When we eat food, we eat all the microbes that live on and in the food. But how many microbes do we eat daily? An interesting study was published a few years ago that tried to answer this question. The researchers found that the average American adult ingests between 1 million to over 1 billion microbes every day!
The University of California researchers conducted the study in 2014 by analyzing meals representing three typical dietary patterns: 1) the average American diet (lots of convenience foods) (2) the USDA recommended diet (emphasis on fruits and vegetables, lean meat, dairy, and whole grains), and 3) vegan diet (excludes all animal and dairy products).
They found that Americans likely consume between one million to about 1.3 billion live microbes daily from foods and beverages. The highest numbers (3-fold higher) were in the USDA recommended meal plan, because it involved 2 meals with fermented foods (that had not been heat-treated or pasteurized, which kill many bacteria). Fresh produce also has high numbers of bacteria (e.g., an apple has 100 million bacteria!).
Fermented foods (e.g. kimchi, sauerkraut, yogurt, kefir, traditional pickles, kombucha, natto, tempeh, miso) are loaded with microbial species. Recent research shows that eating a serving or 2 of fermented foods daily is a quick way to improve health (by lowering inflammation) and increasing the diversity of bacterial species in the gut microbiome.
Ingesting higher numbers of microbes from foods is desirable - because having more species in the gut is considered a sign of health. Some of the microbes we ingest join our existing gut microbes, but others just pass through our gut and leave (the "transient microbiome"). Research finds that microbes can have beneficial effects even as they pass through.
Excerpts from the Lang, Eisen, Zivkovic study (2014) study, from Peer Journal: The microbes we eat: abundance and taxonomy of microbes consumed in a day's worth of meals for three diet types.
...Little is known about the effects of ingested microbial communities that are present in typical American diets, and even the basic questions of which microbes, how many of them, and how much they vary from diet to diet and meal to meal, have not been answered.
We characterized the microbiota of three different dietary patterns in order to estimate: the average total amount of daily microbes ingested via food and beverages, and their composition in three daily meal plans representing three different dietary patterns. The three dietary patterns analyzed were: (1) the Average American (AMERICAN): focused on convenience foods, (2) USDA recommended (USDA): emphasizing fruits and vegetables, lean meat, dairy, and whole grains, and (3) Vegan (VEGAN): excluding all animal products. Meals were prepared in a home kitchen or purchased at restaurants and blended, followed by microbial analysis including aerobic, anaerobic, yeast and mold plate counts as well as 16S rRNA PCR survey analysis.
Based on plate counts, the USDA meal plan had the highest total amount of microbes at 1.3 × 109 CFU per day, followed by the VEGAN meal plan and the AMERICAN meal plan at 6 × 106 and 1.4 × 106 CFU per day respectively. [NOTE: 1.3 × 109 equals 1,300,000,000 CFU or colony forming units, that is live microbes that can possibly multiply and form colonies].
In this study we estimated the total numbers and kinds of microorganisms consumed in a day by an average American adult. We analyzed meals representing three typical dietary patterns, including the Average American, USDA recommended, and Vegan diet, and found that Americans likely consume in the range of 106–109 CFUs microbes per day. The USDA meal plan included two meals with non-heat treated fermented foods, which were likely responsible for the 3-fold higher total microbes in this meal plan compared to the AMERICAN and VEGAN diets.