NEW YORK (AdAge.com) -- The recession is having a slimming-down effect on media businesses, but it's feeding the proliferation of pot bellies and muffin tops across the web.

The ubiquitous "belly fat" ads, placed by numerous direct-response marketers, including some of the web's shadiest advertisers, are finding welcome homes across the web as publishers grow more reluctant to leave any available ad budgets on the table, even those attached to unappealing ads.

Similar creative
These ads, which typically link to sites with names such as Becky's Weight Loss or Helen's Weight Loss, often use the same exact creative -- a before-and-after photo of a woman's belly -- and tout some secret to getting rid of a gut. Users, of course, have to click on the ad to find out more.

Online advertising start-up Rubicon Project estimates that different versions of the "belly fat" ads are now being served by half the ad networks in the U.S., sometimes accounting for as much as 30% of an ad network's total revenue.

It's all part of a larger shift toward direct-response advertising as brand dollars become harder to come by. The belly-fat ads may be unappealing and jarring on some of the higher-end sites that are running them, such as MSNBC.com, but they work, and can bring more revenue than a display ad sold on a cost-per-thousand-viewers basis.

"Ultimately, the economy is what it is, and ad networks are finding that it is easier for them to get direct-response ads right now than it is to get brand dollars," said Rubicon VP J.T. Batson.

Tough to block the ads
But here's the bigger problem: The process of blocking belly-fat ads for publishers that don't want them is proving particularly difficult for ad networks. The creative gets placed by numerous corporations using different tags, URLs and toll-free numbers, making them hard to track and stop automatically.

And when ad networks have unsold inventory, they'll often tap another ad network to fill it, giving belly-fat ads another side door onto websites that might not want them.

New Jersey-based ad network AdBlade is placing some belly-fat ads, including smaller placements on MSNBC, but CEO Ash Nashed said he turns away about 60% of the belly-fat ads out there, including those with forced upsells in the fine print and those where a person doesn't answer the toll-free number. "They do perform well; a lot of people click on those ads, quite frankly," he said.

And it's not just belly fat. Direct-response ads of all kinds, such as those for lowering bills, avoiding computer viruses and checking credit scores, are flooding into unsold ad inventory. Windows that open underneath a page -- the so-called pop-unders of the late '90s -- are making a comeback, and ad execs say they're seeing more in-text ads from the likes of Vibrant Media and Kontera as publishers attempt to squeeze incremental dollars from each page.

'Shortage of alternatives'
"It signifies a shortage of alternatives and a hunger for revenue," said Andy Atherton, chief operating officer of Brand.net. "This isn't a new issue, but in this climate it's harder to say no to any ad if there is money attached to it."

In their quest for hard-to-find ad dollars, publishers are paying more attention to their international traffic, which many used to ignore. A typical U.S. web property gets 30% of its traffic from overseas, but it's difficult to sell ads against those visitors without doing a deal with an ad network based in, say, Germany, to sell to a much smaller German audience, or working with companies such as Adconion or AdGent 007, which can serve international ads to those visitors.