The short answer is no. Although nearly all plants contain antimicrobial compounds, these compounds are present only at low concentrations. Diet certainly influences microbiome composition. But this influence works through the availability of foods that different bacteria prefer. “Food antibiotics” are not a thing.
Sloppy health journalists are responsible for the confusion. They often call pathogens “tough” or “hardy” or “super”, especially if they are antibiotic resistant. But resistance to environmental stresses – which most certainly includes the many toxins [1] found in plant foods – has nothing to do with ability to cause disease.
If it did, we would all be dead of infections from Deinococcus radiodurans. This remarkable bug can withstand desiccation, starvation and radiation doses thousands of times greater than would kill a human. Instead it is completely harmless. It’s not impossible that this bug could survive a trip to Mars on the outside of a spaceship.
From Biogeekery
Plants defend themselves from predators, both macroscopic and microscopic, with chemicals. They are full of antibacterial compounds. Few of these are potent enough to have clinical value.
Even at high concentrations, these compounds do not selectively poison human pathogens over commensals (ie., friendly) bacteria. Plenty of friendly bacteria, such as the Lactobacilli found in your yogurt, are antibiotic-resistant. There is no necessary connection between antibiotic resistance and the ability to cause disease.
There are hundreds of studies reporting inhibition of bacterial growth by plant compounds, but nearly all of these look only at pathogens. One study [2] looked mostly at inhibition/killing of C. difficile strains by plant extracts, but included a number of commensals (3 Bacteroides and 2 Lactobacillus species) as comparators. Rather than copy and paste a big table with a bunch of numbers in it, I’ve summarized the results like this:
Numbers are minimal inhibitory concentration, in mg/ml. Lower numbers mean more potent. “NI” means no inhibition was observed at the highest dose.
There are three takeaways from this study:
- Commensals and pathogens look more alike than different.
- Most of these compounds had no measurable effect, even after concentrating them. The likelihood that they would have an effect in your gut is very small.
- Even the effects that were detected were very weak. Antibiotic MIC values are typically in units of micrograms/ml, that is, a thousand-fold more potent than the numbers in the table.
All the bacteria that live in your gut are fairly hardy. They have to deal not only with a variety of foodstuffs, but each other – bacteria secrete plenty of compounds which inhibit the growth of their competitors.
Your choice of food definitely affects the composition of your gut microbiome [3] [4] , but probably more by addition than subtraction. That is, bugs differ in their ability to extract energy from different foods – some excel at breaking down fiber, others at fats or sugars. Given their preferred food, bugs will flourish regardless of whatever else is thrown at them (except antibiotics).
As long as you feed your bugs with plenty of real food – mostly plants – it shouldn’t matter much how you spice it up.
Footnotes
[1] Naturally Occurring Food Toxins
[2] Antimicrobial activity of natural products against Clostridium difficile in vitro.
[3] The impact of human activities and lifestyles on the interlinked microbiota and health of humans and of ecosystems.
[4] The Western Diet-Microbiome-Host Interaction and Its Role in Metabolic Disease.