Just over a year ago, Weight Watchers shorts were crushed when Oprah Winfrey announced she had purchased a 10% stake in the diet company, sending its stock soaring following a furious short squeeze. Following that news, we noted that "going forward every move in the company stock would be a reflection, literally, of what Oprah Winfrey looks like, and certainly her weight, at any given moment is" as she, both a stakeholder and the most prominent customer of the company's products, would also become its biggest, pardon the pun, proxy.

To be sure, while the fundamentals of WTW remained lousy and the company's growth prospects were limited, the biggest danger was in sudden, unexpected short squeezes whenever Oprah's weight would become a topical feature.

Sure enough, having declined consistently since Oprah's investment last October, and trading near 52 week lows, today Weight Watcher stock soared by 15%, after Winfrey announced that she’d lost 40 pounds using the program. The diet company, whose shares had fallen 54% this year before Thursday’s surge, is unveiling new TV ads featuring Winfrey that tout her weight loss Bloomberg reports.

Though all previous rallies in the stock have faded, any time Winfrey makes an endorsements of Weight Watchers, or updates her weight, the stock gets a temporary jolt. The shares gained 27% over two days last December when Oprah tweeted a video about using the weight-loss program, and there was a 20% bump in January after Winfrey said she had lost 26 pounds while still eating bread every day.

The latest marketing push begins next week, just before the New Year’s holiday. The coming weeks are critical for Weight Watchers: The company typically adds about 40 percent of new customers in the first quarter, when resolutions push people to seek out diets. The stock climbed as high as $12 on Thursday, its biggest intraday gain Since Nov. 4.

Today's surge is also catalyzed by the substantial short interest overhang, which at 51% of the float, scrambles to cover on days like today.

That said, the long-term thesis remains poor: Weight Watchers has been hit hard by the rise of free fitness apps, and a move away from strict calorie counting among dieters. But Winfrey’s wide-ranging influence has brought new life to the brand. Weight Watchers has added subscribers for three straight quarters after years of declines.

The New York-based company hopes that Winfrey’s new ads, which emphasize that she still enjoys pasta and tacos, will convince dieters that its updated program is an effective weight-loss tool. "It’s vitally important that Oprah is living the program and articulating it in a way that’s authentic,” said Maurice Herrera, the head of marketing at Weight Watchers. “It really connects with prospective members.” Despite the subscriber gains, it’s been a rocky year for Weight Watchers. The company has billions in debt, and its stock is heavily shorted. In September, Chief Executive Officer Jim Chambers announced he was leaving after about three years at the helm. That sent the shares plummeting to their lowest level in nearly a year.

As Bloomberg adds, following Chambers departure, Weight Watchers is now being run by a trio of executives who constitute the “interim office of the CEO.”

The ads rolling out next week show Winfrey doing yoga and cooking pasta. As consumers have changed their perception of wellness, Weight Watchers has pivoted to emphasize that weight loss and indulgence aren’t necessarily mutually exclusive. Winfrey will hammer that message home, Herrera said.

“People want to know what’s on her mind and how she’s living her life,” he said. “This will definitely get people’s attention.”

It will also invite a whole new set of shorts who will pressure the stock to new lows, until Oprah next weighing, at which point the cycle will repeat from scratch.