Mental illness is expected to become one of the world’s most serious health problems by 2020. Similarly, obesity and its complications are a worldwide scourge. The pathophysiological pathways associated with mental disorders and obesity are the same. They particularly include chronic inflammation¹. People with more mental disorders are often overweight or obese². Moreover, many data show that the inflammatory response potentially contributes to the pathophysiology of depression³. More than 50% of mental illnesses in adults occur before the age of 14 (vs 25% before the age of 24)⁴. Thus, adolescence is a decisive period of significant biological changes for obesity and mental health. Australian researchers recently studied the relationship between diet, adiposity, inflammation and mental health in 843 adolescents between the ages of 14 and 17 who participated in the Western Australian Pregnancy Cohort (Raine) Study.

Recording of eating habits and biological tests

In order to determine the participants’ eating habits, a Food Frequency Questionnaire (FFQ) was completed by the parents with the help of their children. Two dietary patterns were thus identified:

• A ‘Western’ dietary pattern characterised by high intake of red meat, takeaway, refined foods and confectionery;
• A ‘Healthy’ dietary pattern characterised by high intake of F&V, whole grains and fish.

The BMI of the participants was measured at the ages of 14 and 17 and a blood test was conducted at the age of 17 to determine the level of inflammatory markers (leptin and hs-CRP). To assess mental health, two tests were used at the ages of 14 and 17: a test measuring depression in young people and a test to assess internalisinga and externalising problems in adolescents.

A diet rich in F&V protects against inflammation

Structural equation modellingb was used to test the following hypotheses:

• Hypothesis 1: Dietary patterns and BMI at the age of 14 predict BMI and inflammatory markers at the age of 17:
  The results in 14-year-old adolescents showed a significant relationship between a ‘Western’ diet and high BMI. This dietary pattern at the age of 14 was also significantly associated with high BMI and high levels of leptin and hs-CRP at the age of 17. On the other hand, a ‘Healthy’ diet at the age of 14 was significantly associated with low BMI and low levels of leptin and hs-CRP at the age of 17. Thus, BMI at the age of 14 was able to predict BMI and levels of leptin and hs-CRP at the age of 17.
• Hypothesis 2: Inflammation at the age of 17 predicts depressive symptoms and internalising and externalising problems:
  BMI as well as leptin and hs-CRP levels at the age of 17 were positively associated with depressive symptoms and with internalising and externalising problems.
• Hypothesis 3: Depression at the age of 14 predicts dietary patterns at the same age: The results showed that depression occurring at the age of 14 did not predict dietary patterns at the same age. This hypothesis can thus be ruled out.

  However, the fact of having mental health problems at the age of 14 was a significant risk factor for mental illness at the age of 17.

Magnesium, fibre, flavonoids and carotenoids influence inflammatory markers

The results of this analysis confirm that a healthy diet rich in F&Vis associated with lower rates of obesity, inflammation and mental disorders in adolescents. It was shown that certain nutrients such as magnesium, fibre, flavonoids and carotenoids in fruits and vegetables are capable of reducing the level of inflammatory markers⁵.

a. A type of emotional and behavioural disorder that consists in internalising one’s problems.
b. A diverse set of mathematical models, computer algorithms and statistical methods that fit networks of constructs to data; often useful in the social sciences because of its ability to impute relationships between unobserved constructs (latent variables) from observable variables.

Based on: Oddy WH, et al. Dietary patterns, body mass index and inflammation: Pathways to depression and mental health problems in adolescents. Brain Behav Immun. 2018 Mar; 69:428-439.