Sitting at the table in her suburban kitchen, with her four young children tumbling in and out, Ms. O’Brien, 36, seems an unlikely candidate to be food’s Erin Brockovich.

Her theory — that the food supply is being manipulated with additives, genetic modification, hormones and herbicides, causing increases in allergies, autism and other disorders in children — is not supported by leading researchers or the largest allergy advocacy groups.

Ms. O’Brien encourages people to do what she did: throw out as much nonorganic processed food as you can afford to. Avoid anything genetically modified, artificially created or raised with hormones. Don’t eat food with ingredients you can’t pronounce.

Once she cleaned out her cupboards, she said, her four children started behaving better. Their health problems, which her doctor attributed to allergies to milk and other foods, cleared up.

“It was absolutely terrifying to unearth this story,” she said over lunch at a restaurant in Boulder, Colo. “These big food companies have an intimate relationship with every household in America, and they are making our children sick. I was rocked. You don’t want to hear that this has actually happened.”

| ¶ 11:15 p.m.