The most appropriate management is discontinuation of sugar-free sweeteners. The appearance of this patient's diarrhea coincided with healthy lifestyle changes that include the ingestion of artificial sweeteners. The temporal association between the onset of this patient's diarrhea and his dietary changes makes it highly likely that the exposure to nonabsorbable sugar alcohols (“sugar-free sweeteners”) is the cause of his symptoms. The presence of bloating is also characteristic of diarrhea due to nonabsorbed carbohydrates. In this patient, further testing is not necessary before recommending the discontinuation of sugar-free sweeteners. However, if the likely diagnosis was less clear, assessment of his stool electrolytes would be helpful. In diarrhea caused by malabsorbed carbohydrates, an elevation in the osmotic gap would be expected. The osmotic gap is calculated using the following equation:

290 – 2 × [stool sodium + stool potassium]

A gap greater than 100 mOsm/kg (100 mmol/kg) indicates an osmotic diarrhea. If the gap is less than 50 mOsm/kg (50 mmol/kg), the diarrhea is not osmotic. A gap between 50 and 100 mOsm/kg (50 and 100 mmol/kg) is equivocal. Sugar-free sweeteners are metabolized by gut bacteria, liberating gas and osmotically active substances that cause diarrhea and account for the osmotic gap.

Pancreatic cancer could present with diarrhea and weight loss, but this patient's age, absence of abdominal pain, and correlation of symptoms with dietary changes make this diagnosis less likely. Therefore, a CT scan should be deferred until a dietary cause of his symptoms is excluded.

Patients with microscopic colitis lack signs of systemic inflammation and present with painless watery diarrhea without bleeding. Diagnosis can only be made when biopsies of the colon show a predominance of intraepithelial lymphocytes in the colonic mucosa (lymphocytic colitis) or the addition of a thickened subepithelial collagen band (collagenous colitis). Colonoscopy with biopsies would be useful to exclude microscopic colitis, but this diagnosis is uncommon in younger males and would not cause an osmotic diarrhea.

Celiac disease is thought to affect nearly 0.5% to 1% of individuals in the United States. The typical features of celiac disease are diarrhea, bloating, and weight loss. Tissue transglutaminase (tTG) IgA antibody measurement would be useful to evaluate for celiac disease, but this patient's symptoms began after a dietary change, making celiac disease unlikely. In addition, the empiric use of a gluten-free diet is not recommended in the absence of a confirmed diagnosis of celiac disease.