Does laxative abuse control body weight? A comparative study of purging and vomiting bulimics.

This study examines the daily food intake and eating habits of 30 bulimia nervosa patients of normal weight; 20 vomited daily and 10 purged daily. The aim was to measure and compare food intakes and to examine the belief that laxative abuse is an effective means of controlling body weight. The results indicate that the purgers control their weight by overall dietary restraint, not by the pharmacological action of the laxatives. The purgers' eating patterns were bulimic, but not gross: mean daily energy intake being in a normal range (2210 +/- 210 kcal/day). Binge-eating by the vomiters was of a different order: mean energy intake was very large (6025 kcal/day), nearly three times that recommended and significantly greater (P less than 0.01) than that eaten by the purgers. There was major daily variation (s.d. = 3605) and, on occasions, huge amounts were recorded, up to 30 000 kcal in a day. Despite this, vomiting was highly effective in preventing weight gain, the mean weights of the vomiters being similar (mean = 98 per cent) to their matched population mean weight (MPMW). In contrast, purging was relatively ineffective, for despite smaller energy intakes, all the purgers were above (mean = 114 per cent)--and some markedly above--their MPMW. This difference between the two groups was significant (P less than 0.01). Reasons for persisting with laxative abuse are discussed.