“Let Them Eat Dirt: Saving Your Child from an Oversanitized World” provides suggestions for a microbially rich and healthy childhood.

eat dirt

Let Them Eat Dirt: Saving Your Child from an Oversanitized World talks directly to parents about the importance of microbes to your young kids. Authors  Brett Finlay, PhD and Marie-Claire Arrieta, PhD have an excellent message – let kids get dirty and quit abusing antibiotics. Let Them Eat Dirt is an engaging read clearly written and written clearly by scientist parents who have been in the “parenting trenches”. This microbiome parenting book is a fun read. Several times I laughed out loud at the references to pregnancy and parenting woes. As a scientist, I appreciated their overall message about the importance of microbes to our health.

Let Them Eat Dirt summarizes the current pregnancy and early childhood human microbiome well. It also is nice that there are specific “Do’s and Don’ts” listed at the end of each chapter for the exhausted and busy parent. The references by chapter are summarized at the end of the book. There were a few places when I wished it were referenced within the chapter a bit more, but I’m obsessed with reading microbiome literature. Let Them Eat Dirt does an excellent job covering the topics the parenting world is a-buzz about right now: vaginal seeding, breastfeeding, outside play, antibiotics, autism, vaccines, and probiotics. It’s also great that the authors specifically address current diets and their potential influence on the microbiome from gluten-free to “caveman”.

Scientific Caution

As a scientist, I appreciated that the authors repeatedly reminded the reader that microbiome science is new and findings might change with additional research. However, I wish some of their discussion of the science had been a bit more cautious. Marie-Claire said she wanted to provide information to parents to start a discussion with the family doctor and make the best decision for their family. I respect giving parents information – that’s the purpose of this blog! However, I’m a bit nervous that some of the suggestions made are a little premature. In particular, in the chapter “Gut Feelings: Microbiota and the Brain”, the authors discuss autism spectrum disorders and fecal transplants. What is presented in the book are specific cases where fecal transplants and antibiotics did and did not make a difference for a few autistic children. It is from these initial observations and cases that scientists begin designing experiments and clinical trials. These aren’t published cases and certainly aren’t clinical trials. With autism, I worry that it’s too early to suggest people consider fecal transplants. I worry that desperate families will fall victim to unscrupulous practices, or even worse, attempt a fecal transplant at home.


Shelves full of probiotics. Are they helpful and worth your money?


Throughout “Let Them Eat Dirt”, the authors also recommend using probiotics. On their book’s website they link to the outstanding resource “A Clinical Guide to Probiotic Products” developed first by Health Canada. This resource pulls together the brand-names of probiotics for sale in the U.S. and/or Canada that have passed different stages of clinical trials for specific health concerns. There’s an app I keep on my phone for when those constant questions about probiotics. The Clinical Guides are an excellent and reputable resource.

However, the majority of the world of probiotics is honestly, the Wild, Wild West. The majority of probiotics filling grocery and natural food store shelves have NOT gone through clinical trials and are NOT subjected to rigorous quality control. There may be some probiotics that anecdotally might work for a given problem. My kids and I do take probiotics at times. I select the probiotics based on the strains listed on the label as well as from quality control data from independent labs ( I use LabDoor, but another is Consumer Lab) . However, different strains of bacteria may have very different effects. One company’s Bifidobacterium infantis strain 1128 may be different from another company’s Bifidobacterium infantis strain 11AB. Bacterial strains are like fruit varieties. Granny Smith apples have a green peel and are tart while Gala apples have red peels and are sweet. These are both apples, but different varieties. At this point in time, we really don’t know how bacterial strains may vary.

Finlay and Arrieta acknowledge that probiotics are still in the beginning stages of development. I really appreciate their section on the future of microbiome therapies. Will the field of probiotics catch up? Most certainly. However, as with the fecal transplants and autism, I worry that readers may purchase probiotics that are not helpful. Will those probiotics be harmful? Without rigorous quality control, contaminants can be cultured along with the bacteria. One example was a fungal contaminated probiotic used in NICU’s in 2014 that killed some preterm infants. In most cases, ineffective probiotics are simply a waste of money.

The Take Home

In summary, Let Them Eat Dirt is the first book about the importance of microbes in the first years of life. Authors Finlay and Arrieta nicely interpret the microbiome literature for a lay audience. My only concern is that parents will get false hope that probiotics and fecal transplants are a solution they should seek now. The science is getting there, but science is a slow process. Read the book and let me know what you think. I’d love to hear. Maybe I’m just being overly cautious.

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Disclosure: The publisher provided me with copies of the book for review.

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