Marion Nestle, Vani Hari, Michael Pollan; we have all seen messages from self-appointed "food police" telling us that sugary snacks are bad, GMOs are bad, everything except organic vegetables (they seem to believe those have no pesticides or genetic modification) is bad.

But they may be doing more harm than good, not just for public acceptance of science, but for the people they claim to want to help. The government is doing the same thing. They are increasing their use of public service announcements (PSAs) about the dangers of unhealthy eating. 

Nguyen Pham, Naomi Mandel, and Andrea Morales of Arizona State University write in the Journal of the Association for Consumer Research that these messages backfire among the public - and especially dieters.  While 'if anti-science food fad shills are against it, it must be okay' is usually a fine way to live life, for dieters that can be disastrous. The scholars found that one-sided know-it-all messaging led to dieters eating 39% more cookies after seeing a "food police" style message, compared to people who saw balanced diet messaging.

Mandel warns, "Our work shows that negative messages about unhealthy food will backfire among dieters. If you want to change what they eat, a more even-handed message that contains both positive and negative information is the way to go."  

The researchers conducted three studies to demonstrate that negative one-sided messages about food can lead to backfire effects. In the first study, 380 participants read a positive, negative, or neutral message about dessert. Dieters who saw the negative message had more positive thoughts about unhealthy foods, but non-dieters did not show any difference. Moreover, thoughts about healthy foods or non-food words were unaffected by the messages. "What these results show us," Pham explains, "is that rather than leading dieters to make healthier choices, these food police messages are actually making unhealthy foods even more enticing to dieters."

In the second study, 397 participants read a one-sided positive or negative about sugary snacks and then watched a short video while eating chocolate-chip cookies. Dieters who saw the negative message consumed 39% more cookies than dieters who saw the positive message. As in the first study, non-dieters were unaffected by the messages about food. 

The third study focused on snack choice and examined how reactions to two-sided messages, which contain both positive and negative information about food, might reduce the backfire effects. Among 324 participants, dieters who saw the negative message chose 30% more unhealthy snacks than dieters who saw the positive message, while dieters who saw the two-sided message chose 47% fewer unhealthy snacks than those who saw the negative message.