Effects of sub chronic oral tryptophan administrations on stress-induced mood and eating behaviour in healthy female volunteers differing in the 5-HTTLPR genotype

Serotonin is involved in both the regulation of mood as well as the control of
energy intake. Individuals with different 5-HTTLPR genotypes have dissimilar
serotonergic neurotransmission; and the s-allele of the 5-HTTLPR has been shown
to predispose for a serotonergic vulnerable system, and hence increased
susceptibility to stress, stress-related depression and disinhibited eating
behaviour. This would suggest different emotional (mood) and behavioural
(eating) responses after acute stress exposure depending on genotype. These
stress-induced negative effects can be prevented by augmentation of brain 5-HT
through administration of dietary tryptophan (TRP), the sole precursor of 5-HT.
Previous investigations have shown significant 5-HTTLPR genotype-related
differences in blood plasma TRP levels and brain TRP uptake after acute, oral
TRP administration, but the effects of chronic TRP supplementation are still
unknown. In order to develop a better understanding of serotonergic functioning
in 5-HTTLPR genotypes, and the association with stress-sensitivity and the
effects on mood and eating, the present aim is to examine the effect of stress
on anticipated appetite and food preference, on actual food intake and
preference, as well as the effect of multiple (sub chronic) daily dietary TRP
administration, and the functional role of allelic variation of the 5-HTTLRP
therein.

1) Examining actual changes in food intake and food preference for different
foods following psychosocial laboratory-induced stress;
2) Examining the effect of multiple (instead of single) dietary TRP
administration on acute stress-induced (negative) affect and eating behaviour;
3) Examining whether individuals with different versions of the 5-HTTLPR
genotype and different levels of cognitive stress sensitivity (high vs. low
Neuroticism) react differentially to stress and stress induced changes in mood
and eating behaviour;
4) Examining whether individuals with different versions of the 5-HTTLPR
genotype and different levels of cognitive stress sensitivity (high vs. low
Neuroticism) react differentially to the (beneficial) effects of dietary TRP
augmentation with regard to stress-related changes in mood and eating
behaviour.

This study will be conducted in accordance to a between-subjects randomized
placebo-controlled design.

Half of participants will be provided with TRP-rich drinks (100 ml containing
1.0g of TRP, three times a day), and half will be provided with placebo (PLC)
drinks (100 ml, three times a day) for seven consecutive days. Before start of
the treatment phase (baseline measure), as well as after seven treatment days
(TRP or PLC), all subjects will be exposed to a laboratory stress-induction
procedure.

The drinks (TRP and placebo) originate from natural food sources from which no
adverse effects are reported. The stress-induction tasks (a mental arithmetic
task and a public speaking task) have been used frequently in several studies
and have been proven to be safe research paradigms, which are well tolerated
and do not induce any psychological negative after-effects or damage. There are
no indications that salivary sampling (5 times each test day), blood sampling
(4 times in total), or mood assessments (3 times each test day) elicit any
intolerant discomfort or meaningful affective changes.