When You Start Solid Foods Does Not Appear to Affect IBD Risk, Large Study Finds

Inflammatory bowel disease is becoming more common in children and young adults worldwide, and researchers have long suspected that early-life diet might be one lever worth pulling. A large new study suggests one popular candidate, the timing of when infants first receive solid foods, probably is not that lever.

Complementary feeding timing showed no link to IBD risk

A prospective birth cohort study by Sigvardsson and colleagues, published in June 2026, followed 94,238 children enrolled in two Scandinavian birth cohorts from 1997 through 2023. Over 1,562,350 person-years of follow-up, 400 participants developed IBD. The core finding: whether complementary foods were introduced before 4 months, between 4 and 5 months, or at 6 months or later made no meaningful difference to IBD risk. The adjusted hazard ratio for introduction before 4 months was 1.04 (95% CI, 0.67 to 1.60), and for introduction at 4 to 5 months it was 0.83 (95% CI, 0.63 to 1.10), both compared to introduction at 6 months or later. Neither estimate approached statistical significance. Analyses of individual food groups, including cereals with gluten, dairy, meat, fish, fruits, and vegetables, produced similarly null results. Findings held for both Crohn's disease and ulcerative colitis separately, and also for IBD diagnosed in childhood before age 18.

Why this question matters as IBD climbs in young populations

IBD, which includes Crohn's disease, ulcerative colitis, and IBD unclassified, is a chronic gastrointestinal condition driven by a combination of known genetic and environmental IBD risk factors including family history, antibiotic exposure, delivery mode, and diet. Its incidence is not stable: rising global incidence of IBD in youth is well-documented, with incident cases among children and adolescents increasing by 22.8% from 1990 to 2019. That trend has pushed scientists toward early-life windows, particularly the first thousand days of life, when intestinal microbiota development is most plastic and feeding practices have their strongest influence. Complementary feeding, the period when solid and semi-solid foods are introduced alongside breast milk or formula, was flagged as a top research and prevention priority precisely because it is modifiable. If timing or food-group sequencing shaped IBD risk, parents and clinicians could act on that information. This study suggests, at least at the population level, it does not.

How a binational cohort of 94,000 children made this study credible

Previous research on complementary feeding and IBD was plagued by small samples, retrospective designs, and recall bias. The benefits of prospective cohort studies are well established: measuring exposures before disease onset eliminates the distortions that arise when participants reconstruct years-old dietary memories after receiving a diagnosis. The current study used two cohorts, All Babies in Southeast Sweden (ABIS, n=11,947) and the Norwegian Mother, Father and Child Cohort (MoBa, n=82,291), with feeding data collected via diaries and questionnaires in real time during infancy. The research team categorized introduction timing as before 4 months, 4 to 5 months, or 6 months and later, and also used latent class analysis to define four broader introduction patterns (early, mid, mid-late, and late) across seven food groups. IBD diagnoses were drawn from national patient registers and required at least two ICD-10 codes, a method with a positive predictive value of 93% or higher. The authors adjusted for child sex, birth year, maternal age and education, parental origin, and parental IBD history. Sensitivity analyses layered in breastfeeding duration, formula feeding, maternal smoking, birth weight, delivery mode, gestational age, dietary diversity, and antibiotic use. Results were consistent across both cohorts and all sensitivity analyses.

Key limitations and what this study cannot rule out

The null findings are informative but not the final word. Four hundred IBD cases across nearly 95,000 participants is a relatively modest event count, which limits statistical power to detect small associations with confidence. The follow-up period, mean ages of 16.5 to 25.2 years depending on cohort, captures childhood and young-adult IBD but cannot speak to disease that emerges later in life. The authors also acknowledge that erroneous parental recall of introduction timing, even in a prospective design, could have caused some misclassification and nudged estimates toward the null. The study is restricted to two Scandinavian countries with similar feeding cultures, relatively high breastfeeding rates, and specific IBD risk profiles; generalizability to populations with different diets or higher background IBD prevalence is uncertain. The researchers also cannot exclude stronger associations tied to more extreme feeding timings or finer-grained food classifications not captured in their data. Unmeasured lifestyle factors, such as processed food consumption in later childhood, could also confound the picture.

What researchers should focus on next for early-life IBD prevention

The study's authors frame their null result as useful signal, not a dead end. The consistency across two large national cohorts and multiple analytical approaches makes it unlikely that earlier retrospective null findings were simply artifacts of poor data. Complementary feeding timing can probably be deprioritized as a modifiable IBD risk factor, at least in Scandinavian-style feeding contexts. That shifts attention to other early-life candidates: antibiotic exposure, mode of delivery, breastfeeding duration, and gut microbiome composition in the first months of life. The research group notes that future work should examine more extreme introduction patterns and more granular food-group data, and should follow participants into full adulthood to capture later-onset disease. For now, the practical takeaway is that parents following standard guidelines, introducing complementary foods around 6 months as recommended by Nordic and global health authorities, are unlikely to be influencing their child's IBD risk through that timing decision alone.

Evidence rating

EMERGING — 76/100

Caveats:

• This is an observational cohort study — it can identify associations but cannot establish causation.
• With 400 IBD cases across 94,238 participants, the study may lack power to detect modest associations for individual food groups.
• Follow-up captured IBD primarily in childhood and young adulthood; later-onset IBD risk remains uncharacterized.
• Findings are from two Scandinavian populations and may not generalize to countries with different feeding practices or IBD prevalence.
• No funding source was disclosed by the authors.

Large prospective binational cohort study (n=94,238; 1,562,350 person-years) using national patient registers to ascertain IBD diagnoses with high positive predictive value. Shows no significant association between timing or pattern of complementary food introduction and IBD risk, consistent across both cohorts, sensitivity analyses, and disease subtypes; however, statistical power to exclude modest associations for individual food items was limited. This is the first prospective binational study on this question, though independent replication in non-Scandinavian populations has not yet been conducted.