Omega-6 is a type of polyunsaturated fatty acid (PUFA) that is essential to human health. In recent decades, however, consumption of omega-6 PUFAs has skyrocketed in developed countries (1), paralleling the dramatic increase in modern chronic disease. This has led many to vilify all forms of omega-6.
I wrote several articles on omega-6 years ago, including “How too much omega-6 and not enough omega-3 is making us sick” and “How much omega-3 is enough? That depends on omega-6.” Lots of new research has been published since then, and it’s important to constantly incorporate new information coming out in the medical literature. This article will thus serve as an update on my previous articles, this time focusing on the source of omega-6.
Omega-6 Is Not a Problem in Fresh, Whole Foods
Omega-6 has largely all been grouped together, regardless of the source. But whole-food sources of omega-6 also come packaged with other nutrients like dietary fiber (2), folic acid, niacin, tocopherols, vitamin B6, calcium, magnesium, potassium, phytosterols, polyphenols, vitamin E, and more. Some of these nutrients, like magnesium and vitamin E, have been shown to protect unstable omega-6 fatty acids from being oxidized (3).
Epidemiological evidence supports the idea that different sources of omega-6 might have different effects on health. Nuts and seeds contain large amounts of omega-6, yet are consistently negatively associated with cardiovascular disease (4). A pooled analysis of four prospective studies with follow-up time ranging from six to 18 years found that nut consumption resulted in a 37 percent reduction in cardiovascular-related mortality (5). Nut consumption has also been shown to reduce inflammation (6) and may also reduce risk of type 2 diabetes (7) and cancer (8).
Context does matter, though, and one situation where whole-food omega-6 could potentially become an issue is in people with low intake of omega-3 fatty acids (9). Short-chain omega-6 and omega-3 PUFAs directly compete for the desaturase and elongase enzymes that convert them to their long-chain derivatives. This means that excess omega-6 in the form of linoleic acid may inhibit the conversion of omega-3 alpha-linoleic acid into its long-chain derivatives, EPA and DHA (10). EPA and DHA are components of healthy cell membranes and are particularly important for cardiovascular and neurological health (11, 12). Luckily, as long as we eat adequate pre-formed EPA and DHA in the form of fatty fish, we effectively bypass this issue and can eat whole-food omega-6 without much tribulation.
Should you avoid whole foods high in omega-6?
What Is the Problem? Rancid Vegetable Oils.
The more concerning form of omega-6 is in vegetable oils. Repeated heating of vegetable oils is common practice in the food industry, particularly in large deep-fryers, because it significantly reduces the cost of food preparation. Instead of having to refill their deep-fryers with oil every day, many restaurants add just enough to top it off from the day before, only replacing the entire batch every few days or weeks.
In deep-fat frying, oil is heated to temperatures greater than 400 degrees Fahrenheit, while also being exposed to moisture and air. This causes thermal lipid oxidation, resulting in the formation of polar compounds and yielding new chemical functional groups that deposit in the cooking oil (13). Repeated heating also degrades the natural antioxidant vitamin E (14), which normally protects fatty acids against lipid oxidation.
Several European countries now have national food laws that prohibit reuse of an oil after it exceeds a certain polar compound content level (15). The U.S. has no such regulations (16). However, even the European laws overlook secondary oxidation compounds, which may also be harmful to human health and are not as well studied.
The Effects of Repeatedly Heated Oil on Human Health
Repeatedly heated oil can also cause vascular inflammation and changes to vasculature that predispose to atherosclerosis (22). Studies have shown that oxidized LDL is much more important than total LDL level at determining atherosclerotic risk (23). Repeatedly heated oil has been shown to increase levels of oxidative stress in the body, including levels of oxidized LDL.
So if the problem is high heat, can unheated canola, soybean, or sunflower oil be a part of a healthy diet? To answer this question, we really need to understand how these oils are made.
What about Unheated Vegetable Oils?
There are three ways that oils are commonly extracted from their source:
- Rendering: this method uses heat only
- Chemicals: this method uses a solvent (usually hexane) and then subsequent heating to evaporate off the solvent
- Press it out: this method is purely mechanical. These oils are commonly labeled as “cold-pressed” or “expeller pressed.”
The majority of oils high in omega-6 PUFAs are produced using the second method. This means that even if you don’t heat your vegetable oil during cooking, it has likely already been heated long before it made its way to the supermarket. It may also have trace amounts of solvent remaining (24). After this extraction process, many oils are further refined, removing even more nutrients (25).
Given what we’ve learned, here are a few practical tips for modulating your omega-6 intake:
- Eat real food. Don’t fear the naturally occurring omega-6 in nuts, seeds, pastured meat, and other whole foods, especially if you are eating adequate amounts of omega-3 fatty acids. They are considered essential fatty acids, after all, so you do need some in your diet.
- Avoid industrial seed oils. Nix these nutrient-poor choices in favor of more nutritious and flavorful cooking fats like olive oil, coconut oil, ghee, and other pastured animal fats. Fats with higher saturated fatty acid content tend to have higher smoke points.
- Don’t go overboard with the nut flours. This sort of goes along with “eat real food.” While nut flours can be a great substitute for wheat flour in baked goods, they are easy to eat in large quantities, and the omega-6 fatty acids in these have the potential to be oxidized with heating. Switch it up with coconut flour or cassava flour.
- Eat pre-formed EPA and DHA. Consuming cold-water fatty fish is a good idea for everybody, but it’s especially important for people that have diets high in omega-6 fats.