Propionic Acid: A Culprit in Obesity and Metabolic Dysfunction?

As promised on Tuesday, today is the last post in my continuing propionic acid series  as we wrap up not-celebrating the Biome Buzz’ official First Annual Propionic Acid week.  Today’s post is about just how suspect it is for all our health.

A study published this year by Harvard scientists in the journal, Science Translational Medicine, showed that the propionic acid (PPA) adversely affects metabolism by raising blood sugar levels.[i]

The scientists looked at both animal and humans, and the latter were involved in a double-blind trial with 14 healthy volunteers.  The researchers discovered that PPA stimulates the liver to produce more glucose by increasing levels of the hormones, glucagon and fatty acid-binding protein 4, which signal the liver to release sugar into the blood.  PPA seems to not directly cause this increase but instead, has an effect on the sympathetic nervous system which, in turn, signals to the body that a raise in blood sugar is needed.  Says one of the study’s authors, “…the most interesting thing we determined in these experiments is that a single dose of propionate can increase the hormones in the body that are designed to stimulate glucose production from the liver…There are times when that’s needed, like when you’re starving or have dangerously low blood sugar. But here, it was almost tricking the body into thinking that it needs to produce glucose when it doesn’t.”[ii]  The study in mice did demonstrate that chronic exposure to PPA thereby led to weight gain.

In the humans in the study, this continued release of unneeded blood sugar led  to insulin resistance:  their bodies no longer responded optimally to insulin, which lowers blood sugar levels.  Insulin resistance, over time, leads to metabolic disorders like obesity and type 2 diabetes.

While of course this research has the usual caveats  – it needs to be replicated in larger cohorts and so forth – it really does get you thinking.  PPA is a common food preservative found regularly in cheeses and baked goods (and artificial flavors).  It is also produced by various gut bacteria…and alterations to our bacterial microbiome are almost ubiquitous in the industrialized world. Over the past few decades, we have watched rates of not just autism rise (as I talked about in my last 2 posts – bearing in mind, PPA can cross both the blood-brain barrier and through the placenta), but also rates of obesity and type 2 diabetes.  Is PPA a major factor?

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[i] Tirosh, A, et. al.  The short-chain fatty acid propionate increases glucagon and FABP4 production, impairing insulin action in mice and humans.  Science Translational Medicine. 2019:11(489).  DOI: 10.1126/scitranslmed.aav0120

[ii] https://gizmodo.com/a-common-preservative-in-cheese-and-bread-could-negativ-1834278066