Anti-reflux (AR) formulas thickened with rice starch or carob bean gum are the most effective first choice for formula-fed babies with reflux. These formulas reduce the frequency and volume of spit-up by increasing the thickness of the feed so it’s more likely to stay down. But the “best” formula depends on what’s actually causing your baby’s symptoms, and roughly one-third of formula-fed infants with reflux also have an underlying cow’s milk allergy that requires a different type of formula entirely.
How Anti-Reflux Formulas Work
AR formulas contain a thickening agent, either rice starch or carob bean gum (also called locust bean gum), that makes the formula more viscous once it hits the stomach. This added thickness makes it harder for stomach contents to travel back up into the esophagus. The two thickeners work slightly differently: rice starch thickens mainly after contact with stomach acid, while carob bean gum thickens the formula in the bottle itself before feeding.
Carob bean gum produces a higher viscosity than rice starch, but clinical research has not shown that one thickener performs better than the other at reducing reflux symptoms. The effectiveness of any AR formula also depends on the concentration of the thickener, the protein ratio, and whether the protein has been broken down (hydrolyzed). So two AR formulas with the same type of thickener can still perform differently.
Common AR Formula Options
Most major formula brands sell an AR version. In the United States, rice starch is the more common thickening agent. Enfamil AR and Similac Spit-Up both use rice starch. In Europe and some other markets, carob bean gum formulas are more widely available. When choosing between them, the practical difference often comes down to how your baby tolerates each one rather than one being objectively superior.
One concern parents sometimes encounter with rice-based thickeners is arsenic exposure. The FDA has established action levels for inorganic arsenic in infant rice cereals and monitors contamination in rice-based products. The levels in commercial AR formulas are low, but if this worries you, a carob bean gum formula is a reasonable alternative.
When Reflux Is Actually a Milk Allergy
About 20% of formula-fed infants experience reflux, and roughly a third of those also have a cow’s milk allergy driving or worsening their symptoms. The overlap is significant because cow’s milk protein can irritate the gut lining and slow stomach emptying, both of which make reflux worse. If your baby has reflux along with other signs like eczema, blood in the stool, persistent fussiness, or diarrhea, a milk allergy may be part of the picture.
Research shows that switching to an extensively hydrolyzed formula, where the milk proteins are broken into very small fragments the immune system is less likely to react to, leads to significant improvement in these babies. Joint guidelines from the North American and European pediatric gastroenterology societies (NASPGHAN and ESPGHAN) recommend a two- to four-week trial of an extensively hydrolyzed formula when standard reflux management hasn’t worked. This trial period matters because it takes time for gut inflammation to settle.
If symptoms don’t improve on a hydrolyzed formula, the next step is an amino acid-based formula, which contains individual amino acids instead of any intact protein chains. These are reserved for the small number of babies who react even to extensively hydrolyzed options.
The Recommended Sequence for Formula Changes
Pediatric guidelines lay out a clear order of steps before and during formula changes:
- Avoid overfeeding first. Smaller, more frequent feeds reduce the pressure on the lower esophageal sphincter and can cut down on spit-up without any formula change at all.
- Try a thickened (AR) formula. This is the standard first formula intervention for uncomplicated reflux.
- Trial an extensively hydrolyzed formula for 2 to 4 weeks if thickened feeds don’t help, to rule out cow’s milk allergy.
- Switch to an amino acid-based formula only if the hydrolyzed formula trial shows inadequate improvement.
Giving each formula at least two weeks before switching again is important. Changing too quickly makes it impossible to tell what’s actually helping.
Practical Feeding Adjustments
Thickened formulas flow more slowly through a bottle nipple, which can frustrate babies and cause them to swallow more air. Research on nipple flow rates shows that even a mildly thickened formula can drop the flow rate dramatically, especially through smaller nipple sizes. A preemie nipple with mildly thick formula delivers less than 1 ml per minute, compared to over 80 ml per minute through a level 4 nipple with thin formula.
You’ll likely need to move up one nipple level from what your baby normally uses. If your baby is on a level 1 nipple, try a level 2. Some parents also cross-cut the nipple tip to widen the opening slightly, though this makes flow less predictable. Watch for signs that your baby is working too hard to feed: long feeding times, pulling off the bottle in frustration, or excessive air swallowing that leads to more gas and discomfort.
Beyond the nipple, keep your baby upright for 20 to 30 minutes after feeding. Gravity helps, and laying a baby flat immediately after a feed makes reflux worse regardless of which formula you’re using.
Side Effects to Watch For
The most common side effect of AR formulas is constipation. Thickened formulas are harder to digest, and the larger, heavier feeds can slow things down in the gut. Signs to look for include infrequent bowel movements, hard pellet-like stools, straining or crying during bowel movements, a tight belly, or blood on the surface of the stool from straining.
Some constipation is normal during any formula transition. If it persists beyond the first week or two, or if your baby seems to be in real discomfort, that’s worth raising with your pediatrician. Switching between rice starch and carob bean gum formulas sometimes helps, as babies may tolerate one thickener better than the other. Increased gas is also common, particularly if your baby recently transitioned from breast milk to any formula.
Breastfed Babies With Reflux
If you’re breastfeeding and your baby has reflux that isn’t improving with positioning and smaller feeds, the guidelines recommend eliminating all dairy from your own diet, including both casein and whey protein, for two to four weeks. This achieves the same goal as switching to a hydrolyzed formula: removing cow’s milk protein to see if it’s contributing to symptoms. It requires strict label reading, since whey and casein show up in many processed foods, but it allows you to continue breastfeeding while testing for a milk protein sensitivity.