Unfair comparison

Dissimilar expectations

Look out for comparisons of nutrition interventions where people knew which intervention they received, and knowing this could have changed how they felt or behaved.

People who are given a food, drink, diet or nutrition supplement may feel better (for example, they may have less stomach pain) because they believe they are getting a superior nutrition intervention and expect that it will make them feel better. This can happen even if the nutrition intervention isn’t actually better than the other one it is being compared to. This is called a “placebo effect”.

Knowing which nutrition intervention they got and having expectations about it can also change the way people behave. For example, someone who is told that drinking apple cider vinegar will help them lose weight may also start eating less other foods and exercising more. So they may lose weight because of those changes, rather than because of the apple cider vinegar per se.

One way of keeping this from happening is not to let the people who receive the interventions know which intervention they got (to “blind” them).

REMEMBER: Think about whether the people in the comparison groups knew which nutrition intervention they received and, if so, whether this may have changed how they felt or behaved.