Highlights:
- A new review study concludes that low/no calorie sweeteners use is one easily adopted dietary strategy that can help obtain a modest weight loss, improve adherence to the diet, induce sensory-specific-satiety for sweet foodstuff, and facilitate weight loss maintenance.
- Low/no calorie sweeteners can only modify one single aspect of energy intake: i.e. calories from added sugars. They will exert an effect on body weight if a reduction in daily energy and sugars intake is sustained over time.
- Significant effects on body weight are most likely to be seen in persons who used to consume large amounts of sugar-sweetened beverages and substitute sugary drinks with their low/no calorie sweetened alternatives.
The scientific debate over the role of low/no calorie sweeteners in weight control and obesity has been reinforced after the publication of a controversial guideline by the World Health Organization (WHO) challenging their role in weight loss.1 The controversy is a result of the different interpretation of the current evidence base but may also be driven by a lack of clear understanding of how sweeteners work. A new review study2 by Dr. France Bellisle, published in the journal Obesity Reviews, analysed the current literature to answer a simple question: how do low/no calorie sweeteners work in weight management?
Clarifying what low/no calorie sweeteners are and how they are used
To explore sweeteners’ mechanism of action, it is essential to first understand what these substances are and how they are used by the food industry. Low/no calorie sweeteners are food additives with diverse origin and physicochemical properties, but with a key common characteristic: they all have a much higher sweetening power compared to sugars, and thus, very small amounts are used to confer the desired level of sweetness to foods and drinks, while contributing very little or no energy to the final product. As such, low/no calorie sweeteners are used to displace added or free sugars in foods and beverages and subsequently decrease the energy density (calories) of these products while maintaining their sweet taste.
By understanding what low/no calorie sweeteners are, it becomes clear that none of the approved sweeteners has pharmacological type of properties. They are not weight loss drugs and should not be expected to lead to weight loss by themselves. So, how do they work?
Low/no calorie sweeteners can affect energy intake by reducing sugar calories
Low/no calorie sweeteners can modify one single aspect of energy intake: i.e. calories from added sugars. Consuming foods and beverages with lower energy load (i.e., fewer calories) in place of their regular versions can affect our overall energy intake and ultimately our body weight. For example, a 100 kcal reduction from sugar intake can be achieved by substituting 265 ml of sugar-sweetened soda with a low/no calorie sweetened alternative, or by choosing 280 g of low-fat yoghurt with sweeteners instead of the sugary version.
The calorie reduction achieved with the substitution of sugars with sweeteners can be substantial in beverages (e.g., sodas), significant in semi-solid foods (e.g., yoghurts), but more limited in solid foods (e.g., chocolate). This is because sugars have more functions than simply providing sweetness; they contribute to the bulk and texture, flavour and shelf life of food products, making sugar reduction in solid foods more complex. Therefore, substituting sugar-sweetened solid foods with an alternative with sweeteners will not lead to the same substantial calorie reduction as in beverage substitution.
A modest but robust weight loss effect consistently shown in intervention studies
Extensive clinical research, including a variety of intervention study designs, corroborates that low/no calorie sweeteners can lead to a modest but consistent weight loss of approximately 1-2 kg, when compared to sugars.3,4,5 Most clinical studies have examined the impact of sweeteners over the course of a few months, but randomised controlled trials with a duration of up to 2 years have indicated a similar beneficial effect size.
Their beneficial effect may be explained by energy balance equations, but further weight-related benefits of low/no calorie sweeteners include inducing sensory-specific satiety (i.e., exposure to sweeteners leads to a decrease in desire for the same taste attribute over a short period of time), improving diet compliance, and facilitating weight loss maintenance. Evidence from high-quality original works suggests that low/no calorie sweeteners may contribute to a sustained beneficial change in the energy balance equation directly (by reducing the energy density of a range of products) and indirectly (by facilitating long-term diet adherence and providing sensory specific satiety, while weight loss itself is likely to increase appetite for sweetness).
In relation to their long-term role in weight control, the physiology of weight regulation should be taken into account. It is well-established that a few months/ years after the introduction of a permanent change in energy intake, irrespective of the dietary means, the resulting effect on weight reaches an asymptote, meaning that the rate of weight loss slows down over time as the reduction in body weight, per se, progressively decreases energy needs. Eventually, a new equilibrium is reached between energy intake and expenditure, and body weight is stable, even while the original reduction in intake is maintained. To allow further weight loss, a negative energy balance should be re-established by further reducing intake and/or increasing expenditure. Still, that doesn’t mean that the beneficial effect of sugar substitution with sweeteners does not exist anymore. According to the energy balance equation, a return to full-sugar products would increase daily energy intake and affect body weight with the same predictable time-course: a rapid increase in weight slowly reaching an asymptote over time. That is probably why long-term clinical studies have indicated another benefit of low/no calorie sweeteners’ use, i.e., in maintaining weight loss more efficiently over time.6,7
Is this a “major” or “minor” effect?
The WHO has recognised the weight loss impact of low/no calorie sweeteners as assessed in clinical studies, but considered it to be a “minor” effect. Is this indeed a “minor” effect in the current obesogenic world where no strategy to date has been effective in reversing or even halting the obesity epidemic?
Obviously, the weight loss effect attributed to sweeteners per se is lower compared to weight loss programs affecting the whole diet and lifestyle, new medications, or bariatric surgery. However, it should be reminded that, contrary to whole dietary approaches, sweeteners can only modify one single aspect of energy intake, i.e. sugar calories, and that they are food ingredients, not drugs. The comparison is uneven (e.g., one single dietary tool versus a whole dietary approach or a medicine).
France Bellisle notes that whether the contribution of sweeteners to weight change (1-2 kg) is considered “minor” or “major” is a matter of individual interpretation. However, one aspect that distinguishes the use of low/no calorie sweeteners from other dietary strategies is that their use makes diet more palatable, allowing consumers to keep enjoying sweet taste. In turn, the use of low/no calorie sweeteners may facilitate adherence to calorie-reduced diets, which is important given that compliance is often identified as a crucial factor of success in weight control efforts.
Who could see more benefits with low/no calorie sweeteners’ use?
Significant effects of substituting sugar with low/no calorie sweeteners are most likely to be observed in persons who consume large amounts of sugar-sweetened beverages. As sugary drinks are a major source of added/ free sugars in high consumers, and the energy gap between full-sugar and “light” versions is highest in beverages, replacing sugar-sweetened drinks with low/no calorie sweetened beverages can be an effective strategy for achieving a substantial (even “major”) decrease in energy intake. Persons who do not consume a lot of sugary beverages will have a smaller potential effect when they substitute semi-solid or solid foods containing sugars with sweeteners, as the energy gap between the two versions is more limited, and hence, the overall calorie reduction smaller.
Take home message
As a dietary tool affecting a single aspect of energy intake, low/no calorie sweeteners cannot be expected to make a major difference in the global obesity rates. Similarly, they cannot be expected to have the same effectiveness with weight loss drugs or comprehensive weight loss programs including dietary, behavioural and physical activity interventions. However, the use of low/ no calorie sweeteners is one easily adopted, helpful dietary tool that can be part of all types of weight loss strategies, facilitating adherence to more palatable, calorie- and sugar-reduced diets that do not deprive individuals of sweet taste.
With obesity classified as a global epidemic and public health recommendations stressing the need to limit the intake of added/ free sugars, the way that low/no calorie sweeteners can assist individuals in managing their weight more effectively should be communicated clearly.