Meet Tim: he is an 8-year-old boy, living in the Netherlands with his parents and younger sister. A couple of years ago, Tim was diagnosed with Attention Deficit Hyperactivity/Impulsivity Disorder (ADHD). His psychologist recommended to participate in the TRACE study: this study examines the short- and long term effects of dietary treatments in children with ADHD. In addition, the TRACE-BIOME study examines the underlying mechanisms of a dietary treatment. For this, we collect blood, stool, and saliva samples and we perform a fMRI. These measurements might, among other things, shed light on the role of the brain-gut-axis.

But what’s it like to participate in a scientific study? First of all, Tim was allocated to one of the two TRACE dietary treatments: an elimination diet or a healthy diet. Tim was allocated to the elimination diet. If we want to know if this diet is effective for Tim, we have to do a lot of different assessments (Figure 1).

Figure 1: assessments TRACE study








Before the baseline, 5 week and 1-year assessments, a couple of measurements already take place:

  • Tim wears an Actigraph one week before the assessment, which measures motor activity and sleep-wake rhythm;
  • Parents collect a stool sample from Tim in which his microbiota can be assessed;
  • Parents and teachers fill out different questionnaires about Tim’s behavior, but also about, for example, parenting styles;
  • Parents keep track of a food diary: what does Tim eat during two weekdays and one weekend day?

Before starting the elimination diet, Tim’s parents have a consult with one of the TRACE dieticians, so that they can prepare changing the diet of Tim. Then, it is time for the baseline assessment. Tim and his mother meet the researcher at the hospital for the blood venipuncture. He also has to chew on a cotton pad to collect a saliva sample. After this, they walk to Karakter which is a center for Child and Adolescent Psychiatry. The researcher measures his weight, length, blood pressure and heart rate. Next, Tim has to perform a task on the laptop which he really likes! This task assesses cognitive functions such as sustained attention, working memory, and cognitive flexibility. After the computer task, there is time for a break. Next, they start with behavioral observation. In this task, Tim first plays with his mother and then with the researchers. The different tasks try to elicit ADHD symptoms and emotion (dys)regulation behavior. Finally, the MRI researcher takes Tim and his mother to the fMRI scanner in which he has to do two different tasks. All in all, the assessment takes about 4 hours.

After 5 weeks of the diet, it is time for the second assessment which is the same as the baseline assessment. The researcher has calculated, based on the parent and teacher questionnaires, if there is a significant response to the diet. Tim shows a 40% reduction of ADHD symptoms, which is a significant response! Therefore, they continue the diet. After 4 and 8 months of the diet, his parents receive some online questionnaires. Finally, after one year they are invited for the final assessment, which is again the same as the baseline assessment (without the fMRI).

The following movie explains the assessments described above, in Dutch: 

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Recently, I participated in the Radboud Talks 2019, a scientific pitch competition, where I was lucky to be one of the eight finalists.

Why Radboud Talks? It is a perfect opportunity to share my work/ideas with the world and to gain more experience regarding presentation skills. They organized two workshops beforehand, where I had the opportunity to learn presentation techniques from professionals (actors and science communication advisors). We also received a lot of feedback, so I really learned a lot about how to present my scientific work to a general audience.

Below you can find the video from the preliminaries based on which I was chosen as a finalist. There you can hear about my research project which is about gut bacteria and their potential role in ADHD (Attention Deficit Hyperactivity Disorder). ADHD is a common worldwide neurodevelopmental disorder. Every person with ADHD has a unique combination of symptoms and challenges. Importantly, it has a significant social impact on patients’ lives, causing disruption at school, work and relationships. Despite its societal importance, progress in understanding disease biology has been slow.


The study of the human microbiome has become a very popular topic, because of their revealed importance in human physiology and health maintenance. Numerous studies have reported that gut bacteria may have an effect on our mental health. Some studies showed a potential role of gut bacteria in a psychiatric disorder like depression, autism or Parkinson (1). Above all, diet showed to have a profound effect of ADHD symptoms. This was earlier described in this blog: and we know that diet is one of the main factors influencing gut bacteria. Taking all together, I am curious (and investigating) if gut bacteria play a role in ADHD and if yes what kind of effect do they have on ADHD symptoms.

Bastiaanssen, T., Cowan, C., Claesson, M. J., Dinan, T. G., & Cryan, J. F. (2018). Making Sense of … the Microbiome in Psychiatry. The international journal of neuropsychopharmacology22(1), 37–52. doi:10.1093/ijnp/pyy067


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Our body is colonized by trillions of microorganisms that are important for vital processes. Gut microbiota are the microorganisms living in the intestinal gut and play an essential role in digestion, vitamin synthesis and metabolism, among others. The mouth and the large intestine contain the vast majority of gut microbiota whether the stomach only contains few thousands of microorganisms, especially due to the acidity of its fluids. Microbiota composition is constantly changing, affecting the well-being and health of the individual.

Each individual has a unique microbiota composition, and it depends on several factors including diet, diseases, medication and also the genetics of the individual (host) (Figure). Some medicines, especially antibiotics, reduce bacterial diversity. Strong and broad spectrum antibiotics can have longer effects on gut microbiota, some of them up to several years. Genetic variation of an individual also affects the microbiota composition, and the abundance of certain microorganisms is partly genetically determined by the host.

The main contributor to gut microbiota diversity is diet, accounting for 57% of variation. Several studies have demonstrated that diet’s composition has a direct impact on gut microbiota. For example, an study performed on mice showed that “Western diet” (high-fat and sugar diet), alters the composition of microbiota in just one day! On the other hand, vegetarian and calorie restricted diet can also have an effect on gut microbiota composition.

Prebiotics and probiotics are diet strategies more used to control and reestablish the gut microbiota and improve the individual’s health. Probiotics are non-pathogenic microorganisms used as food ingredients (e.g. lactobacillus present in yoghurt) and prebiotics are indigestible food material (e.g. fibers in raw garlic, asparagus and onions), which are nutrients to increase the growth of beneficial microorganisms.

In the last years the new term psychobiotics has been introduced to define live bacteria with beneficial effects on mental health. Psychobiotics are of particular interest for improving the symptomatology of psychiatric disorders and recent preclinical trials have show promising results, particularly in stress, anxiety and depression.

Overall, these approaches are appealing because they can be introduced in food and drink and therefore provide a relatively non-invasive method of manipulating the microbiota.

Judit Cabana-Domínguez and Noèlia Fernàndez-Castillo

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