Weight Watchers International is an American company that offers various products and services to assist weight loss and maintenance. Founded in 1963 by Queens, New York, homemaker Jean Nidetch, it now operates in about 30 countries around the world, generally under names that are local translations of “Weight Watchers”. The core philosophy behind Weight Watchers programs is to use a science-driven approach to help participants lose weight by forming helpful habits, eating smarter, getting more exercise and providing support.

At 12 months Weight Watchers is associated with 2.6% more weight loss than those who were in a control group.

The term weight-watcher, in the same sense, had circulated publicly for several years before the company was formed.

A 2015 systematic review found that at 12 months Weight Watchers was associated with 2.6% more weight loss than those who were in a control group. There is a lack of evidence beyond this period of time.

Weight Watchers claims that members who both use Weight Watchers’ Web-based eTools and attend meetings lose half again as much weight as those who only attend meetings, citing an unspecified “12 week study comparing people who were instructed to attend Weight Watchers meetings and use eTools to people who were instructed to attend Weight Watchers meetings alone”.

Weight Watchers' core approach is to assist members in losing weight through eating more healthily and getting more exercise. Weight Watchers' primary diet plan has no directly comparable requirements and no food is off limits. Participants lose weight by creating a calorie deficit. Weight Watchers is generally compatible with other diet approaches and/or food intake restrictions, provided participants use the Weight Watchers framework to measure and limit the quantity of food consumed while using the other diet plan to dictate the range of acceptable food choices.

There are two primary ways individuals can work with Weight Watchers: via in-person meetings and an online-only program. Both programs use the same basic materials and computations. For in-person meetings, Weight Watchers encourages members to select a goal weight that results in a body mass index generally accepted as healthy (18 to 24.9), although a member may also establish a goal weight outside of that range after providing a doctor's note to that effect. In order to join Weight Watchers in the United States, one must weigh at least 5 pounds (2.3 kg) more than the minimum weight considered healthy by the company for their height.

Once a member reaches his or hers goal weight, they start a maintenance period. For the following six weeks, the member gradually adjusts their food intake until the member no longer loses or gains weight. If, at the end of six weigh-ins during the maintenance period, the member weighs in within 2 pounds (0.91 kg) of their goal weight, they become a "Lifetime" member.

Weight Watchers’ eTools is a Web-based service for members that includes access to support materials and tracking tools. In some areas Weight Watchers meetings are operated by a locally franchised organization rather than by Weight Watchers International.

In most locations, Weight Watchers holds meetings for members which in some cases may cause positive reinforcement for participants.

Weight Watchers introduced a new plan in December 2015 called SmartPoints – Beyond the Scale. It tries to help people make smarter food choices and build a better relationship with food. Similar to their other points-based plans, every food and drink is assigned a points value. SmartPoints is calculated using calories, saturated fat, sugar and protein. No food is off-limits, but the plan assigns higher points values to foods higher in sugar or saturated fat, and lower points values to lean proteins. Most fruits and vegetables are zero points, similar to the old PointsPlus plan. Some condiments are no longer free, such as ketchup, due to the sugar content.

Prior to the SmartPoints plan, Weight Watchers used PointsPlus, introduced in November 2010. Touted by Weight Watchers as incorporating a decade of science compared to the prior Points-based plans, the focus was on assisting members in creating a calorie deficit to lose weight using a reformulated calculation approach using total fat, carbohydrate, dietary fiber, and protein. A change from the old points system was the identification of Power Foods, and assigning fruits and most vegetables a points value of 0. PointsPlus was calculated using total fat, carbohydrate, dietary fiber and protein. As an alternative to the PointsPlus plan, participants could use the Simply Filling Technique. On the Simply Filling Technique, participants ate from a designated list of foods without the requirement to track. Categories of foods on the list included: most fruits and vegetables, whole grains, non-fat dairy and dairy substitutes, lean proteins, and a handful of other items. Because the plan did not require tracking, participants needed to be mindful to "eat portions that feel right for them. Not so much that they feel too full, and not too little that they still feel hungry."

On December 3, 2012, Weight Watchers introduced additional aspects to the program. This was dubbed "Weight Watchers 360". Additions included introducing more interactivity to meetings, more focus on building healthful habits, and fighting hedonic hunger: "the desire to seek out high-sugar, high-fat foods that bring pleasure." The 360 plan also introduced the ActiveLink physical activity monitor as an optional purchase item.

Jean Nidetch, the founder of Weight Watchers, wrote a book in the early 1970s called The Memoir of a Successful Loser The Story of Weight Watchers which documented the original Weight Watchers plan.

That original plan was supplanted shortly after the book with materials bearing a 1972-73 copyright: “Weight Watchers(R) Program Handbook for Ladies”. This plan was similar to the original plan.

By 1989, the plan had switched to an exchange-based diet. The document's subtitle and copyright dates make determining the exact date difficult, “The Quick Success(R) Program” with the subtitle “New for 1989” has a copyright date of 1987, 1988.

By 1997, the first Points-based program was introduced.

On April 15, 2005, a sputtering low-carbohydrate fad and the end of a licensing deal with Weight Watchers International Inc. had carved a big chunk out of CoolBrands International Inc.'s bottom line. On December 20, 2005, CoolBrands International Inc. said it intended to wield the power of three big-name licensed brands to help it recover from the loss of Weight Watchers from its product lineup.

The original Points Plan was developed in the UK by the Weight Watchers program development team headed by Sarah Watson and Marian Way who took out the first patent for a calculator to embody the algorithm (based on the summation of calories/70 and saturated fat/4 with the sum rounded to the nearest half) the patent was filed on 1 November 1995. In the UK during November 2010 the Points plan had been replaced with ProPoints. This is similar to the Points plan only the calculation now takes protein, carbohydrates, all fat and fiber into consideration. The following main changes were made from the Points to ProPoints plan:

In December 2015 a new scheme was introduced using SmartPoints.

In Ireland there has recently been a new plan launched called ProPoints Plan.Traditional weight loss plans are based on the calories on a food label. But the new ProPoints system incorporates the latest science that shows there is a more accurate way to assess the impact a food has on weight loss. ProPoints values are calculated using 4 macronutrients: fat, fibre, protein and carbohydrate. There is also a new weekly ProPoints allowance and zero ProPoints values fruit and veg. In Australia, Weight Watchers also offers free trials for ProPoints online program to attract customers.

In addition to Weight Watchers membership plans, other products (such as packaged foods, exercise equipment and DVDs, food preparation and storage tools, cookbooks, etc.) are available for purchase. In 2012, the company partnered with Philips to create the ActiveLink activity tracker.

The current spokesperson for Weight Watchers is Oprah Winfrey, an American media proprietor, talk show host, actress, producer, and philanthropist. During her time as a Weight Watchers spokesperson, Oprah Winfrey has revealed that she is an adamant lover of various breads. Prior spokespersons associated with the product were actresses Lynn Redgrave and Jenny McCarthy, Duchess of York Sarah Ferguson, singer/actress Jessica Simpson, and Grammy/Academy-Award winner singer/actress Jennifer Hudson.

From 1978 until 1999, Weight Watchers was owned by the H. J. Heinz Company, which continues to produce packaged foods bearing the Weight Watchers brand. In October 2015 Oprah Winfrey purchased a 10% stake in Weight Watchers. On September 12, 2016, Weight Watchers announced that its chief executive, James Chambers, would resign at the end of September after three years on the job.

The current members of the board of directors of Weight Watchers are Philippe Amouyal, John Bard, Raymond Debbane, Marsha Evans, Jonas Fajgenbaum, Linda Huett, Sacha Lainovic, Steven M. Altschuler and Christopher Sobecki. On October 19, 2015, Oprah Winfrey announced her place on the board of Weight Watchers International.

Weight Watchers has not provided official confirmation of the formulas for calculating nutrition points, and has aggressively sent cease and desist letters to websites and a number of third party tools that claimed to provide Points, or PointsPlus, calculations.

However, several web sites publish a SmartPoints formula, which they derived from published SmartPoints values and the online calculator provided by WeightWatchers to its customers . Their published formulas are based on the food energy content of the food, adding a penalty for sugar and saturated fat content and a bonus for protein content.

Media related to Weight Watchers at Wikimedia Commons