Nutrients
Flaxseeds are an excellent source of the omega-3 essential fatty acid alpha-linolenic acid (ALA), as well as phytoestrogens known as lignans. They are a very good source of dietary fiber, magnesium, potassium, and manganese. They are a good source of the minerals phosphorus, iron, and copper.

Glycemic Index (GI)
In a study to determine the GI of various foods, it was concluded that flaxseed has a low GI of 5.

Omega-3
Flaxseed oil contains alpha-linolenic acid, a type of omega-3 fatty acid similar to the omega-3 fatty acids found in fish oil, the difference being that it contains the shorter-chain alpha-linolenic acid (ALA) rather than the longer-chain fats eicosapentaenoic acid (EPA) and do-cosahexaenoic acid (DHA). Although ALA can be converted to EPA and DHA, the problem is that there are factors that may block the conversion in certain individuals, such as excess cholesterol, a diet heavy in saturated fat, excessive alcohol intake, junk food, smoking, the absence of an enzyme called delta-6-desaturase which is common in diabetics, and other factors.
Omega-3 fatty acids are beneficial in reducing inflammation, improving brain function, alleviating rheumatoid arthritis, reducing blood pressure, protective effect against cardiovascular disease, cancer prevention, and cholesterol reduction.

Cholesterol
Some studies have found flaxseed to be beneficial in reducing cholesterol.
In a study of post-menopausal women, the results of the study concluded that dietary flaxseed supplementation lowered total cholesterol and low-density lipoprotein cholesterol (LDL-cholesterol) by approximately 7% and 10%, respectively.
In another study involving fifty-five hypercholesterolaemic subjects, it was concluded that dietary flaxseed lignan extract decreased plasma cholesterol.

Cancer
Studies have shown flaxseed to inhibit the growth of human estrogen-dependent breast cancer. The lignans in flaxseed are phyto-oestrogens, plant chemicals that mimick the effects of oestrogen in the body by increasing the production of a compound known as sex hormone-binding globulin, or SHBG. This protein regulates estrogen levels by displacing excess oestrogen from cells in the body. It is believed that displacing oestrogen in this manner might help prevent those cancers that depend on oestrogen, such as breast cancer, from starting and developing.
One preliminary study also found that flaxseed oil, which contains no appreciable amounts of lignans, slowed the growth of malignant breast tumors.
There is evidence that ground flaxseed appears to be effective in preventing prostate cancer. In addition to the phytoestrogen effect, flaxseed lingnans bind to male hormone receptors and promote the elimination of testosterone. In a study conducted at the Duke University Medical Center and Durham Veterans Affairs Medical Center involving men with prostate cancer, a low-fat diet (in which fat represented no more than 20 percent of total calories) supplemented with 30 grams of ground flaxseed reduced serum testosterone by 15%, slowed the growth rate of cancer cells, and increased the death rate of cancer cells after only thirty-four days.

Constipation
In a double-blind study, 55 people with chronic constipation caused by irritable bowel syndrome received either ground flaxseed or psyllium seed daily for 3 months. Those taking flaxseed had significantly fewer problems with constipation, abdominal pain, and bloating than those taking psyllium. The flaxseed group had even further improvements in constipation and bloating while continuing their treatment in the 3 months after the double-blind part of the study ended. The researcher concluded that flaxseed relieved constipation more effectively than psyllium.
The fibre in flaxseed binds with water, swelling to form a gel which, like other forms of fibre, helps soften the stool and move it along in the intestines. One study found that flaxseed can help with chronic constipation in irritable bowel disease, Germany's Commission E authorises the use of flaxseed for various digestive problems, such as chronic constipation, irritable bowel syndrome, diverticular disease and general stomach discomfort

Kidney Disease
Flaxseed has shown some promise for treating kidney disease associated with lupus nephritis. Research is however weak and further studies are needed to establish flaxseed in this regard.

Bipolar Disorder
One preliminary study hints that flaxseed oil may enhance the effects of conventional treatments for bipolar disorder when combined with  medications. Although promising, further research is required to substantiate the result of this study.