Artificial or non-nutritive sweeteners (NNS) have been around for over a century, helping people to enjoy sweet foods and drinks without the unwanted calories or carbohydrate that can contribute to weight gain on the one hand and raise blood glucose levels on the other when consumed in excess. Few would argue that NNS do not raise blood glucose levels. Some are suggesting that non-nutritive sweeteners may not actually help people lose weight. A new systematic review helps shed some light. First of all, let’s look at the two major kinds of research study designs.
Randomised controlled trials (RCTs) are considered the “gold standard” research design as they can prove that intervention A causes health outcome B, while all other known factors (known as confounders) have been accounted for by randomisation. For example, two groups of people are given two different diets (X and Y) and their health status is measured over a period of several years. Individuals consuming diet X, which has a low GI, have a decreased risk of developing type 2 diabetes but individuals consuming diet Y, which has a high GI, increase their risk of developing diabetes. Using this example, we can conclude that high GI diets cause type 2 diabetes.
Observational studies. In these, large groups of people have a medical check-up, their dietary patterns are measured, and they are followed up regularly for long periods of time (e.g., 5-20 years). Unlike RCTs, observational studies can only provide evidence of statistical associations between foods/nutrients/dietary patterns and health – they cannot prove that something is actually caused by a particular food/nutrient/dietary pattern. Also, it is not possible to control for all confounders in observational studies, and our tools of observation (e.g., a food frequency questionnaire for measuring a person’s usual food intake) are imperfect.
Sweeteners and soft drinks. The recent systematic review by Paige Miller and Vanessa Perez in the United States looked at all published randomised controlled trials and observational studies and body weight. They found that use of low/no calorie sweeteners led to small but statistically significant improvements in body weight, body mass index (BMI), fat mass and waist circumference in randomised controlled trials. In prospective cohort studies, however, use of low/no calorie sweeteners was not associated with improvements in body weight or fat mass, but was in fact significantly associated with slightly higher BMI. They concluded “that substituting LCS [low/no calorie sweeteners] options for their regular-calorie versions results in a modest weight loss, and may be a useful dietary tool to improve compliance with weight loss or weight maintenance plans”.
Overall, the evidence from the randomised controlled trials is more powerful than the evidence from the observational studies.
Along similar lines, a new systematic review investigating the association between regular and NNS sweetened drinks in observational studies found that both were modestly associated with the risk of developing type 2 diabetes, with regular varieties being slightly more strongly associated than their NNS alternatives. The reason that NNS sweetened foods and drinks are associated with weight gain and risk of type 2 diabetes could be that people usually drink regular or NNS beverages when consuming other highly processed foods (crisps, chips (French fries), pizza, fried fish, chicken, burgers, savoury snacks, pastries, etc…), or alcohol (scotch and diet coke anyone?), and that it’s the overall poor dietary pattern that’s really to blame, not the sweeteners themselves.
The bottom line. Current scientific evidence indicates that non-nutritive sweeteners are safe to consume in moderate amounts, and that they can be useful for reducing some people’s consumption of added nutritive sweeteners, helping them to lose weight, provided they do not treat themselves with other highly processed foods and drinks as a reward for avoiding the added sugars!