What are Slimming World 'Syns' and why are the dieting company's methods controversial?

Weight-loss brand Slimming World has caused dismay with its decision to reclassify Muller Light yoghurts and consign them to its list of “Syns”.

Dieters following the company’s healthy eating plan are allowed a maximum of 15 Syns per day, minor transgressions into the realm of the calorific that can be consumed as part of a balanced regime primarily based around “Free Foods” like fruit and vegetables, eggs, grains and low-fat dairy products.

This process of “food optimisation” is intended to help participants manage their meals in a realistic manner, allowing occasional relief from what can be an austere plan without leaving dieters feeling preoccupied by hunger or snack-related guilt and shame.

A 175g pot of Muller Light was previously considered a Free Food by Slimming World and the decision to chalk it up as one Syn on the points system is bad news for diners who had previously relied on the 99-calorie dessert as a cornerstone of their daily plan.

"Using the very latest information on average protein, carbohydrate, fat, sugar and calorie content of thousands of every day foods together with the rapidly growing number of brands, products and flavours of yoghurt available in every supermarket, our food and nutrition teams have created a much more robust way of categorising yoghurt," the company said.

"That means we can now give product-specific Free Food allowances to the various types of yoghurt (such as Greek, skyr, dairy-free, quark yoghurts, protein yoghurts and more) – based on their specific energy densities, their nutrient content and how filling they are."

Other foods recently downgraded to Syn status by the brand include tinned pasta shapes in tomato sauce (0.5 Syns per 100g), instant mashed potato (3.5 Syns per 100g) and Danone Activia (1 Syn per 125g pot).

The good news for dieters is that all brands of canned jackfruit, seitan (wheat gluten), fat-free natural yoghurt, fat-free Greek-style yoghurt, dairy-free soya yoghurt and fat-free natural Greek and skyr are now considered Syn-free.

Slimming World was founded in Alfreton, Derbyshire, in 1969 and began rolling out classes across the country over the decades, encouraging people to reform their diets and take up exercise to bolster their self-esteem.

The organisation began publishing an eponymous magazine in 1998 as well as a range of healthy eating recipe books and has taken on referrals from GPs since 2001.

It has faced criticism over its Catholic approach to food classification, however.

In December 2017, nutritionist Rhiannon Lambert attacked Slimming World ahead of the publication of her book Re-Nourish.

“Naming certain foods as ‘Syns’ just contributes to an unhealthy anxiety that prevails around food all too often,” she told The Independent.

“Those lucky enough to have never strayed into eating disorders or struggled with their weight may not see it this way but for the ones who are supposed to benefit most from this Slimming World system, those who eat too much or not enough, labelling foods is a negative and guilt-ridden idea.

“We should encourage positive messages surrounding what we can and should eat, not what we can’t and shouldn’t eat.”

Slimming World responded to Ms Lambert's criticism by stating: “Far from making people feel ashamed about what they eat, our plan is about lifting the burden of guilt people feel around food and providing a healthy, flexible and realistic way of eating that fits with every lifestyle and that can be kept up for the long-term.”