Pages within the "support" section:

12. Calculating the net health impact of a dietary change

In a risk-benefit assessment the focus is on evaluating the net health impact of a dietary change or intervention, represented as a change from a reference scenario to an alternative scenario.

The net health impact in DALYs may be calculated as:

where

= sum of DALY losses for reference scenario

= sum of DALY losses for alternative scenario

The summation in these equations is over both health effects (within individuals) and individuals (to provide population totals).

As DALYs represent health loss, a positive result for implies that changing to the alternative scenario has an adverse health impact overall, whereas a negative   implies the alternative scenario is beneficial.

Analogous calculations can be done with the QALY losses from Equations (3) and (4), leading to an estimate for . Then as a final step, the net health impact can be expressed as a change in QALYs (rather than QALY losses):

 

As QALYs represent health loss, a positive result for implies that changing to the alternative scenario has an beneficial health impact overall, whereas a negative   implies the alternative scenario is adverse.

The results for both DALYs and QALYs are subject to the same limitations as before, that the effects have been considered in isolation. How these uncertainties can be taken into account in interpreting the results is discussed in section 15.1.