The weight loss industry is just huge, with the annual revenue of the US weight loss industry some $61 billion. That means lots of businesses are cashing in on obesity, as 108 million people are on diets in the US alone at any point in time.

How lucrative is this business? Just look at how much celebrities are paid to endorse major weight loss programs. The fee is as high as $3 million, ABC News reports.

One of the companies doing exceptionally well in the industry is Weight Watchers, a weight management system that has become a veritable way of life for millions of people across the globe—from the US and China to Europe and New Zealand. It's a case study of how savvy marketing can propel a company to the forefront of its industry.

Weight Watchers is clearly the dominant company among weight-loss centers and programs, banking north of $1.2 billion each year. It is at least three times larger than its primary competitors, Nutrisystem and Jenny Craig. Weight Watchers has some 8 million website visitors per month and 1.72 million paid online subscribers.

So what are the company's marketing secrets? Let's take a look at six savvy principles Weight Watchers has implemented to solidify its position at the top of the weight-loss stack.

1. Give them what they want, not what they need

We are driven by our desires. We buy expensive fast cars because we crave the "success" image associated with them, not because they are a sensible mode of transportation. We want iPhones because they are a status symbol, not because of the crystal clear voice reception. Same with Jimmy Choos, and Louis Vuitton bags. Sales of such products are all driven by wants.

Weight-loss products are no different. We may know that the key to losing weight is to cut out junk food and eat more vegetables. But that's not what we want. We want to be able to eat our donuts and drink our Frappuccinos. And, smartly, Weight Watchers lets us do that.

According to the Weight Watchers PointsPlus system, members have a daily PointsPlus total based on their gender, weight, and activity level, as well as a weekly PointsPlus allowance that allows for fluctuations in daily eating. For example, if you go out to a restaurant for dinner and surpass your daily PointsPlus allowance, you can dip into your weekly reserve without worry, so long as you don't surpass your weekly allowance as well.

That's a brilliant move on Weight Watchers' part. Essentially, the company is telling members, "Go ahead and eat that donut or drink that Frappuccino. As long as you're within your PointsPlus limits, you'll lose weight."

2. Market the feelings, not the product

When people buy a product, they are paying not for what the product can do for them but what feelings it can give them. "Consumers are ultimately paying for feelings," explains entrepreneur Jeff Barnett. Weight Watchers has figured out the ultimate feeling that dieters long for and has enabled it. What do dieters want? They want to feel good. They want to avoid pain. They want to enjoy the food they like. They don't want to feel deprived. And that's what Weight Watchers communicates to its target audience through the voice of celebrity singer and spokesperson Jennifer Hudson, who dropped over 80 pounds:

• Jennifer Hudson (YouTube link): "At this point I feel I can do anything, I feel good."
• Jennifer Hudson (YouTube link): "I feel so comfortable in my jeans…it makes me love myself that much more…loving and free to eat what I love…loving and free to live my life"

3. Let them join for free

A "Join for Free" campaign is always friendly to prospective customers. Weight Watchers lets people attend a free meeting near them. If after the meeting they decide to sign up, they are allowed to receive educational materials. As market analyst Tony Rossel explains, this "opt in" strategy can result in up to a 30% conversion rate.

Consumers react well to this type of strategy because they feel no pressure; and once they see the educational materials and products at a meeting, they want them.

That contrasts with "force free" trials, in which people who didn't request something are given a free trial and then asked to pay after a certain period of time, or "negative option force free" trials, in which customers are asked for credit card information before they get the trial, and then must proactively cancel.

Both of those methods can leave a bad taste in the mouths of consumers since they are more pressure-filled.

4. Make the solution look complicated

Weight Watchers makes eating look complicated. Rather than relying on regular-old calorie-counting for foods, Weight Watchers now uses the PointsPlus system.

It used to rely on calories for its points totals. The problem was that fruits and junk food would be given the same amount of points if they had the same amount of calories (and you know which one is better for you to eat). The current PointsPlus program is much more complicated, and based on a sophisticated mathematical formula.

The company relied on its "nutrition specialists" to develop a system that takes into account how foods are broken down in the body. It all sounds too complicated for any layperson to figure out, so people feel they have to go to Weight Watchers, since the company has the inside scoop on weight loss.

In reality, the PointsPlus system is based on basic food and nutrition science. It's nothing new. Yet, serving a solution that sounds complicated, and more like a "discovery" rather than an old principle, makes customers feel they have to buy. It is a brilliant marketing strategy.

5. Create exclusive products

In addition to just promoting the PointsPlus system—the solution to being overweight—Weight Watchers offers exclusive products to facilitate the implementation of its solution. Those products make it easier for people to follow the program. For example, it sells PointsPlus calculators. It also makes available snack bars, yogurts, ice creams, and other foods that have the PointsPlus value right on the box.

Moreover, it sells food scales that tell consumers the PointsPlus value of their food rather than the weight. People snap up these products because they make the Weight Watchers (complicated) system simple to follow, since they won't have to do any calculations or look up values on their own.

6. Actively court a new audience

Some 90% of dieters are women, as are 90% of Weight Watchers clients. However, the company has noticed growing interest among men to lose weight and so is capitalizing on that interest.

But Weight Watchers isn't pushing its bread and butter—center-based meetings—to men. Instead, it's promoting its online tools and mobile-based apps. Because men generally try to diet on their own, such as joining a health club, or controlling their food intake, Weight Watchers is anticipating that they will be more drawn to these tools than the meetings.

To better target the men's market, Weight Watchers airs commercials during the NBA playoffs. Obviously, the male audience is worth the $1 million per minute advertisement cost.

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Overall, Weight Watchers has risen to the top of the weight-loss industry because it has been so smart in the marketing of its products. Other companies in this market—and even in other industries—can learn a valuable lesson from the granddaddy of weight loss programs by following these six marketing principles:

1. Give your customers what they want, not what they need.
2. Market the feelings, not the product.
3. Let them join for free.
4. Make the solution look complicated.
5. Create exclusive products.
6. Actively court a new audience.