There are two aspects. There is obviously the impact of the tax, which will cause substitution. We have seen it in Mexico. They have introduced an excise tax on sugar, and people are switching. Because sugary drinks have no nutritional value in fact for low-income families, switching to tap water is probably the best choice. However, there are obviously other choices. Cow's milk, unsweetened almond milk, or other milk substitutes are also attractive.
The most important aspect is the fund that would be created through the levy, which would have as its focus to help deal with issues of food insecurity, for instance, subsidies for whole fruits and vegetables. Think about it as a voucher or a prescription for the healthy foods in groceries, and then you're helping to address one of the fundamental issues, which is that people who have lower incomes have the worst health outcomes.
When we think about the social determinants of health, we know that lower socio-economic status is among the most intractable things to change. It impacts mortality and it impacts quality of life.
If you implement things like healthy foods in schools for all children, you're addressing these questions in a way that palliates the impact of lower socio-economic status. You get both substitution and the benefits of the expenditures through the fund created by the excise tax.