My previous blog post described flaxseed’s chemical and therapeutic properties as shown in Dr. Andrew Duncan’s book The Edinburgh New Dispensatory, published in 1803.1 He described flaxseed’s historical uses, its mucilage content, its oil (expressed by crushing the seeds) and the use of its leftover “oil-cake” to feed animals. In describing flaxseed oil (also known as linseed oil), Duncan remarked: “It is … generally rancid and nauseous, and unfit for internal use.”
Well! Nothing could be further from the truth … but it would be churlish to criticize him. After all, refrigeration as we know it did not exist in 1803, although it was being actively studied on both sides of the Atlantic. It was not until 1834 that Jacob Perkins, an American who lived in London, built the first refrigerator, becoming known as the father of refrigeration.
Dr. Duncan, living in 1803, likely had evidence from personal experience that flaxseed oil sitting in a warm, sunny kitchen or on the apothecary’s shelf for a week or two did not taste particularly good. Why was that?
Flaxseed Oil Is Rich in Polyunsaturated Fat
Flaxseed oil is rich in polyunsaturated fats, particularly the omega-3 fat alpha-linolenic acid or ALA, for short. ALA is an essential fatty acid.
Polyunsaturated fats are a type of fat found in foods and in our bodies. Chemically, they are fats that contain two or more double bonds in their carbon backbone. (The prefix “poly” means “more than one.”) Fats with double bonds are more sensitive to oxidation than saturated fats, which have no double bonds along their backbones. Oxidation of polyunsaturated fats produces off flavors or funny smells that people find unpleasant.
The table below compares the polyunsaturated fat content of several vegetable oils. Flaxseed oil is second only to grape seed oil in having a high level of polyunsaturated fat. The values shown below were found in the US Department of Agriculture’s Nutrient Database, which is a good resource whenever you want to know the nutrient content of a food.
Polyunsaturated Fat Content of
Vegetable Oils per 100 grams (g):
Grape seed oil = 70 g
Flaxseed oil = 68 g
Walnut oil = 63 g
Soybean oil = 58 g
Canola oil = 28 g
Olive oil = 10 g
Corn oil = 8 g
Oxidation of Polyunsaturated Fats: Consequences and Prevention
Oxidation of polyunsaturated (and other) fats can occur during food storage and processing when fats are exposed to high temperatures, light or oxygen. In addition to producing off flavors in foods, the oxidation of food fats can affect the nutritional quality of foods and reduce their shelf life. Vegetable oils and fish oils rich in omega-3 fatty acids are sensitive to oxidation.
Food processors go to considerable lengths to protect the nutrient quality of their food products. In some cases they add natural antioxidants to a food product to help prevent the oxidation of polyunsaturated and other fats. Common antioxidants include vitamin C, vitamin D, carotenoids, and flavonoids and other phenols (found in berries, tea, chocolate, wine and other foods). Even hen eggs can work as antioxidants.
In the case of flaxseed oil, processors use three strategies to control oxidation. First, the seeds are crushed at a low temperature during processing to produce what we call cold-pressed flax oil. Secondly, flaxseed oil is placed in dark bottles that protect the oil from light. And finally, flaxseed oil is usually stored in the refrigerator, where it is cool and dark. These strategies help prevent oxidation of the fats in flaxseed oil and maintain freshness.
You might wonder: Why is flaxseed oil more susceptible to oxidation than whole or ground flaxseeds? Whole and ground flaxseeds contain lignans—compounds that act as antioxidants. (Lignans also have anticancer properties in the breast and prostate.) In fact, flaxseed is one of the richest sources of plant lignans identified to date. The process of expressing the oil from crushed flaxseeds removes virtually all of the lignans, making the oil more susceptible to oxidation.
Flaxseed Oil Is Rich in ALA
Refrigerating flaxseed oil because of its high polyunsaturated fat content is worth the trouble. Why? Because flaxseed oil is one of the richest sources of the essential fatty acid of ALA. Dietary ALA is essential in the same way that vitamin C, folic acid, magnesium and calcium are essential: our bodies cannot make it. Therefore, we must obtain ALA from our diets. Humans can make the long-chain omega-3 fats (EPA and DHA) from ALA, although not always in sufficient amounts.
Flaxseed Oil Is Definitely Fit for Internal Use
Dr. Duncan, writing his book in 1803, knew nothing about ALA or its health benefits and so thought flaxseed oil unfit for consumption. Today we know better. Like other fats, ALA has several fates in the body. It is stored in the body’s fat depots where it serves as a reserve energy supply. It is incorporated into phospholipids, which are structural components of cells. And it has important effects within the body:2
- Breast milk contains about five times more ALA than DHA and constitutes about 75-80% of the total omega-3 fat in breast milk. ALA must be important if it’s found in mother’s milk!
- ALA is required for the health of the nervous system. A dietary deficiency of ALA produces poor growth and neurological problems like numbness, pain in the legs, difficulty walking and a fuzzy vision. Adding ALA to the diet relieves these symptoms.
- Consuming a diet high in ALA increases the total omega-3 fat content of cell membrane phospholipids, which in turn makes the membranes more flexible and affects the way they behave in positive ways.
- ALA depresses inflammation by blocking the formation of compounds that promote it. Inflammation is a feature of many chronic diseases like heart disease, type 2 diabetes, the metabolic syndrome, obesity, arthritis, cancer and Alzheimer’s disease.
Check out this summary of the importance of omega-3 fatty acids for adults and infants published by the Flax Council of Canada. Recent studies have explored the health benefits of ALA-rich flaxseed oil, as described below:
- Increases HDL-cholesterol (the so-called good cholesterol) — This finding comes from a study of 110 older adults divided into two groups: a placebo group and a group that consumed 3 grams of flaxseed oil (less than 1 teaspoon) daily for 12 weeks.
- Decreases total cholesterol, LDL-cholesterol (the so-called bad cholesterol), and triglycerides — As reported in the previous study.
- Decreases sd-LDL-cholesterol — In a Japanese study, 15 volunteers consumed 10 grams (a little less than 1 tablespoon) of flaxseed oil daily for 12 weeks and then switched to consuming 10 grams of corn oil daily for 12 weeks. sd-LDL-cholesterol decreased significantly when the volunteers consumed flaxseed oil. sd-LDL-cholesterol or “small dense” LDL-cholesterol is considered a risk factor for coronary heart disease and particularly for heart stenosis (a situation where a heart valve doesn’t open properly).
- Increases the blood levels of brain-derived neurotropic factor (BDNF) — Thirty volunteers were given three flax oil capsules every day for one week. Blood levels of BDNF increased significantly at week’s end. The researchers concluded that ALA protects the brain, a finding supported by studies in animals. (BDNF is a protein involved in learning, brain plasticity and memory, particularly long-term memory.) Through its effects on BDNF, ALA may help in treating stroke patients.
A Diet High in ALA Has Protective Effects
The Lyon Heart Diet Study was among the first to show a benefit of a high ALA-diet in reducing heart disease risk. The volunteers in this study had survived a heart attack. Half of them (144 in number) were assigned to eat a Mediterranean-type diet high in ALA; the other half (83) received no dietary instruction. Their heart health was tracked for 46 months. Those volunteers who ate a Mediterranean-type diet high in ALA experienced a 50-70% reduction in their recurrence of cardiac outcomes like angina, stroke, heart failure and the like after four years of follow-up.3
In the Nurses Health Study,4 women with an ALA intake of roughly 1.2 grams per day had a 38% to 40% lower risk of sudden cardiac death. The health data from more than 76,000 women were analyzed for this study. In a Danish study involving about 230,000 women and men, each additional gram of dietary ALA consumed by men was associated with a 15% lower risk of having a heart event (such as a heart attack or arrhythmia) and a 23% lower risk of dying from a heart event. (No consistent effect was found among women.) An analysis of 27 clinical studies of more than 250,000 adults found that ALA was associated with a lower risk of heart disease overall and a lower risk of death from heart disease.
A high intake of ALA from all sources has been shown to decrease sIL-6R, a marker of inflammation. In a study of 353 middle-age male twins, those with a high habitual intake of ALA had lower levels of sIL-6R. [This odd-looking acronym refers to a compound that regulates the immune system and inflammation. Higher levels of sIL-6R are found in people with arthritis, asthma, Crohn’s disease, multiple sclerosis and other inflammatory conditions.] This beneficial effect on sIL-6R was achieved with an ALA intake of 0.92 – 2.31 grams of ALA per day—the amount found in as little as one teaspoon of flaxseed oil.
An analysis of data obtained from 904 women and men participating in the Framingham Osteoporosis Study found that participants with the highest ALA intake (about 1.4 grams/day) had a 54% lower risk of having a hip fracture compared with those who had the lowest ALA intake.
Flaxseed Oil is Good for You
Flaxseed oil is one of the richest sources of the essential omega-3 fat ALA. One teaspoon of flaxseed oil provides 2.8 grams of ALA; one tablespoon provides about 8 grams of ALA. Studies in humans show that ALA-rich diets reduce the risk of heart disease and sudden cardiac death. ALA may also benefit the brain and reduce the risk of hip fractures. The nutritional qualities of flaxseed oil are protected by refrigeration, making it easy to incorporate into a healthy diet.
1Duncan, Andrew. The Edinburgh New Dispensatory (Dublin: Bell & Bradfute, 1803), p. 249 (PDF p. 280).
2Morris, Diane H. Flax: A Health and Nutrition Primer. Winnipeg: Flax Council of Canada, 2007, pp. 29-32. The primer is available online.
3de Lorgeril, Michel, et al. Alpha-linolenic acid in the prevention and treatment of coronary heart disease. European Heart Journal Supplements. 2001 (June); vol. 3 (supplement D): D26-D32.
4Albert, CM, et al. Dietary α-linolenic acid intake and risk of sudden cardiac death and coronary heart disease. Circulation. 2005;112:3232-3238.