Summary findings of study by Harrold et al., “Non-nutritive sweetened beverages versus water after a 52-week weight management programme: a randomised controlled trial”
- A new year-long randomised controlled trial found that daily drinking of low/no calorie sweetened beverages can help in long-term weight control
- Results showed significantly greater weight loss with low/no calorie sweetened drinks compared with water after 52 weeks, with a modest difference between the groups
- The new study by Harrold et al reinforces current evidence from clinical trials supporting the beneficial role of low/no calorie sweeteners as a means for achieving weight control, contrary to what is suggested in a conditional recommendation by the World Health Organization (WHO)
Clinical research consistently reports reduced calorie intake and weight loss in people who consume low/no calorie sweeteners when compared to sugars. This has been shown in a WHO systematic review and meta-analysis of randomised controlled trials (RCTs),1 as well as in several other systematic reviews published over the last years.2-4 However, most RCTs included in these reviews were of medium duration. With the aim to strengthen the evidence base for making policy recommendations on the use of low/no calorie sweeteners in weight control, this new RCT by Harrold and colleagues studied the effects of low/no calorie sweetened beverage intake versus water on body weight over a period of two years.5-7
This article presents the results of the 1-year study.7
What did the SWITCH study find?
The trial SWITCH (‘The effectS of non-nutritive sWeetened beverages on appetITe during aCtive weigHt loss’) investigated the effects of daily drinking of two servings of low/no calorie sweetened beverages or water on body weight over a 12-week phase of active weight loss, followed by a 40-week period of assisted weight maintenance, and finally a second year of voluntary, unassisted maintenance extension phase.5 A total of 493 adults with overweight or obesity without major health issues were enrolled in the study, and 262 participants stayed in the intervention until the end of week 52.7
During the first 12 weeks of active weight-loss, where participants did weekly sessions of a group weight-loss programme and daily exercise, consuming beverages with low/no calorie sweeteners had similar effects as water on weight loss (approx. -6kg), even in people who would not normally drink diet drinks.6 This weight loss was accompanied by reductions in anthropometric measures, glycaemic control markers, fasting lipid profiles, and sugar consumption.
At the end of the first year, including a 40-week period of monthly group weight management sessions, participants who drank daily two servings of low/no calorie sweetened beverages for one year lost 7.5kg versus 6.1kg for those who drank water.7 Weight loss was significantly greater for low/ no calorie sweetened drinks versus water, but the difference was considered modest. Nearly all other results linked to weight also improved in both groups: reductions in blood pressure, LDL cholesterol and better liver function were reported in both groups. Results were also identical for consumers of low/no calorie sweetened drinks as well as for people who do not normally drink low calorie beverages.
A third phase of voluntary, unassisted weight maintenance is ongoing and will last one more year, meaning that volunteers will have been in the trial for a total of 2 years.
Why are these findings important?
In a Press Release published by the University of Liverpool, the authors stated: “Our study captures the key long-term effects of sweetener use on behaviour, appetite expression, and food preferences as well as weight and other health outcomes. The results reinforce previous study outcomes and that, in comparison to water, drinking non-nutritive sweetened (NNS) beverages does not undermine weight control when compared to water.”
The results of the new study are in line with findings of previous RCTs supporting the beneficial role of low/no calorie sweeteners in long-term weight control. A previous 52-week RCT by Peters et al compared the effects of diet drinks and water on weight loss and maintenance and found that low/no calorie sweetened beverages were superior to water for weight loss (–6.2 vs. –2.5 kg, respectively) and for helping participants to better maintain their weight loss throughout the weight-maintenance phase of one year.8 An older trial has also found that consuming low/no calorie sweeteners can assist with maintaining weight loss over 2 years when used as part of a weight management programme.9 Several other RCTs with a duration up to 6 months reported that substitution of sugars with low/no calorie sweeteners resulted in significant reductions in body weight in adults with overweight and obesity.1-4
Despite evidence from randomised controlled trials being consistently in favour of low/no calorie sweeteners’ use for weight control, in a conditional recommendation WHO suggested non-sugar sweeteners not to be used as a means to control body weight.10 Scientists have expressed concern that the WHO guideline disregarded the evidence from RCTs and solely relied on prospective cohort studies that are prone to bias and cannot infer causality, ignoring the established hierarchy of evidence as described by GRADE.11 Khan and colleagues suggest that when evidence comes from both trials and cohort studies, RCTs should be given precedence.
The WHO justification for disregarding trial evidence was that the results were short-term and thus did not provide evidence of long-term impact. However, the WHO meta-analysis1 included trials of six months to one-year in duration with no evidence of effect modification by study duration. This latest study by Harrold et al provides new data to a large battery of existing and consistent evidence in support of beneficial effects of low/no calorie sweeteners on long-term weight control, rejecting the rationale by WHO.
*This trial was funded by the American Beverage Association.