The headline result of SWITCH is that consumption of NNS versus water was, at the very least, not disadvantageous to weight management. To understand how this result relates to hypothesised effects of NNS, it is necessary to unpick more details of the trial. To be eligible for inclusion, participants had to be consuming ‘regularly more than three cold beverages per week (water, NNS, or sugar-sweetened; NNS and sugar sweetened beverages had to be <2 L per day)’ [2]. For the 52 weeks, participants were asked to consume at least two 300 ml servings per day of their assigned beverage (NNS beverages or water, which could be carbonated or uncarbonated, and which were delivered, free-of-charge, to the participants’ homes). Participants randomised to the water group were asked to abstain from all NNS beverages (including adding NNS to e.g., tea and coffee). All participants were permitted to consume SSBs, and water, but the weight-loss programme included a recommendation to limit consumption of SSBs. In sum, therefore, depending on their assignment, individually, participants could have increased, decreased, or maintained their consumption of sweet-tasting, flavoured beverages. In actuality, the water and NNS beverages participant groups reduced (from similar baselines) their sugars consumption to a similar, substantial extent (39%). At the same time, ‘sweetener consumption’, and therefore presumably sweetness exposure, was reduced in the water group, but not changed in the NNS beverages group. That is, contrary to the sweet-tooth hypothesis, there, was not a greater reduction in sugars intake in the water group commensurate with their reduced sweetness exposure.

A further feature of SWITCH is that a quarter of the participants were NNS beverage ‘naïve’; that is, in the 5-years prior to the trial, they had, at most, consumed NNS beverages infrequently. Analyses presented in Harrold and colleagues’ article [1] indicate that weight loss for participants assigned to NNS beverages in the trial did not differ in respect of NNS naïveté. This is contrary to the sweet-taste confusion hypothesis, because it predicts that increased exposure to sweetness mis-matched with energy intake should acutely undermine appetite control in this group (i.e., place an additional burden on them), compared with the NNS beverage non-naïve participants who had pre-existing experience of this potential disadvantage.

The sweet-tooth and the sweet-taste-confusion hypotheses are hard to test experimentally, though the evidence against them, including these results from SWITCH, is growing e.g., refs. [6,7,8].