Does thinking that you are fat make you fat?

What we have suspected for some time - that constantly being bombarded with pictures of skinny people - may have a negative impact on our own thoughts, feelings and behaviour after all. Indeed, despite the images of super-thin bodies become omnipresent and infecting more and more of our waking moments, at a population level we are becoming more overweight and obese.

It looks like the kind of comparison that this ubiquitous imagery could encourage has a significant impact. Researchers at the Norwegian University of Science and Technology have found that normal weight teenagers who perceive themselves as fat are more likely to grow up to be fat. This is the first study to look at the relationship between perceived weight and actual weight in a longitudinal study of teenagers and young adults. 1196 normal range weight adolescents were followed up as young adults 11 years later. After controlling for covariates such as age, sex etc, adolescents who perceived themselves as overweight had a significantly larger weight gain into young adulthood that adolescents who perceived themselves as having a normal weight (0.66 BMI units; 3.46cm waist circumference). This was unrelated to levels of physical activity.

Thinking that you are fat as an adolescent - even when you are not - can lead to become significant fatter as an adult. 22% of girls rated themselves as overweight as teens, compared to 9% of boys - this might be due to media focus on body image focusing on girls - especially at the time that these young adults were teens. Worryingly, 59% of girls who felt fat as teens became overweight as adults. If we consider waist circumference, 78% of teens who initially perceived themselves as fat later became overweight as adults.

It's difficult to know what causes the increase in weight, and it is likely to be complex. We know that stress can cause an increase in weight - the authors suggest that the psychosocial stress of not being your ideal body type (wherever that idea may come from), as well as thinking of yourself as overweight can lead to weight gain. Perhaps another explanation is that seeing yourself as fat can lead to skipping of meals - and we know that dropping breakfast has been linked to obesity through various mechanisms.

The lesson I take away from this is the importance of anchoring our self-perceptions of weight in fact, rather than glossy imagery that we come across every day. This is even more important in the crucial developmental years of adolescence, where we try to understand and balance the plethora of information telling us how we should be adults and how to be acceptable to ourselves and others. Challenging this information, and developing alternate pathways through healthy diet, exercise and mental wellbeing is so important, and is a set of skills that needs to be taught.