Health related factors for when to start solids

Breastfeeding is a trendy thing right now. Am I right?

From cutesy nursing covers being a go-to baby shower gift to over three million photos on Instagram being tagged #breastfeeding, the public is often pretty public about this issue.

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Except when it's not.

As may be assumed, I am pro-breastfeeding. I do believe it is the ideal choice for infant nutrition, if and when it is possible to be provided. That being said, I am also a parent who has had my fair share of hardships breastfeeding both of our daughters (as shared here). I am also a public health professional that knows far too well,

What is trendy is not always what is true. What is public is not always portraying what is private.

Breastfeeding is no exception, especially in its relationship with starting solids. We promote this image of “Breast is Best!” and yet in many families, babies are weaned off of breastfeeding prematurely - particularly as solids are introduced.

According to the 2018 CDC Breastfeeding Report Card, more than four out of five moms tried breastfeeding. Of those, over half were still breastfeeding at six months and about a quarter by one year. More applicable to our conversation here, is that only 46% of mothers were exclusively breastfeeding at three months and only 25% at six months.

A study published in the journal Pediatrics in 2013 found that overall (among breastfed, formula-fed, and mixed-fed infants), 40% of mothers introduced solid foods before 4 months. The proportions of infants who were introduced to solids according to the recommended age range (between 4-6 months) was highest among infants receiving only breast milk, when compared with formula and mixed-fed infants.

These statistics and findings are concerning when it comes to the conversation about introducing solids. We know that the early introduction of solids ends exclusive breastfeeding and has been associated with reduced duration of any breastfeeding. Given the important health benefits of breast milk and Healthy People 2020 Objectives to promote a higher prevalence of breastfeeding, any interference with breastfeeding an infant, especially at this age, would be unadvised. Additionally, the health concerns of feeding babies too soon (prior to 4 months) may increase an infant's risk of some chronic diseases, such as diabetes, obesity, eczema, and celiac disease. On the contrary, waiting to introduce solids until at least 4 months can improve the health-related outcomes an infant experiences both in the short and long term.

This becomes a bit confusing though. As we saw in last week’s post on what the experts say about when to start solids, there are professional organizations advising babies start between 4-6 months and then those advising to wait until around 6 months. As we will discuss in next week’s post, an infant’s development during this 4-6 window also ought to dictate a family’s decision on when to start solids. For the purposes of this post, we are going to review:

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In this post, we will cover many of the health concerns related to starting solids before 4 months (<17 weeks), between 4-6 months, or after 6 months (>26 weeks). These include nutritional, allergic, chronic disease, and developmental risk factors associated with the introduction of solid foods and the common argument for why families might wait until six months for solids. For the purposes of this post, 4 months equates to 17 weeks or the beginning of the 5th month and 6 months equates to 26 weeks or the beginning of the 7th month (source).

Where applicable, some of the health concerns of feeding babies too soon and/or too late are included in italics following the associated health concern for introducing solids during the 4-6 month range.

Let's address these health-related factors for when to start here.


Health-related factors for when to start for solids

Physiological factors for when to start solids


Understandably, there is a lot of confusion over when an infant’s body is physiologically “ready” to start solids. From articles like this to a growing interest in gut health and topics like leaky gut or “open gut” in infancy or “leaky gut” later in life, parents naturally have questions and concerns. That is why it is helpful to see research such as this confirming that “both renal function and gastrointestinal function are sufficiently mature to metabolize nutrients from complementary foods (i.e. solids) by the age of 4 months and that, to a large degree, gastrointestinal maturation is driven by the foods ingested. “

Explained in layman terms here, Science of Mom does an excellent job explaining this here, by saying, “When infants start eating solid foods, they are shifting from the relatively simple diet of easy-to-digest breast milk and/or formula to a more complex diet with a variety of foods (with milk still being an important one). These foods require more work to digest, which means greater activity of a suite of digestive enzymes. In addition, the kidneys have to work a bit harder to excrete metabolites from these foods.” For more on the science behind open gut, visit here.


Something important to highlight early on in this post is a child’s neurological development and thus readiness to safely handle solid foods. While an infant’s readiness may vary depending on the way solids are introduced (being spoon-fed or with a Baby Led Weaning approach), we know that in general, “the skills required for an infant to safely accept and swallow pureed complementary foods from a spoon typically appear during the 4- to 6-month period, whereas those required to handle lumpy (semisolid) foods or to self-feed, as currently advocated in the “baby-led” approach popular in some countries, will appear later in the first year.” For a more in-depth overview, I encourage you to read this review article or to subscribe here so you get my newsletter next week, which will be all about assessing an infant’s developmental readiness for solids.


Nutritional factors for when to start solids

One of the leading reasons parents introduce foods early is because they believe their infant appears hungry, needs more than milk for proper growth than they initiate by bottle or breast, or out of concern for iron deficiencies. Many similar hypotheses have been tested by leading researchers to conclude the following:

intrinsic regulation of food intake

Infants who are exclusively breastfed until 6 months have been found to have similar nutrient intakes to infants who were introduced to solids at 4 months. Although the source of their calories differed (between 100% breast milk and breast milk+solids), the overall caloric intake was not significantly different. Read more about such research here.


When fed within the 4-6 month window, there is no benefit nor deficit to infant's growth. Infants who are exclusively breastfed for six months do not show deficits in anthropometric measures such as height, weight, or body mass index (BMI). Read more about such research here.

iron status

Many studies have researched if iron status is improved in infants who are exposed to complementary, iron-rich foods earlier versus later (ie. 4 vs. 6 months). Although infants introduced to solids at an earlier age often have higher iron stores at 6 months (compared to infants exclusively breastfed for 6 months), iron levels were adequate in both groups. As shared here, the number of infants with iron deficiency or iron deficiency anemia was not significantly different between those introduced to solids earlier versus later. This suggests that although infants introduced to solids at 4 months may have a higher or perceived "better" iron status, the difference may not be significant when compared to healthy infants who are exclusively breastfed until 6 months. Note this does not apply to infants who are introduced to solids after 6 months. Delaying solids beyond 6 months does increase an infant's risk of iron deficiency.

Allergy-related reasons to wait until six months to start solids

In 2003, the American Academy of Pediatrics (AAP) released a statement recommending the delayed introduction of highly allergenic foods in "high risk" infants.  Such guidelines advised not introducing cow’s milk until age 1 year; egg until age 2 years; and peanuts, tree nuts, and fish until age 3 years were recommended. Unfortunately, we saw a dramatic increase in the incidence and prevalence of food allergy and allergic disease in the years after these guidelines were given. And yet, these recommendations that suggest waiting to introduce top allergens are still ingrained into many of our minds.

Fast forward to the present day, and we know that the timing certain foods are introduced might matter when it comes to preventing food allergies and atopic disease (like eczema and asthma). It is unclear why earlier research showed delayed introduction of solid food to be preventive. However, current data does support how these recommends have changed over the last decade to support earlier introduction of solids as preventative.

“Systematic reviews have concluded that there is evidence of an increased risk of allergy if solids are introduced before 3 to 4 months, but there is no evidence that delaying the introduction of allergenic foods beyond 4 months reduces the risk of allergy, either for infants in the general population or for those with a family history of atopy.” There is observational data, however, to suggest an increased risk with delayed introduction of certain allergens.”

- The Position Paper by the European Society for Paediatric Gastroenterology, Hepatology, and Nutrition (ESPGHAN) Committee on Nutrition Evidence

For parents who may be familiar with more current research on the subject of food allergies, this study summarizes,

“The randomized, controlled Learning Early about Peanut Allergy (LEAP) trial showed that the early consumption of peanut in high risk infants with severe eczema, egg allergy, or both reduced the development of peanut allergy by 80% by 5 years of age. The Persistence of Oral Tolerance to Peanut (LEAP-On) study has now shown that the absence of reactivity is maintained in these infants. However, the LEAP trial did not investigate the efficacy of introduction of other allergenic foods, nor did it examine whether this approach could prevent peanut allergy in children in the general population. The Enquiring about Tolerance (EAT) trial was therefore conceived to determine whether the early introduction of common dietary allergens (peanut, cooked hen’s egg, cow’s milk, sesame, whitefish, and wheat) from 3 months of age in exclusively breast-fed infants in the general population would prevent food allergies, as compared with infants who were exclusively breastfed for approximately 6 months.”

In short, with much research still being conducted on the relationship between starting solids and the development of food allergies, reviews (like this) have,

“concluded that there is evidence of an increased risk of allergy if solids are introduced before 3 to 4 months, but there is no evidence that delaying the introduction of allergenic foods beyond 4 months reduces the risk of allergy, either for infants in the general population or for those with a family history of atopy.”

A review of the EAT trial and some key, practical takeaways can be found here.

Chronic disease-related reasons to wait until six months to start solids

risk of infection

One of the reasons exclusive breastfeeding is often encouraged in developing countries is due to the poor sanitation and access to safe resources like clean water and refrigeration. In such environments, introducing solids opens up an unwanted opportunity for exposure to pathogens that may increase an infant's risk of infection. infection in infants. However, research in developed countries suggests that an infant's risk of infection is not significantly higher among those who had received solids versus those who had not, nor did the risk vary according to when an infant starts solids. The only exception to this, as shared here, may be with an increase in upper respiratory tract infection among infants who are given solids earlier than 4-6 months.

risk of obesity

According to European Food Safety Authority (EFSA) Panel on Dietetic Products, Nutrition and Allergies, starting solids between 4-6 months of age does not have a strong impact on growth velocity (both weight and length) nor risk for obesity later in life. The Position Paper by the ESPGHAN Committee on Nutrition Evidence states that,

“Evidence from 2 large, good-quality studies, however, suggested increased later obesity risk associated with early introduction of solids (<4 months) and a third good-quality study confirmed this association in formula-fed but not breast-fed infants. None of the 4 good-quality studies provided evidence for any clinically relevant protective effect of delaying solid introduction from 4 to 6 to >6 months of age.”

These findings were consistent with data from the EAT study that there were no significant differences in anthropometric measures or in the risk of overweight and obesity at three years of age.

Risk of celiac disease

As updated in a Position Paper by ESPGHAN on Gluten Introduction and the Risk of Celiac Disease and summarized here,

“Neither any breast-feeding nor breast-feeding during gluten introduction has been shown to reduce the risk of CD. Gluten may be introduced into the infant's diet anytime between 4 and 12 months of age. Based on observational data pointing to the association between the amount of gluten intake and risk of CD, consumption of large quantities of gluten should be avoided during the first weeks after gluten introduction and during infancy. The optimal amounts of gluten to be introduced at weaning have, however, not been established. Although the risk of inducing CD through a gluten-containing diet exclusively applies to persons carrying at least one of the CD risk alleles, since genetic risk alleles are generally not known in an infant at the time of solid food introduction, the recommendations apply to all infants.”

If a family has a history of Celiac Disease, you may wish to read more about the current recommendations here.


In Summary

So what does all this mean to you?

Perhaps best summarized by a joint statement from the United Kingdom’s Scientific Advisory Committee on Nutrition and the Committee on Toxicity of Chemicals in food, Consumer products and the Environment may also be extended to parents in all developed countries:

The government should continue to recommend exclusive breastfeeding for around the first six months of life. Advice on complementary feeding should state that foods containing peanut and hen’s egg need not be differentiated from other complementary foods. Complementary foods should be introduced in an age appropriate form from around six months of age, alongside continued breastfeeding, at a time and in a manner to suit both the family and individual child.

The deliberate exclusion of peanut or hen’s egg beyond six to twelve months of age may increase the risk of allergy to the same foods. Once introduced, and where tolerated, these foods should be part of the infant’s usual diet, to suit both the individual child and family. If initial exposure is not continued as part of the infant’s usual diet, then this may increase the risk of sensitization and subsequent food allergy.

Families of infants with a history of early-onset eczema or suspected food allergy may wish to seek medical advice before introducing these foods.

While this statement specifies peanuts and hen’s eggs as the two allergens of mention, this statement generalizes the overarching theme we see most conclusive within the research at the time of this writing.

However, as highlighted in the next and final post from this series on "When to Start Solids," we see that even though there may be benefit for introducing some foods, particularly allergens, before six months, many babies may not show the signs of readiness. Rushing these can negatively impact how both parent and child welcome the start of solids. This reminds us how important it is, with each unique infant, to focus on an infant's cues (for developmental readiness) and not the calendar (for it’s calculated age).