Functional constipation (FC) is defined as the delay or difficulty in stool evacuation that cannot be explained by another medical condition.1 According to the Rome IV criteria, the diagnosis of FC requires the presence of 2 or more of the following symptoms for at least a month: fewer than 3 bowel movements per week, one or more episodes of faecal incontinence per week, faecal retention, painful defecation or hard stools or presence of a large faecal mass in the rectum.2

There are disagreements regarding the prevalence of constipation in children in the literature; however, it is estimated that up to 30% of the children suffer from this type of gastrointestinal disorder.3 Functional constipation accounts for more than 90% of cases of constipation in children4 and several factors interact to protect or promote the onset of symptoms, such as the type of birth,5 breastfeeding6 or the consumption of cow’s milk7 or infant formula.7

Dietary factors also play an important role in the pathophysiology of FC.1 The introduction of complementary foods is an important milestone in the establishment of healthy eating habits and the prevention of gastrointestinal disorders, including constipation. Current guidelines recommend starting to introduce solid foods at age 6 months.8,9 The Ministry of Health of Brazil advises a slow and gradual introduction of complementary feeding, starting with a variety of pureed foods fed with a spoon with progressive changes until reaching the texture consumed by the family.10 Other approaches for the introduction of complementary foods have been proposed to date, such as the baby-led weaning (BLW) method and the Baby-led Introduction to SolidS (BLISS).11 Both methods recommend the introduction of food in strips or sticks, allowing the child to hold them and bring them to the mouth independently under adult supervision.11,12

A review of the benefits of infant-guided introduction to solids found that infants fed by these methods were at lower risk of consuming salt and sugar between ages 25 and 36 months13 and of having a high body mass index (BMI) for age.14 However, none of them evaluated the prevalence of constipation symptoms in infants fed with these approaches.

The aim of our study was to investigate the prevalence of different approaches to the introduction of solid foods and their impact on the prevalence of FC symptoms at age 12 months.

In the initial recruitment, 207 mothers expressed interest in participating in the study, of who 12 did not meet the inclusion criteria. Thus, 195 were considered eligible and randomized to the 3 methods to introduce complementary feeding. A total of 139 mothers attended the intervention, of who 135 completed the questionnaire when the infant was 12 months of age. Fig. 1 presents a flowchart of the sample selection process.

Figure 1.

Study design.

PLW, parent-led weaning. BLISS, Baby-led Introduction to SolidS.

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Table 1 summarises the characteristics of the sample. In the overall sample, the maternal educational attainment in most families was of 15 years or more (76.9%). The total household income ranged from 3 to 10 times the minimum wage (59.8%). The minimum wage in Brazil is R$ 1212.00 and is the most widely used measure of income. As regards the birth characteristics, 84 (62.2%) of participants had a caesarean section and 72 (53.3%) of the infants were female. The percentage of infants breastfed exclusively until 6 months post birth was 54.1%, and at 12 months, 101 (74.8%) were still breastfeeding and 55 (40.7%) were fed infant formula. The median age at which solids started to be introduced was 180 days (180;180) days. At the 12-month time point, most infants did not consume cow’s milk (91.9%), were receiving iron supplementation (72.6%) and were not enrolled in day care (71.1%). We did not find significant differences in any of the analysed characteristics based on the method used for introducing complementary foods (P > .05).

Table 2 describes the associations between the bowel habits of infants and the method of introduction of complementary feeding. Half of the sample (49.6%) exhibited FC symptoms. Out of the total sample, 117 (86.7%) infants passed stools daily, and 9 (6.7%) had type 2 stools on the Bristol stool scale. Most infants (54.1%) exhibited straining during defecation once a week or less, and 114 (84.4%) did not cry or express pain during bowel movements. Laxatives were never used by 85.9% of the sample, and, in the subset that used them, 8 (5.9%) used them once and 11 (8.2%) twice or more. Anal fissures were detected in 6 infants (4.4%), just over half the sample (54.1%) suffered from colic, and most infants (91.1%) had never had bloody stools. We did not find a statistically significant association between FC (P = .183) or gastrointestinal symptoms related to constipation and the method used to introduce complementary foods.

Table 3 describes the association between the presence of FC symptoms with different risk and protective factors. Family, birth and infant characteristics were not significantly associated with the presence of FC symptoms. The PR of constipation symptoms based on the applied method of complementary feeding and using the PLW method as reference was 0.675 for the mixed method (95% CI, 0.436–1.045; P = .077) and 0.799 for the BLISS method (95% CI, 0.546–1.167; P = .245) (data not shown).

The analysis of fibre consumption revealed that out of the 135 infants in the sample, 121 (89.6%) had consumed vegetables, 28 (20.7%) greens and 115 (85.2%) beans the day before data collection. When we compared the approaches to the introduction of solid foods and the consumption of vegetables, greens and beans, we found no significant differences in consumption between the different methods (P = .639, P = .7,86, and P = .213, respectively) (data not shown).

The results of our study show that the prevalence of FC symptoms was high in the infants in the sample. However, we did not find an association between the method used to introduce complementary foods and constipation or its symptoms. The prevalence of FC symptoms found in our sample was higher compared to a randomized trial conducted in Brazil that found a prevalence of constipation of 15% in children who underwent an intervention that addressed feeding habits, such as breastfeeding and healthy introduction to solids.18 Contrary to our study, the researchers assessed for the presence of FC at age 6 years, which may have contributed to the differences in the results. In younger children, which made up our sample, it is harder to measure these symptoms accurately. In addition, there is a risk of selection bias, as including more mothers interested in the subject may have affected the outcomes and led to overestimation of the reported symptoms. Another particularity to take into consideration is that the questionnaire did not ask about the specific period the constipation symptoms occurred, which may have increased the reported frequency of constipation.

The complementary feeding methods used in these infants were safe from a micronutrient intake perspective,19 in addition to increasing exposure to vegetables and protein sources, thus contributing to an improved fibre intake.20,21 Contrary to previous publications, our analysis of the consumption of fibre-rich foods did not identify any statistically significant differences between the groups. This could be related to the fact that all 3 groups received nutritional guidance and may explain why different methods were not significantly associated with FC symptoms.

Breastfeeding is a protective factor for childhood gastrointestinal disorders.6,7,17 One of the mechanisms believed to contribute to the protection of infants against gastrointestinal diseases conferred by breastfeeding is the presence of human milk oligosaccharides (HMOs), abundant in breast milk, as they act as probiotics, nourishing and selecting bacteria in the gastrointestinal tract.22 Despite the high proportion of infants who were breastfed in the sample, we did not find an association between the absence of constipation symptoms and breastfeeding, which may have been due to the influence of complementary feeding, as solid foods had been introduced approximately 6 months before the assessment.

Unlike human milk, the consumption of cow’s milk by infants is a risk factor for constipation. A study conducted in Brazil that assessed the presence of constipation in preschool children found that those who received cow’s milk before age 6 months were up to 15 times more likely to have constipation.7 The consumption of cow’s milk at age 12 months in our sample was low compared to other studies in Brazil, probably due to the high educational attainment and socioeconomic status of the sample.23 However, despite the high prevalence of breastfeeding and infrequent consumption of cow’s milk, in addition to nutritional counselling, the presence of constipation symptoms in our sample was higher compared to the study in preschool children conducted in Brazil.7

Another factor that has been associated with FC symptoms is the mode of delivery. Vaginally delivered infants come in contact with a wide variety of microorganisms as they pass through the birth canal, whereas infants delivered by caesarean section are not exposed to the same microbiota.24 This difference in the colonization of the latter neonates may promote the development of diseases associated with immune system dysfunction.25 A cohort study based on data from the Japan Environment and Children’s Study that included 71 878 mother-infant pairs found an increased risk of FC at age 3 years in children born by caesarean section.5 In our sample, more than 60% of the children had been delivered by caesarean section, and the large proportion of caesarean delivery may have contributed to the high prevalence of FC symptoms observed in our study, although differences based on this variable were not statistically significant.

There are limitations to this study, such as the assessment of constipation symptoms at a single timepoint and the high socioeconomic status of the sample, which limits the generalization of the findings to the Brazilian population. The sample size may have been insufficient to obtain significant results in the tests performed to assess association. In addition, the fact that mothers were interviewed by a team of nutritionists and nutrition students may have kept them from disclosing nutritional problems. The analysis was made with the intention to treat, even though not all participants followed the assigned method. Divergence from the assigned method was most frequent in pairs assigned to the BLISS and PLW methods that ended up following the mixed method. More information about adherence can be found in another study in the same sample.26 The low adherence to the BLISS method may explain the results.

These limitations notwithstanding, our study is the first randomized clinical trial to analyse complementary feeding introduction methods in relation to the presence of constipation symptoms in infants in the Brazilian population. In addition, the mixed method was developed specifically for this research project. Studying the differences between the types of complementary feeding and their impact on infant health is very relevant in terms of giving families the autonomy to choose the most suitable method for them and to support more precise guidance and prescriptions in nutritional care.

In conclusion, we found a high prevalence of FC symptoms in the sample that was not associated with the methods of introduction of complementary feeding. More research is needed to investigate the association of the complementary feeding method with FC symptoms in infants, taking into account food intake and the timing of symptoms.

This study was funded by the Coordination for the Improvement of Higher Education Personnel and the Brazilian National Council for Scientific and Technological Development through master’s and doctorate’s scholarships; the budget for doctoral students and the Research and Events Incentive Fund at the Hospital de Clínicas de Porto Alegre.