Do New Fat Findings Conflict
With Dietary Recs?
(continued from the front page)
Understanding dietary fat recs
In 2009, the AHA recommended that 5 to 10% of one’s overall diet should come from omega-6 fatty acids. At the time, the 2005 USDA Dietary Guidelines for Americans stated that less than 10% of total calories should come from saturated fat, and total dietary fat should range between 20 and 35% of total calories, “with most fats coming from sources of polyunsaturated and monounsaturated fatty acids, such as fish, nuts, and vegetable oils.” This would put the upper limit for omega-6s and saturated fat at roughly a third each, with omega-3s and monounsaturated fat making up roughly the final third.
Though the guidelines for fat consumption have changed since 2005, the encouraged balancing act among types of dietary fat turns out to have been prescient given the current findings.
Polyunsaturated fatty acids (PUFAs) are usually considered the healthiest type of dietary fat and are sub-classified as either omega-3s or omega-6s. In popular thinking, both beat monounsaturated fat by a nose because they are “essential” fatty acids, meaning the body cannot synthesize these vital acids on its own; they must be consumed. However, as we will see, always lumping these two omegas together under the single banner of PUFAs may not be a best practice.
Omega-3 PUFAs that come from plants are comprised of alpha-linolenic acid. By contrast, the most common omega-6 PUFA is linoleic acid (arachidonic acid is the other). The types of omega-3 that come from fish are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).
Monounsaturated fatty acids (MUFAs) are also healthy, but not essential as defined above. These fatty acids include the omega-9s, like olive oil, which is made up almost entirely of oleic acid.
Fats out of balance
So what happens when you remove all saturated fatty acids (SFAs) from your diet and replace them entirely with omega-6 linoleic acid? It turns out there is indeed an important upper limit to consider for omega-6 fatty acids. This is not the case with omega-3 fatty acids, however.
By substituting linoleic acid for saturated fat, the researchers may have delivered their subjects up to 25% of total dietary fat in the form of linoleic acid, and that’s too high. In high amounts, linoleic acid can have an inflammatory effect in the body. There is even an old medical school mnemonic device that addresses this: "Len is your friend," meaning alpha-linolenic acid is anti-inflammatory, while linoleic acid has a more complicated relationship with the body.
As one registered dietician wrote in a comment to the 2013 study from Sydney, Australia, “It was not that saturates 'reduce mortality', but that pro-inflammatory omega-6 polyunsaturates (from corn, sunflower and soya oils) increase cell membrane arachidonic acid (AA) in a manner similar to saturated fat AA, potentially upregulating the more aggressive thromboxane and leukotriene series, sensitizing cells (including vascular endothelial cells) to damage.”
|TYPES OF DIETARY FAT
Polyunsaturated fatty acids (PUFAs)
|Omega-3s – including alpha-linolenic acid (ALA),
EPA and DHA
|Omega-6s – including linoleic acid (LA)
|Monounsaturated fatty acids (MUFAs)
|Omega-9s – including oleic acid
|Saturated fatty acids (SFAs)
|Animal products - meat, dairy, eggs
|Plant products - coconut oil, palm oil, avocado
Trans fatty acids,
such as from hydrogenated oils, shortening, etc.
Later we’ll look more closely at the Minnesota researchers’ explanations for the negative effect in both studies that the omega-6s apparently had, but for now the takeaway is that saturated fat is not the best choice for the lion’s share of your fat sourcing, but high amounts of linoleic acid are likely even worse for you. This is different from saying that linoleic acid is worse for you than saturated fat.
It seems, though, that there is indeed a role for saturated fat in our diet: As an important member of a rotating cast of fats that keep omega-6s from overtaking the stage entirely. This dietary dominance is due in part to the practical difficulty of getting the majority of your fat from omega-3s. Given the modern food supply, maintaining a low ratio of omega-6 to omega-3 fatty acids can be pretty challenging, and all but impossible if you don’t eat a lot of fish. Saturated fat, then, as counterintuitive as it seems, can help correct the imbalance among the essential omegas.
Nowadays, the USDA Dietary Guidelines for Americans do not list an upper limit for overall fat intake, preferring instead to focus on the quality of the whole foods one eats, e.g., keeping refined carbohydrates and empty calories from sugar to a minimum, even if it means consuming more PUFAs, MUFAs and even SFAs. What has emerged only recently is that a balance among mono, poly and saturated fat appears to be more important than any total avoidance of saturated fat that leads to an over-abundance of omega-6 PUFAs in the diet.
With this line of thinking, we should be able to develop fairly precise dietary recommendations from new and old data without conflicts. Here is what such recommendations might look like:
Use all oil sparingly. Oil is fat, and at 9 calories per gram, it will pack calories on at a rate nearly double that of both protein and carbohydrate. Likewise, healthy fat sources like nuts should be consumed regularly but in modest portions, as they are easy to overeat. Follow the serving sizes on packaged nuts and trail mixes, and cook with two or less tablespoons of even the healthiest oils, such as canola.
Favor omega-3 fatty acids, which are found abundantly in anchovies, sardines, salmon and whitefish, as well as in canola oil, flaxseeds, walnuts, cauliflower and Brussels sprouts. For information about fish consumption during pregnancy, visit
http://www.eatright.org/resource/health/pregnancy/what-to-eat-when-expecting/pregnant-safe-sources-of-omega-3-fats from the Academy of Nutrition and Dietetics, which debunks some of the negative misinformation out there. There are plenty of low-mercury, low-contaminant fish to choose from and the consensus from the medical community is that the benefits to even pregnant women of eating 12 ounces per week of low-contaminant fish outweigh the risks (see sidebar).
Recognize there is an upper limit for omega-6 intake. At the same time, recognize that getting your ratio of omega-3s to omega-6s up to an optimal level may be difficult.
To that end, saturated fat plays an important, practical role in the diet: intake likely helps in limiting omega-6 fatty acids from taking over the lion’s share of fat type in a health-conscious American diet.
Do limit non-piscine animal fat. Get the vast majority of your saturated fat from plants. Good sources include avocado, palm oil and coconut oil--there is still no doubt that these plant sources of saturated fat are better for you than butter and bacon. The latter has high amounts of salt and processing in addition to its very high saturated animal fat content, achieving a kind of trifecta of terrible, dietarily speaking.
|Fish Rich in Omega-3s and Considered Lower Risk for Contaminants Includes DHA and EPA levels for 3½ ounces of fish
|Tuna (for pregnant women, up to 6 oz./week)
|King mackerel, shark, swordfish and tilefish are rich in
omega-3s, but contain higher levels of mercury and should be avoided during pregnancy.
Minnesota study notes
In an effort to explain the findings of both studies, the 2016 study authors ask, “Why didn’t lowering serum cholesterol translate to clinical improvement in diet-heart randomized controlled trials? A plausible explanation for the seemingly paradoxical results of the Sydney Diet Heart Study and MCE is that vegetable oil rich in linoleic acid was the agent used to lower serum cholesterol.”
The authors continue, “Consumption of vegetable oils rich in linoleic acid produces a wide range of biochemical consequences, including qualitative changes in lipoprotein particle oxidation that could plausibly increase risk of coronary heart disease.” (Emphasis added.)
“Further, one way to interpret the unfavorable results of the two recovered trials is that high intakes of linoleic acid could have adverse effects in people who are prone to linoleic acid oxidation (such as smokers, heavy drinkers, and older adults).” (Emphasis added.)
Here we see the two groups who fared the worst from receiving too much omega-6 fat: people prone to coronary events and the elderly. But for all of us perhaps the 5% end of the AHA’s 2009 recommendation on omega-6 fatty acid consumption is the wiser end of the range. Yet even 10% would translate into far less overall consumption than the 20 to 25% imposed on these two studies’ subjects by complete substitution of dietary saturated fat with omega-6s (and none from omega-3s, or even monounsaturated fatty acids).
It may be the case that, in addition to other complicated roles it plays, saturated fat plays a key role in our diet in that it keeps us from consuming too much all-too-available linoleic acid. But saturated fat is still likely most beneficial when consumed as less than 10% of total caloric intake, and without a doubt most beneficial when taken exclusively from plant sources like avocados and coconut oil, setting aside all other nutrient needs (such as iron) that may be better addressed with meat.
Alpha-linolenic acid, a better replacement for saturated fat than linoleic acid, may be prohibitively challenged from taking the central healthy-fat dietary role simply due to the practical issues of finding it in ample amounts in a typically diverse modern diet. Fish oil supplements may be one way to up the omega-3s in your diet, but by nature less than a food replacement, pills may not do much to stem the tide of over-consumption of omega-3s in the form of oils and other foods.
It is a good idea to get much of your dietary fat from:
- canola oil
- Brussels sprouts
- mustard seeds
Of all the PUFA-rich oils to cook with, canola oil stands out as among the highest in omega-3 fatty acids. Canola oil is made from a hybrid organism created from the rapeseed plant, making it the poster child in the argument in favor of some GMOs, as opposed to against all of them across the board.
Vegetable oil tends to be rich in omega-6 fatty acids, and is made predominantly from soybean oil but is often a blend of oils from corn, olive, pumpkin seed, grapeseed or canola oil. Of these, the oil highest in omega-6s is grapeseed oil.
Olive oil is monounsaturated, and though not “essential,” still a healthy choice.