BACKGROUND Malnutrition influences healing of gastrointestinal anastomoses. The authors hypothesize that colonic anastomotic healing is decreased by malnutrition and might be improved by preoperative feeding. METHODS Eighty adult male Wistar rats were divided into 4 groups: (1) control rats 1 (C1), fed regular chow ad libitum for 21 days; (2) malnourished pair-fed rats (M), fed 50% of the food ingested by the control rats for 21 days; (3) preoperative nutrition rats (PRE), fed 50% of the average of the controls for 21 days and then fed preoperative nutrition with regular chow ad libitum for 1 week before the operation; and (4) control rats 2 (C2), fed regular chow ad libitum for 28 days. On days 21 (C1 and M) and 28 (PRE and C2), rats underwent 2 colonic transections and, subsequently, 2 end-to-end anastomoses. Rats were killed on postoperative day 5. The anastomoses were resected for tensile strength and histological analysis. RESULTS PRE rats showed increased maximal tensile strength vs the M group (0.09+/-0.01 vs 0.15+/-0.01; P<.05) and similar values of maximal tensile strength as the controls (0.15+/-0.01 vs 0.15+/-0.02; P=.91). Collagen type I was higher in controls vs the PRE group (6.13+/-0.39 vs 4.90+/-1.53; P<.05); nevertheless, the PRE group showed higher collagen type I than M rats (4.90+/-0.36 vs 3.83+/-0.35; P<.05). CONCLUSIONS Preoperative feeding for 7 days increases the maximal tensile strength, as well as the percentage area of mature collagen, approaching similar values as the control group.