Dietary tryptophan, brain serotonin and feed intake of pigs: a case of confusing correlation with causation? A review

Several papers have been published on the effect of tryptophan on feed intake of pigs. Interestingly, some authors suggest that a positive correlation can be explained by increased brain serotonin levels. Traditionally, it has been assumed that increased serotonin (5-HT) availability and stimulation of 5-HT receptors reduce food consumption (Blundell, 1977). This raises the question whether tryptophan increases feed intake because or despite of increased brain serotonin levels (Figure 1). We studied literature on authors' interpretations of the association between tryptophan and serotonin.