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Obesity Canada Clinical Practice Guidelines
Tackling Obesity Full systems Map. UK Government Office for Science 2007
Weight Watchers Review of the Scientific Literature
Interestingly, I couldn’t find any systematic reviews or meta-analyses (the strongest type of evidence) for Weight Watchers published in the last 10 years. I found very few individual research studies published in the same time period.
One study in 2011 involving almost 30,000 people in the UK who received free access to Weight Watchers for 12 weeks found that about half of the people dropped out. The average amount of weight lost was approximately 3kg at 12 weeks. They didn’t follow the people long-term to see if they maintained the weight loss (Ahern et al. 2011. https://doi.org/10.1186/1471-2458-11-434 ).
A study in 2005 compared Weight Watchers to other popular diets at the time. At 1 year later, they found that 26 of the 40 people assigned to Weight Watchers had stuck to the diet. People following Weight Watchers lost an average of 3 kg. People on Weight Watchers lost the same amount of weight as the people following the other diets. Sticking with the diet (any of the diets) was the strongest predictor of weight loss (Dansinger et al. 2005. doi:10.1001/jama.293.1.43 ).
A study published in 2017 funded by Weight Watchers evaluated the more modern Weight Watchers Online program. It involved almost 300 people and lasted 1 year. The average weight lost at 1 year was approximately 2 kg (Thomas et al. 2017. https://doi.org/10.1002/oby.21846 ).
Key Scientific Literature References:
Multiple Diet Types
Cruwys et al. 2020. https://doi.org/10.3390/nu12040970
Jospe et al. 2020. https://doi.org/10.1093/ajcn/nqz330
Kim. 2020. doi: 10.7570/jomes20065
Obert et al. 2017. https://doi.org/10.1007/s11894-017-0603-8
Intermittent Fasting
Cheng et al. 2024. https://doi.org/10.1111/obr.13834
Cho et al. 2019. https://doi.org/10.3390/jcm8101645
Harris et al. 2018. DOI: 10.11124/JBISRIR-2016-003248
Nowosad & Sujka. 2021. https://doi.org/10.1007/s13668-021-00353-5
Silverii et al. 2023. https://doi.org/10.1016/j.numecd.2023.05.005
Torres et al. 2022. doi: 10.2196/35896
Welton et al. 2020. Canadian Family Physician February 2020; 66 (2) 117-125
Paleo
Almeida de Menezes et al. 2019. https://doi.org/10.1186/s12937-019-0457-z
Indumathy & Ramya. 2018. DOI: 10.15613/fijrfn/2018/v5i2/180849
Manheimer et al. 2015. https://doi.org/10.3945/ajcn.115.113613
Markofski et al. https://doi.org/10.1177/1559827619866157
Keto
Bachar & Birk. 2025. https://doi.org/10.1007/s13668-025-00634-3
Bueno et al. 2013. https://doi.org/10.1017/S0007114513000548
Di Rosa et al. 2022. https://doi.org/10.3390/ijerph192013040
Verde et al. 2023.
Wang et al. 2023. https://doi.org/10.3390/nu15194163
Xing et al. 2024. https://doi.org/10.3390/genes14051024
Vegan
Crosby et al. 2022. https://doi.org/10.1016/j.jand.2022.04.008
Kahleova et al. 2025. https://doi.org/10.1186/s12986-025-00912-5
Kashyap et al. 2022. https://doi.org/10.3390/nu14224870
Selinger et al. 2023. https://doi.org/10.1080/10408398.2022.2075311
Termannsen et al. 2022. https://doi.org/10.1111/obr.13462
Blood Type
Barnard et al. 2021. https://doi.org/10.1016/j.jand.2020.08.079
Cusack et al. 2013. https://doi.org/10.3945/ajcn.113.058693
Wang et al. 2018. https://doi.org/10.1093/jn/nxx074
Wang et al. 2014. https://doi.org/10.1371/journal.pone.0084749
Menopause Specific Approaches
Cheng et al. 2018. DOI: 10.1097/GME.0000000000001085
Leitao et al. 2024. https://doi.org/10.1016/j.maturitas.2024.108060
Lin et al. 2021. https://doi.org/10.1016/j.numecd.2020.10.018
Lombardo et al. 2020. https://doi.org/10.3390/nu12082471
Yaqoub Abdullah. 2025. http://dx.doi.org/10.52533/JOHS.2025.50708
Zoe et al. 2021. DOI: 10.1097/GME.0000000000001684
Mediterranean
Mancini et al. 2016. https://doi.org/10.1016/j.amjmed.2015.11.028
Poulimeneas et al. 2020. https://doi.org/10.1017/S0007114520001798
Rose et al. 2024. https://doi.org/10.1111/obr.13824
Zheng et al. 2024. https://doi.org/10.1186/s40795-024-00836-y
Maintaining Weight Loss
Spreckley et al. 2021. https://doi.org/10.1080/17482631.2020.1862481
Tay et al. 2023. https://doi.org/10.3390/nu15051297
van Baak & Mariman. 2019. https://doi.org/10.3390/nu11081916
Varkevisser. 2018. https://doi.org/10.1111/obr.12772
Kristen Yarker, MSc, RD
Registered Dietitian Victoria BC