April, 2007
The Good Fat Chat
Today’s Dietitian
By Jenna A. Bell-Wilson, PhD, RD, LD, CSSD
Vol. 9 No. 4 P. 34
Dietitians know it, and consumers are beginning to realize it: We need fat in our diet. In fact, fat plays a role in heart health. Trans and saturated fats remain hazardous, but polyunsaturated fats have been proven potent health effectors.1-3 Research has shown that not only are some polyunsaturated fats essential, but they should also be included in a cardioprotective diet. The challenge lies in keeping these fats straight—which polys are which, what they do, which are better for heart health, and where they can be found. Polyunsaturated fats take center stage in this good fat chat.
Polyunsaturated Fats
Polyunsaturated fatty acids (PUFAs) have received attention in research and health because two of them are essential fatty acids (EFAs)—cis-linoleic acid (LA) and alpha-linolenic acid (ALA)—and they may play an important role in heart disease protection. PUFAs contain more than one point of unsaturation and influence cell membrane fluidity.4 When a cell membrane is more fluid, it enhances receptor number and enzyme function—key for optimal interaction with hormones and growth factors.4 This quality makes them crucial in times of growth, such as the perinatal period and adolescence. In addition, as a constituent of the cell membrane, PUFAs will alter the cell/tissue response to infection, injury, and inflammation.4
Although PUFAs are found in foods, the body can also convert certain PUFAs into other fatty acids (still PUFAs). ALA and LA are essential, meaning the body cannot create them, but eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), gamma-linolenic acid (GLA), dihomo-GLA, and arachidonic acid (AA) can be eaten and created in the body by ALA and LA. See Table 1 for a who’s who of PUFAs.
In addition to affecting membrane fluidity, PUFAs act as secondary messengers and form products called eicosanoids. Eicosanoids have both proinflammatory and anti-inflammatory qualities. The eicosanoids are prostaglandins, thromboxanes, and leukotrienes.5 EPA, DHA, and AA can also be converted to lipoxins and resolvins that decrease inflammation.4
The formation of eicosanoids is not so straightforward. Researchers hypothesize that ALA and LA compete for conversion enzymes, thereby dictating which eicosanoids are formed and that n-3 and n-6 may also compete for incorporation (or esterification) into the plasma lipid fractions, such as phospholipids and triglycerides.6 ALA, EPA, and DHA form eicosanoids that have anti-inflammatory, antithrombotic, antiarrhythmic, and vasodilator qualities.5 The formation of AA has been linked to the formation of PGE2 and leukotriene B4—proinflammatory eicosanoids.6
PUFAs for Heart Health
Cardiovascular disease (CVD) continues to top the list of causes of death in the United States. Therefore, identifying ways to improve heart health is paramount. PUFAs have shown promise as n-3 has been linked to a reduced CVD risk as an anti-inflammatory, antiarrhythmic, and vasodilator.7 Not to be overlooked, n-6 PUFA LA has been proven helpful in reducing CVD risk through their positive effect on serum lipid levels.8
The benefit of n-3 has been evidenced in various studies and recognized by the American Heart Association (AHA) and American Dietetic Association (ADA) as part of a cardioprotective diet (see “Omega-3 Recommendations for Heart Health”). A meta-analysis of randomized, controlled studies identified a lower incidence of myocardial infarction, cardiac arrhythmias, and hypertension with n-3 intake.9 Similarly, the Nurses’ Health Study revealed that women who consumed fish and had a higher overall n-3 EFA intake had a reduced incidence of coronary heart disease (CHD).10
Sibling Rivalry?
Like Marsha Brady, n-3 gets more attention than n-6 (the metaphorical Jan Brady in this case). The AHA and ADA support the addition of n-3 to a heart-healthy diet—but does n-6 have an effect as well? If n-3 and n-6 compete for enzyme control, it is fair to assume that any benefit found with n-3 could be cancelled by n-6.
To put this consideration to the test, Mozaffarian et al investigated the interplay between PUFA intake and CHD in the Health Professionals Follow-up Study.6 Researchers reviewed the food intake of 45,722 men using a food-frequency questionnaire given at baseline and every four years between 1986 and 2000. During the 14-year follow-up, all cardiac events were recorded. The results showed that those consuming approximately 250 milligrams per day of n-3 had a 40% to 50% lower risk of sudden death, independent of their n-6 intake and CHD-associated risk factors. Although n-6 did not interfere with the benefits of n-3, researchers did not find an association between n-6 intake and CHD risk. The strongest link observed was between ALA and CHD risk in those consuming lower amounts of EPA+DHA, suggesting that plant sources of ALA play an important role in CHD risk reduction when fish intake is insufficient.
Researchers highlight two important findings in this study that can be utilized for practical application: It is more important to help patients add n-3 sources than focus attention on the n-3/n-6 balance, and plant sources of ALA may be a preventative option for individuals who do not consume fatty fish.6
In addition to investigating the impact n-6 intake has on the benefits of n-3, another group of researchers sought to evaluate the effect n-6 had on blood lipid levels compared with n-3 on a low-saturated fat diet.8 Subjects consumed a diet differing in its PUFA source (LA or ALA) for three weeks. Blood lipids were measured after each diet period. The n-3 diet revealed a lower plasma triglyceride, apoprotein AII, and fibrinogen concentration with a higher high-density lipoprotein cholesterol than the n-6 group. The n-6 group also showed greater fibrinogen levels, while n-3 saw an increase in fasting factor VII coagulant activity compared with the saturated fat—both considered unfavorable as predictors of heart disease. However, 5 grams of EPA+DHA had the same effect on total and low-density lipoprotein (LDL) cholesterol as 5 grams of LA. Compared with the saturated fat diet, the n-3 and n-6 diet periods showed lower total and LDL cholesterol, apoprotein B, beta-thromboglobulin concentrations, and platelet counts. The results of this small study suggest that replacing saturated fat with n-3 or n-6 will help improve blood lipid levels. The bottom line remains: It’s time to curb the enthusiasm for saturated and trans fats in the diet.
Fats to Foods
Helping patients include a variety of healthy fats in their diet will help them eat the essentials and deemphasize saturated and trans fat choices. Research has shown that it can be done. Metcalf et al offered subjects an assortment of n-3–rich products (some enriched) such as fish, flaxseed, fortified luncheon meats, sausages, and margarines. Without prompting from researchers, participants made choices that increased their n-3 intake to 200 to 400 milligrams per day, even if they did not choose the fish.11
Here are suggestions for increasing PUFA intake:
1. Go fish. For the fish fans, encourage your patients to find room in their weekly diet plans for tuna, mackerel, salmon, herring, trout, or sardines. Help them find healthy recipes that incorporate these sea creatures and encourage them to try something new when they’re in a rut.
2. Creative ways for ALAs. For patients looking for plant-based sources of their EFA, direct them to oils and nuts. Here are some ideas for including more EFA the plant-based way:
• Top salads with canola-based dressings, sprinkle with flaxseed, or dress with walnuts.
• Everything goes with nuts. Walnuts can be added to a hot bowl of oatmeal, cold cereal, or even a yogurt parfait. Remind patients to choose the unadulterated variety—no salt or oil.
• Healthy spreads. For a margarine or healthy spread, replace butter and partially hydrogenated margarines with vegetable oil blends that offer ALA and LA. The key is to advise patients to compare labels—look for the lowest saturated fat blend they can find, with 0 grams of trans fat per serving.
• Bake with healthy oils and spreads/margarines.
• Stir-fry or sauté with a healthy oil such as canola.
3. Olive’s not the only oil. Encourage your patients to include a variety of healthy oils for the monounsaturated fatty acids and PUFAs.
4. Check for new and improved products. Omega-3–enriched products are popping up on the grocer’s shelves. Not only are there oils and spreads offering EFA, but mayonnaise, salad dressings, eggs, pastas, and baked goods are also hitting the shelves.12
— Jenna A. Bell-Wilson, PhD, RD, LD, CSSD, is a freelance nutrition writer and consultant and nutrition advisor for TrainingPeaks, LLC. She is also a certified specialist in sports dietetics.
Omega-3 Recommendations for Heart Health
The American Dietetic Association (ADA) Evidence Based Guidelines for omega-3 fatty acids and disorders of lipid metabolism recommend consuming marine and plant sources of omega-3s as a part of a cardioprotective diet. The ADA recommends the following:
• two 4-ounce servings per week of fatty fish, such as mackerel, salmon, herring, trout, sardines, or tuna;
• plant-based foods of 1.5 grams alpha-linolenic acids (ALAs) [1 tablespoon canola or walnut oil, 1/2 tablespoon ground flaxseed, less than 1 teaspoon flaxseed oil]; and
• a supplement may be recommended under physician supervision.
The American Heart Association recommends that all individuals include fatty fish in their diet at least two times per week for EPA and DHA. They also advise choosing foods that provide ALA, such as soybeans, canola, walnut, and flaxseed and their oils. See Table 2 for their recommendations for omega-3 intake per population.
— JABW
Resources
• American Dietetic Association Evidence Based Library: www.adaevidencelibrary.com
• American Heart Association: www.americanheart.org
• International Food Information Council: www.ific.org
• National Lipid Association: www.lipid.org
• World Health Organization: www.who.int
References
1. Gardner CD, Kraemer HC. Monounsaturated versus polyunsaturated dietary fat and serum lipids. A meta-analysis. Arterioscler Thromb Vasc Biol. 1995;15(11):1917-1927.
2. Kris-Etherton PM, Hecker KD, Binkoski AE. Polyunsaturated fatty acids and cardiovascular health. Nutr Rev. 2004;62(11):414-426.
3. Kris-Etherton PM, Yu S. Individual fatty acid effects on plasma lipids and lipoproteins: Human studies. Am J Clin Nutr. 1997;65(5 Suppl):1628S-1644S.
4. Das UN. Essential fatty acids - A review. Curr Pharm Biotechnol. 2006;7[6]:467-482.
5. Covington MB. Omega-3 fatty acids. Am Fam Physician. 2004;70(1):133-140.
6. Mozaffarian D, Ascherio A, Hu FB, et al. Interplay between different polyunsaturated fatty acids and risk of coronary heart disease in men. Circulation. 2005;111(2):157-164.
7. von SC, Harris WS. Cardiovascular benefits of omega-3 fatty acids. Cardiovasc Res. 2007;73(2):310-315.
8. Sanders TA, Oakley FR, Miller GJ, et al. Influence of n-6 versus n-3 polyunsaturated fatty acids in diets low in saturated fatty acids on plasma lipoproteins and hemostatic factors. Arterioscler Thromb Vasc Biol. 1997;17(12):3449-3460.
9. Bucher HC, Hengstler P, Schindler C, et al. N-3 polyunsaturated fatty acids in coronary heart disease: A meta-analysis of randomized controlled trials. Am J Med. 2002;112(4):298-304.
10. Hu FB, Bronner L, Willett WC, et al. Fish and omega-3 fatty acid intake and risk of coronary heart disease in women. JAMA. 2002;287(14):1815-1821.
11. Sanders TA, Oakley FR, Miller GJ, et al. Influence of n-6 versus n-3 polyunsaturated fatty acids in diets low in saturated fatty acids on plasma lipoproteins and hemostatic factors. Arterioscler Thromb Vasc Biol. 1997;17(12):3449-3460.
12. Metcalf RG, James MJ, Mantzioris E, et al. A practical approach to increasing intakes of n-3 polyunsaturated fatty acids: use of novel foods enriched with n-3 fats. Eur J Clin Nutr. 2003;57(12):1605-1612.
13. Gebauer SK, Psota TL, Harris WS, et al. n-3 Fatty acid dietary recommendations and food sources to achieve essentiality and cardiovascular benefits. Am J Clin Nutr. 2006;83[suppl]:1526S-1535S.