The significance of learned food aversions in the aetiology of anorexia associated with cancer

Abstract

Summary The results of 24 h food preference tests have suggested that learned food aversions may be involved in the development of anorexia in tumour bearing rats and in patients with cancer. We have performed similar tests over longer periods, up to 10 days, in male rats implanted with Leydig cell tumours, using semisynthetic diets containing differing proportions of fat, protein and carbohydrate.Tumour growth caused anorexia (16-30% decrease in food intake) and cachexia (78% decrease in body fat and 18% decrease in body protein, but 16% increase in body water). Both tumour bearing and control rats preferred a high carbohydrate diet to a high fat diet regardless of their previous diet: tumour bearing rats showed no evidence of a learned food aversion in these experiments. Tumour bearing rats did show an initial preference for a novel high protein diet when this was offered as an alternative to the normal protein diet they had previously been consuming, but this apparent learned food aversion disappeared on the second day of the test and was in fact reversed on all the subsequent days of the test. However, tumour bearing rats did show a sustained preference for a novel low protein diet when this was offered as an alternative to the normal protein diet they had previously been consuming. These results suggest that anorexia in the tumour bearing rats was not caused by a learned food aversion. However the results do indicate that the tumour bearing rats may have developed a specific aversion to protein in the diet.Leydig cell tumours are known to secrete large amounts of oestradiol. However injections of oestradiol in normal male rats caused an increase in body fat content and had no effect on the rats' preference for dietary protein. Clearly hypersecretion of oestradiol was not responsible for the loss of body fat, the fluid retention and the aversion to dietary protein which characterised the tumour bearing rats. The mechanisms by which tumour growth causes anorexia and cachexia in these rats remains obscure. *The major cause of death in patients with cancer is the existence of learned food aversions for periods up to ten generalised body wasting known as cachexia. This syndrome days in tumour bearing rats. Since it became clear during is characterised by abnormally low food intake together with these studies that factors other than previous diet were inappropriately high energy expenditure. Although much is governing the sustained food preference of our tumour now known about the metabolic abnormalities which bearing rats we examined systematically their preferences for underlie the elevation of energy expenditure, considerably the major components of the semisynthetic diets we were less is known about the decrease in food intake which many using, viz. protein, fat and carbohydrate. workers now regard as the primary event in the onset of Bernstein and Fenner (1983) found that these food cancer cachexia (Lindmark et al., 1984;Morrison, 1979).aversions did not occur in all tumour bearing rat models. We One feature...