acid, I could even cut my flax oil ration back to 1 tsp and still be OK. However, it's better to get more omega-3 rather than less, given the afore-mentioned heavy bias toward omega-6 fats in the typical American diet.
What I need to do now is try to avoid more omega-6 fats for the rest of the day; unbalanced omega-6 intake relative to omega-3 intake causes big problems over time, especially with respect to inflammation.
By the way, as a cross-check: Total fat content of an ounce of walnuts is 18 grams, which puts linoleic acid content at 61% -- right in the ballpark of the fatty acid composition chart numbers for walnut oil.
NOTE: When calculating fatty acid content for foods other than oils, make sure to distinguish between % of total fat in the food, and % of the food's total weight. Oils are 100% fat, but walnuts are not (and neither is butter). The "walnut oil" entry in the fatty acid composition chart is only about the *oil* in a walnut, not the whole walnut. Since I'm generally going to eat walnuts rather than pure walnut oil, I need to look the total fat grams (the weight of the fat) in a serving of walnuts, rather than the weight of the whole serving, in order to know how much linoleic or alpha-linolenic acid I'm getting.
One more example: Suppose instead of eating walnuts, I wanted to get my remaining 11.44 grams of omega-6 EFA from peanut butter (Smucker's Natural Chunky Peanut Butter, say, which has no added sugar; just peanuts). Knowing that all the fat in natural peanut butter comes from peanut oil, I can apply the peanut oil table figures to the "total fat grams" for one serving (2 tablespoons, or 32 grams). According to the label, each serving contains 16 grams of total fat. The fatty acid composition chart shows that peanut oil is 31% linoleic acid.
Lining up our units so that they cancel... (11.44 grams linoleic / 1 day) x (1 gram peanut oil /.31 grams linoleic) x (2 TBSP peanut butter / 16 grams peanut oil) = 2.31 TBSP peanut butter / day.
A few additional notes on fat...
What kind of fat is "healthy fat?" Healthy fats and oils are the ones that don't oxidize [break down or burn] readily, or that are consumed before they can oxidize. Oxidized fats and oils are (1) not available for use as energy or for structural purposes because they are in a polymerized unusable form, or (2) contain toxic components.
Avoid partially hydrogenated vegetable fats, and rancid or overheated fats.
Research has shown that the body needs saturated fat in the diet to adequately convert alpha-linolenic acid to EPA and DHA. --KYF, p. 107