The Kind Mama Milk Share has prompted a positive response, with many women touting their vegan, vegetarian or organic diets.
Most experts agree it's safe to feed a child another woman's breast milk, however warm that is, like any bodily fluid, it can carry HIV and other viruses.
While breast milk banks test donors for infection, online message boards like Silverstone's, don't carry the same safety guarantee.
This isn't the first time the actress has caught attention for her alternative approach to motherhood.
She revealed her unorthodox method for feeding her then 10-month-old son Bear - chewing food then spitting it into the youngster's mouth - in a video posted on her blog.
She is seen in the clip holding a small bowl and putting a spoonful of food in her mouth.
She then chews it up before transferring it mouth-to-mouth with Bear reaching up for it.
Check it out here.
- www.nzherald.co.nz