Researchers linked the development of depression to elevated levels of one of the amino acids. Animal experiments and human observations have suggested that the amount of proline acid circulating in human plasma depends on the severity of depression.
A growing body of scientific literature is linking the gut microbiome to symptoms of depression. However, many of these studies have little to do with the association of certain bacterial populations or diet with major depressive disorder, leaving many questions about the biological mechanism that allows the gut microbiome to influence depression. And now a new study, conducted by scientists from King's College London, has taken a significant step forward in filling the existing gaps.
British researchers have shown in a variety of animal models that there is a possible relationship between the severity of depression and serum levels of the amino acid proline. And this indicator, as the study found, depends on both nutrition and the activity of proline-metabolizing bacteria in the intestine. For the first time in medical history, a link has been demonstrated between proline levels and depressive behavior.
Previous studies have concluded that proline, along with other dietary components, is likely to play an important role in the development of major depressive disorders. But now it has been established that elevated levels of proline are associated not only with significant, but also with moderate depression. Therefore, anti-depression drugs may be targeted specifically to target this amino acid. (READ MORE) 
King's College London
Medicine
one of the largest, oldest and most prestigious universities in England, the founding college of the University of London