Fussy babies and Formula-Blaming: The Truth About Lactose Intolerance


by Milk-Drunk with expert advice from Pedro Prieto, MA, MS, PhD, and Jacqueline Winkelmann, MD, FAAP

There are so many worries during the first year of a baby’s life, but few are more distressing to a new parent than a baby’s fussiness. Yep, babies cry…a lot. They cry because they’re hungry, cold, wet, bored, scared…the list goes on and on. As parents, we want nothing more than our babies to be happy, comfortable, and safe (spoiler alert, this does NOT end when your baby grows up!). We try to understand why our baby is crying, we try to decipher what’s going on, and certainly want to fix whatever the problem is. 

As babies experience rapid growth in their first weeks of life, new parents learn to read signs of discomfort and attempt to provide relief from the real or perceived sources of fussiness. When a baby shows signs of gastrointestinal distress (gas, loose stools, stomach pain), parents often think their newborn’s distress is due to what they’re eating, especially if they’re a formula fed baby. In fact, parents will make an average of 2-3 baby formula switches in their baby’s first year of life. 

Is the discomfort caused by lactose intolerance?

Lactose and Lactose Absorption: The Science (bear with me)

Lactose is a disaccharide (carbohydrate/sugar) made up of two sugars, glucose and galactose. It is the main carbohydrate source in breastmilk and in many of the standard infant formulas on the market. Lactose is crucial to keep cells functioning correctly during rapid developmental stages. But it does more than just supply cells with energy: it helps grow “healthy bacteria” in the intestines and facilitates calcium absorption from the gut. However, it cannot be absorbed from the gastrointestinal (GI) system intact; it must be broken down, absorbed and transported into the bloodstream. The enzyme lactase, secreted by the intestinal cells, breaks down the lactose into more easily absorbable glucose and galactose molecules. 

If there is a mutation in the gene that encodes lactase, or the body is unable to make it, the lactose molecule remains intact through the small and large intestine. Lactose tends to draw water into the inside of the intestine and can also be fermented and produce gas, so the result is, you guessed it, symptoms of lactose intolerance include diarrhea, gas, bloating, and tummy pain! To make matters worse, if there is no lactose absorbed for energy, baby will have to use the limited reserves of fat and protein to produce the necessary energy to maintain life. In other words, the inability to digest lactose can really wreak havoc on a baby’s (and an adult’s) GI system.

How common is Lactose Intolerance in infants?

Lactose intolerance, medically known as lactase deficiency, is frequent in adults (up to 60%-70% of adults are lactose intolerant) but quite rare in infants. The prevalence of lactose intolerance is most common in African Americans, Hispanics/Latinos, and Asians, while least prevalent in people of European descent.

During gestation, baby will produce an adequate amount of lactase by around 37 weeks, so full term newborns have plenty of lactase, and lactase drops during childhood, adolescence and adulthood. Lactose intolerance is rare in children younger than 5 years of age. It is most often seen in adolescents and young adults.

Types of Lactose Intolerance

Congenital lactose intolerance- officially known as Congenital Lactase Deficiency (CLD) is the inability to produce active lactase from birth. It is a RARE disorder (1 in 60,000 babies or less). Newborns will present with watery diarrhea shortly after consuming breastmilk or infant formula (remember, lactose is the primary carbohydrate found in milk from breastfeeding). Diagnosis must be made quickly to prevent serious dehydration, and baby must be started on a lactose-free baby formula.

Developmental (neonatal) Lactase Deficiency. A different type of lactose intolerance is associated with the maturity of a newborn’s gastrointestinal system. This is called developmental lactase deficiency because it is associated with pre-term babies of less than 34 weeks of gestation who are born before their gastrointestinal tissues are mature enough to produce lactase. This deficiency is transient, and it subsides as the intestines gain the ability to produce lactase.

Primary Lactase Deficiency. During late childhood, the production of lactase decreases. While the gene that encodes lactose may be fully functional, a different segment of DNA suppresses its expression.  This lactase deficiency is not universally distributed. Around 70% of the adult population has some level of lactose intolerance, but its incidence varies according to ethnicity and age; Hispanics, Southern Italians, Arabs, and Ashkenazi Jews have 60-100% incidences and Northern Europeans of 2-30%. This type of intolerance is the one that is familiar to most adults.

Secondary Lactase Deficiency. In addition to other causes of intolerance to dairy products, there are instances, in adults, in which lactase synthesis is hampered by external factors. After injury, surgery, infection or during periods of prolonged inflammation, the intestine may decrease the production of lactase, resulting in transient lactose intolerance. In cases of this type of intolerance, it is necessary to manage the cause as well as the resulting intolerance simultaneously. We also see this in children when they have gastroenteritis, most commonly due to a virus.

Who benefits from a Lactose-Reduced baby formula?

Treatment for lactose intolerance involves offering baby a lactose-reduced formula, but the evolution of these “special formulas” has more to do with a demand on the market than true science. Because lactose intolerance is so common in adults, parents might associate GI distress in their little one with lactose intolerance. We now know this is quite rare in young children under the age of five.

In lactose-free or lactose-reduced formulas for lactose intolerant children, the lactose sugar has been replaced by other sugars. Infant formula companies tend to add corn syrup or sucrose (table sugar). At this time, the FDA does not regulate the percentage of corn syrup and sucrose allowed in infant formula. In contrast, the EC (European Union Commission, equivalent of the US FDA) standards regulates these carbohydrates, and limits them in European baby formulas.

What babies should drink lactose-free or lactose-reduced formula?

While we now know true lactose intolerance is extremely rare in infants, there are a few circumstances where a lactose-free or reduced formula might be indicated. Always discuss with your pediatrician or health care provider before starting or switching to any special formula for your child’s diet.

  • Premature babies– since the lactase enzyme is produced close to 37 weeks of gestation, babies born before that time might benefit from a lactose reduced formula until they can “catch-up” with enzyme production. 
  • Babies born with galactosemia- galactosemia is a rare, inherited medical condition where are unable to safely digest galactose, one of the two sugars that make up lactose. The condition is diagnosed at birth through newborn screening tests. Babies with galactosemia cannot tolerate breastmilk or standard infant formulas with lactose and must be given lactose-free formula that is not derived from cow’s milk. 
  • Babies born with Congenital Lactase deficiency- another very rare condition where babies cannot produce the lactase enzyme and therefore cannot digest lactose in either breastmilk or standard cow’s milk formula. 

Is lactose intolerance the same thing as a milk allergy?

No, not at all. Many parents confuse the terms lactose intolerance and milk allergy. While they may share similar symptoms, they are entirely different conditions. Lactose intolerance is a problem related to the absence of a digestive enzyme, lactase, and deals with the carbohydrate source of formula (or breastmilk). A milk allergy involves an immune system reaction to the protein component of cow’s milk and cow’s milk products like ice cream. Cow’s milk allergy is sometimes called cow’s milk protein allergy, or CMPA. While lactose intolerance is rare in children under the age of 5, CMPA is much more common (3-7% of babies) and usually diagnosed before 1 year of age. If your baby is having trouble digesting formula, it is much more likely to be a protein problem than a carbohydrate problem.

Symptoms of Cow’s milk allergy, or CPMA, can include

  • Rash, hives, dry, scaly or itchy skin
  • Digestive system symptoms: diarrhoea, severe diarrhea, colic, constipation, abdominal pain, vomiting, reflux
  • Respiratory symptoms:  noisy breathing, coughing, runny nose

Treatment for CMPA involves specialized formulas with partially broken-down proteins. Your baby’s pediatrician or health care provider should guide you through this formula change

The takeaway regarding fussy babies

As parents, we want our babies to be happy and content (so we can be happy and content as well!). When babies fuss or show signs of discomfort, we tend to want to find an answer and many times the immediate reaction is- “it must be the formula.” Keep in mind, breastfed babies fuss too! If your baby is truly showing signs of significant distress, including skin rashes, GI, or respiratory symptoms, get medical advice from your baby’s pediatrician, dietitian, or health care provider. They can guide you through formula changes if necessary, so you can avoid getting caught up in the formula marketing hype and can make informed decisions for your baby and make sure they get enough calcium and Vitamin D. As babies’ systems develop and mature, they will be able to tolerate much more, so hang in there, this too shall pass! 

Pedro Prieto is an infant formula industry veteran with 25 years of experience in first synthesis, product design and clinical trial of human milk oligosaccharides for pediatric nutrition and holds a PhD, and MS degrees in Biochemistry and Nutrition as well as an MA on Administration of Higher Education Institutions. Dr. Jacqueline Winkelmann is a board certified pediatrician in Southern California. They are both Bobbie Medical Advisors.


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The content on this site is for informational purposes only and not intended to be a substitute for professional medical advice, diagnosis or treatment. Discuss any health or feeding concerns with your infant's pediatrician. Never disregard professional medical advice or delay it based on the content on this page.

The content on this site is for informational purposes only and not intended to be a substitute for professional medical advice, diagnosis or treatment. Discuss any health or feeding concerns with your infant’s pediatrician. Never disregard professional medical advice or delay it based on the content on this page.

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