According to the brand, between 2004 and 2014, UK Weight Watchers members lost a staggering eight million stone, and that's not all.
A recent study found that joining Weight Watchers is five times more effective than dieting alone. On average, those who spent three months with Weight Watchers lost an average of 8.6lbs, compared with those who dieted alone, who lost an average of 1.8lbs.
The plan also has a number of celebrity fans, including Oprah Winfrey, who lost more than two stone on the plan, and Jennifer Hudson, who went from a size 16 to a size 6 during her time as a spokeswoman for the brand.
There have been some changes to Weight Watchers over the years - you may remember Weight Watchers Discover Plan, or ProPoints, which is the previous incarnation of the SmartPoints that dieters follow today.
So if you want to follow the plan now, what's involved?
What is the Weight Watchers SmartPoints plan?Weight Watchers says that SmartPoints is 'a revitalisation of the ProPoints system', and aims to 'nudge you towards nutritious, healthier foods so that you eat better, feel better, have more energy and lose weight.'
As always, each food and drink you consume is assigned a points value, based on the amount of calories, saturated fat, sugar and protein it contains. With SmartPoints, lean protein content lowers the point count of an item, while sugar and saturated fat will increase the SmartPoint value. Some foods, like fresh fruits and vegetables, have a SmartPoint value of zero, so you can fill up on these without having to count them.
When you join Weight Watchers, you'll be assigned a daily allowance of SmartPoints, based on your age, height, gender and your starting weight, as well as a weekly allowance that you can use if you need to - for instance, if you're going out for dinner, or celebrating a special occasion.
How can I do the Weight Watchers SmartPoints plan?With Weight Watchers, you can either become an online member, or go to regular group meetings.
If you choose to be an online member, the Weight Watchers website has all sorts of resources to help members - you can track how many SmartPoints you've got left, record the exercise you've done and calculate the amount of SmartPoints in whatever you're eating.
If you decide to go to meetings, you'll get weighed and discuss different issues with your leader, such as why you're overeating, strategies for dealing with special events like birthdays and easy ways to fit exercise into your lifestyle.
You can also swap Weight Watchers recipes with your group leader and fellow members, to ensure that you don't get bored!
You'll also be encouraged to develop other health habits, like regular exercise and drinking plenty of water. If you follow the plan properly, you can expect a steady, sustainable weight loss of up to 2lbs per week.
What does a typical day on the Weight Watchers SmartPoints plan look like?
More: This Weight Watchers Quorn Sausage Bake is just 10 SmartPoints per serving
Your total number of SmartPoints depends on the factors we discussed earlier, but a typical day in Weight Watchers food should always be centred on nutritious, high protein, low sugar and fat foods that fill you up and leave you satisfied.
For breakfast, you could have overnight oats or a smart cooked breakfast, made with mushrooms, tomatoes, eggs and lean meats. Lunches are often soups or salads, like this Weight Watchers tomato and red onion soup.
Dinner could be a Weight Watchers pasta bake or tandoori salmon with spicy mango salsa - and you should still be able to fit in a healthy snack or two.
What are the pros and cons of the Weight Watchers SmartPoints plan?The SmartPoints plan aims to help you change your behaviour towards food and exercise, so you'll be able to lose weight and keep it off long-term. It's a really flexible plan so you can fit it around your lifestyle, you'll get loads of ideas for recipes and the ready meals and snacks from the Weight Watchers range are handy if you're always on the go.
It will also help you if you struggle to stay motivated on diets, as the weekly weigh-ins will be a good motivator and you'll have support from your leader if you go to meetings.
Like all diets, it requires discipline for you to stick to it. But you'll have plenty of support and attending the meetings can really help you stay on track.
What is the Weight Watchers No Count plan?Most people who follow Weight Watchers choose to count their points, but they also offer a No Count plan as an alternative. With this plan, you stick to eating a list of healthy foods that you don't have to weigh, measure or count.
You also get 2tsp of healthy oil (olive, sunflower, safflower, rapeseed or flaxseed) to cook with each day, and a weekly allowance of points to spend on foods that aren't on the No Count list.