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Infant Formula - Part One

Bridget Young, PhD, CLC and Parul Bhatia, MD

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Infant formula expert Bridget Young discusses the ins and out of different types of infant formulas, highlighting sources of macronutrients, and indications for use of standard and non-standard formulas.


  • Formula is made to mimic breastmilk; it is composed of macronutrients (proteins, fats, carbohydrates) and micronutrients (vitamins and minerals).

  • If a baby responds poorly to a formula, it is most likely a reaction to the protein component.


  • How is formula designed and regulated?  Formula is designed to mimic breast milk and allow the baby to gain weight.  The FDA regulates infant formula and defines infant formula as a replacement for breast milk for babies 0-12 months.  

    • Therefore, while formulas may be marketed as “newborn” formulas, there may be little or no difference in the composition of that formula as compared to a formula that is marketed to older babies.

  • What are the components of formula?  Formula contains macronutrients (proteins, fats, carbohydrates) and micronutrients (vitamins and minerals).  The macronutrients make up 99% of formula and the macronutrient combinations account for the differences between formulas.  There are 29 essential micronutrients in every infant formula, as required by the FDA.

  • More about the protein content.  If a baby is going to respond poorly to a formula, statistically, the most likely reason, is secondary to the protein components.  There is a huge variety in protein sources. Most basically, there are diary based and soy based formulas. Within the dairy (bovine) based formulas, there are two main types of proteins - whey and casein.  Whey proteins remain soluble in an acidic environment (stomach) and casein proteins will coagulate in this environment. This means that whey is generally easier to digest than casein. And if a baby has a milk protein allergy, most commonly it is to the casein protein.

    • Breast milk is roughly 60% whey and 40% casein.  Cow’s milk is roughly 20% whey and 80% casein; therefore, many formula manufacturers add additional whey to make the ratio more comparable to breast milk.

      • However, there is no way to know how much was added back.  The label will say whey protein or whey concentrate and that is the only way to check whether the more digestible additional whey has been added.  Additionally, if the whey is higher on the ingredient list, one can infer more has been added back.

        • Therefore, when switching formulas for a possible sensitivity, one may be able to try a cow’s milk based formula with more whey added in, before switching to a hydrolyzed formula.

  • When is soy formula recommended?  The short answer is very rarely.  The indications for soy based formula include infants with galactosemia and hereditary lactase deficiency and/or if a family preference is for a vegan option of formula.  

    • Soy formula should not be used for the following situations:

      • Cow’s milk protein allergy; as there is a high cross reactivity between cow’s milk proteins and soy.  In true allergy situations, infants should be switched to a protein hydrolyzed formula.

      • Premature infants; as the levels of micronutrients is not high enough for a premature baby, especially for bone metabolism.

        • Even in a premature baby who is thriving at 2-3 months, soy formula should be used with caution for the above reason.

    • If used, is soy formula safe for male and female infants?  This questions centers around the phytoestrogen components of soy.  There is not enough evidence to make any public health recommendations about not feeding soy products to male infants.  Interestingly, some studies have shown that girls who have had soy formula may have earlier breast bud development, heavier menstrual bleeding and if uterine fibroids develop, they tend to grow faster in girls who have had soy formulas.  Whether these outcomes matter is still up in the air and is an active area of research.

Bhatia J et a.  Use of Soy Protein-Based formulas in Infant Feeding.  Pediatrics. May 2008: Vol 121, Issue 5. PMID: 18450914

  • What is the main carbohydrate source in infant formulas?  As breast milk is the standard for replication and breast milk is 100% lactose based, most standard formulas have lactose as the primary carbohydrate source.  In some specialty formulas, corn sugar-based carbohydrates are used as the primary carbohydrate source instead of lactose . These include corn syrup solids, corn syrup, corn maltodextrin, glucose syrup solids, brown rice syrup and/or sucrose.   

    • As a note, these corn syrups are different from the much maligned  high fructose corn syrup. These carbohydrates in formulas will be broken down to 100% glucose. Sucrose, which is in a few formulas, is a disaccharide of glucose and fructose and will be broken down to mostly glucose with a little bit of fructose.

    • Why do we have non-lactose based carbohydrate sources?   Full term healthy babies should be born with the ability to digest lactose easily.  However, lactase, the enzyme that digests lactose, increases dramatically in expression in the small intestine in a baby right at the end of term.  So much so that there can be a difference in lactase expression even between a 37 and 41 week baby and clinically this can be important. In an early term or late preterm baby that is having a lot of gas, changing to a formula with other carbohydrate sources (other than lactose) is reasonable.

      • Premature babies have insufficient expression of lactose and therefore, premature formulas have other carbohydrate sources besides just lactose.

      • After gastroenteritis, infants and children may have a transient lactase deficiency as the sloughing of intestinal cells that occurs with GI illness may transiently decrease the baby’s ability to digest lactose.

  • Do the fat sources differ between formulas?  All formulas use a vegetable oil blend.  What oils they use can differ.

    • The only oil that may cause a clinical issue is palm oil and this may cause stiff stools.  The reason palm oil is in a lot of formulas is because there it is a rich source of palmitic acid, which is in very high levels in breastmilk.  A portion of palm oil will form calcium soaps in the gut and then excreted in stool. It is perfectly safe, but it will reduce the absorption of calcium and fat from this formula.   

  • When are medium chain triglycerides (MCTs) important?  These are not in standard formulas but are in some premature and some speciality GI formulas.  MCTs are absorbed easily in the upper part of the small intestine and provide a simple way to get high calorie formula absorbed.  If a baby has transitioned to a hypoallergenic formula and still having trouble, switching to a hypoallergenic formula with MCT higher on the ingredient list may be beneficial.  

Editor’s note:  Formulas with MCTs are also used in patients with ‘short gut’ to aid in absorption.  

  • What about the additives arachidonic acid (AHA) and docosahexaenoic acid (DHA)?  There have been many studies and Cochrane reviews on this topic; the general consensus is that these additives probably provide a little benefit in terms of neurological development and therefore, many formula companies add AHA and DHA to their formulas.

    • The European Commission, which is the equivalent to the FDA, recently stated that all stage one infant formulas have to have DHA added by the year 2020.   

Charles E. -

Can we get a list of which of the common formulas fit into which group (higher whey, partly hydrolyzed, etc?

Kimberly G. -

Does anyone have a chart/resource that breaks down the difference in formula brands. Which ones are partially hydrolyzed, which ones have palm oil, etc.

Solomon B., MD -

Hi Kim and Charles- our expert Bridget Young has given us permission to share a "cheat sheet" she created for practitioners...hope this helps! Here is the link to it:

Laurel S. -

Great, thanks for the cheat sheet. I would love to have heard about all the european formulas that everyone is now using. Is the european version of their FDA as strict as our FDA? And it looks like the iron concentration varies not only by formula type but by which country the hipp/holle is from, Dutch vs German. I am trying to find labels of the different versions to try to sort this out but it would be great to hear from the experts what they know about these formulas.


I enjoyed this presentation and searched out Dr Young's website. I was disheartened to print out her "How to Choose Baby Formula Like a Pro" tip sheet and read the bullet "your pediatrician likely dose not have this information. This is no fault of his/hers! There is severe lack of nutrition education i medical school and practice." Many of us do have training in nutrition and formulas in residency and were supported by wonderful dietitians. We may not have the full scope of this talk, but to say our profession as a whole is severely lacking something is not an appropriate generalization. Please don't throw other professions under the bus, we won't do the same to yours.

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For Whom the Bell's Tolls Full episode audio for MD edition 206:52 min - 97 MB - M4AHippo Peds RAP August 2018 Written Summary 404 KB - PDF