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Researchers looking for post-breastfeeding dietary patterns in two prospective birth cohorts that predispose infants to asthma found one, and it wasn't what anyone expected.

After switching from breast milk, babies up to age 1 whose protein intake came largely from meat products -- as opposed to dairy, fish, or egg proteins -- showed more than eight-fold greater odds of developing asthma by age 6 (OR 8.47, P=0.001) relative to non-meat protein consumption, reported Alexander Hose, MA, MPH, of Ludwig Maximilian University in Munich, at the virtual European Respiratory Society annual meeting. Asthma prevalence reached 30% in some subgroups.

Wheezing was also significantly more common with this dietary pattern, which Hose and colleagues called "unbalanced meat consumption" (UMC); this continued up to age 10, when the odds ratio stood at nearly 5.

Non-atopic asthma appeared to be somewhat more common than atopic illness, although small numbers of the latter made it impossible to reach a definite conclusion.

Breastfeeding duration was an important factor, probably because early switching to regular baby foods prolonged the exposure. Odds of developing asthma by age 6 increased nearly 12-fold in UMC-fed infants whose breastfeeding stopped by week 19 of life, versus about four-fold in those continuing longer on breast milk.

Moreover, UMC was also linked to a certain intestinal microbiome profile featuring unusually high levels of Lactococcus, Granulicatella, and Acinetobacter species.

This type of microbiome scavenges iron in the gut, Hose said, potentially explaining why the children became especially susceptible to asthma. In addition, he said, milk proteins may have the opposite effect on asthma risk by generating a type of "nutritional immunity."

Although the precise mechanisms connecting the intestinal microbiome to airway disease aren't known, the existence of a is well established; one recent trial, for example, showed that probiotics can prevent coughs and wheezing in older adults. The phenomenon has also been proffered as an explanation for the gastrointestinal symptoms of COVID-19.

Data for the study came from two European birth cohort studies, and , in which a total of about 1,400 infants were followed through age 10. In both, parents kept detailed records of their infants' feeding (along with a host of other environmental factors), and children's medical records were accessed as well.

An important limitation of the analysis is that these cohorts were recruited in rural areas, because asthma's relationship to animal exposure was one of the principal goals when the projects were launched in the 2000s. In part because of this design, Hose and colleagues were able to distinguish "industrial" meat, milk, and yogurt from that produced at home; there was a trend toward greater asthma risk with store-bought protein products.

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