So many people blazing right past the nuance and calling this study wrong. In fairness, that title doesn't do any favors.

1. There is obviously a correlation between obesity and mental health disorders. The study doesn't deny this.

> Children with obesity are more likely to be diagnosed with depression, anxiety, or attention-deficit hyperactivity disorder (ADHD). But the nature of the relationship between obesity and these mental health conditions is not clear. Obesity might contribute to mental health symptoms, or vice versa. Alternatively, a child's environment might contribute to both obesity and mood and behavioural disorders.

2. All the children studied were 8 years old, and from Norway. This means results may differ for different age groups and different cultures. (Right, Americans? You weren't thinking this study was all about you, right?)

> Dr Hughes and colleagues examined genetic and mental health data from 41,000 eight-year-old children and their parents from the Norwegian Mother, Father, and Child Cohort Study and Medical Birth Registry of Norway. They assessed the relationship between children's body mass index (BMI) – a ratio of weight and height – and symptoms of depression, anxiety and ADHD.

> ...

> "At least for this age group, the impact of a child’s own BMI appears small. For older children and adolescents, it could be more important," said Neil Davies, Professor at University College London (UCL)

3. The study focuses almost entirely on the link between BMI and symptoms of depression, anxiety, or ADHD.

> The analysis found a minimal effect of a child's own BMI on their anxiety symptoms. There was also conflicting evidence about whether a child's BMI influenced their depressive or ADHD symptoms. This suggests that policies aiming to reduce childhood obesity are unlikely to have a big impact on the prevalence of these conditions.

4. The conclusion does not rule out a correlation between obesity and mental health. The conclusion is that there are underlying environmental causes at play that are better targets to fix both problems. Fixing obesity crises may not improve mental health issues, and fixing widespread mental health issues won't necessarily improve obesity statistics.

> "Our results suggest that interventions designed to reduce child obesity are unlikely to make big improvements in child mental health. On the other hand, policies which target social and environmental factors linked to higher body weights, and which target poor child mental health directly, may be more beneficial," Hughes concluded