Of course the amount of sugar they consume from soft drinks will decrease if they’ve changed all the soft drinks to contain aspartame instead of sugar.

The question is does this actually improve people’s health?

There are lots of suggestions that artificial sweeteners are harmful to health in their own ways

https://www.healthline.com/nutrition/artificial-sweeteners-and-weight-gain#:~:text=Several observational studies on artificial,than weight loss ( 16 ).

And the evidence they reduce weight compared to sugar is not clear cut.

This seems like a study designed to make the sugar tax seem like a good thing, but it misses the crucial point, which is whether this improves health.

They’ve failed to mention that the decrease in sugar consumption will correspond with an increase in aspartame consumption