Oprah and Dr. Oz turned flaxseed into a celebrity, but there is still a lot of confusion around the different forms it comes in (whole seeds, milled/ground, oil) and its effects (particularly the phytoestrogen properties of lignan).  Here are some flax facts to help sort through the hype.

Flax seeds come in brown or yellow (golden). Most types have similiar nutritional values except a type of yellow flax called Linola or solin, which is very low in omega-3. [Flax (Wikipedia)]

It's better to eat ground flax, since it's difficult for the body to break down the whole seed. [Flax FAQ (Healthy Flax)]

Flaxseed oil is also known as linseed oil. [Flax (Wikipedia)]

Flaxseed oil does not contain the lignan or fiber components of the seed. [Flaxseed and flaxseed oil (Mayo Clinic)]

Flax seeds are stable while whole, but milled and ground flaxseed can go rancid without refrigeration and proper storage. [Flax (Wikipedia)]

Due to its high levels of fiber, flax seed can be used as a laxative. But excessive consumption without liquid can result in constipation or diarrhea. [Flax (Wikipedia)]

Raw flax seed contains a chemical that can be toxic if consumed in large quantities. [Flax (Wikipedia)]

Flax seeds contain high levels of omega-3 fatty acids in the form of alpha-linolenic acid. [Flaxseed and flaxseed oil (Mayo Clinic)]

There are three types of omega-3 fatty acids: alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Fish and marine plants have EPA and DHA, which is what most studies on the health benefits of omega-3 has been based on. [Is Omega-3 in Fish Oil Better Than In Flax Seed Oil? (Women's Health)]

ALA in flax seed must be converted to EPA and DHA. Only about 5% converts to EPA and up to 3% to DHA. [Is Omega-3 in Fish Oil Better Than In Flax Seed Oil? (Women's Health)]

Flax seeds contain lignans, which is an anti-oxidant as well as a type of phytoestrogen, a plant chemical that acts in a similar way to estrogen. [Flaxseed oil lends itself to many uses (LA Times)]

The hormonal ffects of lignan is similar to those seen in soy isoflavones, another source of phytohormones. [Flax Seed, the Mighty Little Wonder (The Nutrition Fact)]

The phytoestrogen properties may have hormonal effects, which effects those with or at risk of breast and prostate cancer. However, the current debate is whether it is beneficial or dangerous. Women who are pregnant or breastfeeding is advised to stay away from flaxseed and flaxseed oil due to possible harmful hormonal effects. [Flaxseed and flaxseed oil (Mayo Clinic)]

There is ongoing debate about the effects of phytohormones, especially the impact on men's health and breast cancer.  There have been studies showing both health risks and benefits, although ultimately inconclusive. The Mayo Clinic has a list of purported effectiveness of flaxseed treating various diseases and conditions, all rated with a C grade (Unclear scientifice evidence). [Flaxseed and flaxseed oil (Mayo Clinic)]

As with most things in life, moderation will probably work best for all.