due to poor sanitary conditions, total global diarrhea mortality occurs almost exclusively in underdeveloped countries. since, in these countries, sanitation is greatly overlooked, in the case of diarrheal disease, the emphasis must be oriented to treatment rather than prevention. an important aspect in the treatment of diarrheal disease is to avoid the malnutrition it causes and therefore, proper feeding during and after the diarrheal episode is a crucial issue. accordingly, we studied a diarrhea rat model, based on the replacement of part of the dietary corn starch by lactose which produces diarrhea of increasing severity that reproduces the negative nutritional effects of diarrhea. five levels of replacement (0, 30, 50, 70 y 90%) were studied and feces were collected on day 1-3, 4-6, 11-13 and 18-20 of the experiment. this resulted in an increment in fecal mass (diarrhea) which was proportional to the replacement level; it reached its maximum during the first week and declined thereafter. during the same period, reductions on the apparent digestibility of the dietary protein, fat, carbohydrates and energy were detected. these reductions were proportional to the severity of diarrhea and occurred in conjunction with a reduction in food intake. these two conditions resulted in a deficient growth which was also proportional to the severity of the lactose induced diarrhea. this model reproduces the negative effects that diarrhea has on infantile nutrition and it may be useful in pre-selecting the most appropriated foods to be tested in human studies.