How to Tell if Baby Formula Is a Good Fit

By Nutritional Weight & Wellness Staff
November 21, 2017

In this article, we will explore the question of how to determine the right formula for your baby.

Introduction to Dr. Bridget Young:

But first, let us introduce Dr. Bridget Young. Dr. Young knew that many parents approach this same formula query with high emotions (and lack of sleep), and with that in mind she created a website to help parents figure out what baby formulas are best for their babies.

We sat down with her to learn what infant formula questions she’s frequently asked and provide her kind responses based on considerable experience.  

 Mom breastfeeding baby

Formula vs. Breast Milk?

Dr. Young clarified that while she created a website – – dedicated to baby formula, first and foremost she is an advocate for breast milk. As a Certified Lactation Counselor she stresses this to her clients, but is quick to say that sometimes, for a variety of reasons, breastfeeding doesn’t always work out.

Her second choice? Donor breast milk from a donor bank, but Dr. Young qualified this by sharing that this milk is extremely difficult and expensive to get and is usually prioritized for extremely premature babies in the neonatal intensive care unit (NICU).

The third choice, and one that many parents find themselves facing, is bottle feeding with an infant formula.

Confused By Formula?

“That’s a confusing step for parents! I am a Certified Lactation Counselor and in that role we have tons of resources for families on breastfeeding only. But there comes a time when they need to supplement or it’s best for a family to stop breastfeeding – and at that point there are no unbiased sources of information.”

Dr. Young shared that very few professionals in the pediatric world are well versed when it comes to the  grocery store aisle full of baby formula options. Lactation consultants don’t get any training about baby formula, same goes for pediatricians.

“That was the biggest question I could not answer – what baby formula do you recommend? Our baby got a rash, diarrhea (fill in the blank). There is this massive hole in resources for desperate parents who are just trying to find out what’s best for their baby – that’s why I started the website.”

Resources on Breastfeeding:

If you are looking for resources on breastfeeding, we highly encourage you to contact a Certified Lactation Professional – a  profession dedicated entirely to getting you and your baby on the right track.

Here’s a directory we trust and recommend, International Lactation Consultation Association directory.

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So let’s jump into what you should look for when choosing an infant formula.

How to Start Finding Formula for your Infant

Dr. Young boils this answer into two parts – first “All formulas are not the same. There are a lot of differences and that’s overwhelming, but it can be a positive thing because by working with a professional or understanding the ingredients yourself you can find one that is perfect for your baby.”

Second, “There’s also no such thing as a poison formula! A lot of parents will be feeding a formula and their baby is finally thriving – then they learn something about the ingredients and panic because they don’t like it. Do I wish we had tighter regulations for formula, yes, but there are minimal requirements that ensure baby will safely grow.  

If baby is thriving, then you have found the perfect one for your baby.”

protein size in formula matters

Protein Size for formula matters 

What You Should Look for in Infant Formula

“The formula ingredient that will make the largest impact on baby is the protein source. It’s the one ingredient that’s most likely to cause a (poor) reaction.” Dr. Young stresses this again and again.

As parents purchasing infant formula, it’s important to know that there are two ways of classifying proteins – the protein source (whey, and/or casein, soy protein) and protein size (intact proteins (from soy or cows) are a large size and then you can break those down into smaller sizes) – that’s where you get this massive variety.

  • Most baby formulas on the market are intact proteins.

  • Then, smaller size proteins are partially hydrolyzed proteins, and those are generally marketed as “comfort” or “sensitive” formula.

  • The next step down in proteins is a fully hydrolyzed formula in which proteins are even smaller. These often show up in a hypoallergenic formula, which is a good choice for infants with a true cow’s milk allergy (which Dr. Young says isn’t as common as people think).

  • Finally, the smallest protein size is no protein at all; these are free amino acids formulas designed for babies who are quite ill and have digestive disorders.

But … all those proteins are literally right next to each other on the shelves at your local grocer. No wonder so many people are overwhelmed!

By understanding your options in protein source and size you can better identify a baby formula that you want to start with.

So … What Baby Formulas Do You Recommend?

“This is by far the number one question I receive, and it’s truly different for every baby,” says Dr. Young. But if you have medically decided you need to supplement with infant formula, Dr. Young would first ask how old your baby is and if there is an immediate parental history of autoimmune disease.

If your baby is young (under six months) and or the autoimmune history exists, Dr. Young says to start your infant formula trials with a partially hydrolyzed protein that isn’t super harsh and is the size of breast milk proteins. Plus, there’s no harm in providing these hydrolyzed proteins to your infant, though this is an active area of research (whether or not protein size may have an impact on autoimmunity).

There are several options of partially hydrolyzed formula on the market, and Dr. Young provides some specific recommendations to start with on her website.  Dr. Young has no affiliation with any companies; her recommendations are based on her own research and knowledge.

If baby is healthy and has passed the six-month mark, then he or she can take a full intact protein. That protein size provides a lot of choice for parents, including organic formula and formula without corn syrup. There are a lot of great options for organic infant formulas free of corn-based sugars.

Visit Dr. Young’s website to see some recommendations.

How Long to Test a Baby's Formula

When it comes to choosing a baby formula, give it time. Just like an adult, if you're doing an elimination diet, you don't expect results overnight. Same goes for a baby, you need to give the baby time to recover from one formula before judging a different formula.

Young suggests a slow transition of at least a week or ten days. Granted, “Ten days is an extremely long time over a two month life!” so it may feel tenuous, but it's worth it to judge whether or not switching formula made an improvement.

Switching formulas too rapidly doesn't give time for any healing to occur before an improvement can be observed. Overwhelmed? Dr. Young says to “Treat it scientifically with a lot of observation.”

 Baby drinking baby formula from bottle

How Much Baby Formula Should You Feed Baby?

Dr. Young would encourage you to speak with your baby's pediatrician for an accurate estimate. What you'll be looking for to see if your quantity of infant formula is right is a good output of urine, depending on the baby's age, and bowel movements.

The rule of thumb for exclusively formula-feeding babies is to start with 2 ½ ounces per pound of body weight with a max of 32 ounces of formula, which is the most any young babies should need before 6 months old.

This is just a starting point. Some babies will naturally drink more, and some will naturally drink less than this amount. Babies' intakes will also increase with growth spurts and then decrease.  A lot of variation that is normal.

Cues your baby has had enough to eat:

Dr. Young still encourages feeding on demand, just like you would feed a breastfed baby. Of course the older they get, the larger their bottles will be.

Stop feeding them when they start to exhibit cues that they are full such as turning head away from the bottle, pushing the bottle away, squirming and attempting to move or arching their back away from bottle. Don't encourage them to finish the bottle when they are full.

How to Tell If Baby is Allergic to Cow's Milk

A true cow's milk allergy is much rarer than people think. Often babies will have a sensitivity to the cow's milk protein, perhaps becoming gassy or cranky, but they don't have an allergy response which would be a rash, blood in baby's poop or congestion.

So what causes the sensitive tummies? Developing intestines, says Dr. Young. “Every day their intestines mature, and they're able to digest more complex things.”

So while your infant may have sensitivities, don't count it as food allergies straight away, and always call your child's pediatrician.

Would Organic Work Better?

Dr. Young is often asked, “Is organic better?” but she cautions that this is not the first question parents should be asking. Instead, focus on the protein size and source as discussed earlier “… because that has a lot more impact on their baby's diet at the beginning.”

If you could have the non-organic protein source that's ideal or the not ideal protein source that is organic, go with the ideal protein source.  

That said, if you've done your research and found the protein source you want and have two options, one organic and one not, then Dr. Young says “Of course I'd recommend organic, if your budget allows. If it doesn't, that is NO problem.”

She cautions parents not to feel bad or stress if finances don't allow for organic.

Symptoms of baby not tolerating formula.

First things first, if you're worried baby's digestive health is struggling, talk to your pediatrician.

Second, know that just like there is no perfect formula, there is no perfect baby. So while some of baby's symptoms may be due to the type of formula, they also might not be, which doesn't make the process easier.

Signs that you shouldn't ignore though – and again call your doctor right away – are a severe rash, blood in the baby's diaper, which can be either bright red, or causing it to either be dark or with black flecks or chunks, or chest congestion with mucus or wheezing after eating. These are more severe allergic reactions to formula that we'd want to adjust right away.

What about colic and acid reflux?

Dr. Young shares that those are actually very normal and while we wish babies don't have to suffer, their health is usually not in danger.

Ask Your Baby's Pediatrician:

One more thing about calling your baby's doctor about your baby's symptoms– remember, they work for you! They are used to parents calling at all hours, and they'd much rather hear from you than not hearing from you until two days later when the problem has gotten worse. You're not bothering your doctor, and if they make you feel as if you are, find a new provider.

More Resources about Baby's Formula

We know that we've barely scratched the surface when it comes to everything there is to know about infant formulas.

There are some great resources Dr. Young has available, for free, on her site. Amazing information to bookmark for future reference. Her Baby's Formula Shopping Guide is specifically helpful!

On you'll find additional information on topics like:

  • Switching Formulas safely

  • Baby Lactose Intolerance

  • Soy Formula Information

  • Sensitive baby formula versus gentle formulas

More resources from Nutritional Weight and Wellness

By the time you become well versed in baby formula options your little one will be starting to experiment with solids! When it comes to that phase we've got a guide in place for what to feed your baby and at what ages.

About the author

This blog content was written by a staff member at Nutritional Weight & Wellness who is passionate about eating real food.

View all posts by Nutritional Weight & Wellness Staff


When talking about which formula to choose, you really need to teach that breastfeeding is the BEST source of nutrition for your baby!
November 23, 2017 at 9:23 pm


Dr. Young's views about this were shared in part one of this article here. "Dr. Young clarified that while she created a website – – dedicated to baby formula, first and foremost she is an advocate for breast milk..."

Lisbeth Marquez
My partner and I changed the babies. Milk but idk if it’s causing her or not but last night she threw up like around 5 in the morning and then her poop is coming out in lil balls
April 19, 2019 at 11:56 am


It sounds like the change you made may have caused some upset and constipation for your baby and there may be something in the new formula or milk that your baby is sensitive to. This blog post on choosing a formula may help give you direction. We hope that your baby is feeling better soon!

Is it bad to have bub on a allergy formula (rice based) if not needed?
Just trying the elimination process as bub has been consitpated since a 5days old.
Also nice to find information on formula. It is made so difficult with most professionals lack of knowledge.
January 30, 2020 at 10:29 am


A short-term trial (1-2 weeks) of a hypoallergenic formula or non-cow’s milk based formula to see if it helps with the constipation issue is likely fine. If no changes or improvements are seen, however, we recommend talking with your pediatrician about other remedies or making an appointment with one of our counselors, as there are a lot of factors that can contribute to constipation.

Keats Marley
This is one of the best articles I have ever read in the recent times. Thank you very much for sharing this kind of article with us and I'm looking forward to reading more such articles in the future as well.
February 3, 2020 at 6:06 am


Thank you for reading and for your kind words. Please feel free to sign up for our newsletter for more articles every week. 

Lanna Rowe
I have a concerning my daughters formula. We did a process of elimenation reguarding her formula and have yet to find one that agrees with her body. Some cause a rash, constipation, extreme gas, throw up, and have even caused bloody stools. Any advice?
March 6, 2020 at 5:54 pm


Oh man, that’s awful. I don’t know that I can offer much via a blog question, as there’s a lot we don’t know about baby’s health, mom’s health, or family history. I’d recommend a nutrition consultation, or finding a pediatric dietitian near you that could help.

I’d also recommend discussing allergy testing with your pediatrician if you haven’t done so already.

Additionally, here’s some ideas for formulas:

  • Nutramigen by Enfamil (the milk proteins are hydrolyzed [broken down] for digestibility)
  • Similac Alimentum (the milk proteins are hydrolyzed [broken down] for digestibility)
  • Neocate (for severe milk allergies; contains no whole-food proteins; needs doctor prescription)
  • Earth’s Best Sensitivity formula (if only mild milk sensitivity)

Homemade formula – the Weston A. Price Foundation provides several variations, plus videos and nutrition breakdown, of homemade formulas.

Is it normal to have green Poo and constipation after switching from cow milk formula to goats milk. Second day today
April 4, 2020 at 1:54 pm


Any dietary change for baby can certainly cause digestive changes. One way to minimize reactions/symptoms is to make the formula switch gradually if possible, as outlined here. (we have featured this expert on our blog before) You may have to give the formula a little more time before you see baby’s stool normalize. If symptoms worsen or additional symptoms appear, please contact your pediatrician.

My baby is drinking soy milk.. He is very gassy he only of 1 stool a day and its normal soft but some days he may skip and doesn't have any stool at all he's always grinding could it be his formula
June 24, 2020 at 4:20 am


Soy formula is not typically recommended unless the baby has a rare true allergy to cow's milk. Plant-based proteins lack some of the essential amino acids found in breast milk and cow's milk. These amino acids are essential to the development of the brain, heart, and muscles. Soy also contains phytoestrogens which may cause estrogen-like activity leading to complications later in life. Also, the vast majority of soy grown in the US is genetically modified, potentially making it difficult for babies to digest. If you choose to use a soy formula try to choose an organic soy.

When i change the formula of my baby his ooop becomes dark grey, so we stop it and we back again his first formula but suddenly his yellow poop did not come back and the dark grwy color continue.. What should we do? We can't go to the pedia because of pandemic.
October 2, 2020 at 1:39 am


Dark gray stools tend to be diet related and are normal. If your baby's stools are lighter gray, chalky or white, you should call your pediatrician because it could be a problem with bile production.

Hi, my baby is 5 weeks old now and I breastfed for 2 weeks but couldn't anymore as my milk didnt have enough nutrients. Then I put her onto formula, this was week 3 of her life but the formula caused constipation so week 4 I changed to another formula but that caused a rash so now week 5 I'm on my 3rd type of formula, hopefully this one will work. What my question actually is, it that she is refusing to drink the required amount. And it was like this with all the formulas. Now she is supposed to be drinking 120ml each feed every 3 hours but she is only drinking 30ml but she drinks every 1 and a half hours. Is that okay? Is it because I've changed the milk so often? And will it get better? Is she receiving enough nutrients?
April 22, 2021 at 2:44 am


Our nutritionist weighed in and said it's fine if baby is drinking smaller amounts more frequently. Baby may be going through a growth spurt and cluster feeding, or baby naturally prefers to eat less but more frequently. As long as baby is gaining weight, he/she should be getting the nutrition they need. The pediatrician's office may allow you to bring baby in weekly for weight checks for peace of mind or if there are concerns. We'd also recommend running these concerns by the pediatrician to get their take.

Thank u so much for the feed back, I really appreciate it... You guys are so helpful.
April 22, 2021 at 2:34 pm


We're so glad to be able to help!

This is the third formula change for my 5week old baby. This one actually works better but he still has excessive gas. He strains a lot and is fussy. What can I do to help him?
October 15, 2022 at 1:28 pm


When it comes to choosing or switching to a new formula, give it time. You will need to give the baby time to recover from one formula before jumping to the next one. You could also add a probiotic to help with the gas and digestive upset, about 1/4 teaspoon of Bifido Powder mixed into a bottle twice a day. (if you find baby is not finishing the bottle, you can dip the tip of your pinky finger into the powder and place in baby's mouth). If they are still experiencing discomfort, you could make a one-on-one appointment with one of our nutritionists. 

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