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Functional Foods for Heart Health

by Susan Kundrat, MS, RD/LD on Feb 01, 2003

Learn which foods you should be eating today to stave off heart disease tomorrow.

The statistics about heart disease are not very heartening: Since 1918, cardiovascular disease (CVD) has been the leading cause of mortality in the United States every single year (Hasler, Kundrat & Wool 2000). According to the American Heart Association (AHA), CVD claims the lives of nearly half of the 2.4 million Americans who die each year—almost as many lives as the next seven leading causes of death combined (AHA 2002). More than 60 million Americans suffer from some form of CVD, a term that encompasses heart diseases, congestive heart failure, congenital heart defects, hardening of the arteries, stroke, high blood pressure and other diseases of the circulatory system (AHA 2002).

But there is good news to report, too. More and more studies are determining how the foods we eat can positively affect cardiovascular health, and we are learning how to enhance our diets by consistently eating a heart-protective diet. Additionally, a growing number of consumers are starting to recognize that making proactive lifestyle changes that can prevent CVD (specifically changes in nutrition and exercise training) is a better choice than treating CVD with conventional medications. These advances in medical research and consumer awareness mean the time is right for fitness professionals to get the message about heart-protective foods out to the public.

Defining Functional Foods

When researchers study the specific foods that may make a difference in the management of CVD, they talk in terms of functional foods. According to the American Dietetic Association’s (ADA) Position Paper on Functional Foods, functional foods have “. . . a potentially beneficial effect on health when consumed as part of a varied diet on a regular basis at effective levels” and can include whole, fortified, enriched or enhanced foods (ADA 1999).

Functional foods are intended to enhance—not replace—a healthy diet. Starting with a foundation of a balanced diet that includes a variety of whole grains, fruits and vegetables, plus lean protein sources with low total saturated fat, clients can obtain additional benefit by adding functional foods. Research has shown that individuals can reduce their risk of CVD by eating specific amounts of the following types of functional foods: soy, oats, psyllium, flaxseed, tea, nuts, grapes, fatty fish and cholesterol-lowering margarines. (For the purposes of this article, the specific amount of each food needed to boost heart health is referred to as “the effective daily intake,” although this term is not formal or official nomenclature.)

Soy

In October 1999, the U.S. Food and Drug Administration (FDA) approved a health claim under the National Labeling and Education Act of 1990 allowing manufacturers to state that soy can reduce the risk of CVD when consumed as part of a diet low in saturated fat and cholesterol. The FDA arrived at this decision after looking closely at clinical trials pertaining to soy and heart disease. Perhaps the strongest evidence came from a 1995 review of 38 clinical trials involving more than 700 people (Anderson, Johnstone & Cook-Newell 1995). In this meta-analysis, researchers reported a 12.9 percent (%) decrease in low-density lipoprotein (LDL, or “bad”) cholesterol, a 9.3% reduction in total cholesterol, a 10.5% decrease in triglycerides and an insignificant increase (2.4%) in high-density lipoprotein (HDL, or “good”) cholesterol. After reviewing a total of 43 studies, the FDA investigators concluded that an average daily intake of 17 to 31 grams (g) of soy protein significantly lowered both total and LDL cholesterol.

Based on these findings, the FDA determined that the effective daily intake of soy protein is 25 g of soy protein a day, or 6.25 g per Reference Amount Customarily Consumed (RACC). (The RACC for any given food is established by dividing the total average daily intake by the likely number of servings per day, which ranges from two to four for the foods discussed in this article.) As a result, food labels on soy products specify 6.25 g per serving.

It should be noted that the FDA’s label ruling does not include specific recommendations regarding isoflavones, the estrogen-like compounds in soy. Based on the available research, isoflavones were not determined to have a primary role in the lowering of blood lipids. However, some studies suggest that soy isoflavones may benefit health in other ways—for example, by enhancing the flexibility of the arteries and by decreasing LDL-cholesterol oxidation, which can cause damage. In addition to isoflavones, a number of other soy components—such as amino acids, saponins, phytic acid, trypsin inhibitors, fiber and globulins—may play roles in lipid metabolism.

Clients should add soy to their diets gradually; if it is added too quickly, some people experience indigestion, gas and bloating, most likely because of the fibers in soy. I recommend starting out with one serving of soy food a day and working up to two to three servings to reach the effective daily intake of 25 g. Soy protein is found naturally in soy milk, tofu, tempeh, roasted soy nuts and miso; it is also present in many processed and fortified foods, energy bars and drinks on the market.

Oats

More than 40 human studies over a period of 30-plus years have documented the cholesterol-lowering benefits of oats (Kapica 2001). As in studies involving soy, the largest decreases in blood cholesterol levels have been observed in subjects who had the highest baseline cholesterol to begin with. Research also indicates that oat intake does not negatively affect HDL cholesterol and may actually increase HDL levels.

The oats component found to lower cholesterol is the soluble fiber beta-glucan.

In January 1997, the beta-glucan in oats was awarded the first food-specific health claim by the FDA for the fiber’s potential “as part of a diet low in saturated fat and cholesterol” to “reduce the risk of heart disease” (Kapica 2001). The award was based on the findings of 37 human clinical intervention trials conducted between 1980 and 1995. Seventeen of these trials demonstrated that oat bran or oatmeal had a statistically significant effect on total and LDL cholesterol in subjects with high cholesterol who ate either a typical American diet or a low-fat diet.

The Quaker Oats company, which petitioned the government for the award, determined that 3 g of beta-glucan soluble fiber would be required to achieve a 5% reduction in total blood cholesterol; this effective daily intake is equivalent to approximately 1 cup of cooked oat bran, 11/2 cups of cooked oatmeal or 3 cups of Cheerios®. Consequently, the FDA requires that an oats food bearing the health claim contain at least 1 g of beta-glucan per serving.

There may be many mechanisms by which beta-glucan soluble fiber lowers cholesterol. The most common one cited is beta-glucan’s ability to bind bile acids in the small intestines, thereby increasing cholesterol excretion. Other ways beta-glucan may decrease blood cholesterol are by reducing fat and cholesterol absorption; reducing cholesterol formation by decreasing carbohydrate absorption and blunting the serum insulin response; and inhibiting cholesterol synthesis through the short-chain fatty acids generated when soluble oat fiber is fermented in the colon. Limited research has also noted that oats may play a role in decreasing high blood pressure, another CVD risk factor (Kapica 2001).

Other components of oats besides beta-glucan may contribute to oats’ effectiveness in reducing blood cholesterol. Plant sterols, tocotrienols, monounsaturated fatty acids and the lysine- to-arginine ratio in oats have also been noted to have beneficial effects on lipid metabolism (Kapica 2001).

On a practical note, clients can get the heart benefits of oats in several forms. Instant oatmeal, rolled oats, oat bran and whole oat flour are all good sources.

Psyllium

Psyllium is another soluble fiber shown to be very effective in lowering blood cholesterol levels. In February 1998, the FDA extended the health claim regarding oats and CVD to include fiber from the seed husk of psyllium. (Even though psyllium and oats are in different food groups, both contain significant amounts of soluble fiber.)

The FDA made this decision after reviewing 21 human studies that found significant scientific data to support the relationship between soluble fiber from psyllium seed husk and a reduced risk of CVD (Hasler, Kundrat & Wool 2000). Based on this review, the FDA determined that the effective daily intake of soluble fiber from psyllium required to significantly reduce serum lipids was 7 g (equivalent to 10.2 g of the seed husk); this amount would be expected to reduce total cholesterol by 4% to 6% and decrease LDL cholesterol by 4% to 8% (Hasler, Kundrat & Wool 2000). For a manufacturer to use the psyllium health claim on a label, the food needs to provide 1.7 g of soluble fiber from psyllium husk per serving.

Although most studies on psyllium have been short-term, one large, multicenter study examined the long-term efficacy and safety of adding psyllium to the diets of subjects who had been on a heart-healthy, AHA food plan (Anderson et al. 2000). In the 163 subjects who fully complied with the study protocol (5.1 g of psyllium twice daily), total cholesterol decreased by approximately 5% and LDL cholesterol by almost 7% (Anderson et al. 2000).

Clients may be most familiar with psyllium seed husk from the product Metamucil. For cholesterol-lowering purposes, clients would need to consume three servings of Metamucil per day (one serving contains 3.4 g of seed husk) to reach the effective daily intake of 10.2 g of psyllium seed husk. Psyllium seed husk, which can also be obtained in bulk form in natural food stores, can be consumed as a powder in juice, smoothies or cooked cereals. Because esophageal and gastrointestinal obstructions can occur if psyllium seed husk is consumed with insufficient liquid, health claim labels are required to alert consumers to the need to drink fluids when taking this product.

Flaxseed

Another food that has gained recent attention for its potential role in cardiovascular health is flaxseed. One reason flaxseed has garnered interest is that it contains significant amounts of both the omega-3 fatty acid alpha linolenic acid and lignans, a class of phytoestrogens (Hasler, Kundrat & Wool 2000). Although bodybuilders have been using flaxseed oil for quite some time, consuming the entire seed appears to have the greatest overall health benefit.

While much of the research on flaxseed has focused on its use for cancer prevention, studies are now looking closely at its role in CVD protection. Research findings indicate that the fiber in flaxseed may combine with essential fatty acids to promote heart health. When consumed in amounts ranging from 15 g to 50 g per day for 3 to 6 weeks, flaxseed has been shown to lower total cholesterol by approximately 6% to 7% and decrease LDL cholesterol by 9% to 11% without significantly changing HDL cholesterol (Flax Council of Canada 2002).

Because flaxseed is high in fiber, it has a laxative effect and should be added to the diet gradually. It is usually best to start with approximately 1 to 2 teaspoons of ground flax meal per day and work up to 2 tablespoons (1 tablespoon of ground flax equals approximately 8 g).

The best way to enhance product freshness and potency is to purchase whole seeds and then grind them in a coffee grinder (but be sure to use a different grinder than the one used for coffee beans!). If preground seeds are used, they should be stored in a tightly sealed container in the refrigerator. Ground flaxseed meal may be used in baking (muffins, breads, etc.), sprinkled on cereal, added to fruit drinks or smoothies, or even mixed with peanut butter or soy nut butter and used as a spread.

Tea

Tea is the second most popular beverage in the world, surpassed only by water (Hasler, Kundrat & Wool 2000). Like fruits and vegetables, tea contains natural antioxidants that may play an important role in maintaining optimal health. Dietary antioxidants can neutralize free radicals in the body, helping to maintain healthy cells and tissues. Both black and green teas contain comparable and significant amounts of flavonoids, a class of antioxidants.

Although much of the research on tea has focused on its role in cancer prevention, several epidemiological studies have noted a lowered risk of heart disease or heart attack with increased consumption of tea. In one study (the Boston Area Health Study), consuming one or more cups of tea per day reduced the risk of having a heart attack by 44% (Sesso et al. 1999). Additional research (the Rotterdam Study) found that tea may also protect against severe aortic atherosclerosis (Geleijnse et al. 1999). This study of 3,454 men and women 55 and older found a significant inverse association between tea consumption and hardening of the arteries. With one or two cups of tea per day, the decrease in severe plaque formation was nearly 50%; with four or more cups per day, the reduction was nearly 70%.

Tea’s beneficial effects on heart health may be due to several reasons (Hasler, Kundrat & Wool 2000). For example, tea inhibits LDL oxidation and decreases the stickiness of blood, reducing the risk of blood clots. While more research is needed to determine the exact mechanisms involved, consuming one to two cups of green or black tea daily may be a prudent way to boost heart health.

Nuts

It wasn’t until the early 1990s that the first published studies began to highlight the heart-healthy benefits of nuts. Although walnuts were the first type of nuts investigated, several additional studies have demonstrated that a variety of other nuts—such as almonds, macadamia nuts, pistachio nuts, pecans, peanuts and hazelnuts—can significantly reduce both total and LDL cholesterol when consumed as part of a diet low in cholesterol and saturated fat.

The cholesterol reduction associated with nut consumption has been attributed to the replacement of saturated fat in the diet with the monounsaturated fatty acids found in nuts (Hyson, Schneeman & Davis 2002). In addition, nuts are a good source of many other nutrients that may enhance heart health—for example, fiber, vitamin E, magnesium and other plant chemicals (phytochemicals). Nuts are also a rich source of the amino acid arginine, which plays a role in maintaining the health and flexibility of arteries (Hyson, Schneeman & Davis 2002).

In one recent report from the ongoing Physicians’ Health Study, researchers found that more frequent nut consumption was associated with a decreased risk of sudden cardiac death (Albert et al. 2002). Compared with men who rarely or never consumed nuts, those who ate nuts two or more times per week had nearly a 50% lower risk of sudden cardiac death and a 30% lower risk of dying at all from coronary heart disease. Other studies have found decreases as great as 13% in total cholesterol levels and 16% in LDL-cholesterol levels when nuts replaced saturated fats in the diet (Hasler, Kundrat & Wool 2000). These studies confirmed that macadamia nuts, pecans and walnuts, in particular, can lower cholesterol when they are part of a long-term diet.

Because nuts are high in calories and total fat (2 ounces [56 g] of almonds = 332 calories, 2 ounces of walnuts = 344 calories and 2 ounces of pecans = 378 calories), clients who increase nut consumption must decrease calories in other areas of their diets. Stress to clients that they will see the greatest benefit if the fat and calories from nuts replace—rather than augment—other high-fat foods in the diet.

Purple Grapes

Numerous studies over the last 20 years have tried to explain why the French population has a lower incidence of CVD than other Western populations, despite the fact that French foods tend to be so high in fat. By closely examining what has come to be known as the “French Paradox,” researchers finally solved the puzzle in 1979 when they linked wine intake to a reduced risk of CVD in both men and women from 18 countries (Hasler, Kundrat & Wool 2000). The health benefits of wine have been attributed, in part, to the high concentrations of antioxidants in grapes (particularly red grapes).

Individuals who choose to avoid alcohol can reap the heart-health benefits of grapes that are not processed into wine. Grapes contain a variety of natural antioxidants, including catechin, epicatechin, resveratrol and proanthocyanidins, which inhibit the oxidation of LDL cholesterol, lessen the stickiness of blood platelets and promote relaxation (dilation) of blood vessel walls. In a study that compared commercial grape, orange and grapefruit juice consumption, only grape juice was found to reduce the stickiness of blood, a factor that contributes to heart attacks.

As with nuts, if purple grape juice or red wine is added to the diet, clients need to be aware of the additional calories they are consuming (170 calories in 8 ounces of purple grape juice and 106 in 5 ounces of red wine). Current government recommendations are no more than one glass (5 ounces) of wine per day for women and no more than two glasses a day for men (U.S. Department of Agriculture & U.S. Department of Health & Human Services 2000).

Fatty Fish

The inverse relationship between fatty-fish consumption and CVD was first uncovered decades ago when it was reported that Greenland Eskimos had low rates of the disease, despite consuming a diet high in fish fat. Fatty fish (mackerel, herring, sardines, salmon and tuna) and their oils are good sources of the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). One of the main heart-protective effects of fish oils appears to be their ability to reduce blood triglycerides.

Although further studies are needed to establish optimal doses for omega-3 fatty acids to prevent and treat heart disease, it has been suggested that eating one fatty-fish meal per day provides approximately 900 milligrams; this amount has been shown to have a beneficial effect on mortality rates in patients with CVD (AHA 2002). Eating more moderate amounts of fish (one to two servings per week) has also been associated with reduced coronary heart disease mortality in some studies. Therefore, it would be prudent to recommend that, to enhance their heart health, clients eat at least two servings of fatty fish each week (3 to 6 ounces per serving), prepared without added saturated fat. ‰

Sterol- & Stanol- Enriched Margarine

The cholesterol-lowering effect of plant sterols, which are natural components of vegetable fats/oils, was first identified in the 1950s. Subsequent studies have shown a similar effect on lipid levels from plant stanols, which are derivatives of plant sterols. Both of these plant-derived components resemble cholesterol, which allows them to compete with cholesterol during digestion; this, in turn, reduces the amount of cholesterol absorbed by the body.

Margarine containing plant-derived stanols has been on the market in Finland since 1995, when a clinical trial in that country found that stanols significantly reduced total and LDL cholesterol by 10% and 14%, respectively, in 153 patients with mildly high cholesterol (Miettinen et al. 1995). More recent studies appear to confirm the ability of plant sterols and stanols to decrease blood cholesterol levels, LDL cholesterol in particular. Sterols and stanols have both reduced LDL-cholesterol levels by 9% to 20% when consumed in amounts ranging from 2 g to 3 g per day, although there has been considerable variability among individuals (Lichtenstein & Deckelbaum 2001).

In September 2000, the FDA allowed manufacturers of products containing sterols and stanols to use a health claim associating these components with a reduced risk of coronary heart disease. Foods bearing a health claim for plant sterols must contain at least 0.65 g of plant sterols per serving, whereas labels for plant stanols must show at least 1.7 g of plant stanols per serving.

Two daily servings (i.e., the RACC) of sterol- and stanol-enriched margarines equal about 160 calories for the regular versions and 90 calories for the light versions. The regular versions may be used for baking or sautéing. The light versions are better used only as spreads and are not appropriate for cooking.

The Take-Home Message

As CVD continues to be the leading cause of mortality in the United States, more and more consumers are seeking alternatives or adjuncts to current medical treatment. Along with exercising and managing stress, eating healthy foods has been shown to reduce the incidence of CVD. The trouble is, too few people know which foods can boost heart health.

Fitness professionals can get the word out about the value of eating soy, oats, psyllium, flax, purple grapes, nuts and cholesterol-lowering margarines on a consistent basis. Helping clients understand the benefits of these particular foods is an important part of consumer education about cardiovascular health.

References

Albert, C.M., et al. 2002. Nut consumption and decreased risk of sudden cardiac death in the Physicians’ Health Study. Archives of Internal Medicine, 162, 1382-7.

American Dietetic Association (ADA). 1999. Position of the American Dietetic Association: Functional foods. Journal of the American Dietetic Association, 99, 1278-85.

American Heart Association (AHA). 2002. 2002 Heart and stroke statistical update. www.americanheart.org; retrieved October 10.

Anderson, J.W., et al. 2000. Long-term cholesterol-lowering effects of psyllium as an adjunct to diet therapy in the treatment of hypercholesterolemia. American Journal of Clinical Nutrition, 71, 1433-8.

Anderson, J.W., Johnstone, B., & Cook-Newell, M.E. 1995. Meta-analysis of the effects of soy protein intake on serum lipids. New England Journal of Medicine, 333, 276-82.

Flax Council of Canada. 2002. Flaxseed: High intakes of alpha-linolenic acid (ALA) reduce risk of cardiovascular diseases. www.flaxcouncil.ca; retrieved October 13.

Geleijnse, J.M., et al. 1999. Tea flavonoids may protect against atherosclerosis: The Rotterdam Study. Archives of Internal Medicine, 159, 2170-4.

Hasler, C.M., Kundrat, S., & Wool, D. 2000. Functional foods and cardiovascular disease. Current Atherosclerosis Reports, 2, 467-75.

Hyson, D.A,. Schneeman, B., & Davis, P.A. 2002. Almonds and almond oil have similar effects on plasma lipids and LDL oxidation in healthy men and women. Journal of Nutrition, 132, 703-7.

Kapica, C. 2001. Oats: Nature’s functional food. Nutrition Today, 36, 56-60.

Keevil, J.G., et al. 2000. Grape juice, but not orange juice or grapefruit juice, inhibits human platelet aggregation. Journal of Nutrition, 130, 53-6.

Krauss, R.M. 2000. AHA Dietary Guidelines: Revision 2000: A statement for healthcare professionals from the nutrition committee of the American Heart Association. Circulation, 102, 2284-99.

Lichtenstein, A.H., & Deckelbaum, R.J. 2001. Stanol/sterol ester-containing foods and blood cholesterol levels: A statement for healthcare professionals from the nutrition committee of the Council on Nutrition, Physical Activity and Metabolism of the American Heart Association. Circulation, 103, 1177-9.

Metamucil. 2002. Frequently asked questions. www.metamucil.com; retrieved October 13.

Miettinen, T.A., et al. 1995. Reduction of serum cholesterol with sitostanol-ester margarine in a mildly hypercholerolemic population. New England Journal of Medicine, 333, 1308-12.

Sesso, H.D. et al. 1999. Coffee and tea intake and the risk of myocardial infarction. American Journal of Epidemiology, 149, 162-7.

Soy Protein Partners. 2002. Soyfoods Guide.

U.S. Department of Agriculture & U.S. Department of Health & Human Services. 2000. Nutrition and Your Health: Dietary Guidelines for Americans.

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About the Author

Susan Kundrat, MS, RD/LD

Susan Kundrat, MS, RD/LD IDEA Author/Presenter

Susan Kundrat, MS, RD, LD, is an IDEA contributing editor and owner of Nutrition on the Move, a sports and wellness nutrition consulting business located in Urbana, Illinois. She consults with many high-school and college teams and is the sports nutritionist for the Northwestern Wildcats athletic program. Her new book on sports nutrition will be published by Healthy Learning Press sometime in 2004.