Do non-nutritive sweeteners help weight loss?
Low-sugar and no-added-sugar foods and drinks with non-nutritive sweeteners (NNS) are popular and growing steadily. However, the use of NNS for weight loss is controversial. We review the evidence around alternative sweeteners and find the picture is far from clear.
Simple in theory…
If NNS foods and drinks have fewer kilojoules than their traditional sugar-sweetened counterparts, and if they help create a sustained kilojoule-deficit, you’d expect weight loss. And in intervention studies this has indeed occurred. A 2016 systematic review concluded that NNS in place of sugar in children and adults leads to reduced energy intake and body weight. On the other hand, observational data suggest regular consumption may contribute to obesity, type 2 diabetes and cardiovascular disease (although reverse causation may be at play). These puzzling adverse effects have sent researchers searching for explanations.
A 2016 review examining NNS and metabolic dysregulation says while experimentation in humans is difficult due to the long time frames over which dietary factors impact health, animal studies indicate NNS promote food intake, weight gain and metabolic alterations in a wide range of animal species. The authors conclude that substitution of NNS for sugars may not produce benefits but may increase metabolic risk and need to be thoroughly evaluated in humans.
NNS may not be inert
A 2015 review paper on the physiological mechanisms by which NNS impact body weight and metabolism suggests that rather than being inert, NNS may influence feeding and metabolism via a number of central and peripheral mechanisms:
Humans are naturally attracted to sweetness, but NNS taste sweet without the accompanying energy of sugars and this may have consequences on taste biology. As well as those in the mouth there are sweet taste receptors in the brain, pancreas and gut and these are involved in glucose sensing, secretion of satiety hormones and glycaemic control. Both sugar and NNS have been shown to elicit these effects in animal studies, although data are conflicting. Studies in humans have also produced conflicting data. Casting doubt on animal studies, however, the authors of the 2016 Systematic Review concluded most animal studies did not mimic NNS consumption by humans.
Alterations in gut microbiota have been linked to obesity, and NNS have been associated with alterations in microbiomes in both mice and humans (we have a feature on this topic coming up in a future issue).
Our beliefs and expectations about food, such as lower energy content, can influence brain function and metabolism. For example, a beverage labelled a “treat” elicits a greater hypothalamic response than the same one labelled “healthy”. It has also been shown that eating a food believed to be lower in kilojoules has reduced satiety and produced “rebound” eating in some (but not all) studies.
Do NNS increase appetite for sweet taste?
It has been suggested that NNS enhance the natural appetite for sweetness, increase the liking for sweetness and increase consumption of sweet food and drinks (known as the sweet tooth hypothesis). However, review paper author France Bellisle found no consistent association between NNS consumption and heightened appetite for sweet products across a variety of study types and in different population groups. He does say longer term randomised studies are needed to confirm the benefits of NNS in different aspects of weight control, prevention of weight gain, weight loss and/or weight loss maintenance.
Eating behaviour is also influenced by psychological factors. A study of three separate experiments measuring the impact of NNS on how individuals think about and respond to foods and drinks found consuming a NNS beverage influenced psychological processes in ways that may over time increase energy intake.
Compensatory eating is one way NNS may actually increase energy intake. This effect is described as conscious overconsumption to compensate for energy saved by choosing a food or drinks with NNS. However, in his review of NNS in prevention and management of overweight and obesity, Peter Rogers claims the evidence doesn’t support such a hypothesis and even if there were an effect, the energy dilution effect of NNS would outweigh any increase in energy intake. However, the existence of compensatory eating and its overall impact is still an area of scientific disagreement.
Benefit vs risk
In a review paper titled ‘The paradox of artificial sweeteners in managing obesity’, author Jason Roberts suggests that whether the use of NNS helps weight loss depends on individual factors including how much they compensate for the NNS, the composition of their regular diet and their overall compliance with a weight loss program.
A 2017 systematic review and meta-analysis concludes that RCTs don’t clearly support the intended benefits of on NNS for weight management and routine intake may be associated with increased BMI and cardiometabolic risk, and further research is needed to characterise the long-term risks and benefits. Previous reviews in 2013 and 2014 came to a similar conclusions. The authors of the 2013 review suggested for optimal health only minimal amounts of sugar and NNS be consumed while the 2014 review authors added overall diet quality must be considered when incorporating NNS foods and drinks into the diet.
The use of NNS for weight loss and obesity prevention are controversial and the existing evidence remains unclear. From a public health point of view, there is little support for the use of NNS to prevent or manage obesity. In the clinical management of individuals, NNS may be helpful in some patients in the context of overall diet and lifestyle advice for weight management, however compensatory eating is (arguably) a potential risk that needs to be managed for optimal outcomes.