Again we greet a gray November morning with Louis Navellier, sending us an ad full of sunshine, bright colors, and glowing promises. This time, he tells us that he thinks we’ll see …

“Up to 790% Gain in this Diet Stock — between today and February 14.”

This is fertile ground for Navellier, he has spent a lot of time shouting about this stock in past years, and about others in the same business, like Nutrisystem (shouting metaphorically, at least, in person he doesn’t seem to be much of a shouter).

Today’s teaser is for one of is more expensive newsletters, Quantum Growth at $4,000 a year. Here’s what he tells us:

“Right now I want you to invest in a diet stock.

“I found NutriSystem in 2005. Shortly after we alerted our subscribers to this diet stock, earnings soared nearly 2,000%, and sales shot up 460%.

“The stock exploded 1,167%.

“And now I believe have found the NEXT NutriSystem.”

I’ve got visions of pumpkin pie and turkey slathered with gravy bouncing in my inner eye at the moment, and haven’t gotten to the gym as often as I’d like this month … so frankly, this ad just seems mean. But perhaps there’s some money in it, let’s see:

“The diet game is seasonal, obviously, and THIS is the start of that season. From here to February 14, Americans join gyms, cut carbs and do everything they can think of to lose the belly, shape up and feel good.

“It’s a business built on failure, when you think about it: The weight you lose comes back eventually, and you become that thing most prized of CEOs, a repeat customer.

“So dieting is a perfect business and a big one, too. We will spend $35 billion this season on dieting. The diet that works best gets a ton of media buzz and pass-along recommendations—creating exactly the explosive move we look for in a Quantum stock.

“Just like we saw in NutriSystem in 2005.

“This new diet breakthrough

“Our diet company is recommended by 20,000 doctors—it is simple, safe and quick. The goal is 20 pounds, on average, in one month. It’s a meal plan, so you don’t count calories and you can follow it anywhere. Cost is $10 a day.

“After the Atkins, South Beach and stimulant diets of the past several years, this diet is catching on because it isn’t a fad.

“The company itself has seasoned managers with almost 30 years’ of experience. Right now, the company is expanding into disease management, too. Margins here are eye-popping.

“Recent reports show a 34% rise in sales and a 70% rise in earnings.

“Yet the stock itself has lagged the market until the last few weeks. This diet stock could take off any day—and unless you act now, you’ll miss out on a clear shot at 600%, 700%, even 790% gain.

“By February 14!”

So how about it? Are you starting a diet maybe around, perhaps, Friday? Or looking for a way to fatten up your portfolio? Louis Navellier’s diet stock of the day is …

Medifast (MED — click here for a free instant analysis of Medifast from MarketClub)

This is an interesting niche in the diet business, which has several pretty big publicly traded players, including Weight Watchers and NutriSystem and the somewhat related Herbalife as well as Medifast. MED is, as you might guess from their ticker, the one that tries to go for the medical niche — their logo looks like the Caduceus, the winged staff with the serpents that we often see associated with medical, um, stuff.

So this firm is more entwined with doctors than the other diet companies, but that’s also partly because they use physician offices to sell their stuff — diet plans and food being another of those lovely high margin add-ons that a doctors office can sell without hassling about insurance. Not that I’m being cynical, I’m sure those 20,000 doctors think the plan is A-OK and they’re not just recommending it because they sell it.

Medifast has been a Navellier pick in the past, and his firm was the largest holder of MED shares at one point a couple years ago — at which point the then-CEO was embroiled in a scandal much like the one that got John Mackey in trouble a couple years earlier (posting about his company on Yahoo Finance message boards). At the time Navellier called Medifast “a bunny stock — always hopping around,” according to this Barron’s article.

And yes, MED is very highly rated by Navellier’s screening system — here’s the latest “score card” on the stock from his system. And, to give credit where it’s due, he did publicly predict an earnings surprise this past quarter and told folks to buy back in October — and MED did indeed beat earnings by about 20%, and the price is up significantly (also about 20%) since the earnings were released, a couple days before Halloween.

So … is MED for you? It was also glowingly profiled by IBD back in September and has often been a growth darling, so if that’s the kind of adrenaline rush you enjoy that might float your boat. All of these companies have somewhat different models, NutriSystem has numbers that look fairly similar to Medifast, in part because they both sell the actual meals (NTRI is a bit cheaper, since they have taken a recent hit to earnings growth) … Weight Watchers (WTW) is much larger than NTRI and MED and, since they don’t do the actual meal sales as a large part of their business, their profit margins are a bit healthier.

All three of these stocks trade at a Price/Earnings/Growth ratio of 1.4-1.5 or so, meaning that if analysts are right, they’re priced pretty similarly relative to their growth prospects — but those growth prospects are very different. MED is the blowout darling in terms of growth, as you would expect from a Navellier stock, with analysts expecting earnings growth of 25% a year for the next five years, while on the other end of the spectrum Weight Watchers, with it’s more modest PE of 10, is expected to see earnings growth of 7% over the next five years. And be careful what you wish for if you’re looking for the “next Nutrisystem” — that one has been frightening if you haven’t managed to get out on the upswings.

The business in general takes big swings and can be dominated by fads, as we’ve all seen, so if you do choose to invest in one of these firms it pays to keep an eye on them — MED has swung more dramatically than some others, as befits a smaller firm (and one touched by a bit of scandal in the past), and since they are tied in closely with doctors they depend fairly heavily on those continued relationships, and on their ability to continue citing promising health benefits for diabetics with their targeted meals. To tell you the truth, if I were to invest in a diet stock I might be the boring guy who buys Weight Watchers shares with a 2.6% yield, I’m not sure my stomach can take this kind of volatility … but then again, us boring guys aren’t getting rich overnight, either.

Got a hankering for a diet company? Let us know whether it’s MED or another that floats your boat, that’s what the friendly little comment box below is for.

And as always, if you’ve subscribed to Navellier’s Quantum Growth we want to know what you thought of it — click here to share your opinion with a brief review. Thank you!

Note: edited to reflect the fact that I had a brain hiccup in saying that this stock was less volatile than NTRI, and to remove the chart that I used to confuse myself for no good reason.