Flaxseed and fish oil both contain omega-3 fatty acids, which help to treat or prevent many different diseases, including cancer, cardiovascular disease, ADHD and asthma, according to WebMD. Flaxseed and fish oil may also be used for depression, rheumatoid arthritis and other autoimmune diseases.
Research suggests that flaxseed helps to prevent colon, prostate and breast cancer, notes WebMD. Flaxseed may reduce the risk of cardiovascular or lung disease. It contains antioxidants, which help to prevent disease. The lignans contained in flaxseed may help to treat diabetes. Flaxseed may reduce inflammation from certain conditions, such as asthma or Parkinson's disease. Some menopausal women take flaxseed to reduce hot flash occurrences.
People with conditions related to the blood system, arteries or the heart often take fish oil supplements, according to WebMD. Studies suggest that fish oil improves cognitive function, and it may decrease the chances of getting Alzheimer's disease and other forms of dementia.
Although taking fish oil as instructed seems to prevent heart disease and stroke, taking too much may actually increase the risk of having a stroke, states WebMD. Fish oil may be used to treat dry eyes or glaucoma, psoriasis and weight loss caused by cancer drugs. It may be used post-surgery to prevent kidney damage and regulate blood pressure.