Three new studies examine the link between a healthy microbiome (the bacteria that make you up, explored in January on The PediaBlog here and here) and a healthy human.

The first study, published in Pediatrics last month, found that childhood allergies are less likely in households which wash dishes by hand instead of a dishwasher. Both eczema and asthma were significantly reduced in this study involving over 1,000 children living in Sweden, where 84% of families use dishwashing machines. Overall, washing dishes by hand reduced the risk of allergies in children by 43%. Two other food-consumption factors enhanced the effect on reducing the risk of allergies: eating fermented foods, like sauerkraut and pickles, and purchasing foods directly from a farm. The researchers believe that protection from allergies is based on the hygiene hypothesis, which previously explained why children who grow up on farms and are exposed to a greater diversity of bacteria and other microorganisms are less prone to allergic conditions:

The hygiene hypothesis stipulates that microbial exposure during early life induces immunologic tolerance via immune stimulation, and hence reduces the risk of allergy development.


Breastfeeding has been recognized to promote a healthy microbiome and a well-functioning immune system. Researchers recently looked at several factors that influence a baby’s gut microbiome, including gestational age at birth, whether a newborn was delivered vaginally or by cesarian section, fetal and infant tobacco exposure, and the presence of pets in the home. Honor Whiteman says breastfeeding is also a huge factor:

They also found that babies who were breastfed at 1 and 6 months had specific gut microbiome compositions, compared with babies who were not breastfed, which the researchers say may affect immune system development. In addition, babies who were breastfed at 1 month were at lower risk of pet-related allergies.


Whiteman spoke with the principle investigator:

“For years now, we’ve always thought that a sterile environment was not good for babies. Our research shows why. Exposure to these micro-organisms, or bacteria, in the first few months after birth actually help stimulate the immune system,” says Dr. Johnson.

“The immune system is designed to be exposed to bacteria on a grand scale,” she adds. “If you minimize those exposures, the immune system won’t develop optimally.”


Finally, researchers from Georgia State University looked at the impact of dietary emulsifiers on the development of inflammatory bowel disease (ulcerative colitis and Crohn’s Disease) and the obesity-related metabolic syndrome. Will Dunham says emulsifiers are chemicals used in food processing to prolong shelf life and alter texture in foods like ice cream, mayonnaise, margarine, creamy sauces, candy, bread and other baked goods, making “products like mayonnaise smooth and creamy instead of an unappetizing amalgam of water and oily globules”:

A key feature of inflammatory bowel diseases and metabolic syndrome is a change in the gut microbiota – the roughly 100 trillion bacteria that inhabit the intestinal tract – in ways that promote inflammation. In mice given emulsifiers, the bacteria were more apt to digest and infiltrate the dense mucus layer that lines and protects the intestines.


The researchers helped Dunham put 2-and-2 together:

Incidence of inflammatory bowel disease and metabolic syndrome started rising in the mid-20th century at roughly the same time that food manufacturers began widespread emulsifier use, the researchers said.

“We were thinking there was some non-genetic factor out there, some environmental factor, that would be explaining the increase in these chronic inflammatory diseases,” Georgia State immunologist Andrew Gewirtz said.

“And we thought that emulsifiers were a good candidate because they are so ubiquitous and their use has roughly paralleled the increase in these diseases. But I guess we were surprised at how strong the effects were.”