Should Formula Be Continued During Infant Diarrhea?
Do not stop formula feeding when your baby has diarrhea—continue giving full-strength formula immediately after rehydration. 1
Key Management Principles
Continue Formula After Rehydration
Standard cow's milk formula can be safely continued in most formula-fed infants with acute diarrhea once rehydration is complete; switching formulas is unnecessary and provides no clinical benefit. 1
Full-strength formula should be started promptly after rehydration—do not dilute the formula. 1 The older practice of gradually reintroducing diluted formula (mixing formula 1:1 with water) is outdated and currently being re-evaluated. 1
Delaying re-feeding after rehydration is harmful because fasting increases intestinal permeability and slows mucosal recovery. 1
When to Consider Lactose-Free Formula
Most infants do NOT need lactose-free formula, even though many develop temporary lactase deficiency during diarrhea. 1
About 88% of infants hospitalized with rotavirus diarrhea have acquired lactase deficiency, but most remain asymptomatic—lactase deficiency must be distinguished from true lactose malabsorption. 1
Switch to lactose-free formula only if diarrhea clearly worsens when regular formula is reintroduced after rehydration. 1 In these cases of confirmed lactose intolerance, immediate switch to full-strength lactose-free or soy-based formula reduces stool output and shortens diarrhea duration by roughly 50%. 1
Do not rely solely on stool pH or reducing substances to diagnose lactose intolerance without accompanying clinical symptoms—this leads to unwarranted dietary restrictions. 1
Red Flags: When Diarrhea Suggests Cow's Milk Protein Allergy
If diarrhea persists beyond 7 days after appropriate rehydration, consider cow's milk protein allergy (CMA), especially with these warning signs: 1
- Blood-streaked stools
- Protein-losing enteropathy (hypoalbuminemia, edema, notable weight loss)
- Failure to thrive
For suspected CMA, lactose-free formula alone is insufficient because it still contains cow's milk proteins. 1 You must use:
Extensively hydrolyzed formula (eHF), or
Amino-acid-based formula (more effective than eHF in severe intestinal disease for reducing need for parenteral nutrition) 1
Breast milk remains the preferred enteral feed for infants with suspected CMA when available, associated with shorter duration of parenteral nutrition and better outcomes. 1
Practical Feeding Instructions During Diarrhea
While managing diarrhea with oral rehydration solution (ORS): 2
- Give ORS using cup and spoon rather than bottles to avoid interfering with future feeding patterns
- After rehydration is complete, resume full-strength formula immediately
- Offer small amounts of food frequently (every 3-4 hours)
- After diarrhea stops, give one extra meal each day for a week to restore nutritional losses 2
Common Pitfalls to Avoid
Do not routinely switch to lactose-free formula for all infants with diarrhea—this is unnecessary in most cases. 1
Do not use soy formula for suspected CMA in very young infants, as newborns with intestinal injury have higher risk of soy-protein intolerance. 1
Do not keep prepared formula warm in bottle heaters or thermoses—this promotes bacterial growth. 2
Do not withhold feeding to "rest the bowel"—there is no justification for fasting, and it worsens outcomes. 2