4th January 2017

 

A number of headlines today suggest that low calorie drinks do not offer a benefit for weight loss and may even make you fatter. This is based on a paper published in the journal PloS Medicine which states that there is an absence of consistent evidence to support the role of low calorie drinks in weight control and that they should not be promoted as part of a healthy diet.

This is contrary to current UK dietary advice on drinks as part of the Eatwell Guide, which states that you can ‘Swap sugary soft drinks for diet, sugar-free or no added sugar varieties to reduce your sugar intake in a simple step’. So why is this paper suggesting otherwise?

The paper, by authors from a variety of institutions including the University of Sao Paolo, Brazil, Washington University in the US and Imperial College London, is an opinion piece, which means that it has not systematically reviewed the evidence for low calorie drinks and weight control. Recent studies (Rogers et al 2016, Miller and Perez 2014) that have taken a systematic approach to the evidence around low calorie drinks and weight have found that, in prospective cohort studies, which look at what people consume and follow them over time there were mixed results and in some cases, consumption of low calorie drinks was associated with slightly higher levels of obesity.

However, in intervention studies, where people are given different drinks (either sugary or low calorie) and the effects on their calorie intake and their weight are monitored, systematic reviews have found that consuming low calorie drinks is associated with slightly lower calorie intakes and lower body weight. This apparent contradiction may come from the different study designs. In the prospective cohort studies, where low calorie drinks were associated with higher weight, this relationship may have been affected by overweight people being more likely to choose low calorie options. However, the intervention studies allow researchers to control what people consumed and to monitor the effects of low calorie drinks alone and in these studies it appeared that consuming low calorie drinks resulted in lower calorie intakes and lower body weight because people did not fully compensate for the lower calories in the drinks by eating more.

Professor Peter Rogers, member of BNF’s Scientific Advisory Committee and lead author of a recent systematic review on low energy sweeteners said: “This paper underestimates the effects seen in intervention trials, which are clear from our meta-analysis and that of Miller and Perez. Of course, the effects are modest, low calorie sweeteners alone cannot be expected to prevent obesity. Sugar intake is not the only cause of obesity - far from it. Further, low calorie sweeteners replace only some sugar in the diet. The evidence is that where they replace sugar there is not full compensation for the reduction in calories eaten, and there is over the longer term a corresponding relative reduction in weight and fatness in children and adults”.

Overall, there is evidence that low calorie drinks can help to reduce calorie intakes and body weight, provided the diet overall is calorie controlled and people do not compensate for the lower calories by consuming more from other foods and drinks. Sugary drinks are one of the main contributors to sugars intake for both adults and children and swapping these for water, low fat milks, diet or sugar-free versions is a simple way to reduce sugars intake. However, choosing low calorie drinks is only one small step of the many needed to control obesity. No single approach is likely to be effective in tackling the obesity epidemic and many other dietary and lifestyle changes are needed to have a significant impact on risk of obesity in the UK population.

 

For more information about the biology and psychology of appetite control, including sweetness and sweeteners, see this review paper in the December 2016 issue of Nutrition Bulletin