How to Tell if Baby Formula Is a Good Fit

By Jackie Cartier
November 21, 2017

This blog post is the second post of a 2-part series on baby formula. You can read Part 1, How to Choose The Best Formula for Your Baby, here.

Last month we introduced you to Dr. Bridget Young and her comprehensive website We shared what Dr. Young suggests parents to look for, and be aware of, when deciding which formula they are going to introduce to their infants. Today we’re back with how Dr. Young suggests you decide if the formula you are trying is a good fit for your baby. First, how long are you supposed to test each formula?

How Long to Test a Formulababybottle.jpg

When it comes to choosing a 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 the next. Dr. Young suggests giving it 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 it made an improvement. Switching 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.”

How Much Should You Feed Baby?

Dr. Young would encourage you to speak with your doctor for an accurate estimate. What you’ll be looking for to see if your quantity of formula is right is a good output of urine, depending on the baby’s age, and stool. The rule of thumb for exclusively formula-fed 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 baby 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.

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

As stated in the previous blog post, a true cow’s milk allergy is much rarer than people think. Often babies will have a sensitivity to this protein source, perhaps becoming gassy or cranky, but they don’t have an allergy response which would be a rash, blood in stool or congestion. So what causes the sensitivity? 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 a food allergy straight away, and always call your doctor.

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 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. 

What Are Signs A Formula Isn’t Working?

First things first, if you’re worried baby is having an issue, call your pediatrician.

Second, know that just like there is no perfect formula, there is no perfect baby. So while some signs from baby may be due to the 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 stool, 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.

One more thing about calling your doctor– 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 Questions & More Answers

We know that between last week and this blog post we’ve barely scratched the surface when it comes to everything there is to know about baby formula. Thankfully, that’s what is for! Here are some great resources Dr. Young has available, for free, on her site. Amazing information to bookmark for future reference.

By the time you become well versed in 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 them and when

To learn more about feeding babies and children check out these resources:

About the author

Jackie Cartier is Content Strategy Manager for Nutritional Weight & Wellness. She was once a client, seeking natural solutions to her achy runner knees and hormonal imbalances. From then she was hooked and eventually ended up on their team, spreading the real food message on the blog and through social media. 

View all posts by Jackie Cartier


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. 

Leave a comment

Your email address will not be published. Required fields are marked *

Back To Top