To our knowledge, this is the first systematic review of randomized trial evidence that examines comparative sweetener effectiveness in diabetic, overweight/obese, and healthy populations. Despite tremendous interest in hypocaloric sweeteners as a potential tool to prevent obesity and its complications, we found little evidence to support their health benefits as compared to caloric alternatives. Based on analyses of two trials, we found that the inclusion of non-caloric sweeteners in the diet resulted in reduced energy intake compared to the caloric (sucrose) groups - approximately 500 kcal/day less over 10 weeks or 250 kcal/day over 4 weeks. The longer of these trials found that those in the non-caloric sweetener group also had a decrease in BMI compared to an increase in BMI in the sucrose group (-0.40 versus 0.50 kg/m2
, and -1.00 versus 1.60 kg, respectively) [63
]. Given that the control group was asked to ingest supplemental calories in addition to their regular ad lib
diet, a BMI reduction of approximately1 kg/m2
over 10 weeks (or 0·1 kg/m2
/week) may be overly optimistic. However, even a reduction in BMI of 0.05 kg/m2
/week would be clinically relevant if sustained for a year or more. The remaining analyses comparing non-caloric and caloric sweeteners were non-significant.
• 53 randomized controlled trials were included - all small and largely short-term (only 13 trials with ≥1 week durations)
• 2-hour blood glucose (mixed evidence, τ2 = 3.66 (95% CI 1.66,7.31): fructose versus sucrose (MD -0.54 mmol/L (-1.06,-0.03)), fructose versus glucose (-0.89 mmol/L (-1.21,-0.59)), fructose versus other sugars (-0.85 mmol/L (-1.47,-0.21)) in non-diabetic participants
• 2-hour blood glucose (direct evidence): fructose versus glucose (-4·81 mmol/L (-6.34,-3.29), I2 = 0%, τ2 = 0 (0,7.47), 5 trials in 52 diabetic participants)
• change in BMI: non-caloric mixture versus sucrose (MD -0.9 kg/m2 [-1.5,-0.4], in 41 overweight participants, over 10 weeks), non-caloric aspartame versus sucrose (-0.3 kg/m2 (-1·1,0·5), 133 healthy participants, over 4 weeks)
• energy intake (over one day): non-caloric aspartame versus sucrose (-283 kcal (-414,-153), 133 healthy participants, over 4 weeks), non-caloric mixture versus sucrose (-491 kcal (-806,-177), 41 overweight participants, over 10 weeks)
• total cholesterol: FOS versus sucrose (0.26 mmol/L (0.03,0.48), I2 = 0%, τ2 = 0 (0,0.01), 2 trials with a total of 12 healthy and 10 type 2 diabetic participants, over 4 weeks)
Head-to-head comparisons between saccharides did not identify any statistically significant differences. The confidence limits of these results either included minimally important differences or the group sizes were too small (< 30) to have good estimates of standard deviation [74
]. The one exception was the comparison between sucrose and FOS, which suggested that total cholesterol was reduced to a greater extent with sucrose than with FOS. However, the confidence intervals for this analysis included values that were not clinically relevant (0.03 to 0.59 mmol/L). There was no evidence that HFCS or fructose increased levels of cholesterol relative to other sweeteners.
Although we found that fructose reduced 2-hour blood glucose concentrations by 4.81 mmol/L compared to glucose in diabetic participants, data comparing non-caloric and sugar alcohols to the more commonly used sucrose or HFCS were inconclusive. Contrary to perception and current recommendations, no substantive evidence describing important long-term benefits of hypocaloric sweeteners for diabetic patients were identified. Also, despite popular belief, no high-quality RCT evidence was found indicating that fructose causes or exacerbates hypertriglyceridemia [6
Although the identified trials were numerous, they were very small and largely short-term. We found 13 trials with participant follow-up longer than 1 week and group sizes ≥ 10: 3 that compared non-caloric sweeteners to sucrose, and 10 that were head-to-head comparisons of saccharides. Ten of 13 trials had a Jadad score of 1 and none adequately concealed treatment assignment prior to assignment. Although blinding the participants would have been impossible in many of the trials due to taste differences between sweeteners [63
], the reporting of important design descriptors were largely absent, indicating a substantial risk for bias [12
]. The longest trial was only 10 weeks - not long enough to determine whether substituting a non-caloric sweetener for a caloric sweetener is sustainable in daily practice. To detect an important reduction in weight over at least one year such as 2.5 kg/m2
(less than 0.05 kg/m2
/week) in a RCT would require a minimum of 85 participants (assumptions: 25% loss-to-follow-up, α = 0.05, power = 90%, SD = 3 kg/m2
Our network meta-analysis had several limitations: 1) the sugar alcohol and other sugar categories contained multiple sweeteners that are likely to have different blood glucose profiles thereby inducing heterogeneity, 2) power to detect inconsistency is limited by the number of trials included in each test, and 3) the back-calculation method used to detect inconsistency involved multiple tests thereby increasing the false-positive rate. However, we did not detect any inconsistency.
Another limitation was that only three studies restricted the total energy consumed by each participant. Therefore, participants may have supplemented energy lost with non-caloric sweeteners with other food products - sweetened or otherwise. However, it may be argued that this is a strength of the trials - in that they reflect what happens in real world self-management diet practices. Lastly, and perhaps most importantly, all studies were small, thereby underestimating standard deviation and as a result underestimating confidence interval widths and increasing the likelihood of false-positive findings [74
]. Despite this, the confidence intervals for many analyses were wide and did not exclude a minimally important difference. Small study bias (or publication bias) may also play a role in our findings concerning longer-term outcomes.
In theory, substituting non-caloric and lower caloric sweeteners for simple sugars should reduce energy intake and thereby the risk of obesity and its consequences. However, there are a number of reasons why increasing use of non-caloric and lower caloric sweeteners might not lead to the expected improvements in energy regulation. First, use of hypocaloric sweeteners might not induce weight loss even in the short term. For example, if reductions in calories due to sweeteners are offset by increases in caloric intake from other sources [75
], or offset by decreases in caloric expenditure [77
]. Although our data suggest that non-caloric sweeteners may lead to clinically relevant weight loss through reduced energy consumption, this conclusion was driven by a single trial with a total of 41 participants. Unlike caloric sweeteners (which may partially compensate added calories with reduced energy intake from other sources) [79
], non-caloric sweeteners are not known to suppress appetite, and therefore would not reduce the motivation to eat. Furthermore, it has been suggested that the psychobiological signals with non-caloric sweeteners may directly influence physiological regulatory mechanisms and thus further reduce their potential for reducing net energy intake [75
]. Second, if calorie reduction is not maintained, short-term reductions in weight due to the use of hypocaloric sweeteners might not be sustained. Third, it is possible though speculative that any health benefits due to weight loss from non-caloric sweeteners might be wholly or partially offset by currently unrecognized adverse events due to their use. The lack of data on the long-term benefits of non-caloric sweeteners means that it is currently impossible to determine whether these substances will improve public health.