Graham Finlayson, Professor, School of Psychology, University of Leeds (UK), WP2 co-chair.

‘Free sugars’ also known as ‘added sugars’ are defined as those sweet carbohydrates (e.g., sucrose, dextrose) included during the manufacturing process as well as those naturally occurring in syrups, honey and fruit juices. Free sugars included in food products serve to increase the palatability of the product but this often occurs at the cost of an increase in energy-density and/or the displacement of other more nutrient dense foods in the diet. Indeed, free sugar intake is one nutritional component that has gained focus from health advisors and policy makers seeking to influence obesity because of its low nutritional value (lack of vitamins, minerals or fibre) and its potential to add to overall energy consumed, facilitating weight gain, and potential altered appetite and endocrine responses to carbohydrates (sugars) relative to other macronutrients.

Simply restricting free sugars from the diet without substitution may reduce diet palatability or contribute to changes in sweet craving, resulting in poor acceptance and adherence to the diet. The replacement of free sugars with non-nutritive sweeteners and sweetness enhancers (S&SEs) in food products is one of the most cited dietary strategies to reduce sugar intake while maintaining acceptance and palatability of the diet. S&SEs have many forms and identities, including artificial sweeteners (e.g., Aspartame, Neotame), natural sweeteners (e.g., Stevia, monk fruit), polyols (e.g., sorbitol, maltitol), sweet proteins (e.g., thaumatin) or chemical compounds (e.g., steviol glycosides).

The common mechanism linking most different S&SEs is that they convey sweet taste while contributing no substantial energy to the nutritional profile of foods. Recent evidence has demonstrated an increase in the number of S&SE-sweetened products consumed globally, highlighting a general acceptance among most consumers. Similarly, consumers have expressed a desire for ‘clean label’ foods, creating a drive towards ‘natural’ plant-based sweeteners, despite neither natural nor synthetic sweeteners being metabolically inert and both having an “E”-number denomination. Nevertheless, the complete removal of sugars from solid foods such as baked goods is technically very challenging without having a negative impact on the quality of the product. Sucrose in a baked product serves several functions, namely, to sweeten, act as a bulking agent, retain moisture, add organoleptic properties, and extend the product shelf-life. Consequently, most of the research has utilised beverages as the vehicle of administration. Therefore, evidence regarding the effects of S&SEs in solid foods is limited.

S&SEs have increasingly been employed over recent years to reduce the energy and sugar content of foods; however, there remains disagreement regarding the precise effects of these on subjective states and behaviours that contribute to body weight and composition, including appetite, food intake and food reward. Moreover, a recent review demonstrated that observational studies tend to report a negative effect of the inclusion of S&SEs in the diet, where RCTs tend to report a beneficial effect. The World Health Organisation is currently drafting new recommendations for the use of S&SEs as a means of achieving weight control or reducing the risk of noncommunicable diseases. The draft recommendations are being based on a recent systematic review commissioned by the WHO that identified no long-term benefits to weight from the inclusion of S&SEs in the diet, as well as identifying potentially undesirable long-term effects in increased risk of type 2 diabetes, cardiovascular diseases and mortality in adults. Notable from this report was that short-term weight loss was not considered a positive outcome, despite abundant evidence that SSE can help with short-term weight loss when their use leads to a reduction in total energy intake.

At present, there is currently insufficient evidence to reach a clear consensus about the effect of acute and repeated S&SE consumption on appetite and energy intake. Indeed, the 11 S&SEs that are currently approved for use in the EU are chemically heterogeneous and absorbed, metabolised, and excreted differently. Furthermore, most investigations of the relationship between S&SE intake and health outcomes have used beverages as the vehicle ; these have recently been reviewed. Since the amount of S&SEs in the food supply is increasing in response to consumer demand, policy (e.g., ‘sugar taxes’ and EU initiatives), there is a pressing need to examine the appetite-related behavioural and metabolic consequences of consuming S&SEs particularly in semi-solid and solid food matrices. Furthermore, it should be acknowledged that differences between acute and longer-term effects of S&SEs may not be the same and this needs investigating further.

This is precisely the challenge that we are addressing in the Phase 2 studies of Work Package 2 in the SWEET project. Phase 2 involves 5 double blind, cross-over trials across 5 intervention centres, where over 200 study volunteers will consume a sucrose-sweetened control product and 2 reformulated products based on the same food matrix but with no added sugar and sweetened with different modulations of S&SE. The products have been carefully developed in WP1 to cover bakery (e.g. cake and biscuits), dairy (e.g. yoghurt), confectionary (e.g. chocolate) and breakfast cereal food groups.

The objective of these studies is to evaluate both acute (1-day) and repeated (two-week, daily) effects of a diversity of existing and/or novel combinations of sweeteners and sweetness enhancers (S&SEs) on metabolic, sensory, neuro-behavioural and microbiota-mediated processes involved in satiety, consumer preference and health, and examine mechanistic processes, genetic background, safety issues and psychological drivers. The full protocol for Phase 2 can be accessed for free from BMJ-Open (Gibbons et al. 2022).


Gibbons C, O’Hara B, O’Connor D, et alAcute and repeated impact of sweeteners and sweetness enhancers in solid and semi-solid foods on appetite: protocol for a multicentre, cross-over, RCT in people with overweight/obesity – the SWEET Project BMJ Open 2022;12:e063903. doi: 10.1136/bmjopen-2022-063903