On a recent Thursday, Vani Hari, perhaps Public Enemy No. 1 of big food companies, sat at ABC Kitchen in the Flatiron district wearing a purple sweater with a giant pink heart and pink heart-shaped crystal earrings. Ms. Hari, 35, who is better known as Food Babe, the name of her blog, flipped through photographs of her that her mother had recently unearthed, pausing at one taken immediately after college at a Mexican restaurant.

“Look what I’m drinking,” she said gleefully. “A Coke! I would never drink that now.”

In the last two years, first Ms. Hari, then her husband, who are based in Charlotte, N.C., quit lucrative jobs as consultants to make their living from Foodbabe.com, where Ms. Hari challenges companies like Coca-Cola for using ingredients she says are harmful. (Metrics can vary, but according to her figures, Food Babe has more than three million readers a month; comScore shows 1.1 unique visitors for January, roughly double the traffic of a year ago.)

Other Food Babe targets have included Starbucks (accusations of “hazardous chemicals” in pumpkin spice lattes), Chick-fil-A (which she called Chemical-Fil-A), Whole Foods (for genetically modified and hidden ingredients) and Subway. To protest the sandwich chain’s use of azodicarbonamide in its bread, Ms. Hari posted a video of herself chewing another item in which the chemical is found: a yoga mat. In less than 24 hours, Ms. Hari’s petition to the company to remove the dough conditioner had 50,000 signatures. The next day, Subway, which Ms. Hari said had not replied to any previous correspondence, emailed her to say it was already in the process of removing the chemical, which had been approved by the Food and Drug Administration.

It’s tough to argue with a crusade to help Americans eat better and to win more transparency from both food companies and the federal agency, but Ms. Hari, a former computer science major with no training as a food scientist, nutritionist or chef, has managed to become a flash point. Her click-me headlines (“Do You Eat Beaver Butt?” for a post about what’s in so-called natural flavorings) and camera-ready looks have won her a rabid #Foodbabearmy, billings as an expert on television shows, a book (“The Food Babe Way”) that made its debut at No. 4 on the New York Times best-seller list last month, and a spot (along with Beyoncé and Kim Kardashian) on Time Magazine’s “30 Most Influential People on the Internet.” But her statements — often incorrect — and faulty reasoning have produced numerous memes and parodies, not to mention aggressive reactions from doctors and scientists, who call her scientifically illiterate.