The best formulas for constipation share a few key features: partially hydrolyzed whey protein, no palm oil in the fat blend, and added prebiotics or probiotics. No single brand is universally “the best,” but understanding which ingredients soften stools and which ones firm them up lets you pick a formula that actually addresses the problem.
Constipation is more common in formula-fed infants than breastfed ones. In one prospective study, breastfed infants had a 0% incidence of hard stools across all time points measured, while formula-fed infants reached up to 2.1%. The difference comes down to formula composition, and the good news is that specific ingredients can close that gap.
Why Palm Oil Matters Most
The single biggest dietary driver of hard stools in formula-fed babies is palm olein oil, used as a fat source in many standard formulas. When palm oil is the primary fat, a chemical called palmitic acid sits in a position on the fat molecule that makes it break free during digestion. Once loose, it binds with calcium in the gut and forms insoluble “calcium soaps,” which are essentially tiny chunks of calcium and fat that harden the stool.
A meta-analysis of randomized clinical trials found that infants fed palm-oil-free formulas had significantly softer stools than those fed palm-containing formulas, with a mean stool consistency difference of about 0.35 points on a 1-to-5 firmness scale. That may sound small on paper, but it’s the difference between comfortably soft and noticeably firm for a baby. The researchers concluded that stool patterns in infants fed palm-oil-free formula were closer to those of breastfed infants. Stool frequency was also higher in the palm-free group.
When shopping, check the ingredient list for “palm olein oil” or “palm oil.” Formulas marketed for sensitive tummies or gentle digestion often skip it, but not always. Read the label rather than relying on front-of-package claims.
Partially Hydrolyzed Protein Softens Stools
Standard formulas use intact cow’s milk protein. Partially hydrolyzed formulas break that protein into smaller pieces before it reaches your baby, which makes it easier to digest. In a randomized controlled trial, infants with difficult stooling who were switched to a partially hydrolyzed whey protein formula had significantly softer stools and higher stool frequency (1.5 stools per day vs. 1.0 in the standard formula group) within 14 days. The improvement in consistency appeared within the first three days.
This is why “gentle” or “comfort” formulas, which typically use partially hydrolyzed whey, tend to help with constipation even though they aren’t specifically labeled for it. The protein change alone can make a meaningful difference.
Prebiotics and Probiotics
Some formulas include prebiotics (fibers that feed beneficial gut bacteria) or probiotics (live beneficial bacteria), both of which can improve stool patterns. Strains in the Bifidobacterium family have the strongest track record for constipation in children. Bifidobacterium breve and Bifidobacterium lactis DN-173010 both increased stool frequency in controlled trials. Lactobacillus strains have also shown benefit, particularly in combination with prebiotics (a pairing called a “synbiotic”).
Not every formula that lists probiotics uses a strain studied for constipation, so this ingredient alone shouldn’t be the deciding factor. But when a formula combines a relevant probiotic with the protein and fat features described above, it adds another layer of support.
What About Locust Bean Gum?
Locust bean gum is a thickener used in anti-reflux (AR) formulas. If your baby has both reflux and constipation, this is worth knowing: in a large real-life study of over 2,400 infants, a locust bean gum-thickened formula significantly softened stools and increased stool frequency, bringing both closer to breastfed-infant norms. The percentage of infants with hard stools dropped from 14.4% to 2.6% after one month. Parents of about a third of infants reported faster bowel transit.
AR formulas aren’t designed for constipation alone, and the thickening can take some getting used to (thicker bottles need larger nipple holes). But if your baby is already on an AR formula or needs one, the locust bean gum variety is unlikely to worsen constipation and may actually help.
Ingredients That Don’t Help as Much as You’d Think
You may see formulas advertising “sn-2 palmitate,” a structured fat designed to mimic the way palmitic acid is arranged in breast milk. The idea is that when palmitic acid is locked into the middle position of the fat molecule (called sn-2), it gets absorbed instead of forming calcium soaps. A six-month randomized trial confirmed that formula with over 40% sn-2 palmitate did reduce calcium and fat loss in stool. However, it did not produce softer or more frequent stools compared to standard formula. So while sn-2 palmitate may improve nutrient absorption, it’s not a reliable fix for constipation on its own.
How to Switch Formulas
Most pediatricians recommend a gradual transition over about five days. A common approach is to mix the new formula with the old in increasing proportions: start with roughly 25% new formula, move to 50/50 after a couple of days, then 75%, and finally 100%. By around day five, most babies have adjusted. Expect some temporary changes during the switch, including extra gas, mild fussiness, or a slight change in stool color. These are normal and typically resolve within a few days.
Give the new formula at least two weeks before deciding if it’s working. The randomized trial on partially hydrolyzed formula saw clear improvement within 14 days, so that’s a reasonable window for evaluation.
Signs the Problem Isn’t Just Formula
Normal infant straining and grunting during a bowel movement doesn’t necessarily mean constipation. The key signs to watch for are hard stools (either large and firm or small hard pellets), pain during bowel movements, blood on the surface of hard stool, or consistently going less than once a day.
A formula switch is a reasonable first step for mild constipation, but certain symptoms point to something that needs medical attention rather than a dietary change. A swollen or distended belly, vomiting with fever, refusing to eat, or unusual lethargy alongside constipation all warrant a call to your pediatrician promptly. Persistent constipation that doesn’t respond to a formula change within two to three weeks is also worth discussing with your baby’s doctor, as there are occasional underlying causes that go beyond what any formula can address.