New-fangled fasting trends may have thrown doubt on the adage that breakfast is the most important meal of the day.

But research shows a morning bowl of cereal such as Cheerios may lower the risk of depression.

People who skipped breakfast were found to have a 70 per cent higher risk of the blues – and there was also a near threefold increase in the risk of attention deficit hyperactivity disorder (ADHD).

Both links are put down to changes in brain chemicals that occur when food is eaten after nocturnal fasting.

In the new study, researchers used data from more than 800,000 people, including nearly half a million from the UK, to compare breakfast cereal intake with the risk of various mental illnesses. Results show that skipping breakfast was associated with a 70 per cent increase in the risk of depression, with those missing it having a 2.57 times higher risk of ADHD.

Just how breakfast could have such an effect is currently unclear. One theory suggested by the researchers is that blood sugar levels drop during sleep, while levels of the stress hormone cortisol increase. Higher levels of cortisol may reduce the effectiveness of the brain chemicals serotonin and dopamine, both of which are involved in the regulation of mood and emotions.

Eating breakfast, suggest the researchers, reverses this process by providing nutrients to the central nervous system that counteract the adverse effects of nocturnal fasting. Low levels of serotonin are believed to be linked to depression, and studies suggest that ADHD could be linked to low levels of dopamine, which helps to control movements and emotions.

Researchers from Chongqing Medical University, China, whose study appears in the journal BMC Psychiatry. said: ‘Our findings suggest that omitting breakfast may serve as a potential risk factor for both depression and ADHD.

‘These findings warrant further investigation into the underlying mechanisms and emphasise the importance of regular breakfast consumption for mental and physical wellbeing.’