Milk-based, pre-packaged meal replacements containing lactose are widely used in weight reduction programs. In these programs, a substantial quantity of lactose is ingested without other food. This maneuver speeds gastric transit and minimizes lactose absorption in lactase deficient subjects thus, gaseous symptoms might be expected. In the present study, we investigated the symptoms that resulted from ingestion of two commercially available Slim-Fast supplements: a milk-based powder mixed with one cup of conventional skim milk, and a very low lactose, fruit-flavored drink. In addition, a lactose-hydrolyzed milk-based product was studied. Ten lactose maJabsorbers were studied in a blinded crossover protocol. Subjects ingested standard supplement servings (without other food) at breakfast and lunch. As shown in the Table, the lactose-rich supplement resulted in an enormous increase in gas excretion 30 flatus passages in 16 hours! This flatulence far exceeds that which we have previously observed when comparable amounts of lactose in milk were ingested with meals. No significant abdominal pain nor diarrhea was observed. This study demonstrates that: I) food replacement with milk-based supplements causes flatulence in lactose malabsorbers; 2) in subjects who do not have IBS, this flatulence is not associated with abdominal pain or diarrhea; 3) this flatulence can be prevented via the use of lactose-hydrolyzed or non-milk based supplements.