The research team also find that infants on solid foods at or before three months of age showed changes in levels of bacterial by-products, such as short-chain fatty acids (SCFA).
“How the early introduction of solid foods would cause the later development of obesity has been unknown, but our findings suggest that disruptions to gut bacteria may be one explanation,” says Dr Noel Mueller, assistant professor at the department of epidemiology at Johns Hopkins Bloomberg School of Public Health.
Early introduction to complementary or solid foods in infancy has been linked with an increased risk of childhood obesity, oxidative stress, and immune-mediated conditions, but the mechanism underlying these associations is not yet well understood.
It has been suggested that alterations in the infant gut microbiota may be on the pathway with studies identifying adult-associated microbes dominating the infant microbiota after weaning.
SCFAs are metabolites derived from the breakdown of indigestible dietary polysaccharides by the colonic microbiota and may play a role in mediating these conditions associated with an altered gut microbiota.
Higher concentrations of butyrate and other SCFAs in the stool may indicate that these metabolites are being excreted rather than absorbed.
One study found that higher SCFAs in the stool- a likely result of gut microbiota dysbiosis - was associated with obesity and hypertension, among other cardiometabolic risk factors.
Mueller and his colleagues began looking at data following 67 infants in a community, for the first year of life that explored early-life factors that may lead to obesity in later life.
The team also interviewed the mothers every three months about the infants’ diets and other factors also collecting stool samples from the infants.
They then compared the timing of solid food introduction with the bacterial species and by-products found in the month-3 and month-12 stool samples.
Results indicated that samples from infants on solid foods at or before three months, at the month-3 time point and even at the month-12 time point, contained a significantly higher diversity of bacteria compared to samples from infants who had started later on solid foods.
In particular, the bacterial populations of Bilophila wadsworthia and Lachnospiraceae Roseburia were associated with early (vs. later) complementary feeding and with higher butyric acid concentrations at 3 and 12 months, respectively.
Further analysis found stool-sample levels of total SCFAs and butyric acid to be higher in the stools of infants started on solid foods by three months at the 12-month testing mark.
However, this was not observed at 3 months, suggesting a delayed and sustained impact of early solid-food introduction.
“The findings are consistent with the emerging evidence that gut microbiome changes are key factors in the development of common metabolic and immune conditions and suggest that scientists are on the right track in studying these changes,” concludes Mueller.
B. wadsworthia and L Roseburia
In the study’s discussion, the team cited studies that showed Bilophila wadsworthia and Lachnospiraceae Roseburia were associated with early complementary feeding and with higher butyric acid concentrations at 3 and 12 months of age, respectively.
L. Roseburia are known butyrate producers, and in adults, are thought to have beneficial effects on the gut mucosa and cardiometabolic health.
However, the team also acknowledge that the role of this genus in the health of infants had not been well studied and may represent accelerated microbiome maturation.
B. wadsworthia belongs to the Desulfovibrionaceae family, which are known for their sulphate-reducing capabilities and have been previously found in healthy infants.
Sulphates are found in a variety of infant formulas and breastmilk, and so early introduction to complementary foods may reduce dietary sulphate, thus decreasing the abundance of B. wadsworthia.
The authors add that further research is needed to determine if these measures of microbiome diversity and short-chain fatty acid concentration truly drive the development of obesity and other disorders.
Mueller and colleagues are continuing to conduct studies of diet and the gut microbiome in infants and children, and the associations between these factors and outcomes such as obesity and immune-related disorders.
Source: BMC Microbiol
Published online ahead of print: doi.org/10.1186/s12866-020-01723-9
“Timing of complementary feeding is associated with gut microbiota diversity and composition and short chain fatty acid concentrations over the first year of life.”
Authors: Moira Differding et al.