To her thousands of fans and followers, Vani Hari -- the "Food Babe" blogger -- is a savior, brazenly taking on corporations in the name of better eating as she questions processed-food ingredients and manufacturing methods. But to her critics, she is a misinformed opportunist, seeking publicity at every turn while promoting causes like GMO labeling.

One thing is for sure: As she bashes mainstream food marketers, including Kraft Foods Group and Subway, Ms. Hari is emerging as a powerful brand herself, routinely appearing on national TV, where she is often presented as a food expert. In doing so, the Babe is positioned to capitalize on her growing fame with a burgeoning business model that includes making money by referring her loyal readers to several organic and GMO-free food brands via her website.

Under the program, known as affiliate marketing, she often posts editorial content praising these small brands, including links to their sites where readers can purchase the goods. She gets a cut of some of the transactions, according to the rules explained on some of her partners' websites. Ms. Hari also sells "eating guides" for $17.99 a month and charges for speaking appearances.

How Ms. Hari turned a food blog into a full-time business speaks to the rising power of food activists, whose growing clout with everyday consumers recently prompted Sanford C. Bernstein to label the trend a risk for the packaged-food sector.

Advocate or entrepreneur?
While plenty of food bloggers sell ads and use affiliate marketing and sponsored posts to make money, Ms. Hari gets some of the greatest attention. As a result, she has emerged as a recognizable -- if polarizing -- figure in the food world and beyond.

Ms. Hari does not hold a nutrition or science degree, which leads some critics to label her an opportunist. "Historically, consumer advocacy has come from nonprofits," said Maureen Ogle, an author and historian who has written about the food and beverage industry, in an email. "But the Babe isn't an advocate. She's an entrepreneur who clearly, obviously, is only in this for her own profit."

Ms. Hari, who left what she said was a lucrative management-consulting job in late 2012 to pursue full-time activism and blogging, responded in an interview that "I'm not doing this to make money." She added: "This is my life. This is my passion. This is my calling. There is no way I would put myself on the line like I do because of money. This is all about what I've learned, and I have to tell everyone."

But as Ms. Hari attacks mainstream food brands, she is drawing the the ire of some registered dietitians and food scientists who say she lacks the credentials to speak with authority.

Bloggers like her "know enough to sound credible, but they don't know the real science [or] how to interpret peer-reviewed research to fully understand the issues that they might be preaching about," said Julie Upton, a registered dietitian who runs a popular nutrition blog called Appetite for Health. "I stay awake at night worried that my profession is going to become a hobby because of these people."

Ms. Hari countered that "I've never said I was a scientist or a nutritionist," but "I don't think you need to have those degrees to be intellectually honest, to be able to research, to be able to present ideas."

It began as a hobby
Ms. Hari, 35, began making health a priority more than 10 years ago after her poor diet landed her in the hospital, she says in her bio on her website. She launched her blog in April 2011, describing the endeavor in the bio as a venture that started as a way to "share my healthy lifestyle with friends and family. Little did I know at the time that this blog would change the world." She continued that "I used my newfound inspiration for living a healthy life to drive my energy into investigating what is really in our food, how is it grown and what chemicals are used in its production. I had to teach myself everything."

In her previous career as an independent management consultant, she most recently did work for Bank of America, she said. Earlier in her career she was employed by Accenture, according to her LinkedIn page, which states that she has a degree in computer science from the University of North Carolina.

As Ms. Hari pursues her self-described mission of being "the person to carry the voice of millions," she has also taken steps to form a viable business. She established Food Babe LLC on Aug. 1, 2011, according to filings with the North Carolina Secretary of State's office. While her principal office is in Charlotte, her business is incorporated in Delaware, which is known for business-friendly regulations.

Ms. Hari declined to answer a question about why she incorporated in Delaware. She also declined to reveal her annual revenue from the site, including how many food guides she has sold or how many brands with which she has business relationships. "This is information that is not important to my activism and my work," she said, noting that she discloses partner brands when she mentions them in posts. "In order to be an activist you do need funds to do your work, and this is the most honest way that I think I can do that," she said.

Part of her business model appears to be rooted in her affiliate-marketing partnerships. One of the companies she has recently plugged on her site is called Green Polka Dot Box, which sells home-delivered natural, organic and non-GMO foods. The company's affiliate partners can earn 30% of the company's annual $49.95 per-person membership fee for each person referred, plus $2 for every food purchase that person makes as long as they are a member, according to terms of the program listed on the company's website.

Ms. Hari declined to disclose the details of her arrangement with Green Polka Dot Box, but said that she is not currently working with them. The company declined comment, citing confidentiality agreements.

Another company she has plugged in editorial posts is Nutiva, which sells organic "superfood" such as hemp and chia seeds. The company's affiliate-marketing program promises a 10% cut of sales on referrals, according to its website. The company did not return calls for comment.

The FTC requires disclosure
The Federal Trade Commission requires that bloggers such as Ms. Hari disclose paid endorsements "clearly and conspicuously" on their websites.

Ms. Hari typically discloses her commercial partnerships at the tail end of her posts. Her disclosure states that "posts may contain affiliate links for products Food Babe has approved and researched herself. If you purchase a product through an affiliate link, your cost will be the same (or at a discount if a special code is offered) and Food Babe will automatically receive a small referral fee. Your support is crucial because it helps fund this blog and helps us continue to spread the word."

An FTC spokeswoman declined to comment when asked if the disclosure met the "clear and conspicuous" threshold. Linda Goldstein, an ad lawyer and partner at Manatt, Phelps & Phillips, said the rules are subjective and judged on a case-by-case basis. She said the FTC might favor a stand-alone message that does not include extraneous language, such as how the blog reader's support is crucial.

Ms. Hari's eating guides include meal calendars, recipes and grocery shopping lists with "approved brands." Another revenue opportunity comes from speaking appearances, according to her website, which instructs viewers to inquire with her about availability and rates.

"I do have to support myself and I am very transparent about how I do that," Ms. Hari said. "I don't just put ads on my site to put ads. If I wanted to make a lot of money I could put a thousand ads on my site." She added: "I can't tell you how many people I turn away every single day. I only work with the brands I wholeheartedly support and they support my mission."

Ms. Upton -- whose site uses sponsored posts -- did not disparage Ms. Hari for making money. "Running these blogs is not cheap … they have to be making some money somewhere," she said.

Drawing attention -- and page views
But Ms. Hari gets more attention than most of her blogging peers as a result of her knack for drawing publicity (and page views) from her high-profile corporate takedowns. She often fires up her fan base, which she calls the "Food Babe Army," on her Facebook page, which has more than 633,000 likes, and Twitter handle, which has more than 63,000 followers.

Traffic to her website is growing: Foodbabe.com averaged 310,000 unique monthly U.S. visitors in the first five months of 2014, up from 166,000 in the last five months of 2013, according to ComScore, which began tracking the site in August of 2013. By comparison, Ms. Upton's Appetite for Health site -- which according to her is among the top three for readership for dietitian-run sites -- draws about 80,000 unique monthly views, she said.

Foodbabe.com's web traffic surged in February and March, with 411,000 and 445,000 unique visits, respectively. The peak coincided with two posts she made: one about Subway in which she charged that the chain was using a dangerous chemical in its bread; and one in March, when she went after pizza chains with a variety of accusations.

Ms. Hari's criticism of Subway focused on its use of azodicarbonamide, a chemical commonly used as a dough conditioner in bread baking. She described it as a "dangerous plastic chemical" that was also used to make yoga mats and shoe rubber and launched a petition for its removal on Feb. 4.

The chain responded two days later, saying it was already in the process of removing the chemical, implying the Babe's petition had nothing to do with it. "Azodicarbonamide is used in most bread and by most brands, but removing it has long been part of our bread improvement program," Subway said in a statement.

Ms. Hari in a blog post told her readers that "we know this is just a corporate spin and how big companies operate. They don't want us to know how much power we have over their decisions."

Is the chemical unsafe? Not according to the Food and Drug Administration's website, which states that it is "not recommending that consumers change their diets because of exposure to [azodicarbonamide]." The agency notes that it approved the additive "based on a comprehensive review of safety studies, including multi-year feeding studies."

John Coupland, a professor of food science at Penn State University, wrote in Popular Science magazine that to compare azodicarbonamide's use in bread and yoga-mat production is not helpful. "To see the same chemical, particularly one with a scary name, in two such incongruous places is a sure way for a campaigner to trigger a disgust response but not a great way to decide if it's safe," he said.

Companies fear her 'army'
Fergus Clydesdale, professor of food science at University of Massachusetts, Amherst, said Ms. Hari is "very clever -- she seems to know what buttons to hit" when it comes to stoking concern in consumers over what's in their food. He noted, though, that many scary-sounding chemicals and ingredients occur in foods naturally. By her logic, Mr. Clydesdale said, one could argue that peaches are poisonous because they contain a high level of cyanide in the pit. He added that, in general, many of her claims contain "a misunderstanding of what dangerous levels are" in food. He cited a basic toxicology tenet popularized by scientist Paracelsus: the dose makes the poison.

In an interview, Ms. Hari countered that she is merely exposing issues that no one else is digging into. "The stuff that I am sharing is a lot about transparency and making sure people understand what is in their food and give them the choices," she said. "I question what has happened because I was profoundly impacted by the way I was eating."

She also expressed distrust of the FDA, alleging that "unfortunately the FDA approved a lot of these chemicals three decades ago or sometimes longer ago, and unfortunately we don't know the [correct] dose."

Ms. Hari's growing clout is evident in the responses she gets from corporations in her crosshairs. For instance, Anheuser-Busch InBev and MillerCoors on June 12 agreed to post their beer ingredients online just a day after Ms. Hari launched a petition drive via her website calling on major brands to publicly reveal what is in their beer, which they are not required to do by law.

The Babe's campaign -- which got coverage in major media outlets such as the Chicago Tribune, USA Today and ABC News -- included suggestions about what could be in beer, including "ingredients found in airplane deicing liquid, genetically modified ingredients, and even fish swim bladders."

When the nation's two largest brewers responded, they revealed beer formulas on their websites including mostly harmless ingredients like water, barley malt, and yeast. But the Babe claimed victory when Anheuser-Busch InBev a few days later listed high fructose corn syrup as an ingredient in Bud Light Lime. "We are changing history together. It's a magical moment," she declared in Twitter and Facebook posts.

What's more, A-B InBev hosted Ms. Hari for a visit at its St. Louis headquarters just two weeks after she launched her petition drive targeting it. As she traveled to the meeting, she noted her visit in an email to her subscribers that also linked to a post about travel eating tips. The post plugged several brand-name products and included a link to a website where people can buy a Think Sport insulated bottle -- complete with a coupon code (FOODBABE10) good for a 10% discount.

Other marketers have tried to resist her. For instance, Kraft Foods Group initially rejected her calls in April 2013 to remove artificial yellow dyes from Kraft Macaroni & Cheese. In a petition campaign, Ms. Hari alleged the dyes contained "known carcinogens" and can cause an increase in hyperactivity in children." Kraft initially pointed to an FDA finding deeming the dyes to be safe. But the marketer seven months later announced it would remove the dyes from some varieties.

Kraft at the time said the decision was not the result of the petition drive. But Ms. Hari claimed victory, noting on her website the "Food Babe Army" was "able to force one of the largest food companies in the country to change." A Kraft spokesman recently reiterated to Ad Age that the change -- which involved replacing dyes in some varieties with colors derived from spices -- had been in the works as far back as mid-2012.

Several companies declined to comment specifically on Ms. Hari's tactics, perhaps as a sign of the fear she instills in corporate America. Speaking on the condition of anonymity, a communications executive at one company she has targeted said: "Most companies are of the opinion that you might as well respond quickly [to her] rather than be faced with an ongoing onslaught of continued misinformation and her spinning up her army of people to continue to keep your name in the press in a non-positive light."

Pleasing the 'mob'
Mr. Clydesdale compared the responses by corporations to Ms. Hari and other activists bloggers to pleasing the mob. "The bloggers are the mob, and whatever it is they want, give it to them," he said. "It's bothersome because we're dismissing science."

Ms. Hari said she believes in modern medicine. "Half of my family are doctors, so I know there is profound, amazing work that doctors do every single day," she said. "But I also think that we should take a look at some of these natural therapies and look at our food and see how that affects us."

She frequently uses her Facebook page to personalize the issues she covers. For example, on June 25 she posted about how she struggled with weight gain while in the corporate world. She then linked to an Oct. 2013 post from her website about how stress can cause weight gain. In that post she promoted and linked to a company called The Maca Team, which sells organic raw maca powder. On her site, Ms. Hari wrote that the Peruvian-grown plant can reduce stress and do everything from "improve mental clarity" to "treat PMS."

According to The Maca Team's affiliate program, partners can earn 20% on each sale they refer. Ms. Hari's June 25 Facebook post drew 2,708 likes and 1,538 shares within 15 hours. One fan asked, "Can this be taken while breastfeeding?" Another fan wrote: "I just ordered some! Thank you also...for continuing to educate us."

But some fans expressed concern about the post, including one person who wrote: "I love the exposure work of Food Babe so much, but if the direction is going to be the whole hearted advertisement of superfoods and supplements that actually have long histories of use by indigenous peoples to us western folks as universally good for everyone, sadly I shall have to be more judicious about my support."