Slimming World and Weight Watchers help hundreds of thousands of people lose weight every year, but not without controversy. Hatty Willmoth explores the pros and cons of these plans, and how they compare to nutritional therapy as an alternative.

Slimming World and Weight Watchers are the UK’s go-to weight-loss services, having helped millions to lose weight since the 1960s.

They’re even available on the NHS. For example, your GP might be able to prescribe you three months of a Slimming World membership, depending on where you live.

But these groups have both faced their fair share of controversy over the years, and in May 2024, Slimming World was the subject of a BBC radio documentary investigating links between membership and eating disorders.

Experts featured on the File on 4 programme suggested that those with a history of disordered eating could be at risk of relapse by signing up to Slimming World, and that other individuals could develop dysfunctional eating habits too.

They attributed this to Slimming World’s complicated rules, celebration of weight loss, and lack of eating disorder expertise.

But it is also up for debate whether the methods of Slimming World and Weight Watchers are aligned with the latest nutritional science, or sufficiently cater to the varying needs of individuals.

In this respect, nutritional therapy offers an alternative – but it is much less affordable.

What is Slimming World?

Slimming World is the largest weight-loss service in the UK, with 700,000 current members in the UK and millions who have given it a go since it was set up in 1969.

Their “generous no-hunger eating plan” – not a diet, the website says – is called ‘Food Optimising’ and involves splitting food into three categories.

Free Food is their ‘healthiest’ category, comprised of over 350 “satisfying” and “everyday” foods to be enjoyed in unlimited amounts, including vegetables, fruit, lean meat, eggs, potatoes and pasta.

Secondly, Healthy Extras is a group of foods that Slimming World encourages its members to eat every day but in measured amounts, and includes wholemeal bread, breakfast cereals, milk, cheese, nuts and seeds.

Finally, Syns – short for ‘synergy’ – are foods that Slimming World say are the least filling and highest in calories, such as alcohol, biscuits, cake, chocolate and high-fat foods. These – as well as Healthy Extras – have ‘Syn values’ attached to them, and most members are encouraged not to exceed 15 Syns per day.

For instance, one teaspoon of olive oil counts as 2 Syns, a chocolate bar might be 12 Syns, and a small avocado is 9½ Syns.

Slimming World members also use their app to track Syns, track weight loss, and access content such as recipes, meal plans, workouts, podcasts and success stories, among other features.

There is an online social Slimming World community, and members are encouraged to attend regular in-person meetings, guided by ‘Consultants’, where members are weighed and then discuss their weekly weight-loss progress with others on the programme.

What is Weight Watchers?

Weight Watchers, on the other hand, says their weight-loss programme – “not a deprivation diet” – makes nutrition simple.

To start, you pick a programme. Weight Watchers offers three different paths: their standard Points programme, a version for people taking GLP-1 weight-loss medication such as Ozempic, and a version for people with diabetes.

Then, there’s a quiz. This will ask about weight, height, weight-loss goals, sex and age to work out a Points budget.

Members are then encouraged to download the Weight Watchers app, which includes food, activity and weight trackers; recipes, coaching support, tips and advice, articles, workouts, meditations and a members-only social community.

Finally, it’s time to start tracking. At Weight Watchers, every food has a Points value, and members must track their food to ensure they stick to their daily budget.

In a statement for this article, Weight Watchers said that their system was “our way of simplifying the complexity of nutrition science for weight management”.

Rather than just considering calories, a food’s Points value accounts for “nutritional factors, like added sugars, fibre, protein, and saturated fats vs unsaturated fats, to create a single number”.

The healthier the food, the fewer the Points, says Weight Watchers. More accurately, the lower a food is in sugar and saturated fats, and the higher it is in fibre, protein and unsaturated fats, the fewer the Points, as decided by the Weight Watchers algorithm.

The minimum budget you can be allocated is 23 Points. The Points system is updated regularly, but as of May 2024, a Starbucks croissant is worth 10 Points, an avocado is worth 2 Points, and 12 tortilla chips are worth 4 Points.

Much like Slimming World’s Free Foods, Weight Watchers also has a list of over 200 ‘ZeroPoint’ foods which can be eaten in unlimited amounts, such as vegetables, fruits, lean protein, wholegrains, and healthy fats.

What is nutritional therapy?

Nutritional therapist and Clinic Tutor at ION, Georgina Corley-Cadogan says: “Nutritional therapy is a 360-degree approach, tailored to the individual and their specific needs.”

She explains that a nutritional therapist considers their client’s age, gender, time of life (e.g. menopause), medical conditions, medications, medical history, responses to certain foods, genetic predispositions and nutrient inadequacies.

To get this information, a client usually fills out a long questionnaire and a food diary before their first consultation, so their nutritional therapist has an insight into their whole-body health, dietary habits and wellness goals.

Then they meet one-to-one to work out steps that the client can take to improve their health, and perhaps lose weight if relevant.

Functional testing may be offered – for example, checking for nutrient deficiencies or assessing the gut microbiome – to provide a deeper understanding of the client’s health.

What happens next depends on that person’s individual needs, but a nutritional therapist is unlikely to recommend food tracking, point-based budgets, or rigid food categorisation.

Instead, a client could be advised to swap out their sugary breakfast or snacks for healthier alternatives, introduce more oily fish into their diet, supplement vitamin D, or avoid screens close to bedtime to improve sleep quality.

For weight loss, Cadogan’s approach includes, “eating non-processed, whole foods; increasing fibre and vegetables; introducing healthy fats, lean protein and complex carbs; reducing or eliminating snacking between meals; reducing alcohol and increasing water intake.”

But recommendations will depend on the client, as well as the preferred methods of the nutritional therapist according to their interpretation of the latest science.

Following the latest nutritional science

Both Slimming World and Weight Watchers say their methods adhere to the latest nutritional science – but differ considerably, to one another and to nutritional therapy.

For instance, tracking Syns may be part of the Slimming World programme, but tracking Points is central to Weight Watchers.

Their website reads: “Science shows food tracking is the biggest predictor of success – the more you track, the more weight you’ll lose!”

However, Cadogan says that the pressure to track food may create “food anxiety”, and File on 4 identified food tracking as a possible catalyst for negative eating behaviours.

The companies’ unlimited foods also diverge. Weight Watchers describes their ZeroPoint foods as “nutritional powerhouses” that act as the foundation for a healthy pattern of eating.

Their ZeroPoint list has been adjusted several times in recent years, but currently includes non-starchy veggies, fruit, eggs, yoghurt, cottage cheese, fish, shellfish, chicken/turkey breast, tofu, tempeh, corn, popcorn, beans, peas, and lentils.

Again, this reflects their general stance, favouring protein, fibre and unsaturated fats, and de-incentivising sugar and saturated fats.

Free Foods include fruits, vegetables, proteins and carbohydrates, so Slimming World members can eat as much pasta, potatoes and rice as they like.

Meanwhile, foods that are higher in fat have Syn values attached to them at Slimming World, and must be limited, regardless of type.

Carbohydrates vs fats: which should be avoided?

In a statement for this article, Slimming World said their plan “is based on nutrition science that shows that foods higher in protein and carbohydrate are more satiating than foods high in fat.

“Encouraging a higher intake of more satiating foods helps to limit energy intake and results in weight loss.”

They went on to say that a British Nutrition Foundation (BNF) report found: “Slimming World members are receiving advice that closely aligns with the main current healthy eating recommendations.”

However, the UK’s healthy eating guidelines are routinely criticised by those in nutritional therapy for aligning with outdated science.

Much like Slimming World, the Eatwell Guide demonises fats and promotes high-carbohydrate eating.

Cadogan says: “Carbohydrates such as potatoes and pasta convert easily and quickly to glucose, which causes weight gain, increased cravings and increased risk of metabolic dysfunction, increasing the risk of developing heart disease and type 2 diabetes. Portion control should still be observed.”

She continues: “Fats are essential for weight loss and supporting key functions in the body. Research has found that a low-fat diet is not recommended for weight loss or for general health.

“Good quality fat keeps us fuller for longer, contains essential fatty acids, can be a source of energy, and supports leans body mass, which is especially important when losing weight.”

And, while Weight Watchers don’t penalise fats outright, they still treat unsaturated fats as ‘good’ and saturated fats as ‘bad’; a binary categorisation that is controversial at best.

Risk of eating disorders

Although both Weight Watchers and Slimming World seem to go to great lengths to extol the freedoms, flexibilities and feel-good qualities of their programmes, they fundamentally work by categorising food as varying degrees of ‘healthy’ and ‘unhealthy’, and restricting the latter.

Such food rules have been linked to problematic eating behaviours, as explored by File on 4. The programme also criticised Slimming World for their terminology, especially the word ‘Syn’.

Slimming World says that Syns enable members to “guiltlessly enjoy the foods that many weight loss plans ban outright”.

But Cadogan says that labelling foods as Syns “creates an anxiety around food and food groups” and increases “guilt and shame” when those foods are eaten, while failing to give members “education around these foods and what they do to the body”.

After all, Syns were called ‘Sins’ until the early 2000s and, as File on 4 pointed out, Slimming World food diaries denoted Syns with a devil emoji until very recently.

Slimming World says they were “shocked and saddened” by the BBC report and are in the process of reviewing some of their terminology, so ‘Syns’ may not stick around for long.

Weight Watchers may not categorise foods with such controversial language as Slimming World, but Cadogan says that relying on an app to dictate a food’s value “doesn’t encourage an understanding around how each food group supports functions in the body” and isn’t sustainable long term.

Weight Watchers may also make it easier for people who should not be trying to lose weight to join their services.

At Slimming World, new members have to be in the ‘overweight’ or ‘obese’ BMI categories, but Weight Watchers sets the limit at a BMI of 18.5, only blocking people from signing up if they are ‘underweight’.

Someone with a ‘healthy’ BMI can therefore join Weight Watchers and start losing weight, no problem – and that could potentially pose a risk to people with eating disorders.

Let's get personal

It may be inevitable that any diet plan hoping to address the needs of everyone will have flaws – but Slimming World and Weight Watchers both claim that they cater to each person’s unique needs.

Slimming World says: “Food Optimising is so flexible you can tailor it precisely to you.”

Whereas Weight Watchers says: “While WW is all about the needs of the individual, Slimming World takes a different and much more generalised approach with food optimising.”

Yet while Weight Watchers gives individuals different Points budgets, and Slimming World allows members to eat a wide array of foods within their framework, the values attached to foods at both companies are the same across the board.

Cadogan believes: “The downside of groups like Slimming World and Weight Watchers is the ‘one size fits all’ approach.

“As we know, we are all very individual in how we respond to dietary changes. We’ve all had that friend that has done great on a specific programme, only for us to try it and not see the same results.” However, nutritional therapy is totally personalised.

Weight loss isn't just about food

Nutritional therapy also looks at more than just food when it comes to losing weight. Cadogan says: “Achieving long-term weight loss isn’t simple… We need to look at all systems of the body.”

So, she helps clients wishing to lose weight introduce more movement into their day, not just in the form of strenuous exercise, but reducing sedentary time.

“Sleep plays a huge role in weight loss,” she adds, “as poor sleep disrupts our hormones which relate to hunger and fullness, which sends mixed messages to the brain.”

Stress is another focus. “Chronic stress can cause the body to go into fat-storage mode,” Cadogan explains.

“A connection has been found between the stress hormone cortisol and being overweight, …[and] that higher cortisol levels are associated with carrying that extra weight around our abdominal area.

“Gut support is essential as increased inflammation has been linked to weight gain and difficulty losing weight.” As such, Cadogan recommends plenty of fibre, vegetables, and anti-stress techniques. Probiotic foods may also help.

Slimming World and Weight Watchers venture beyond food too; each has an exercise programme.

Slimming World’s scheme is called ‘Body Magic’ and encourages members to get a little out of breath for 30 minutes a day, at least five times a week.

They don’t reward physical activity with Syns because they say, “this won’t help build positive habits – or healthy attitude to fitness in the long-term”.

At Weight Watchers, members are given a weekly FitPoints goal and are encouraged to exercise to earn these – and more FitPoints mean more food Points.

Weight Watchers also gives its members advice on their mindset and sleep.

Losing weight on a budget

It is perhaps unsurprising that Slimming World and Weight Watchers are more popular than nutritional therapy. Personalised, one-to-one private healthcare comes at a price, and nutritional therapy remains a luxury that many can’t afford.

Slimming World and Weight Watchers are much more accessible for people trying to lose weight – who are statistically likely to be from less privileged socioeconomic backgrounds.

If you pay in full, Slimming World only costs £5.95 per week, and Weight Watchers works out even cheaper at £18.95 per month.

But they both have discounted options, and both companies are partnered with the NHS so can be prescribed for free, depending on location.

And they can work for some people. Slimming World’s research suggests their members lose an average of 5% of their body weight after three months on the programme, and that greater engagement leads to enhanced weight loss outcomes.

Cadogan says: “Some people find group programmes effective, as it gives a form of accountability which helps with compliance to a healthy eating programme, especially in the beginning when embarking on something new. Groups can also help create a sense of community.”

But if you are considering signing up to a weight loss group, you may wish to keep a close eye on your relationship with food. After all, food isn't simple and neither are we.

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