April 2014 Issue

The Omega Fats
By Jill Weisenberger, MS, RDN, CDE
Today’s Dietitian
Vol. 16 No. 4 P. 20

Learn more about the various types of omegas and how they can contribute to overall health.

Many consumers have heard about the health benefits of omega-3 fatty acids, but most are unaware of the other omega fats that play various roles in improving overall health. Dietitians know there are several omegas found in foods and supplements, but it’s important to know exactly what they are, what role they play in the body, how they contribute to health, and what foods contain them so RDs can counsel patients more effectively.

What’s in a Name?
When talking about fatty acids, it helps to review or define common and often confusing terms. All fatty acids that bear the “omega” label are unsaturated, containing one or more double bonds. Omega fatty acids are classified according to the location of the first double bond by counting carbon atoms beginning with the last carbon. For example, the first double bond of an omega-3 fatty acid appears three carbons from the terminal end of the fatty acid chain. Likewise, the first double bonds of the omega-6, -7, and -9 fatty acids begin six, seven, and nine carbons from the end of their fatty acid chains, respectively.

Unsaturated fatty acids are further classified as either monounsaturated fatty acids (MUFAs), because they have only one double bond (eg, omega-7 and -9 fats), or polyunsaturated fatty acids (PUFAs), because they have more than one double bond (eg, omega-3 and -6 fats). The nomenclature of each fatty acid uses the number of double bonds, the position of the first double bond, and the number of carbon atoms in the chain (see table below). For example, alpha-linolenic acid (ALA), an omega-3 fat, is identified as 18:3, n-3. The 18 refers to the number of carbon atoms; the 3 refers to three double bonds; and n-3 identifies the location of the first double bond on the carbon chain.

Fatty Acids’ Many Roles
The length of the carbon chain, the degree of saturation, and the position of the double bonds affect the role fatty acids play in the body. Dietary fats may be oxidized as energy or stored as triglycerides. In addition, dietary fats regulate gene expression, modulate ion channels, are incorporated into cell membranes where they affect membrane fluidity, and more.1

Without specifying a preference for MUFAs or PUFAs, the 2010 Dietary Guidelines for Americans recommend replacing some saturated fats with unsaturated fats to reduce cardiovascular disease risk factors.2

PUFAs

Omega-3 Fatty Acids
Omega-3 fatty acids grabbed the interest of scientists in the 1970s when they studied the diets and health of the Inuit population of Greenland. Compared with Danish controls, the Inuit subjects suffered from heart attack and diabetes at one-tenth the rate.3 Studies pointed to omega-3 fatty acids from the Inuit population’s traditional marine-based diet as cardioprotective.4 The Inuits’ high intake of seafood provided them 10.5 g of omega-3 fatty acids daily in the form of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). The Danish participants consumed only 0.8 g/day.3 The idea that these fatty acids protected the heart was further supported when researchers observed that populations in countries with high fish intakes had lower rates of heart disease.5

Enthusiasm among researchers concerning the link between omega-3s and heart health continued with the results of the GISSI Trial. Italian researchers randomized more than 11,000 individuals who had survived myocardial infarction (MI) within the previous three months to receive either 840 mg of EPA + DHA in the form of a 1-g fish oil supplement or placebo. The authors reported, among other positive findings, that omega-3 supplementation reduced sudden death by 45%.6

The same researchers conducted a subsequent study with subjects diagnosed with congestive heart failure and found that omega-3 fatty acid supplementation significantly protected against all-cause mortality and death and hospitalization for cardiovascular events.1

A 2008 review concluded that fish or fish oil providing approximately 250 mg of EPA + DHA daily significantly lowers the risk of coronary heart disease (CHD) death by 36% compared with not consuming EPA + DHA.7

Several recent randomized, controlled trials have had fewer positive findings. The differences may have resulted from the study designs. For example, subjects in the GISSI study were randomized shortly after suffering an MI. In a subsequent trial, in which the findings were neutral, subjects were enrolled much later and had received optimal medical care in the interim.1

Other research shows that omega-3 fatty acids in fish may have health effects beyond the heart. Studies suggest that EPA and DHA intake is critical for the development of the fetal brain and retina.8 In fact, one small study found that mothers who took DHA supplements during pregnancy gave birth to children who demonstrated better problem-solving skills at 9 months old.9

It’s been suggested that depressed patients and those with Alzheimer’s disease may have low levels of DHA.5 Recent studies have found that EPA and DHA supplementation may reduce symptoms of depression1 and improve cognitive functioning of patients with mild Alzheimer’s disease.8 Moreover, these fatty acids potentially have strong anti-inflammatory effects. Other areas of research include their role in the treatment or prevention of age-related macular degeneration, ADHD, rheumatoid arthritis, and asthma.1

EPA and DHA often are the focus of research, but the shorter-chain omega-3 fatty acid ALA also provides health benefits. “There’s a growing evidence base demonstrating a beneficial role of ALA in the primary and secondary prevention of cardiovascular disease,” says Jennifer Fleming, MS, RD, LDN, clinical project coordinator at Penn State University. “Based on the epidemiologic data, there are comparable CVD [cardiovascular disease] benefits for EPA + DHA vs. ALA. However, despite there being some clinical trial evidence about CVD benefits of ALA, there have been more studies conducted with EPA + DHA.” Other studies also support ALA’s potential benefits in chronic inflammation, the metabolic syndrome, inflammatory bowel disease, cancer, lupus, and rheumatoid arthritis, she adds.

However, the various omega-3 fatty acids don’t have the same fate in the body. Elongase and desaturase enzymes do convert ALA into the longer-chain omega-3 fatty acids, but the rate of conversion is low, with only about 5% to 15% of ALA converting to EPA and less than 1% of ALA converting to DHA.5

Omega-6 Fatty Acids
Linoleic acid (LA), an omega-6 fat, is the most common PUFA in the diet. The appropriate intake of LA and other omega-6 fatty acids is controversial. LA is the precursor to arachidonic acid (AA), which can be metabolized into bioactive eicosanoids associated with inflammation and chronic disease.

Researchers have debated the merits of limiting omega-6 fatty acids in the diet to decrease the production of inflammatory compounds. There has been further concern that high LA intake will result in decreased production of omega-3 anti-inflammatory eicosanoids because of the competition of enzymes between the two classes of PUFAs.

However, a 2009 American Heart Association (AHA) science advisory, based on a combination of 34 case-control, prospective cohort, ecological, and randomized controlled trials, stated that consuming at least 5% to 10% of energy from omega-6 fatty acids decreases the risk of CHD relative to lower intakes.10 The Food and Agricultural Organization of the United Nations and the World Health Organization reported a similar conclusion and recommend that an intake of omega-6 fats should equal 2.5% to 9% of energy.11

Nonetheless, the subject still is being debated. A reanalysis of the Sydney Diet Heart Study concluded that substituting LA for saturated fats increased death among men who had a recent coronary event.12 This study used safflower oil and safflower oil margarine in place of other fats, resulting in an LA intake of 15.4% of energy, which is greater than both recommended amounts and usual intakes. In addition, researchers didn’t measure trans fat intake.

“Omega-6 fatty acids are not responsible for ill health,” says Kevin Fritsche, PhD, a professor of nutrition at the University of Missouri and coauthor of a systematic review on the topic published in the July 2012 issue of the Journal of the Academy of Nutrition and Dietetics. Increasing LA in the diet doesn’t significantly increase AA in the tissues; thus only a small portion of LA contributes to inflammatory eicosanoids, he explains.

According to Fritsche, what many people don’t understand is that AA also is important for resolving inflammation. “Arachidonic acid is not just a bad guy; it also helps the body recover.” The same proinflammatory compounds trigger resolution and bring tissues back to health.

Moreover, Fritsche says, omega-6 fatty acids are unlikely to block the formation of anti-inflammatory compounds from omega-3 fatty acids. Omega-3 and -6 fatty acids longer than 18 carbons bypass the rate-limiting enzyme. “Small amounts of AA and DPA [docosapentaenoic acid, an omega-3 fatty acid], which are found in meat and eggs, are taken up very efficiently by the cells.” Instead of being oxidized by the cells for energy, they’re converted to eicosanoids.

Results of the systematic review should reassure nutrition professionals that both omega-3 and omega-6 fatty acids are beneficial, Fritsche says.

MUFAs

Omega-9 Fatty Acids
Omega-9 fatty acids can be synthesized in vivo; therefore, they aren’t essential to the diet. However, dietary omega-9 fats affect cardiovascular risk factors. When they replace saturated fatty acids in the diet, LDL cholesterol levels improve, HDL cholesterol levels remain stable, and insulin resistance improves.13 When replacing carbohydrate in the diet, omega-9 fats increase HDL cholesterol levels and decrease triglyceride levels.

Oleic acid is the predominant omega-9 fatty acid in the diet. Researchers became interested in omega-9 fats because of the observed health benefits of consuming a Mediterranean-style diet, which is high in oleic acid mainly from olive oil. However, some studies in which the source of oleic acid primarily is animal foods don’t show protection against coronary heart disease.14,15

Omega-9 fatty acids and diets rich in canola oil appear to lower dangerous belly fat, according to Peter J. Jones, PhD, a professor of nutrition and food science and the director of the Richardson Centre for Functional Foods and Nutraceuticals at the University of Manitoba in Canada. As demonstrated by the Canola Oil Multicentre Intervention Trial (COMIT), high intakes of oleic acid, but not PUFAs, cause increased production of a signaling molecule called oleoyleanolamide. “This turns up energy expenditure and suppresses food intake,” Jones says. Through oleoyleanolamide and improved body composition, omega-9 fatty acids may improve both cardiovascular risk and insulin resistance, he says.

As the lead researcher of COMIT, Jones says that 130 subjects consumed a daily smoothie rich in various blends of oils as part of a heart-healthy, weight-maintenance diet. “The mix of oleic acid and DHA was superior to any of the other four mixtures tested,” he says. “It lowered LDL cholesterol levels, boosted HDL cholesterol levels, totally blew the doors off triglyceride levels with a 25% reduction, and the icing on the cake was a reduction of both systolic and diastolic blood pressures.”

Omega-7 Fatty Acids
Because of the potential health benefits of omega-7 fats reported in the media, clients and patients may ask you about palmitoleic acid. It’s purported to reduce inflammation, increase satiety, promote weight loss, lower cholesterol and triglyceride levels, and improve insulin resistance.

There are two forms of this fatty acid, explains Irena B. King, PhD, a professor in the division of epidemiology and the department of internal medicine at the University of New Mexico. The cis isomer is made in the body and consumed when we eat macadamia nuts, and the trans form is naturally present in meats and dairy, she explains.

Unlike the metabolic effects of most trans fats, some research suggests that trans-palmitoleic acid has positive health effects, including improved insulin resistance and blood lipids.16 However, don’t jump on the omega-7 bandwagon just yet, King says, because more research must be done. “There are both positive and negative associations with omega-7 intakes. It’s not so clear-cut,” she says.

Guiding Clients and Patients
It’s common for clients and patients to ask which fats are the most healthful and which are the best cooking oils to use, says Bonnie Schmidt-Hayes, MS, RD, LD, CLS, a clinical lipid specialist at Case Western University Hospitals Harrington Heart and Vascular Institute Lipid Clinic in Cleveland. “I counsel on overall diet quality, with an emphasis placed on plant-based eating, including plant-based fats,” she says, adding that she advises patients to use olive and canola oils for most of their cooking.

Long Island, New York-based nutritionist Karen Ansel, MS, RDN, coauthor of The Calendar Diet: A Month by Month Guide to Losing Weight While Living Your Life, also favors MUFA-rich olive and canola oils. She says canola has an additional advantage, as it also provides plant-based omega-3 fatty acids.

Consistent with the AHA’s recommendations,17 both Schmidt-Hayes and Ansel suggest clients eat fatty fish such as salmon, tuna, mackerel, and lake trout twice per week to obtain EPA and DHA. For convenience, Ansel suggests buying tuna, salmon, and sardines in cans or pouches. “What could be easier than tossing them into a salad or pasta? It literally takes less than a minute,” Ansel says.

Schmidt-Hayes recommends patients consume nuts and seeds a few times each week. And for clients who love butter, she suggests a trans fat–free margarine or a plant stanol/sterol–fortified margarine.

Most recipes can be adjusted for fat quality, but some beg for solid fat, says Ellie Krieger, MS, RDN, a television personality and the author of Weeknight Wonders: Delicious, Healthy Dinners in 30 Minutes or Less. For classic cookies such as chocolate chip, she recommends using one-half butter and one-half canola oil. Her fix for cakes is to replace 1/2 cup butter with 1/3 cup canola oil, and if the cake is too dense, whipping the egg whites can increase the airiness.

And for oven-fried chicken, Krieger sprays oil directly on the food. “It gives it a nice, even coating. You can use less oil, and it’s more uniform,” she explains.

However, Jones says it’s important to warn clients about consuming too much healthful fat as well. “Quantity matters,” he says. “Overeating and becoming overweight will blunt the beneficial effects, even if you choose to eat the right fats.”

Yet each unsaturated fatty acid offers something unique, so dietitians can feel confident in recommending a variety of foods rich in unsaturated fats.

— Jill Weisenberger, MS, RDN, CDE, is a freelance writer and a nutrition and diabetes consultant to the food industry, including Omega-9 Oils and Good Fats 101. She has a private practice in Newport News, Virginia, and is the author of Diabetes Weight Loss — Week by Week.

 

Sources and Dietary Reference Intakes of Selected Fatty Acids


Fatty Acid

Major Food Sources

US Dietary Reference Intake (DRI)

Usual Daily Intake

Alpha-linolenic acid (18:3, n-3)

Flax, chia and hemp seeds, walnuts, canola and soybean oils

Adequate Intake (AI): 1.1 to 1.6 g, 0.6% to 1.2% of energy intake

1.4 to 1.8 g

Eicosapentaenoic acid (20:5, n-3)

Fish and seafood

No DRI established

30 to 40 mg

Docosahexaenoic acid (22:6, n-3)

Fish and seafood

No DRI established

60 to 80 mg

Linoleic acid
(18:2, n-6)

Soybean and corn oils, shortening

AI: 12 to 17 g, 5% to 10% of energy intake

13 to 18 g

Arachidonic acid
(20:4, n-6)

Meat, poultry, eggs

No DRI established

120 to 180 mg

Palmitoleic acid
(16:1, n-7)

Macadamia nuts, blue-green algae

No DRI established

1.2 g

Oleic acid
(18:1, n-9)

Olive and canola oils, avocado, beef tallow, lard

No DRI established

27 g

— Source: Vannice G, Rasmussen H. Position of the Academy of Nutrition and Dietetics: dietary fatty acids for healthy adults. J Acad Nutr Diet. 2014;114(1):136-153.

 

References
1. Baum SJ, Kris-Etherton PM, Willett WC, et al. Fatty acids in cardiovascular health and disease: a comprehensive update. J Clin Lipidol. 2012:6(3):216-234.

2. US Department of Agriculture, US Department of Health and Human Services. Dietary Guidelines for Americans, 2010. 7th ed. Washington, DC: US Government Printing Office; 2010:24.

3. Kromhout D, de Goede J. Update on cardiometabolic health effects on ω-3 fatty acids. Curr Opin Lipidol. 2014:25(1):85-90.

4. O’Keefe JH Jr, Harris WS. From Inuit to implementation: omega-3 fatty acids come of age. Mayo Clin Proc. 2000:75(6):607-614.

5. Vannice G, Rasmussen H. Dietary fatty acids for healthy adults. J Acad Nutr Diet. 2014:114(1):136-153.

6. Dietary supplementation with n-3 polyunsaturated fatty acids and vitamin E after myocardial infarction: results of the GISSI-Prevenzione trial. Lancet. 1999:354(9177):447-455.

7. Mozaffarian D. Fish and n-3 fatty acids for the prevention of fatal coronary heart disease and sudden cardiac death. Am J Clin Nutr. 2008;87(6):1991S-1996S.

8. Swanson D, Block R, Mousa SA. Omega-3 fatty acids EPA and DHA: health benefits throughout life. Adv Nutr. 2012:3(1):1-7. 

9. Judge MP, Harel O, Lammi-Keefe CJ. Maternal consumption of a docosahexaenoic acid-containing functional food during pregnancy: benefit for infant performance on problem-solving but not on recognition memory tasks at age 9 mo. Am J Clin Nutr. 2007;85(6):1572-1577.

10. Harris WS, Mozaffarian D, Rimm E, et al. Omega-6 fatty acides and risk for cardiovascular disease: a science advisory from the American Heart Association Nutrition Subcommittee of the Council on Nutrition, Physical Activity, and Metabolism; Council on Cardiovascular Nursing; and Council on Epidemiology and Prevention. Circulation. 2009;119(6):902-907.

11. UN Food and Agriculture Organization. Fats and Fatty Acids in Human Nutrition: Report of an Expert Consultation: 2010. Geneva, Switzerland: UN Food and Agriculture Organization; 2010.

12. Ramsden CE, Zamora D, Leelarthaepin B, et al. Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis. BMJ. 2013;346:e8707. doi: 10.1136/bmj.e8707.

13. Gillingham LG, Harris-Janz S, Jones PJ. Dietary monounsaturated fatty acids are protective against metabolic syndrome and cardiovascular disease risk factors. Lipids. 2011;46(3):209-228.

14. Jakobsen MU, O’Reilly EJ, Heitmann BL, et al. Major types of dietary fat and risk of coronary heart disease: a pooled analysis of 11 cohort studies. Am J Clin Nutr. 2009;89(5):1425-1432.

15. Warensjo E, Sundstrom J, Vessby B, Cederholm T, Riserus U. Markers of dietary fat quality and fatty acid desaturation as predictors of total and cardiovascular mortality: a population based prospective study. Am J Clin Nutr. 2008;88(1):203-209.

16. Mozaffarian D, Cao H, King IB, et al. Trans-palmitoleic-acid, metabolic risk factors, and new-onset diabetes in US adults: a cohort study. Ann Intern Med. 2010;153(12):790-799.

17. Fish 101. American Heart Association website. http://www.heart.org/HEARTORG/GettingHealthy/NutritionCenter/Fish-101_UCM_305986_Article.jsp. March 20, 2013. Accessed January 26, 2014.

 

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