Faulty logic

“No comparison needed!”

Unless a nutrition intervention is compared to something else, it is not possible to know what would happen without it.

Without a comparison, it is difficult to say that a nutrition intervention is the reason something happened.

If people get better or worse after following a nutrition intervention, you are comparing how they were after this intervention to how they were before it. The problem with such “before and after” comparisons is that you don’t know what would have happened if the person had not followed that intervention.

For example, if a group of people with headaches followed a gluten-free diet and their headaches got better, it might seem like this diet helped. However, their headaches probably would have gotten better without the gluten-free diet. The best way to find out if the gluten-free diet made a difference would be to compare one group of people with headaches who followed the gluten-free diet to another group with headaches that did not – and to make sure that it was a fair comparison of interventions.

BEWARE of nutrition intervention claims when you don’t know what the comparison was, and when they are based on “before and after” comparisons.

REMEMBER: Ask what the nutrition intervention was compared to, and whether it was a fair comparison of interventions.