Slim-Fast sales have halved in six years and the brand has seen sales slip 25 percent in the past 12 months alone.
Sales were more than $600m in 2000.
These harsh figures prompted Unilever to focus on protein and fiber-centric Slim-Fast options that are proving more successful with a new band of consumers more interested in body shape control than out-and-out calorie-restricting dieting of the kind the brand was founded on.
The company has repositioned the brand to meet modern dieting expectations while also simplifying its offerings to revolve around the bars and protein shakes it began with, but with the marketing message altered significantly.
"We're being more selective with TV now," Slim-Fast's brand development director, Virginia Blake West, told New Nutrition Business magazine. "We're using seasonal periods and day-part selections to reach our targets more effectively and balancing that with our online presence - more than just a mass presence."
But new lines are not out of the question and it has debuted a protein chew and is working with a technology that aims to make its shakes more filling by inserting them with a gas."We have products that can be used flexibly, but we also recommend structure," Blake West said.
That's our opportunity and our sweet spot: to provide a flexible way of consuming diet products with an approach that can fit into a do-it-yourself type of lifestyle."
Unilever has acknowledged that the rise and fall of the Atkins diet in 2003 and 2004 had left the North American market in disarray and that consumers were no longer willing to strictly follow one plan.
"Generally speaking, if you ask them, 'How are you dieting today, and how is it different than three to four years ago?', they'll pretty much say, 'I'm doing my own diet now.'," Blae West said. "They're cobbling together different philosophies and approaches from the wide range of what they see and are exposed to out there."
The global weight management sector is valued at more than $7bn and increasingly ingredients are being offered by suppliers that have been clinically backed to promote satiety or increase metabolism, or influence body shape through fat burning or more.
Unilever paid $2.3bn for Slim-Fast in 2000, at which point it was growing by 20 percent per annum.
The rise of GlaxoSmithKline weight loss drug Alli contributed to the challenges being faced by the brand as it had risen quickly to capture a large proportion of the weight loss market since its launch in 2007.