Artificial Sweetener Fails to Fool the Brain

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The implicit advantage that artificial sweeteners have over sugar is that, being virtually devoid of calories, they’re a better option for those wanting to control their weight. However, as I described in a recent blog post here, there is no good evidence that artificial sweeteners promote weight loss compared to sugar. Plus, there is actually some evidence that artificial sweeteners may promote weight gain: in one study (referred to in the blog post linked to above), rats eating artificially-sweetened yoghurt were found to eat more and get fatter than rats fed yoghurt sweetened with sugar.

Some evidence has suggested that artificial sweeteners have the capacity to stimulate appetite, so I was very interested to read this week about a study which looked more deeply into the effect that artificial sweeteners have on the brain. In this study, women were given a drink a solution containing either the artificial sweetener sucralose (brand name Splenda) or sucrose (table sugar). As they drunk this their brain activity was monitored using what is known as ‘functional magnet resonance imaging’ (basically, this allowed researchers to see what parts of the brain are activated once individuals had tasted the sucralose/sucrose solution).

One part of the brain that the researchers focused on in this study is known as the ‘insula’. The insula is involved in the brain’s sensing of taste, and it also believed to play a role in enjoyment and the sensation of ‘pleasantness’. Interestingly, drinking sugar activated the brain regions involved in registering pleasure more extensively than drinking sucralose.

This difference was found despite the fact that individuals were unable to distinguish between sucrose and sucralose on the basis of taste. In other words, while individuals are unable to consciously distinguish between sugar and sucralose, the brain appeared to know the difference. And it appears that an artificial sweetener may simply not give the level of pleasure and satisfaction that may be derived from sugar. This, in turn, could lead individuals to seek satisfaction from other foodstuffs.

Now, if this is true of artificial sweeteners in general, then it might help to explain why rats eating an artificially sweetened food end up eating more and getting fatter than rats eating the same food sweetened with sugar. It might also explain why there is such a dearth of good evidence regarding the ‘benefits’ of artificial sweeteners with regard to weight control. The results of this study seem to suggest that you just can’t trick the brain into thinking it’s had something (sugar) when it hasn’t.


Frank GK, et al. Sucrose activates human taste pathways differently from artificial sweetener. Neuroimage. 2008;39(4):1559-69

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