There is a class of essential dietary fat that has long been referred to as "fish oil" that is now increasingly referred to as "the omegas."Both names are misleading and wrong.
But fish oil was not always limited to fish. Paleoanthropologists seeking insights into our native diets point out that there is n-3 PUFA in the flesh of antelope, thought to be much like the kind of meat our ancestors ate. We all know that "we are what we eat," but tend to overlook that what we eat is, also, what it eats!
We have radically altered the diets of feed animals, seemingly oblivious to the fact that the flesh of cattle would change with what we feed them. As much as 35 percent of the calories in some cuts of beef come from fat, and much of that fat is saturated—the variety long associated with increased risk of heart disease (an area of some debate now, but that's a topic for another day). In contrast, as little as 7 percent of calories in the flesh of antelope come from fat, almost all of it polyunsaturated (generally considered a healthful kind of dietary fat), and a considerable portion of it— you guessed it—n-3 PUFA.
In other words, we domesticated the fish oil out of hoofed animals vaguely related to antelope. Fish oil is also antelope oil, and it could have been cow oil, too, but it's not.
Nor does the fishy story end there. There are some indications, as fish farming represents an ever larger portion of the fish market, that we may be doing the same to fish. If we farm salmon and change their diets, we could—in principle—remove the fish oil from fish. Thankfully, we're not there yet, but levels of n-3 PUFA do tend to be higher in wild salmon.
Which leads to point No. 2, that n-3 PUFAs are not found in all fish, a fact I believe is widely known. Only cold-water, fatty fish are good sources. Those include salmon, mackerel, tuna, halibut, and swordfish among others. Some popular fish, such as tilapia, contain virtually no "fish oil," but are instead a source of n-6 PUFAs, or so-called "omega-6s." Omega-6s are also essential, but we tend to get too much of them as is.
Before we deal with point No. 3, a bit of background is now warranted. First, essential fatty acids are "essential" in exactly the way vitamins, minerals, and amino acids are essential. The term applies to any nutrient needed to perform a particular function, or build a particular component of the body, and that the body can't make itself. Many animals, for instance, can make vitamin C, so it's an essential nutrient for us, but not them. We ourselves can make vitamin D from sunlight, so it's only an essential nutrient for us when we are too much in relative shadow.
Essential amino acids are key components of proteins used to build such things as muscle. Think of them like the construction materials for a house. Before all is done, a builder needs a variety of such materials, from timber to wiring to roofing shingles. The house can't be put together right if any key material is deficient. Our bodies, which need to replace cells, hormones, enzymes, and more on a daily basis, are just the same.
In the case of essential fatty acids, they are used in particular to manufacture cell membranes—the barriers between what is in a cell, and what is out—and hormones. The two most important classes of essential fatty acids are the n-3 PUFAs and the n-6 PUFAs. A PUFA is a fat that, as the "poly" in the name suggests, has more than one unsaturated site, which in the case of fat molecules, means a double bond between neighboring carbons. The number refers to the position of the double bond closest to one end of the fat molecule, known as the "methyl'" end. We'll come back to that in a moment.
The n-3 and n-6 PUFAs may be thought of as the Yin and the Yang of hormone production. Both are used in making a large family of hormones called prostaglandins which, in particular, regulate the immune system and the body's inflammatory responses. It's a bit of an oversimplification, but for the most part, n-6s go down a path that leads to pro-inflammatory hormones that amp up immune responses, while n-3s go down a path that leads to anti-inflammatory compounds that dial it down.
Neither is good, nor bad—it's balance that matters. And we are way out of balance. The paleoanthropologists tell us that our native intake of n-3 and n-6 fats occurred in a ratio of between 1 to 1, and 1 to 4 (with a slight excess of n-6 PUFAs). Our modern diets provide us these fats in a ratio of roughly 1 to 20, with a massive excess of n-6s. There is a vast, and in my opinion convincing, body of evidence linking this imbalance to everything from allergies to autoimmune diseases like rheumatoid arthritis.
Restoring our native balance of dietary fats is best achieved by increasing our intake of n-3 PUFAs. For the most part, that has meant eating more fatty fish, or taking supplements. But now it's time to get back to that "methyl" group we left dangling a couple of paragraphs ago.
For whatever reason, the carbons in a fat molecule are labeled using letters from the Greek alphabet. The first carbon is "alpha," and the last is "omega." The carbon at the methyl end is considered the "omega" carbon. Since PUFAs are named based on the position of the double bond closest to that omega carbon, they are often called "omega-3" or "omega-6" fats. Now you see why calling n-3 PUFAs just "omegas" is both wrong, and rather meaningless; that vague reference doesn't really indicate any specific class of fat. Still, the "omegas" label has caught on as a chic reference to n-3 PUFAs in pop-culture writing. I see it all the time, for instance, on the Huffington Post.
And now that we have the omegas sorted out, it's time at last for the alpha. As it turns out, there is, indeed, an alpha among the so-called "omegas"!
There are three important n-3 PUFAs. As noted at the start, not all of them are found in fish—two of the three are. Those two—EPA (eicosapentanoic acid) and DHA (docosahexanoic acid)—are the fatty acids most directly associated with potential health benefits from reduced inflammation, to reduced cardiac risk. Both EPA and DHA can be made from the third important n-3 PUFA, alpha Linolenic acid (ALA)—and that, in fact, is just what fish do. They eat ALA, and make EPA and DHA in their flesh.
We do the same, but we do it variably, and not all that well. So historically, the thinking has been that we need to focus on getting EPA and DHA directly from food, and hence the popular notion that n-3 PUFAs are "fish oil," along with an explanation for the popularity of fish oil (or krill oil) supplements.
But it turns out the alpha among the omegas may not just be important as a precursor to EPA and DHA, but in its own right. We have long had hints of this, but the latest is hot off the presses. A meta-analysis published in the American Journal of Clinical Nutrition, representing more than 250,000 people, shows an inverse association between ALA and cardiovascular event rates. The findings do not rise to the level of proof, but they offer a strong suggestion that ALA offers health benefits of its own.
We can get ALA from plant foods. Concentrated sources include walnuts and flaxseeds, and I encourage making these a routine part of your diet. The benefits of EPA and DHA may be distinct, so I also encourage eating fatty fish routinely (such as twice a week), and/or taking a supplement made from fish, krill, or algae. For now, I do all of these: Walnuts, flaxseeds, and salmon are routine elements of my diet, and I take a krill oil supplement.
The "alpha and the omega" expression, indicating the first and last letters of the Greek alphabet, has long been used to refer to the be-all, end-all. As it turns out, there probably is no "alpha and omega" among the omega-3 fats; all three are important for health. And so, most of us would benefit from ingesting more of these so-called "omegas"—including the alpha.
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David L. Katz, MD, MPH, FACPM, FACP, is a specialist in internal medicine and preventive medicine, with particular expertise in nutrition, weight management, and chronic-disease prevention. He is the founding director of Yale University's Prevention Research Center, and principal inventor of the NuVal nutrition guidance system. Katz was named editor-in-chief of Childhood Obesity in 2011, and is president-elect of the American College of Lifestyle Medicine.