Our research and evidence

At Slimming World, we have more than 48 years of experience with, and understanding of, weight management and the most effective ways to support our members to achieve their weight loss goals. Now, with digital technology, that support is more widely accessible and effective than ever.

About Slimming World

Slimming World’s digital weight management service, launched in 2004 in the U.K. and in 2016 in the U.S., is a multi-component digital translation of our evidence-based, face-to-face lifestyle weight management service. Our online service puts personalized, group-based weight management support in a fun, warm and friendly environment at anyone’s fingertips.

Slimming World invests in the continued evaluation and development of our program to ensure we continually improve our services to provide the best support for our members and to ensure that we meet government healthy lifestyle guidelines.  

As well as our current active research projects we are open to new projects and collaborations that may provide new insights, especially here in the U.S. market. Please contact us at support.team@slimmingworld.com to discuss possible collaborations or research proposals you may have.

Highlights of some of Slimming World’s extensive evidence-base are presented below. For a comprehensive summary of all Slimming World related evidence, you can download our full research portfolio here.

Health care providers and health professionals can download Slimming World's Health Professional booklet for additional information on our weight management program. 


Evidence of Slimming World's effectiveness

The largest published evaluation of a national lifestyle weight management service, comprising over 1.3 million U.K. Slimming World members, shows how participation in the weight loss program produced clinically significant weight losses at three months after joining the service. Here’s a summary of the evidence.


N Mean joining BMI (kg/m2) Mean weight change (kg)  Mean weight change (%) Mean BMI change (kg/m2) % Male
1,356,105 32.6 (6.3) -3.9 (3.6) -4.4% (3.8) -1.4 (1.3) 5.0%

Note: data presented are mean (SD)

Greater engagement with the service enhanced weight loss outcomes. For over 478,000 participants attending at least 75% of weekly sessions, weight loss was even more clinically significant. 

N Mean joining BMI (kg/m2) Mean weight change (kg)  Mean weight change (%) Mean BMI change (kg/m2)
478,772 33.2 (6.3) -6.8 (3.7) -7.5% (3.5) -2.5 (1.3)

Note: data presented are mean (SD)

Stubbs et al, 2015.  Weight outcomes audit in 1.3 million adults during their first 3 months’ attendance in a commercial weight management programme.  BMC Public Health 2015, 15:882.  

The same dataset showed that weight outcomes continued to improve with long-term engagement. In a further evaluation of over 70,000 members attending at least 75% of weekly sessions over a 12-month period, participants lost more than 13% of their weight, which is highly associated with significant health benefits such as lowering the risk of developing Type 2 diabetes, reducing high blood pressure and improving blood cholesterol. 

N Mean weight change (kg)  Mean weight change (%) Mean BMI change (kg/m2) Mean weeks attended % Male
71,989* -12.7 (8.4) -13.2% (7.4) -4.7 (3.0)


(86% of possible sessions)

Note: data presented are mean (SD)

Lavin, J.H., Pallister, C., Morris, L. and Stubbs, R.J. (2013). 12 month weight outcomes in 45,395 high-engagers with the Slimming World weight management programme. Obesity Facts, 6(1):189.

*Data updated since publication

Slimming World’s program is also used as a clinical intervention in the U.K. in partnership with the National Health Service (NHS), where the majority of patients referred by their health care team achieve clinically significant weight loss at three and six months.

N Referral length Start weight (kg) Mean weight change (kg)  Mean weight change (%) % Male
34,2711* 12 weeks 99.4 (20.0) -4.0 (3.7) -4.0% (3.6) 10.7%
4,7542** 24 weeks 108.2 (20.7) -8.9 (6.0) -8.6% (5.3) 12.1%

Note: data presented are mean (SD)

*Stubbs R.J, Pallister C, Whybrow S, Avery A, Lavin J. (2011) Weight Outcomes Audit for 34,271 Adults Referred to a Primary care/Commercial Weight Management Partnership Scheme. Obesity Facts 4:113-120

**Stubbs, R. J., Brogelli, D. J., Pallister, C. J., Whybrow, S., Avery, A. J. and Lavin, J. H. (2012), Attendance and weight outcomes in 4754 adults referred over 6 months to a primary care/commercial weight management partnership scheme. Clinical Obesity, 2: 6-14.

Facilitating healthy behavior change

Slimming World’s lifestyle weight management program facilitates widespread behavior change to support weight control in those engaging with the service, while also having a positive influence on the wider family network.  We also look to understand how the program affects measures beyond just weight. In 2009, we surveyed 2,821 people to show the effective impact on behavior change and health and wellbeing:

  • 78% reported buying more fruit and vegetables
  • 74% ate less fatty foods
  • 61% ate fewer sugary foods.
  • 58% ate fewer packaged meals and take out
  • 37% had more energy
  • 33% reported they now enjoy exercise 
  • 31% saw improvements in shape and posture
  • 29% had become more mobile in daily life
  • 25% saw mood improvements
  • 25% felt calmer and less stressed
  • 22% were sleeping better
  • 80% reported improved health

Not only did health and physical activity levels of those accessing Slimming World improve, but also that of their partners and children. This analysis was conducted on a representative sample of 2,812 from over 20,000 respondents accessing Slimming World’s participant support services and resources. 

C. Pallister, A. Avery, J. Stubbs, and J. Lavin. 2009. Influence of Slimming World's lifestyle programme on diet, activity behaviour and health of participants and their families. Journal of Human Nutrition and Dietetics. 24(4), pp351-358.

Digital delivery evaluation

Digital interventions constitute a novel approach for convenient, cost-effective and scalable weight management. Results of Slimming World’s digital service evaluation were presented at the International Congress of Obesity, 2016. This research looked at the impact of Slimming World’s large-scale, digital weight management service.

N Mean joining BMI (kg/m2) Mean weight change (kg)  Mean weight change (%) Mean BMI change (kg/m2) % Male
57,654 31.9 (6.3) -2.6 (3.1) -2.9% (3.3%) -0.9 (1.1) 7%

Note: data presented are mean (SD)

Results of the evaluation demonstrated that participants who entered their weekly online weight more than twice out of a possible 13 times achieved clinically significant weight losses.

N Mean joining BMI (kg/m2) Mean weight change (kg)  Mean weight change (%) Mean BMI change (kg/m2) % Male


31.9 (6.2)

-3.0 (3.1)

-3.5% (3.3%)

-1.1 (1.2)


Note: data presented are mean (SD)

Clinically significant results were even more pronounced for those who entered their weekly online weight more than 10 times out of a possible 13. 

N Mean joining BMI (kg/m2) Mean weight change (kg)  Mean weight change (%) Mean BMI change (kg/m2) % Male
15,351  32.0 (6.2) -5.2 (3.5) -5.8% (3.5%) -1.9 (1.2) 7%

Note: data presented are mean (SD)

Sacher, PM., Kolotourou, M., Morris, L., Dowse, E and Lavin, J. 2016.  The role of large-scale, eHealth weight management interventions in addressing the global obesity epidemic. Obesity Reviews. 17 (Suppl.2), 16.