A recent study involving PHI|Lab‘s Laura Cornelsen and Richard Smith, published in the British Medical Journal modelled the effect of a 20% price increase on sweet snacks (chocolates, confectionery, biscuits) and found it could potentially lead to on average reduction in energy by about 8,900 kcal on average per person. This in turn could lead to an average weight loss by 1.3kg over one year with associated reduction in obesity prevalence by 2.7 percentage points. In comparison, a similar price increase on sugary drinks would lead to about 203g weight loss over one year – a substantially smaller effect.
The underlying reason for this relatively large difference is behind the simple fact that sugary drink consumption tends to concentrate among children, whereas sweet snacks are consumed throughout the life course. The graphs below show the National Diet and Nutrition Survey estimates on how these two food groups contribute to overall energy and free sugar intakes. It can be pretty easily observed that among adults (>19 years old) sweet snacks contribute to ~9-12% of total energy intake and between 20-25% of sugar intake while the contribution of sugary drinks to total energy is <2% of total energy and <13% of sugar intake.
So was SDIL badly targeted? The answer is no because what the below figures show is that it would be wrong to measure the impact of SDIL at population level because at best we would find very small effects. Instead, it is crucial to look at the effects of SDIL among children and teenagers in particular.