What is brown kelp? Wikipedia has the answer:

Fucus vesiculosus, known by the common name bladder wrack or bladderwrack, is a seaweed found on the coasts of the North Sea, the western Baltic Sea, and the Atlantic and Pacific Oceans, also known by the common names black tang, rockweed, bladder fucus, sea oak, black tany, cut weed, dyers fucus, red fucus, and rock wrack. It was the original source of iodine, discovered in 1811, and was used extensively to treat goitre, a swelling of the thyroid gland related to iodine deficiency.

Researchers from the University of California at Berkeley have found that brown kelp has an anti-estrogenic effect in the body.  They were looking for an alternative theory as to why Japanese women are less likely to develop breast, womb, or ovarian cancer.  These types of cancer are caused by estradiol, the predominant estrogen in the female body during reproductive years.

A traditional Japanese diet contains between 3 and 13g of seaweed every day.  Could this be the reason why estrogen-related cancers are relatively unknown in Japan?  The research points towards Yes.

The study below was a simple one: feed rats seaweed and see if it lowers their estradiol levels.  They gave rats either 175 or 350mg of seaweed per kg of bodyweight and measured estrogen levels.  The rats receiving the higher dose of seaweed lowered their estradiol levels by 40%.

Since eating seaweed definitely lowered estrogen levels in rats, the researchers next tested the effect of seaweed on human ovary cells.  And again, the higher the concentration of kelp, the lower the amount of estradiol the ovary cells made.

In the final part of this study, the researchers tested whether kelp would block estradiol and progesterone receptors in human cells.  Again, kelp beat estrogen.

The reason why kelp is such a powerful anti-estrogenic remains unknown.  All we can say for sure is that it definitely works.

Adding in seaweed supplements and eating foods containing seaweed on a regular basis will be a valuable anti-estrogenic tool for your health and nutrition toolbox.

Here’s the citation for this study (it has graphs and lots more cool sciency stuff if you’re interested):

J Nutr. 2005 Feb;135(2):296-300.
Brown kelp modulates endocrine hormones in female sprague-dawley rats and in human luteinized granulosa cells.
Skibola CF, Curry JD, VandeVoort C, Conley A, Smith MT.