For centuries, flaxseed has been utilized as both a food and medicinal ingredient in traditional Indian and Chinese practices. Its notable abundance of alpha-linolenic acid, lignans, and lignin has propelled flaxseed into the spotlight as an essential component of functional foods that support cardiovascular health. This article explores the potential of flaxseed and its constituents in lowering cholesterol levels.
Constituents Found in Flaxseed
Alpha-Linolenic Acid
Flaxseed stands out as one of the most abundant plant sources of alpha-linolenic acid. A tablespoon of flaxseed oil contains roughly 7.3 grams of alpha-linolenic acid, while a tablespoon of flaxseed holds about 1.6 grams. Within the body, alpha-linolenic acid can undergo further metabolism, transforming into docosahexaenoic acid and eicosapentaenoic acid. These omega-3 fatty acids have demonstrated various health benefits for conditions such as cardiovascular disease, hypertension, and atherosclerosis.
Lignans
Flaxseed stands out as an abundant source of lignans, with secoisolariciresinol diglucoside (SDG) being its primary lignan component. In comparison to vegetables, fruits, legumes, cereals, and seeds, flaxseed boasts a staggering 75-800 times higher concentration of active lignans. If one prefers dietary supplements, there are options available that offer lignans extracted from flaxseed, typically ranging from 5 to 300 milligrams in lignan content.
Upon consumption of flaxseed, the SDGs undergo a transformation within the human gut, facilitated by bacteria residing there. This conversion yields enterolignans, namely enterodiol and enterolactone, both possessing mild estrogenic properties. Furthermore, flaxseed SDGs possess antioxidant characteristics, which can combat oxidative stress and contribute to safeguarding against cardiovascular disease.
Consistently, studies have revealed that diets rich in lignan-containing foods like flaxseed and other plant sources correlate with a decreased risk of cardiovascular disease.
Soluble Fibers
Flaxseed contains a beneficial combination of fiber, with approximately two-thirds being insoluble fiber and the remaining one-third being soluble fiber. Among the soluble fiber content, a significant portion consists of mucilage gums. Research suggests that incorporating higher amounts of soluble fiber into the diet can potentially lower the risk of cardiovascular disease by reducing levels of LDL cholesterol or bad cholesterol.
Soluble fiber has the ability to bind with bile acids in the intestine, resulting in an increased excretion of these acids through feces. As a response, the body needs to replenish bile acids, and since cholesterol serves as a precursor for bile acid production, the increased excretion leads to a greater utilization of cholesterol for bile acid synthesis. Consequently, this process contributes to decreased circulating cholesterol levels.
Is Flaxseed Effective in Reducing Cholesterol Levels?
Flaxseed is believed to offer various health benefits due to its components such as alpha-linolenic acid, secoisolariciresinol diglucoside, and fiber. These active constituents may work together to make flaxseed a functional food. The potential cardiovascular benefits of consuming flaxseed, including flax lignans, flax fibers, and flaxseed oil, have been extensively studied in both animals and humans. These studies have shown improvements in lipid profile and reduction in inflammatory markers.
Several human clinical trials have examined the impact of flaxseed consumption on cholesterol levels. Some trials have reported an 8-14 percent decrease in LDL cholesterol levels after consuming 30-50 grams of flaxseed daily for four to 12 weeks. On the contrary, several other trials failed to observe noteworthy decreases in LDL cholesterol levels upon incorporating 30-40 grams of flaxseed into the daily diet. In a six-month double-blind randomized controlled trial, participants who were given 30 grams of ground flaxseed daily experienced increased levels of alpha-linolenic acid and enterolignans in their plasma.
Flax Lignans
Studies conducted on both animals and humans have indicated that secoisolariciresinol diglucoside (SDG), the primary lignan found in flax, and its byproducts have beneficial effects on cholesterol levels. They have been shown to decrease total cholesterol, triglycerides, and LDL cholesterol, while increasing HDL cholesterol. Flax lignans have also demonstrated the ability to slow down the progression of atherosclerosis and improve blood pressure. Furthermore, a human study revealed that a daily supplement of 100 milligrams of flax SDG reduced levels of harmful cholesterol, increased levels of beneficial cholesterol, and lowered the risk of liver disease in individuals with moderately high cholesterol.
Flax Fibers
Consuming flaxseed mucilage has the potential to contribute to the prevention of cardiovascular disease (CVD) by reducing cholesterol levels. In individuals with Type 2 diabetes, an intake of 5 grams of flaxseed gum per day resulted in decreased levels of harmful cholesterol. Moreover, a prospective cohort study conducted on European participants without pre-existing CVD over a span of approximately six and a half years reported that consuming flax-fiber-enriched beverages led to lowered cholesterol levels. Another study demonstrated that including flaxseed dietary fiber in one's diet reduced triglyceride levels and increased feelings of satiety.
Flaxseed Oil
In an eight-week human study, individuals who consumed 6 grams of flaxseed oil per day experienced a reduction in triglyceride levels. However, among patients undergoing hemodialysis, there were no significant changes observed in total cholesterol, LDL cholesterol (considered "bad" cholesterol), or HDL cholesterol (considered "good" cholesterol) levels. A study conducted on rats indicated that flaxseed oil has a cholesterol-lowering effect. However, in a separate animal study comparing the effects of flaxseed and flaxseed oil, hamsters that were fed flaxseed demonstrated a reduction in cholesterol levels, whereas those fed flaxseed oil did not exhibit the same cholesterol-lowering effect.
Possible Negative Consequences of Flaxseed Consumption
While flaxseed is generally well-tolerated and rarely causes allergic reactions, there are some concerns regarding potential adverse effects. Flaxseed naturally contains compounds known as cyanogenic glycosides which can be converted to thiocyanates in the body. Excessive amounts of thiocyanates have the potential to interfere with thyroid gland function. Nevertheless, incorporating moderate amounts of flaxseed into the diet is unlikely to result in any negative consequences for individuals in good health. Nonetheless, individuals with thyroid problems should exercise caution and consider avoiding large quantities of flaxseed.
Another possible side effect relates to digestion. Flaxseed, especially when consumed raw, is rich in globulins and albumins, which are proteins that can reduce digestibility and absorption in both animals and humans. Consuming large amounts of flaxseed may lead to mild digestive issues, such as bloating, gas, abdominal pain, and nausea. It is advisable to start with small doses and gradually increase to 1-2 tablespoons per day. Additionally, the inclusion of flaxseed in the diet can promote more frequent bowel movements due to its high fiber content, as it acts as a natural laxative.
While limited human studies exist, many healthcare professionals may not recommend the consumption of flaxseed during pregnancy due to its lignan content, which can exhibit estrogen-like effects in the body. Animal studies have demonstrated that flaxseed and flaxseed lignans can potentially influence birth weight, the development of the offspring's reproductive system, milk production, and the composition of fatty acids in milk. It is unlikely that smaller doses of flaxseed would have adverse effects. However, it is generally advised to limit the intake of flaxseed and other dietary sources of phytoestrogens during pregnancy and lactation.
Utilizing Flaxseeds Effectively
The utilization of flaxseeds in various food products is rapidly increasing in North America. These products encompass breads, cereals, crackers, energy bars, meals, oils, pastas, snacks, waffles, and even pet foods. Flaxseeds are available in different forms such as whole flaxseed, ground (or milled) flaxseed, and flax oil, all of which can be found in stores. To preserve their sensitive nutrients and prevent the oils from going rancid, it is recommended to choose flaxseed and flax oil with opaque packaging, as light can be damaging. Refrigeration helps extend the shelf life of whole flaxseed, ground flaxseed, and flax oil. Whole flaxseed can be stored at room temperature in a cool, dry place for up to a year.
The body may absorb the nutrients in ground flaxseed more effectively than those in whole flaxseed. Ground flaxseed can be incorporated into various recipes such as muffins, pancakes, waffles, bread dough, and added to smoothies, juices, and hot or cold cereal. Additionally, ground flaxseed can serve as an egg substitute by combining 1 teaspoon of ground flaxseed with 3 teaspoons of water as a replacement for one egg.
Heart disease and stroke are commonly attributed to high blood pressure and cholesterol levels. Research suggests that flaxseed may contribute to reducing blood pressure, total cholesterol, and LDL cholesterol levels. These findings support the notion that flaxseed and its components have the potential to lower cholesterol and consequently reduce the risk of heart disease.
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