This research line focusses on two major topics: 1) how the brain (e.g. via genetic vulnerabilities) and cognitive stress vulnerability may mutually promote stress-related disorders and 2) how food may intervene in such brain by stress interactions. In addition, a further aim of the research line is 3) to inform the broader public about the truth (scientific consensus/support) regard claims/assumptions presented by media and press about foods/nutrients influencing brain and behaviour.
1) Gene-brain x cognition vulnerabilities for stress and stress-related disorders
A first line of research involves the exploration of the singular and interactive effects of bio-genetic (e.g. 5-HT, TPH2, 5HTTLPR), cognitive (neuroticism/rumination) and environmental (frequency of harmful life events) vulnerability factors on stress responsiveness and the onset/development of stress-related psychopathology including depression, declined sleep, and eating-related problems.
2) Nutritional Neurosciences: beneficial effects of food on brain & Behaviour
Since brain neurotransmitters and hence biochemical processes are partly controlled by dietary amino acid uptake into the brain, food is sometimes (under exceptional occasions) able to influence brain and behaviour.
A most illustrative example concerns the brain serotonergic (5HTergic) system; that is directly controlled by its plasma essential dietary amino acid precursor Tryptophan. A rise in plasma (and brain) TRP can be accomplished by increasing dietary intake of TRP, TRP-enriched protein and/or by increasing the amount of sugar/carbohydrates in food. Both factors are shown to lead to a rise in plasma TRP relative to the sum of other large neutral amino acids (LNAA’s) that compete with TRP for transport into the brain (e.g. Fernstrom, 1990, Wurtman et al., 2003, Markus, 2008). Sugar and carbohydrates do not contain TRP, but cause an increase in brain TRP (and thus 5-HT) by evoking an insulin response that sends the LNAA’s (except for TRP) into peripheral tissue (via this route increasing the plasma TRP/LNAA ratio).
Tryptophan intake improved mood (reduced depression, Fatique and increased Vigor) only in participants carrying a genetic brain 5-HT vulnerability (S/S-allele 5-HTTLPR). (Markus & Firk, 2010.Neuropsychopharmacology, 34, 2667–2674).
Based on these findings, the current research line aims to investigate beneficial effects of certain foods, nutrients and/or supplements on brain biochemistry and related behaviour. In particular, possibilities are explored whether food/dietary manipulations may particularly interfere with the likelihood of developing stress-related disorders in those that already possess both genetic-brain x cognition stress vulnerability factors in combination. Such research has only been recently started and already reveal some support for beneficial effects of 5-HT enhancing foods on stress related behaviour; including effects on emotional-eating (e.g. Markus et al., 2015, Schepers and Markus, 2015), stress-responsiveness (e.g. Markus et al., 2012, Cerit et al., 2013, Capello and Markus, 2014) and sleep quality (e.g. van Dalfsen and Markus, 2015). The current chair aims to continue and intensify further research on this topic.
Increased intake of High-fat Sweet snacks (HFSW) over High-fat Savoury snacks (HFSA) was greater in participants with genetic 5-HT vulnerability (S/S-allele 5-HTTLPR genotype) than in control participants (L/L-allele 5-HTTLPR) and only in S/S carriers was prevented by Carbohydrate (CHO) compared to placebo (PLC) intake (Markus et al., 2015. Stress, 18(2); 149-159).
3) Informing the broader public
Even though food-behaviour assumptions sometimes reflect sound (biochemical) theoretical mechanisms of actions that are supported by the scientific literature (e.g. involving anti-oxidation, brain energy, cell-structures and/or neuro-communication), most food-behaviour claims are based on just one or few (often methodologically-limited) studies and are seldom supported by international scientific consensus or meta-analyses of randomized-controlled-designs (RCT). For the broader public, it is however often hard to distinguish between good and bad scientific research and practice, making it even harder to discern facts from myths. Moreover, media and press (and even biased scientists) may sometimes falsely interpret, or even misuse, scientific findings of which the general public/consumers are not aware. A third aim of the research line is to inform the public about facts vs myths regarding the influence of foods on the brain and behaviour.
One important starting point is to convince society/the broader public that the scientific truth is not likely found in one uncontrolled study or on the internet, but at least needs careful scientific evaluation of the average findings of multiple and only well-conducted RCT studies (e.g. preferably by using meta-analyses).