At Weight Watchers, diet marketing is more about science than sizzle -- overt sexual appeals about as welcome as a third helping of pie. Tempting as it might seem, the marketer is just not going there, even as it deals with new competition, including a comeback attempt by Slim-Fast, which this week breaks provocative ads that tout the bedroom benefits of losing weight.

The shifting $38 billion U.S. diet landscape has led to some big changes at Weight Watchers as it fends off upstarts, including free calorie-counting apps. The marketer is adopting a more holistic approach that emphasizes wellness as much as calorie counting. And as talk about the nation's obesity crisis increases, Weight Watchers is for the first time adding a business-to-business pitch: making direct appeals to corporate clients that are seeking to defray rising health-care costs.

"We are viewing ourselves more and more as a health-care company," Weight Watchers International CEO David Kirchhoff said recently during a panel discussion on a study called "The Truth About Wellness," by McCann, the marketer's ad agency. As health care moves toward more emphasis on preventative care, "we are positioning ourselves to be good community-based partners," he said.

As the 50-year-old company builds its business-to-business sales force, its consumer marketing touts the new "360°" program, which adds lifestyle and environment management to its well-known food-tracking point system. "We have to be in a position where we are helping people establish skills forever that allow them to start living in a consistently healthier way, with the outstanding byproduct of being able to put on a smaller pair of jeans," Mr. Kirchhoff says on a video on the marketer's website.

Of course, Weight Watchers isn't above tapping celebrities to show off their thinner bodies in its ads, whether it's Jessica Simpson twirling in the sun or Jennifer Hudson in tight pants. And the company recently signed up comedian and TV star Ana Gasteyer to appear in ads for its online product in which she spoofs Nat King Cole's "Orange Colored Sky" and Peggy Lee's "Fever" with lyrics such as "my arms don't jiggle when I clap."

But the marketer is mostly sticking to its roots of emotionally tinged, before-and-after marketing backed by the science of its point system. "We try and take the high ground," Weight Watchers Senior VP-Marketing Cheryl Callan said. Weight loss is "a highly emotional issue and there are enormous barriers for people to take action and do something. There's shame, there's guilt, there's all sort of feelings that you are dealing with. So to go after the "better sex thing' seems to cheapen that."

Slim-Fast apparently has no such fear. The Unilever meal-replacement brand, which has struggled lately, is running a provocative campaign, including print ads in April magazines, that assert folks are more interested in losing weight for purposes of sex rather than health or self-improvement. Running in titles including Self and Allure and created by Bull-Whitehouse, ads feature silhouettes of women expressing their public -- and private -- reasons for wanting to lose weight. On the left, a word bubble states her fake motivation: "I want to get into my new pants," while a thought bubble on the right reveals the truth: "I want to get into someone else's new pants."

The company declined to comment on the campaign, but it's obviously aimed at and lifting sales. Slim-Fast liquid sales fell 5.4% in 2012 to $77 million, although it still controls a leading 40.8% of the liquid/powder meal-replacement category, according to market researcher Packaged Facts. Unilever spent $16.9 million in measured media on the brand in 2012, according to Kantar Media.

At stake is a piece of a weight-management market that is estimated to grow to nearly $41 billion by 2016, according to Packaged Facts, which counts diet foods and beverages as part of the total. An estimated 39% of U.S. adults are "watching their diet," according to Experian Marketing Services data cited by Packaged Facts.

Weight Watchers' 360° program includes digital tools meant to help users survive in a food environment that Mr. Kirchhoff compares to a "bad neighborhood with lots of crime." Theses include a "spaces" feature that has tips for staying on track at various locales, like advising travelers to "ask the hotel to de-stock the minibar." A "routines" section allows users to track habits like how many walks they take during the day.

The update follows a drastic overhaul in late 2010 of the point system, which was rebranded as "points plus" and redesigned to factor in protein, carbohydrates, fat and fiber. The change catapulted Weight Watchers in 2011 into "the best financial performance in its history, with revenue 25.3% higher than in 2010," according to a Packaged Facts report. But revenue flattened in 2012 as North American meeting attendance fell, the report notes. And "Weight Watchers 360° has been less than a roaring success," the report states.

"We have reason to believe that our January ads lacked the persuasion we needed," Mr. Kirchhoff conceded on a recent earnings call, adding that the benefits of 360° have "proven difficult to communicate in a quick, compelling way." And those Jessica Simpson ads? "The news and the gossip around [her] pregnancy may have overshadowed any focus on her weight-loss success," he said.

The company is tweaking its campaign this spring with ads in which Ms. Hudson states that people lose "five times more weight following the Weight Watchers approach than trying on their own." The appeal seems to be a retort to the rising number of free, do-it-yourself apps, such as My Fitness Pal. Weight Watchers also launched a digital-ad-agency review to replace incumbent Razorfish, and plans to cut marketing outlays by $25 million globally. Digital-ad spending might have "hit a point of diminishing returns," Ms. Callan said.

Weight Watchers International reported marketing expenses of $343.5 million last year, an increase of $51.2 million, according to its annual report.

Corporate outreach is housed under a division called Weight Watchers Health Solutions. Historically, the marketer relied on consumers to start Weight Watchers groups at their workplace. The new top-down approach engages corporate leaders. In some cases, companies are picking up part or all of the cost for employee Weight Watchers memberships.

New clients include the New York Stock Exchange, NBC Universal and American Express, which pays 100% of the cost for its employees to attend Weight Watchers meetings for a year, according to the Packaged Facts report. (Weight Watchers declined to comment on specific corporate accounts.) Tom Futch, VP-health solutions, described it as a "full consultative approach" that helps companies "better understand how to drive health and wellness with their employees."

Which sounds like a lot more than counting points.

Contributing: Ann Christine Diaz

The nation's obesity epidemic is only getting worse. Or is it?

A few recent studies suggest that there might actually be improvement in trends among children. The first evidence came late last year when Centers for Disease Control and Prevention researchers released data in a medical journal showing that from 2003 through 2010 the prevalence of obesity decreased slightly to 14.94% from 15.21% among low-income preschool children. A study by the Robert Wood Johnson Foundation found declining childhood-obesity rates in Philadelphia, New York City, Mississippi and California. The report credited nutrition mandates in schools and other government programs.

Earlier this month the Partnership for a Healthier America, which is backed by first lady Michelle Obama and corporations including Walmart, reported positive steps including that more than 1,700 cities had "physical-activity-promotion events in 2012," and "2.95 million kids got moving."

But the sobering reality is that under current trends, roughly half of all Americans will be obese by 2030, the report noted. The latest figure from the CDC pegs the obesity rate at 35.7%. -- E.J. Schultz