It is not well understood why tail biting develops among pigs. Some research has studied environmental factors. This study focused on investigating the effect of nutritional factors. Twenty-four pigs were used to test the effects of low protein, low energy or standard diets on their chewing behaviour and preference for blood. Pigs were housed individually. Two tail models were positioned at the front of each pen at certain times during the experiment, so that chewing behavour could be recorded for six weeks. The tail models were sections of sash cord and one was soaked in pig’s blood and the other in deionized water. Blood samples from each pig were collected at slaughter to be analyzed for free tryptophan concentrations. Pigs on the low energy and low protein diets had similar weight gain, which was significantly lower than those on the standard diet. The preference scores did not differ among the treatments. However, there was a positive correlation between tryptophan concentration and preference scores during the last week for pigs on the low protein diet. The positive correlation could have resulted because the low protein intake resulted in high tryptophan and serotonin concentrations which then acted on the brain as a signal that the body needs more protein. Low protein diets did not result in differences in total chewing or preference for chewing blood-soaked tail models. Reduced weight gain or low protein content in the diet may contribute to the development of tail biting. However, these factors may not reliably predict which pigs will tail bite.