Viral Gastroenteritis: This is the most common cause of acute diarrhea in adults, often presenting with non-bloody diarrhea, and can be accompanied by a white tongue due to dehydration or oral candidiasis. The absence of fever and vomiting does not rule out this diagnosis, as symptoms can vary.

Irritable Bowel Syndrome (IBS): Although IBS is a chronic condition, an acute exacerbation could present with non-bloody diarrhea. The white tongue could be unrelated or due to poor oral hygiene.
Food Poisoning: Certain types of food poisoning (e.g., from Staphylococcus aureus or Bacillus cereus) can cause non-bloody diarrhea without fever or vomiting, especially if the incubation period is short.
Lactose Intolerance or Other Carbohydrate Malabsorption: These conditions can lead to acute episodes of non-bloody diarrhea after consuming lactose or other poorly absorbed carbohydrates, potentially accompanied by a white tongue if there's associated oral thrush.

Inflammatory Bowel Disease (IBD): Although less likely, an initial presentation of IBD (Crohn's disease or ulcerative colitis) could include non-bloody diarrhea. Missing this diagnosis could lead to delayed treatment and complications.
Celiac Disease: An autoimmune reaction to gluten, which can cause diarrhea and malabsorption. It's crucial not to miss this diagnosis due to the potential for long-term complications if left untreated.
Infectious Colitis (e.g., Clostridioides difficile): While less common in healthy individuals without recent antibiotic use or hospital exposure, C. difficile infection can cause non-bloody diarrhea and is critical to diagnose due to its potential severity and treatment requirements.

Whipple's Disease: A rare, systemic bacterial infection that can cause diarrhea, among other symptoms. It's very uncommon but important to consider in cases where common diagnoses are ruled out.
Tropical Sprue: A rare condition that causes malabsorption and can lead to chronic diarrhea, typically seen in individuals who have traveled to or live in tropical areas.
Giardiasis: An intestinal infection caused by the parasite Giardia lamblia, which can lead to non-bloody diarrhea. It's more common in individuals with exposure to contaminated water or travel history, but can be considered in the differential for persistent or severe cases.