INTRODUCTION
Flaxseed is widely used in various products, including snack bars, pancakes, cereals, muffins, and trail mix. It also serves as a topping for cereals, salads, and yogurt. Ground flaxseed is commonly added to muffins and breads. Its popularity likely stems from its potential health benefits, particularly for diabetes and other conditions. However, it’s worth noting that the outer hull of flaxseed can be challenging to digest, leading some people to chew it thoroughly or opt for flaxseed supplements.
Flaxseed is claimed to offer several health benefits, such as being a rich source of nutrients like protein, fiber, and omega-3 fatty acids. Its lignans may help protect against cancer, and its ALA content supports heart health.
POTENTIAL HEALTH BENEFITS
LIPID PROFILES AND LIVER FUNCTIONS Flaxseed contains 32-45% of its mass as oil, of which 51-55% is alpha-linolenic acid (n-3 fatty acids, omega-3 fatty acids). Flaxseed meal was found to be more beneficial on some chronic conditions such as high triglycerides and liver steatosis than soy protein meal, in a study of rats. [3] A study found, intake of flaxseed lignan (secoisolariciresinol diglucoside [SDG]) attenuated high-fat, diet-induced hypercholesterolemia in mice. In moderately hypercholesterolemic men, oral administration of SDG (20 or 100 mg) decreased the level of blood cholesterol and liver disease risk factors induced by hypercholesterolemia. [9] In another study of rats, researchers investigated the impact of dietary flaxseed. Obese male and female rats were studied alongside their lean counterparts. After 12 weeks of ingesting different diets (control, control with flaxseed, high fat/high sucrose, or HFHS plus flaxseed), several findings emerged: Obese Rats were associated with a higher liver weight, elevated cholesterol, triglyceride, and saturated fatty acid levels. HFHS diet further exacerbated these effects. Flaxseed Benefits (including flaxseed in the HFHS diet): reduced liver weight, depressed plasma levels of liver enzymes (aspartate aminotransferase and alanine aminotransferase), improved hepatic cholesterol and triglyceride content, and Enhanced fatty acid profile. In summary, flaxseed improved liver lipid composition and reduced tissue injury markers despite a high-fat, high-sucrose diet. While this study was conducted in rats, it highlights the potential benefits of flaxseed for rats suffered from non-alcoholic fatty liver disease. (A1)
INSULIN LEVEL Researchers from George Washington University Medical Center randomly assigned male SHR/N-cp rats to diets either 20% casein, 20% soy protein concentrate, or 20% flaxseed meal for 6 months. They found, plasma insulin concentration was significantly lower in rats fed flaxseed meal than those fed either casein or soy protein concentrate. [4]
CANCER Studies showed that flaxseed lignan (secoisolariciresinol diglucoside) and oil inhibit established breast tumor growth in athymic mice with or without tamoxifen treatment. [5] Further, in a murine mammary tumor model, an incidence of palpable tumors before sacrifice, a number of tumors per mouse, and a number of large tumors (>6 mm diameter) at necropsy were statistically significantly lower in the high flaxseed group compared to controls, suggesting a beneficial effect on tumor progression of small dietary doses of flaxseed. [6] In another aspect, the proinflammatory cytokines IL- 1α and IL-1β promote tumor angiogenesis that might be counteracted by the IL-1 receptor antagonist (IL-1Ra), anakinra, a clinically approved agent. It was found that tumors treated with tamoxifen and fed flaxseed (Flax) or enterolactone ENL exhibited decreased in vivo release of IL-1β derived from the murine stroma and decreased microvessel density. [7] Further, tamoxifen, flaxseed, and ENL increased IL-1Ra levels significantly. Thus, flaxseed may have benefits of people at risk of certain cancers.
CARDIOVACULAR EVENTS Preventing the occurrence of cardiovascular disease (CVD) with nutritional interventions is an unique therapeutic strategy. The increased use of omega fatty acids is a powerful example of one such nutritional strategy that may produce significant cardiovascular benefits. Marine food products have provided the traditional dietary sources of omega fatty acids. Flaxseed is an alternative to marine products. It is one of the richest sources of the plant-based omega-3 fatty acid, alpha-linolenic acid (ALA). Based on the results of clinical trials, epidemiological investigations and experimental studies, ingestion of ALA has been suggested to have a positive impact on CVD. Because of its high ALA content, the use of flaxseed has been advocated to combat CVD. [8]
In October 2010, researchers from Tufts University reported that five intervention studies using flaxseed lignan supplements indicated beneficial associations with C-reactive protein, and a meta-analysis that included these studies also suggested lignans have a lowering effect on plasma total and low-density lipoprotein cholesterol. Three intervention studies using sesamin supplements indicated possible lipid- and blood pressure-lowering associations. Eleven human observational epidemiological studies examined dietary intakes of lignans in relation to cardiovascular disease risk. Five showed decreased risk with either increasing dietary intakes of lignans or increased levels of serum enterolactone (an enterolignan used as a biomarker of lignan intake), five studies were of borderline significance, and
one was null. [10]
CHOLESTEROL Flaxseed show benefits to people with high cholesterol levels. Clinical have shown that flaxseed can modestly reduce serum total and low-density lipoprotein cholesterol concentrations, reduce postprandial glucose absorption, and decrease some markers of inflammation. [2] Clinical studies have further shown that intake of flaxseed or secoisolariciresinol diglucoside isolated from defatted flaxseeds was associated with lowered serum total cholesterol and LDL-cholesterol, while flaxseed oil alone in human subjects had no effects on the lipid profiles. [1] Secoisolariciresinol diglucoside is an important ingredient for flaxseed's lipid-lowering effect.
SKIN CONDITIONS In a study, dogs received supplemental flaxseed oil (200 mg/kg/d), eicosapentaenoic acid (EPA; 50 mg/kg/d)-docosahexaenoic acid (DHA; 35 mg/kg/d), or mineral oil. Total plasma concentrations of alpha-LLA and EPA increased and those of arachidonic acid decreased significantly with administration of EPA-DHA, and concentrations of alpha-LLA increased with flaxseed oil supplementation; nevertheless, there was no significant change in the concentrations of these fatty acids or eicosanoids in the skin. Results indicated that at the dose used, neither the concentrations of fatty acids in skin or plasma nor a decrease in the production of inflammatory eicosanoids was a major factor involved in the mechanism of action in dogs with atopy that responded to fatty acid supplementation. [12] Ultraviolet C exposure led to oxidative stress and apoptosis in rats as reflected by increased malondialdehyde, protein carbonyl contents and decreased enzymatic and nonenzymatic antioxidant levels, flaxseed oil may help preventing photoreactive damage. [11]
REFERENCE
[1] Prasad K. Flaxseed: a source of hypocholesterolemic and antiatherogenic agents. Drug News Perspect. 2000 Mar;13(2):99-104. [2] Bloedon LT, Szapary PO. Flaxseed and cardiovascular risk. Nutr Rev. 2004 Jan;62(1):18-27. [3] Bhathena SJ, et al, Dietary flaxseed meal is more protective than soy protein concentrate against hypertriglyceridemia and steatosis of the liver in an animal model of obesity. J Am Coll Nutr. 2003 Apr;22(2):157-64. [4] Velasquez MT, et al, Dietary flaxseed meal reduces proteinuria and ameliorates nephropathy in an animal model of type II diabetes mellitus. Kidney Int. 2003 Dec;64(6):2100-7. [5] Chen J, et al, Effects of flaxseed lignan and oil on bone health of breast-tumor-bearing mice treated with or without tamoxifen. J Toxicol Environ Health A. 2011 Jan;74(12):757-68. [6] Birkved FK, et al, Investigation into the cancer protective effect of flaxseed in Tg.NK (MMTV/c-neu) mice, a murine mammary tumor model. Genes Nutr. 2011 Nov;6(4):403-11. [7] Lindahl G et al, Tamoxifen, flaxseed, and the lignan enterolactone increase stroma- and cancer cell-derived IL-1Ra and decrease tumor angiogenesis in estrogen-dependent breast cancer. Cancer Res. 2011 Jan 1;71(1):51-60. [8] Rodriguez-Leyva D et al, The cardiovascular effects of flaxseed and its omega-3 fatty acid, alpha-linolenic acid. Can J Cardiol. 2010 Nov;26(9):489-96. [9] Fukumitsu S et al, Flaxseed lignan lowers blood cholesterol and decreases liver disease risk factors in moderately hypercholesterolemic men. Nutr Res. 2010 Jul;30(7):441-6 [10] Peterson J et al, Dietary lignans: physiology and potential for cardiovascular disease risk reduction. Nutr Rev. 2010 Oct;68(10):571-603. [11] Tülüce Y, et al, Photoprotective effect of flax seed oil (Linum usitatissimum L.) against ultraviolet C-induced apoptosis and oxidative stress in rats. Toxicol Ind Health. 2011 Jun 10. [12] Mueller RS , et al, Plasma and skin concentrations of polyunsaturated fatty acids before and after supplementation with n-3 fatty acids in dogs with atopic dermatitis. Am J Vet Res. 2005 May;66(5):868-73. (A1) Mihir Parikh et al, Beneficial Effects of Dietary Flaxseed on Non-Alcoholic Fatty Liver Disease, Nutrients. 2024 Feb 6;16(4):466.