Flaxseed for Cholesterol Reduction
Flaxseed for Cholesterol Reduction
By Lynn Keegan, RN, PhD, HNC-BC, FAAN
Director, Holistic Nursing Consultants, Port Angeles, WA
Dr. Keegan reports no consultant, stockholder, speaker’s bureau, research, or other financial relationships with companies having ties to this field of study.
Historically, flaxseed, purported to be one of the original medicines used by Hippocrates, has been highly regarded because of its healing properties. Flaxseed recently has gained attention in the area of cardiovascular disease primarily because it is the richest known source of both alpha-linolenic acid (ALA) and the phytoestrogen lignan, as well as a good source of soluble fiber.1
The Problem of High Cholesterol
The average American diet contains 34% fat—11.2% saturated fat, 14.9% monounsaturated fat, and 7.8% other fats.2 One study examining the association between lipoprotein (Lp(a)) and coronary heart disease among women with Type 2 diabetes found that increased Lp(a) levels were independently associated with cardiovascular risk among diabetic women.3
Diet to Reduce Cholesterol
In 1985, the National Heart, Lung, and Blood Institute of the National Institutes of Health launched the National Cholesterol Education Program (NCEP) to reduce illness and death from coronary heart disease in the United States by reducing the percentage of Americans with high blood cholesterol. Traditional and complementary health care providers have focused on NCEP consensus guidelines to reduce dietary saturated fatty acids, cholesterol, and excess body weight.4 The goal of the National Cholesterol Education Program is to discover and validate ways that diet may influence the progression of cardiovascular disease, including lipoprotein oxidation, thrombosis progression, cardiac arrhythmia, and medication interaction. Some areas of investigation include the role of various fatty acids and supplements—in the form of vitamins, minerals, herbs, and functional foods—as well as traditional foods and diets from other parts of the world. Some of the new and relevant nutritional approaches include specific fatty acids (omega-3, monounsaturated, and trans fatty acids), dietary supplements (herbs, antioxidants, vitamins C and E, coenzyme Q10, B vitamins and homocysteine, L-arginine, Chinese red yeast rice, garlic, soy, flaxseed, and dietary fiber), food and drink (tea, nuts, plant-sterol and stanol-ester-containing spreads, alcohol, and grapefruit juice), and the Mediterranean diet.4 The focus of this article is on flaxseed, one of these cholesterol-lowering nutritional options.
Botany and History
Flaxseed, Linum usitatissimum, which means most useful, originated in Mesopotamia. Flax was first planted in the United States after the early colonists arrived in North America. Canada currently is the major producer of this plant. Most flaxseed grown in the United States comes from farms in North Dakota.5
Mechanism of Action
Oxygen free radicals (OFRs) have been implicated in the development of hypercholesterolemic atherosclerosis. Omega-3 fatty acid suppresses the production of interleukin-1, tumor necrosis factor and leukotriene B4, and OFRs by polymorphonuclear leukocytes (PMNLs) and monocytes. Lignans possess anti-platelet activating factor (PAF) and antioxidant activity. PAF, Interleukin-1, tumor necrosis factor, and leukotriene B4 stimulate PMNLs to produce OFRs. It is believed that flaxseed can reduce the levels of OFRs and hence prevent the development of hypercholesterolemic atherosclerosis.6
Animal Studies
Three animal-based studies support the use of flax to reduce cholesterol.
One study investigated the effects of flaxseed on the prevention of ovariectomy-induced increases in total cholesterol and atherosclerotic lesions. Seventy-two female Golden Syrian hamsters were randomly assigned to six groups (n = 12): sham, ovariectomized (ovx), or ovx plus either 17-beta-estradiol (10 mcg/kg body weight) or semi-purified diet adjusted for macronutrients and fiber to contain one of the three doses of flaxseed (7.5%, 15%, or 22.5%) for 120 days. Flaxseed was effective in preventing the ovx-induced rise in plasma total cholesterol. Triglyceride concentrations were significantly higher in the flax-fed hamsters. The study found flaxseed to be beneficial in reducing plasma cholesterol and plaque formation induced by ovarian hormone deficiency.7
Another study examined the effects of dietary flaxseed and defatted flaxseed meal (FLM) on serum and tissue fatty acid profiles. Pregnant Sprague-
Dawley rats were fed diets containing 0, 20%, or 40% flaxseed or 13% or 26% FLM by weight. Flaxseed changed fatty acids profiles more than FLM, but FLM and 40% flaxseed significantly reduced serum cholesterol. Dietary 40% flaxseed may have increased oxidative stress, as evidenced by a reduction in liver vitamin
E.8
A third study investigated the effects of dietary flaxseed on high-cholesterol diet-induced atherosclerosis, lipid profile, and OFR-producing activity of PMNLs (PMNL-CL) in rabbits. The rabbits were divided into four groups: control; flaxseed diet (7.5 g/kg daily, orally); 1% cholesterol diet; and 1% cholesterol diet plus flaxseed (7.5 g/kg daily, orally). Flaxseed reduced the development of aortic atherosclerosis by 46% and reduced the PMNL-CL without significantly lowering the serum cholesterol. In normocholesterolemic rabbits, flaxseed increased serum total cholesterol and decreased PMNL-CL without significantly affecting serum triglycerides. The authors concluded that modest dietary flaxseed supplementation is effective in reducing hypercholesterolemic atherosclerosis without lowering serum cholesterol. Its effectiveness against hypercholesterolemic atherosclerosis could be due to suppression of enhanced production of OFRs by PMNLs in hypercholesterolemia. Therefore, dietary flaxseed supplementation could prevent hypercholesterolemia-related heart attack and strokes.6
Human Studies
Human studies have shown that flaxseed can modestly reduce serum total cholesterol and low-density lipoprotein (LDL) cholesterol concentrations; reduce postprandial glucose absorption; decrease some markers of inflammation; and raise serum levels of the omega-3 fatty acids, ALA, and eicosapentaenoic acid.1
A double-blind randomized study examined the effects of flaxseed on lipid metabolism and biomarkers of bone turnover in postmenopausal women who were not on hormone replacement therapy. Subjects consumed 40 g/d of either ground flaxseed or a wheat-based comparative control regimen for three months. In addition, all subjects received 1,000 mg calcium and 400 IU vitamin D daily. Flaxseed supplementation lowered both serum total cholesterol and non-high-density lipoprotein cholesterol by 6% (P < 0.05), whereas the comparative control regimen had no such effect. The flaxseed regimen reduced serum levels of both LDL and high-density lipoprotein (HDL) cholesterol by 4.7% and triglycerides by 12.8%, although the decreases were not statistically significant. The flaxseed regimen significantly reduced serum apolipoprotein A-1 and apolipoprotein B concentrations by 6% and 7.5%, respectively (P < 0.005).9
A Canadian study evaluated health aspects of partially defatted flaxseed in relation to serum lipids, indicators of oxidative stress, and ex vivo sex hormone activities. Twenty-nine hyperlipidemic subjects (22 men and 7 postmenopausal women) completed two three-week treatment periods in a randomized, crossover trial. Subjects were given muffins that contributed approximately 20 g/d fiber from either flaxseed (approximately 50 g partially defatted flaxseed) or wheat bran (control) while they consumed self-selected National Cholesterol Education Program Step II diets. Both muffins had similar macronutrient profiles. Treatment phases were separated by at least 2 weeks. The results found that partially defatted flaxseed reduced total cholesterol (4.6 ± 1.2%; P = 0.001), LDL cholesterol (7.6 ± 1.8%; P < 0.001), apolipoprotein B (5.4 ± 1.4%; P = 0.001), and apolipoprotein A-I (5.8 ± 1.9%; P = 0.005), but had no effect on serum lipoprotein ratios at week 3 compared with the control. There were no significant effects on serum HDL cholesterol, serum protein carbonyl content, or ex vivo androgen or progestin activity after either treatment. Unexpectedly, serum protein thiol groups were significantly lower (10.8 ± 3.6%; P = 0.007) at week 3 after the flaxseed treatment than after the control, suggesting increased oxidation. These data indicate that partially defatted flaxseed is effective in lowering LDL cholesterol. No effects on lipoprotein ratios, ex vivo serum androgen or progestin activity, or protein carbonyl content were observed. The significance of increased oxidation of protein thiol groups with flaxseed consumption requires further investigation.10
|
Nutritional Aspects of Flaxseed Flaxseed contains other nutrients that make eating the whole seed superior to consuming just the extracted oil. Whole flaxseeds have a characteristic soft crunch. However, the nutrients in ground seeds are absorbed more easily. Flax seeds contain a high-quality protein. Flaxseeds:
Source: George Mateljan Foundation . Flaxseeds. Available at: www.whfoods.com/genpage.php?tname=foodspice&dbid=81. Accessed July 5, 2005. |
In another study, 199 menopausal women were randomly assigned to consume 40 g/d flaxseed (n = 101) or wheat germ placebo (n = 98) for 12 months. At baseline and at month 12, serum levels of lipids, bone mineral density, and menopausal symptoms were evaluated. Flaxseed reduced serum total (-0.20 ± 0.51
tal (-0.20 ± 0.51 mmol/L; P = 0.012) and HDL (-0.08 ± 0.24 mmol/L;
P = 0.031) cholesterol concentrations compared with wheat germ placebo. Bone mineral density did not differ significantly between the two arms. Both flaxseed and wheat germ reduced (P < 0.0001) the severity scores of menopausal symptoms, but no statistical difference was found between the two arms. These findings suggest that incorporation of flaxseed into the diet for one year produced a favorable, but not clinically significant, effect on blood cholesterol in healthy menopausal
women.11
| Table 1 | |||
| Nutritional information for flaxseed Serving size: 2 tablespoons Calories: 95.33 | |||
| Nutrient Omega-3 fatty acids Manganese Dietary fiber Magnesium Folate Copper Phosphorus Vitamin B6 (pyridoxine) |
Nutrient Amount 3.51 g 0.64 mg 5.41 g 70.14 mg 53.86 mcg 0.20 mg 96.49 mg 0.18 mg |
DV (%) 140.4 32.0 21.6 17.5 13.5 10.0 9.6 9.0 |
Density 26.5 6.0 4.1 3.3 2.5 1.9 1.8 1.7 |
| Adapted from: George Mateljan Foundation. Flaxseed. Available at: www.whfoods.com/genpage.php?tname=foodspice&dbid=81. Accessed July 5, 2005. | |||
| Table 2 | ||||
| Comparison of commercially available flaxseed and flaxseed oil products | ||||
| Product | Alpha-linolenic acid content | Fiber per serving | Lignans (Yes/No) | Calories |
| Whole flaxseed Flaxseed powder Flaxseed oil Linseed bread Flax Plus cereal |
2.2 g/Tbsp 5.4 g/Tbsp 7.5-10 g/Tbsp Not listed 600 mg/serving |
3.3 g/Tbsp 3.0 g/Tbsp 0.5 g/Tbsp 5 g (slice) 5 g |
Yes Yes No Yes Yes |
59/Tbsp 0/Tbsp 130/Tbsp 100/slice 120 per ¾ cup |
| Sources: U.S. Department of Agriculture Nutrient Database for Standard Reference; and online retailers. | ||||
Formulation and Dosage
Flaxseeds are slightly larger than sesame seeds, have a hard shell that is smooth and shiny, and range in color from deep amber to reddish brown. Flax is an excellent source of omega-3 fatty acids and a good source of omega-6 or linoleic acid. Flaxseed oil contains 45-60% omega-3 fatty acid. Because flaxseed contains some protein, fiber, vitamins and minerals, and lignans, freshly ground seeds are more nutritious than their oil. Flaxseed increases the nutritional value of bread doughs and pancake, muffin, or cookie mixes when sprinkled on top of any of these before baking. When buying seeds, be sure they are not split, as splitting exposes the inner seed to light and heat and decreases the nutritional value. Preground flaxseed is available as flaxseed meal. One ounce (4 tablespoons) of flaxseed meal will yield about 6 g protein and 8 g fiber. (See Tables 1 and 2 for nutritional information on flaxseed.)
Whole flaxseeds can be stored at room temperature for up to a year. For optimum freshness seeds should be ground as needed with the unused bulk kept refrigerated in an airtight, opaque container.
Adverse Effects
When first beginning a flaxseed consumption regime, patients should be advised to start slowly, as too much too soon will cause a cathartic bowel effect. It is best to begin by grinding 1 tablespoon of seeds in the morning. After the body has adjusted to the increase in fiber, one can add another tablespoon to the evening meal, gradually increasing to 4 tablespoons per day. After ingesting 1 or more tablespoons of the ground seed, it is a good idea to drink a full glass of water to assist in the assimilation and elimination of the additional fiber.
When using freshly ground seeds it is important to completely stir the grindings into the food. When pouring the seed grindings on top of a salad or yogurt, for instance, one risks inhaling the powdery residue from the ground seeds.
It is important to store the seeds in a cool, dark place to decrease the chance of rancidity. The nutrients that give flax its nutritional benefits, essential fatty acids, also give it a short shelf-life. A number of flaxseed recipes call for adding flax to baking foods. However, when baking with flax, the heat generally destroys the positive effect of the freshly released oils.
Conclusion and Recommendation
The pharmaceutical use of statins works to reduce cholesterol, but these drugs have side effects. Flaxseed is an option for patients needing slight reductions or for those wishing to make dietary choices that reinforce healthy lipid levels. For those needing more serious reductions (those on pharmaceutical drugs), flaxseed might be employed as an adjunct to conventional interventions. Both animal and human studies validate that flaxseed is beneficial in reducing plasma cholesterol health. Dietary flaxseed supplementation may prevent hypercholesterolemia-related heart attack and strokes. Anyone with hypercholesterolemia hoping to lower her cholesterol can benefit by adding freshly ground flaxseed to her daily diet. Dietary flax is no quick fix for women, but rather a cholesterol-lowering mechanism that works over a period of time. It is best combined with a program of weight reduction, exercise, and optimal nutrition.
References
1. Bloedon LT, Szapary PO. Flaxseed and cardiovascular risk. Nutr Rev 2004;62:18-27.
2. Binkoski AE, et al. Balance of unsaturated fatty acids is important to a cholesterol-lowering diet: Comparison of mid-oleic sunflower oil and olive oil on cardiovascular disease risk factors. J Am Diet Assoc 2005;105:1080-1086.
3. Shai I, et al. A prospective study of lipoprotein(a) and risk of coronary heart disease among women with type 2 diabetes. Diabetologia 2005;[Epub ahead of print].
4. Platt R. Current concepts in optimum nutrition for cardiovascular disease. Prev Cardiol 2000;3:83-87.
5. George Mateljan Foundation. Flaxseeds. Available at: www.whfoods.com/genpage.php?tname=foodspice&dbid=81. Accessed July 8, 2005.
6. Prasad K. Dietary flax seed in prevention of hypercholesterolemic atherosclerosis. Atherosclerosis 1997;132:69-76.
7. Lucas EA, et al. Flaxseed reduces plasma cholesterol and atherosclerotic lesion formation in ovariectomized Golden Syrian hamsters. Atherosclerosis 2004;173:223-229.
8. Wiesenfeld PW, et al. Flaxseed increased alpha-linolenic and eicosapentaenoic acid and decreased arachidonic acid in serum and tissues of rat dams and offspring. Food Chem Toxicol 2003;41:841-855.
9. Lucas EA, et al. Flaxseed improves lipid profile without altering biomarkers of bone metabolism in postmenopausal women. J Clin Endocrinol Metab 2002;
87:1527-1532.
10. Jenkins DJ, et al. Health aspects of partially defatted flaxseed, including effects on serum lipids, oxidative measures, and ex vivo androgen and progestin activity: A controlled crossover trial. Am J Clin Nutr 1999;
69:395-402.
11. Dodin S, et al. The effects of flaxseed dietary supplement on lipid profile, bone mineral density, and symptoms in menopausal women: A randomized, double-blind, wheat germ placebo-controlled clinical trial. J Clin Endocrinol Metab 2005;90:1390-1397.
Director, Holistic Nursing Consultants, Port Angeles, WA Dr. Keegan reports no consultant, stockholder, speakers bureau, research, or other financial relationships with companies having ties to this field of study. Historically, flaxseed, purported to be one of the original medicines used by Hippocrates, has been highly regarded because of its healing properties. Flaxseed recently has gained attention in the area of cardiovascular disease primarily because it is the richest known source of both alpha-linolenic acid (ALA) and the phytoestrogen lignan, as well as a good source of soluble fiber.1Subscribe Now for Access
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