Artificial sweeteners such as saccharin and aspartame have the ‘promise’ of being better than sugar for weight control because, although sweet, they contain virtually no calories. It’s a nice theory, though the reality is I cannot find one single properly conducted (randomised, controlled) study in humans exists in the scientific literature to support this. Now, there’s only two potential explanations for this. Either such studies have not been done, or one or more studies have been done but have not been published.
I actually don’t know which of these is the truth, but I am aware of previous research in animals which suggests that artificial sweeteners are not all they’re cracked up to be. In one study, rats were fed with either saccharin or sugar-sweetened yoghurt in conjunction with their normal diet . Compared to those eating sugar-sweetened yoghurt, the rats eating saccharin-laced yoghurt consumed more calories and got fatter too. The authors of this study concluded that “…using artificial sweeteners in rats resulted in increased caloric intake, increased body weight, and increased adiposity [fatness]”, adding that “These results suggest that consumption of products containing artificial sweeteners may lead to increased body weight and obesity by interfering with fundamental homeostatic, physiological processes”.
Recently, I came across another animal study which gives me cause for concern. Here, rats were split into three groups, each of which was given unlimited amounts of standard rat food (chow) and water . The groups were also given access to yoghurt sweetened with either saccharin, aspartame of sugar (sucrose).
In short, here’s what the results showed:
Rats eating the artificially sweetened yoghurt ate more chow than those eating the sugar-sweetened yoghurt. In the end, overall calorie intakes were the same. This suggests that when reduced-calorie foodstuffs are consumed, there can be a natural drive to seek those ‘missing’ calories elsewhere.
What was really interesting about this study, though, was that the rats consuming artificial sweetener gained weight at a rate faster than those eating the sugar. But the calorie intakes were essentially the same, meaning that change in weight could not be explained by differences in food intake. The authors cite another study from 2010 which essentially found the same thing .
It’s not clear what mechanisms are at work here. However, it was noted in a previous study  that rats experienced a boost in their temperature after eating sugar-sweetened food which was not present after eating saccharin-sweetened food. This suggests that consuming calories from sugar boosts the metabolism in a way that artificial sweeteners may not.
We do not know if these results apply to humans. However, one good thing about animals is that do give researchers the ability to strictly control and measure what they eat and the impact on weight. Here again we have evidence which shows that artificial sweeteners can stimulate weight gain. In the absence of good human evidence to the contrary, I’d say the evidence suggests that artificial sweeteners are unlikely to deliver on their weight loss promise.
1. Swithers SE, et al. A role for sweet taste: Calorie predictive relations in energy regulation by rats. Behavioral Neuroscience. 2008;122(1):161-173
2. De Mats Feijo F, et al. Saccharin and aspartame, compared with sucrose, induce greater weight gain in adult Wistar rats, at similar total caloric intake levels. Appetite 2013;60(1): 203–207
3. Polyák E, et al. Effects of artificial sweeteners on body weight, food and drink intake. Acta Physiologica Hungarica 2010;97(4):401–407