Asthma has become increasingly prevalent in Western societies, and while many theories have been explored as to the reason for this rise in prevalence, many are beginning to explore connections between dietary intake and associations with the microbiome as a manifestation for this malady. High fat, low fiber diets – which are common in the West – are associated with high rates of asthma. Investigators in Australia sought to explore this relationship further by understanding the cellular underpinnings of these associations. Specifically, they explored whether or not high fiber diets in mice could suppress the onset of Allergenic airway disease (ADD -i.e. asthma). Furthermore, maternal fiber intake was also examined to see what affects would result for the progeny when challenged with asthma inducing conditions. They published the results in Nature Communications.
Using 16S sequencing the researchers first confirmed that the high fiber diet shaped gut microbiome composition in mice. Specifically, a significant difference was observed between control diet and no fiber diet. Bacteroidetes were highly abundant in mice that were fed the high fiber diet, including high acetate producing Bacteroides acidifaciens strain, while Proteobacteria were found abundant in the no fiber diet. High fiber diet mice also displayed higher levels of short-chain fatty acids, metabolic products of the gut microbiota that provide overall positive health benefits.
Turning next to the pathology, experimenters were first able to validate that HDM did indeed induce AAD, as confirmed by inflammatory cells and signal markers found in the bronchoalveolar fluid of mice. Indeed, mice that were on the high fiber diet did not develop AAD symptoms. Interestingly, this was also shown in control animals who were administered HDM but were provided acetate (a short-chain fatty acid) in their drinking water.
Mice were then bred and split into three dietary groups based on diet, a control group, high fiber group, and no fiber group. Allergenic airway disease (AAD) was induced using a house-dust mite (HDM) model which replicates certain aspects of human asthma. Diets were provided three weeks prior to sensitizing the animals to HDM, and AAD was evaluated after 16 days following 15-day HDM exposure.
Pregnant mice were also subjected to the three different diet regiments in the previous experiment. The offspring were born and given a control diet, but after 6 weeks they were administered AAD. The mice that were born from mothers on the high fiber diet did not develop AAD into adulthood, demonstrating that maternal diet can suppress AAD in adult offspring. Interestingly, these findings were correlated with human data that demonstrated that high fiber diets in mothers’ in late-stage pregnancy was correlated to high acetate in serum samples. Maternal acetate levels above median levels of samples taken was associated with significantly less visits to the general practitioner for wheezing complaints and/or asthmatic incidences in their children.
Increasing numbers of studies are showing similar patterns that behaviors of the mother can affect microbiome transfer to progeny, consequently affecting the health and development of the offspring. One of these important factors as we have seen is the diet of the mother. As further evidence is uncovered as to the importance of high fat diets and specifically the diet of the mother, it will be important to have conversations on the best way to educate the public about this evidence as well as implement recommendations for dietary habits during pregnancy.