What You Need to Know About Fats

The Good, the Bad, and the Ugly

Confusion about the harmful and beneficial health effects of fats abounds. Low-fat, no-fat, good fat… Where does the truth in all this really lie? As you might suspect, the answer is more complex than the no-fat/low-fat proponents would have you believe. Fats form the lipid membrane that surrounds each cell in your body, and the relative proportions of different fats present in the membrane plays a critical role in normal cell functions. In this article, we explore the different kinds of dietary fats, common myths associated with them, and the ideal fats to consume through diet and/or supplementation.

Before we begin, we interject a brief note on fat nomenclature. Fatty acids are comprised of long chains of carbons (up to 25 carbons) with hydrogens attached to them. Saturated fats contain only single bonds between carbons. On the other hand, unsaturated fats or poly-unsaturated fatty acids (PUFAs) contain at least one bond that is a double bond; hence the fat is not fully saturated This type of bond is less stable than a single bond, and therefore unsaturated fats tend to be a liquid at room temperature. For example, butter is a saturated fat, whereas olive oil is an unsaturated fat.

Unsaturated fats can be subdivided into omega-3, omega-6, and omega-9 fatty acids. The number simply refers to the location of the double bond. For instance, an omega-3 fatty acid has its first double bond located three carbons in from the methyl end of the carbon chain; omega-6s have their first double bond six carbons in; and so forth. This categorization scheme is shown in this figure:

Plant-Based Omega-3s

The richest source of plant-based omega-3s is flaxseed oil, which contains a fat called alpha-linolenic acid (ALA). ALA has specific health benefits, including reduction of cholesterol and blood pressure. For instance, a 2013 study examined the effects of flaxseed in 110 patients with peripheral vascular disease, assessing effects on blood pressure.^[1] Participants were randomized to receive 30 g ground flax or placebo for six months. Results showed that systolic blood pressure (the top number in a blood-pressure reading) was 10 points lower, and diastolic blood pressure (the lower number) was seven points lower in the flaxseed group compared with placebo after six months. The effect was seen only among patients who had high blood pressure at the beginning of the study, but not in patients with normal blood pressure. Another study showed that high-dose consumption of an oil rich in ALA (3.5 g/d) resulted in a significant reduction in the triglyceride fraction of the cholesterol profile, in patients at elevated risk of heart disease due to metabolic syndrome.^[2] There was also a modest decline in blood pressure. There is a popular misconception, however, that consumption of flaxseed oil is sufficient as an omega-3, and/or that it is a good option for individuals who do not want to take fish-based omega-3s. Unfortunately, while ALA certainly possesses its own unique health benefits, its effects do not compare in scope or magnitude to that of the fish-derived omega-3s, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

Many are under the impression that ALA is an effective precursor for EPA and DHA, and can be converted as needed. Unfortunately, a wealth of science has shown that the conversion of ALA into EPA and DHA is extremely limited due the inefficiency of a key enzyme, delta-5-desaturase.^[3] The delta-5-desaturase and delta-6-desaturase enzymes, responsible for converting ALA to EPA and DHA respectively, are extremely slow, and severely limit the amount of EPA and DHA actually formed. In an excellent review of the topic, nutritional scientist Leah Gillingham writes: “While humans have the required enzymes to biosynthesize omega-3 long-chain polyunsaturated fatty acids (PUFA), studies demonstrate that … only ~5% of ALA is converted to eicosapentaenoic acid (EPA) and <0.5% of ALA is converted to docosahexaenoic acid (DHA)”.^[3] Studies feeding human subjects very large amounts of ALA from flax oil have shown only very small changes in actual EPA or DHA levels in vivo.^[3] Therefore, in order to obtain the specific health benefits associated with EPA and DHA, direct consumption of fish or marine-derived omega-3 fats is necessary.

Fish-Derived Omega-3s

The two important fish-derived omega-3s are EPA and DHA. These fats have been the subject of literally hundreds of thousands of studies exploring their effects on cardiovascular health including cholesterol, blood pressure and glucose, brain function, mood, inflammation, chronic pain, immune function, and cancer. There is good evidence showing specific benefits from EPA and/or DHA in all of these areas.^[4–9] Thus, we can see that the range of health benefits derived from these particular fats is far more expansive than those attributed to plant-based omega-3s. We have also seen that the body cannot synthesize adequate amounts of EPA or DHA in vivo, making intake of preformed EPA and DHA a very important dietary and supplemental consideration.

The area of highest importance for fish oil from a public-health perspective is cardiovascular disease. Very large trials have shown that supplementation of fish oil reduces the risk of heart attack and stroke; in particular, it reduces the risk of sudden fatal heart attack. In a well-known study called the GISSI-Prevenzione trial, over 11,000 patients who had already had one heart attack in the last three months, and who were on all the standard medications used to treat this, were randomized to one of four additional treatment groups: 1) vitamin E, 2) 1 g EPA+DHA per day, 3) both, or 4) none (control group) for a duration of 3.5 years.^[4] The study results showed that supplementation with fish oil resulted in a decrease in the risk of death overall by 14%, and risk of death from cardiovascular disease by 17%, compared to placebo.^[4] There was also a significant reduction in nonfatal heart attack and stroke.^[5]

In addition to disease outcomes such as heart attack and stroke, fish oil has been found to reduce known cardiovascular risk factors, such as cholesterol and blood pressure. In a recent study, 24 patients with high cholesterol were randomized to receive either 1800 mg/d EPA or 10 mg/d pravastatin (a cholesterol medication) for three months.^[7] The patients who received EPA experienced an 8.7% decrease in central systolic blood pressure, and an 8% decrease in brachial systolic blood pressure (the blood pressure test done on the upper arm). Another study published in The American Journal of Clinical Nutrition examined the effect of fish oil on cholesterol components.^[8] Supplementation with 3.4 g/d EPA for eight weeks was shown to reduce triglycerides, one of the harmful components of total cholesterol, by 27% compared to placebo.^[8] Unlike prevention of heart disease, where even 1 g of combined EPA+DHA have benefits, at least 2 g of EPA+DHA are needed to reduce this component of cholesterol. Fish oil does not impact LDL, also known as “bad cholesterol,” but does increase HDL or “good cholesterol.”

Fish oil has also been extensively studied for its effects on mood. The EPA component is critical for fish oil’s antidepressant and mood-stabilizing effects. The weight of studies shows that an oil rich in EPA is needed for effectiveness in this area.^[10] For instance, a meta-analysis of 15 randomized controlled trials involving 916 participants found that those studies using a fish oil with greater than 60% EPA showed effectiveness in reducing symptoms of depression measured through standardized depression-rating scales.^[11]

Supplements containing less than 60% EPA were ineffective. Fish oil is thought to have a number of mechanisms in the brain; one of the primary mechanisms is through anti-inflammatory effects, while another involves alteration of cell-to-cell signaling by changes in cell-membrane composition and fluidity.^[12] Fish oil has also been shown to reduce stress-induced changes in heart rate and smooth-muscle contraction.^[6]

Finally, fish-derived omega-3s are among the most potent natural anti-inflammatories,^[13] useful in conditions like asthma, rheumatoid arthritis, and inflammatory bowel disease. EPA and DHA have been shown to competitively inhibit the production of proinflammatory cytokines such as prostaglandin E2 and leukotrienes. Now, there is also newer evidence suggesting that they are involved in the production of molecules called resolvins, whose role it is to signal for the resolution of inflammation.^[13] This is a unique function that has not been described for other dietary fats.

Omega-6 Fatty Acids

Omega-6 fatty acids are those found in vegetable oils such as corn, sunflower, and safflower oil. One of the predominant omega-6s is alpha-linoleic acid, not to be confused with alpha-linolenic acid from flax. Today, omega-6 oils are ubiquitous. Traditionally, the human diet used to contain a much lower ratio of omega-6 to omega-3. Today, our diet is predominantly omega-6, almost to the exclusion of omega-3s. On this basis, it is not recommended to supplement with omega-6 or to require a minimum amount consumed through the diet, as most North Americans already consume too much; instead, it is more important to increase omega-3 intake in relation to omega-6.^[14] There are also several omega-6 oils that are available as supplements, such as evening primrose oil, black currant oil, and borage oil, all of which contain gamma-linolenic acid (GLA). Preliminary science suggests that there may be a role for this fat in very specific circumstances, such as in cyclical mastalgia (painful breasts prior to menses), where it has been shown to be almost comparable to anti-inflammatory medications (NSAIDS) for pain reduction.^{[15, 16]}

Myth-Busting “Omega-7s”

There is currently considerable marketing hype regarding the importance of omega-7 fats, and there are a number of new products geared towards this. Like the other omega oils, omega-7 is an unsaturated fat, with a double bond at the carbon-7 position. Unfortunately, despite the media and industry attention, there is very little human or other data on the effects of omega-7s. A search of the Pubmed database, the largest science database in North America, shows no clinical trials in existence on omega-7s. It seems that this agent is as yet quite unproven, and it is too early to attribute to it any important medical role. At the very least, it seems unlikely to achieve the kind of scientific prominence held by fish-derived omega-3s. For now, focus on omega-7s appears to be largely a marketing tactic based on very minimal evidence.

Omega-9

Finally, we turn our attention to an important dietary oil: extra virgin olive oil. Extra virgin olive oil is the richest source of omega-9 fatty acids, in particular oleic acid, which is a mono-unsaturated fatty acid or MUFA. In addition to its fat content, olive oil is a rich source of polyphenol antioxidants, which account in part for its therapeutic properties. Olive oil is the “secret” component of the now-acclaimed Mediterranean diet. Olive oil is considered by naturopathic doctors to be a “prescription food.” It is prescribed as a medicine at a daily dose of 2–4 tbsp. per day in order to benefit various metabolic parameters including blood pressure, blood glucose, and cholesterol. Olive oil has also been shown to reduce inflammation, an effect that is likely due to its polyphenol content. Olive-oil polyphenols are highest in cold-pressed, extra virgin olive oil; therefore this is the only kind that should be used for therapeutic purposes. Studies confirm the health effects of extra virgin olive oil (abbreviated EVOO). One study of women with prediabetes found that using olive oil in cooking was able to reduce the postmeal spike in insulin levels, indicating better blood glucose regulation.^[17] Another study found that EVOO consumption led to an increase in the anti-inflammatory activity of HDL cholesterol (good cholesterol) among healthy older adults.^[18] A third study showed that EVOO consumption of 4 g/d resulted in a significant reduction in liver synthesis of cholesterol, designated by Apo-B levels.^[19] Finally, another study showed that consumption of a diet rich in EVOO led to a 7.9-point reduction in systolic blood pressure among patients with hypertension.^[20] There were also reductions in oxidized LDL cholesterol and C-reactive protein, a marker of inflammation. A newer area of interest for EVOO is cognitive function. For example, a 2013 study of 285 subjects at high risk of cardiovascular disease found that supplementation with olive oil for over six years resulted in significantly better performance scores in all cognitive domains, and significantly better performance across fluency and memory tasks. Notably, the EVOO group also had over 60% reduced chance of developing mild cognitive impairment over the study period, compared to patients who consumed a low-fat diet.^[21] 

The table below shows a summary of fat intake recommendations based on the evidence discussed in this article.