Slimming World invests in the continued evaluation and development of our programme to ensure we continually improve our services to provide the best support for our members, to evaluate the effectiveness of our programme, and to ensure that our approach remains fully in line with national guidance.

Evidence of Slimming World's effectiveness

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.

Efficacy

We regularly conduct service evaluations and have published the largest evaluation of a national lifestyle weight management service, comprising over 1.3 million UK Slimming World members¹.

Our most recent service evaluation continues to demonstrate the significant weight loss outcomes achieved by those engaging with Slimming World. Three months after joining, members achieved, on average, a clinically significant weight loss of 5%².

N	Joining BMI (kg/m2)	Weight change		BMI change	% Male
		kg	%
1,094,676	33.0 (6.4)	-4.5 (3.6)	-5.0 (3.6)	-1.6 (1.3)	7.6

Note: data presented are mean (SD)

Greater engagement with the service enhanced weight loss outcomes at 3 and 12 months. Over 120,000 members who attended at least 75% of sessions across a year lost 14% of their weight, which is associated with significant health benefits.

	N	Joining BMI (kg/m2)	Weight change		BMI change	% Male
			kg	%
3 months	422,216	33.6 (6.5)	-7 (3.5)	-7.7 (3.3)	-2.6 (1.2)	8.2
6 months	120,107	35.1 (6.7)	-13.8 (8.8)	-14.1 (7.5)	-5.1 (3.1)	8.7

Note: data presented are mean (SD); outcomes at 3 and 12 months for those attending 75% of weekly sessions

Slimming World on Referral efficacy

Slimming World on Referral is a subsidised partnership enabling health practitioners to refer patients to a local Slimming World group for weekly weight management support at no cost to the patient. Slimming World pioneered this NHS partnership programme with Greater and Central Derby Primary Care Trusts in 2001 and it is now an established obesity therapy in many Local Authorities, CCGs and workplaces. Published evaluation data shows the majority of patients referred by their healthcare team achieve clinically significant weight loss at three and six months.

The most recent audit analysed weight outcomes of over 28,000 patients referred to Slimming World by their health practitioner in 2016^{3 4}. Data shows an average clinically significant weight loss of over 5% was achieved by the end of the 12-week referral period. Also, over half of members (54%) continued to attend (self-funded) after the 12-week referral period was complete.

N	% male	Joining BMI (kg/m2)	Referral length	Weight change
				kg	%	BMI
28,167	15.5	37.1 (6.3)	12 weeks	-5.7±4.1	-5.6±3.8	-2.1±1.5

Note: data presented are mean (SD)

Greater engagement with the service enhanced weight loss outcomes at 3 and 12 months. Over 5000 members who attended at least 75% of sessions across a year lost 15% of their weight, which is associated with significant health benefits.

	N	Joining BMI (kg/m2)	Weight change		BMI change	% Male
			kg	%
12 Weeks	18,357	37.2 (6.3)	-7.3 (3.9)	-7.1 (3.4)	-2.6 (1.4)	16.7
12 Months	5263	38.2 (6.6)	-16.3 (9.8)	-15.3 (7.9)	-5.9 (3.4)	16.2

Note: data presented are mean (SD)

Health inequalities

Obesity prevalence is higher among those living in areas of greater deprivation so it’s important weight management services effectively support people in these areas. In a secondary analysis of our latest referral audit, data from 27,560 patients showed clinically significant weight losses were achieved irrespective of socioeconomic status⁵.

Note: figure shows average % weight change at 12 weeks by deprivation decile* 
*Deprivation deciles are based on the Index of Multiple Deprivation, which are official measures of relative deprivation. Decile 1 represents the 10% most deprived areas within England.

Online programme

As an alternative to the in-person service, Slimming World also provides evidence-based weight management support through a convenient online programme. This programme is based upon the same principles and philosophy of the in-person service, delivered via the Slimming World website and app. Tools to support members include an online community, virtual live events, goal setting and weighing-in functionalities, a planner to encourage members to think ahead and physical activity videos.

In 2020, Slimming World partnered with Public Health England in their “Better Health” campaign. In the first six months, over 27,000 individuals joined Slimming World’s Online programme. Three months after joining, members had achieved an average weight loss of 2.7kg (3%)⁶. High engagers, who recorded nine or more weights over three months, showed even greater weight loss of 4.2kg (4.7%).

Offer Length	N	% male	Joining BMI (kg/m2)	Weight change
				kg	%	BMI
12 Weeks	27,248	5.3	33.4 (6.8)	-2.7 (3.0)	-3.0 (3.1)	-1.0 (1.1)
12 Week High Engagers	9531	5.4	30.3 (6.7)	-4.2 (3.4)	-4.7 (3.5)	-1.5 (1.2)

Consistent outcomes were seen regardless of starting BMI or level of deprivation, and over a third (34.9%) of people continued to access the programme after the initial three-month ‘Better Health’ campaign offer.

Facilitating healthy behaviour change

Slimming World’s lifestyle weight management programme facilitates widespread behaviour 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 programme affects measures beyond just weight.

In 2021 we published research⁷ which shows the significant improvements in members’ wellbeing and positive behaviour changes made since joining, including:

• significantly increasing fruit and vegetable consumption
• eating fatty and sugary foods less often
• drinking sugary drinks less often
• cooking from scratch more often
• increasing physical activity levels

References

1. Stubbs RJ, Morris L., Pallister C., Horgan G., Lavin J, H. (2015) Weight outcomes audit in 1.3 million adults during their first 3 months’ attendance in a commercial weight management programme. BMC Public Health 10;15: 882.
2. Toon, J., Bennett, S, E., Avery, A., Roberts, K, E., Holloway, L., Pallister, C., Lavin, J. (2019) Levels of engagement as a predictor of long-term weight loss in over 1 million adults attending a commercial weight management programme. Obesity Facts (12) p176. https://doi.org/10.1159/000497797
3. Toon, J., Bennett, S, E., Avery, A., Roberts, K, E., Holloway, L., Pallister, C., Lavin, J. (2019) Longer term weight outcomes following a 12-week referral to a multicomponent lifestyle weight management programme across high BMI patients. Obesity Facts (12) p177. https://doi.org/10.1159/000497797. 
4. Toon, J., Bennett, S, E., Avery, A., Roberts K, E., Holloway, L., Pallister C., Lavin J. (2019) Longer term weight outcomes following a 12-week referral to a multicomponent lifestyle weight management programme across high BMI patients. Obesity Facts: The European Journal of Obesity. 12 (1), p177.
5. Toon, J., Bennett, S, E., Avery, A., Roberts, K, E., Holloway, L., Pallister, C., Lavin, J. (2019) Clinically significant weight loss for patients across socioeconomic backgrounds following referral to a multicomponent weight management programme. Obesity Facts (12) p236. https://doi.org/10.1159/000497797. 
6. Toon, J., Geneva, M., Sharpe, P., Lavin, J., Bennett, S., & Avery, A. (2022). Weight loss outcomes achieved by adults accessing an online programme offered as part of Public Health England’s ‘Better Health’ campaign. BMC public health, 22(1), 1456. https://doi.org/10.1186/s12889-022-13847-w.