Flaxseed is the seed of the flax plant and can be considered a functional food, with a variety of health benefits. The three major components of flaxseed are alpha-linolenic acid (an omega-3 fatty acid), lignans (a phytochemical) and dietary fiber. Each is associated with a specific effect on the body. For example, alpha-linolenic acid (ALA) may help lower the risk of cardiovascular disease. Lignans may inhibit the action of estrogen in the body and act as an antioxidant. Fiber may help regulate digestive function as well as lower cholesterol levels. 

Flaxseed is available in whole or ground form that may be easily added to foods or beverages (e.g., yogurt, oatmeal, juice). It is also available in oil form, which may be used in salad dressings or cooked vegetables. However, flaxseed oil does not contain the fiber or lignans naturally available in the whole or ground flaxseeds. In some cases, lignans made be added back into the flaxseed oil before processing is completed.

One tablespoon (15 milliliters) of ground flaxseed contains approximately 1.75 grams of ALA and a total of 2.2 grams of dietary fiber (both soluble and insoluble). One tablespoon of flaxseed oil contains about 7.5 grams of ALA.

Flaxseed supplements are available, although most experts generally recommend most people receive nutrients and other healthful substances from foods rather than supplements.

The Food and Nutrition Board (FNB) has determined adequate intake levels for some components of flaxseed, such as ALA (1.1 grams per day for women; 1.6 grams per day for men) and fiber (21 grams per day for women; 38 grams per day for men). However, no dietary recommendations exist concerning flaxseed. A safe and effective dose of flaxseed has not been established by scientific studies.

Moderate consumption of flaxseed appears to be safe, although it may not be recommended for everyone. For example, flaxseed may not be appropriate for people with certain allergies, conditions that cause chronic diarrhea, for women with hormone-sensitive conditions, pregnant or breastfeeding women, or people with blood disorders.

Consumers are encouraged to consult their physician or registered dietitian about whether flaxseed is appropriate for them.

No health claims have been approved by the U.S. Food and Drug Administration associating flaxseed with a reduced risk of any disease or condition. However, dietary guidance claims do exist for fiber, one component of flaxseed. Additional types of claims may also be seen on the flaxseed product labels.