Flax seeds (Linum usitatissimum) — also known as common flax or linseeds — are small oil seeds that originated in the Middle East thousands of years ago.
Lately, they have gained popularity as a health food. This is due to their high content of heart-healthy omega-3 fats, fiber, and other unique plant compounds.
Flax seeds have been linked to health benefits, such as improved digestion and a reduced risk of heart disease, type 2 diabetes, and cancer.
They’re easily incorporated into your diet — grinding them is the best way to make the most of their health benefits.
Flax seeds are usually brown or yellow. They’re sold whole, ground/milled, or roasted — and are often processed into flaxseed oil.
This article tells you everything you need to know about flax seeds.
Flaxseeds have 534 calories per 3.5 ounces (100 grams) — corresponding to 55 calories for each tablespoon (10 grams) of whole seeds.
They consist of 71% fat, 21% carbs, and 14% protein.
One tablespoon (10 grams) of whole flax seeds provides the following nutrients:
Calories: 55Water: 7%Protein: 1.9 gramsCarbs: 3 gramsSugar: 0.2 gramsFiber: 2.8 gramsFat: 4.3 grams
Carbs and fiber
Flax seeds are made up of 21% carbs — a whopping 95% of which is fiber.
This means that they’re low in net digestible carbs — the number of total carbs minus the amount of fiber — making them a low-carb food.
Two tablespoons (20 grams) of flax seeds provide about 6 grams of fiber. For reference, people should usually eat 14 grams of fiber for every 1000 calories they consume.
25% soluble fiber (cellulose, lignin, and hemicellulose)75% insoluble fiber (gums, pectin, and beta-glucan)
Soluble fiber helps regulate blood sugar and cholesterol levels. It also promotes digestive health by feeding your beneficial gut bacteria.
When mixed with water, the mucilage gums in flax seeds become very thick. Combined with the insoluble fiber content, this makes flax seeds a natural laxative.
Consuming flax seeds can help promote regularity, prevent constipation, and reduce your risk of diabetes. The soluble fiber in flax seeds can lower LDL cholesterol, which decreases your risk of cardiovascular disease.
Protein
Despite containing essential amino acids, they’re low in the amino acid lysine that’s needed for human protein synthesis.
Therefore, they’re considered an incomplete protein.
Still, flax seeds are high in the amino acids arginine and glutamine — both of which are important for heart and immune system health.
Fat
Flax seeds contain 71% fat, with 1 tablespoon (10.3 grams) providing 4.3 grams.
This fat content in 100 grams of flax seeds is composed of:
3.66 grams saturated fatty acids7.53 grams of monounsaturated fatty acids28.7 grams of polyunsaturated fatty acids
Flax seeds are one of the richest dietary sources of ALA. In fact, they’re only exceeded by chia seeds.
ALA is an essential fatty acid, which means that your body cannot produce it. Thus, you need to obtain it from the food you eat.
Flaxseed oil contains the highest amount of ALA, followed by milled seeds. Eating the seeds whole provides the least amount of ALA, as the oil is locked up inside the fibrous structure of the seed.
Flax seeds have a high content of omega-3 fatty acids, but they don’t contain as much omega-3 as fish oils. Omega-3 can have a wide range of health benefits, including:
reducing cardiovascular disease risksimproving eye and brain healthreducing risks of inflammatory conditions like arthritis and asthma
Fatty fish and fish oil contain the active forms of omega-3s, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), whereas the ALA in flax needs to be converted into these forms after ingestion.
p-Coumaric acid. This polyphenol is one of the main antioxidants in flax seeds.Ferulic acid. This antioxidant may help prevent several chronic diseases.Phytosterols. Related to cholesterol, phytosterols are found in the cell membranes of plants. They have been shown to have cholesterol-lowering effects.Lignans. Lignans are present in almost all plants, acting as both antioxidants and phytoestrogens. Flax seeds are exceptionally rich in lignans, containing up to 800 times more than other foods.
Brown flax seeds have slightly higher antioxidant activity than yellow varieties.
Lignans
Flax seeds are rich dietary sources of lignans. These nutrients function as phytoestrogens.
Phytoestrogens are plant compounds that are similar to the female sex hormone estrogen. They have weak estrogenic and antioxidant properties.
Lignans are fermented by bacteria in your digestive system and may reduce the growth of several cancers — especially hormone-sensitive types, such as breast, uterus, and prostate cancer.
Blood cholesterol
Blood cholesterol levels are a well-known risk factor for heart disease. This is especially true for high levels of oxidized LDL (bad) cholesterol.
One study noted that daily consumption of milled flax may lower cholesterol by 11% in the short-term.
These studies also indicate a 15% reduction in the number of LDL (bad) cholesterol particles.
This is supported by animal studies showing that flax seeds may improve cholesterol levels and the composition of blood fats.
These seeds may be very useful when consumed along with cholesterol-lowering medication.
This cholesterol-lowering effect is thought to be caused by the high fiber, protein, and lignan content in flax seeds.
Omega-3 fatty acids
Omega-3 fatty acids are essential. They may have benefits for various aspects of heart health, including blood platelet function, inflammation, and blood pressure.
Plant-based ALA fatty acids seem to benefit heart health similarly to fish oils, which are rich in EPA and DHA.
Blood pressure
Eating flax seeds is an effective way to lower blood pressure.
A randomized, double-blind trial in patients with peripheral arterial disease found that consuming 30 grams of milled flaxseed daily for six months significantly reduced both systolic and diastolic blood pressure.
On average, systolic blood pressure dropped by about 10 mm Hg, with effects appearing within one month and lasting up to a year.
Overall, more participants in the flaxseed group experienced blood pressure reductions compared to the placebo group, suggesting a meaningful cardiovascular benefit.
Digestive health
Diarrhea and constipation cause major distress and may even threaten your health.
The insoluble fiber content in flax seeds adds bulk to your digestive waste, acting as a laxative and relieving constipation.
Soluble fiber is also thought to bind to water in your digestive tract. This causes it to swell and increase the bulk of your stool, preventing diarrhea.
Diabetes
A meta-analysis of 13 randomized trials found that flaxseed supplementation significantly reduced HbA1c in people with type 2 diabetes, particularly in those with poorer baseline blood sugar control.
However, it showed no consistent effects on fasting glucose, body weight, blood pressure, insulin resistance, or most lipid measures overall.
Some subgroup analyses suggested benefits for cholesterol and fasting glucose in specific higher-risk groups, but results were mixed and need further confirmation.
Though the link between flax seeds and type 2 diabetes is still unclear, they may be considered a safe and healthy addition to your diet if you have type 2 diabetes.
Cancer
Flax seeds may suppress the formation of several types of cancer, such as those of the colon, breast, skin, and lungs.
One study concludes that flaxseed contains bioactive compounds (such as lignans and omega-3s) that have potential anticancer effects, including reducing tumor growth and influencing cancer-related pathways.
However, most evidence is preclinical or limited, so while flaxseed may help prevent cancer, stronger human studies are still needed to confirm its effectiveness.
Dry flax seeds are usually well tolerated, and allergy is rare.
Still, it’s recommended to drink plenty of water when eating these seeds.
Cyanogenic glycosides
Flax seeds naturally contain plant compounds called cyanogenic glycosides. These substances can bind with sulfur compounds in your body to form thiocyanates.
One study notes that flaxseed contains compounds like cyanogenic glycosides that can release hydrogen cyanide, posing a theoretical toxicity risk, but typical dietary amounts produce levels far below those needed to cause harm.
Overall, it concludes that no clinically significant toxicity has been observed in humans, and harmful effects would require unrealistically high intake levels.
Phytic acid
Similar to other seeds, flax seeds contain phytic acid.
Phytic acid is often referred to as an antinutrient, as it may reduce the absorption of minerals like iron and zinc.
Still, phytic acid doesn’t cause any lasting reduction in mineral absorption and does not affect any subsequent meals.
Therefore, this should not be a major concern — except for people who are deficient in minerals like iron and/or follow an imbalanced diet.
Digestive problems
For people who are not used to eating a lot of fiber, incorporating flax seeds too quickly can cause mild digestive problems. These include bloating, gas, abdominal pain, and nausea.
It’s best to start with small doses and work your way up to 1–2 tablespoons (10–20 grams) daily.
Adding flax seeds to your diet may also increase bowel movement frequency, as flax seeds are a natural laxative.
Risks during pregnancy
Though human studies are limited, some health professionals fear that consuming flax seeds during pregnancy may have undesirable effects.
This is due to the phytoestrogens in the seeds, which may act similarly to the female sex hormone estrogen.
Animal studies show that flax seeds and flaxseed lignans may cause lower birth weight and affect the development of the offspring’s reproductive system — especially if consumed during early pregnancy.
It’s unlikely that smaller doses of flax seeds will have an adverse effect.
Blood-thinning effects
Large doses of omega-3 fatty acids may have blood-thinning effects.
If you have a bleeding disorder or are taking blood thinners or other medications, consult with your healthcare professional before incorporating large amounts of flax seeds into your diet.
