Every day, most of us eat foods that were made to last: breads, tortillas, yogurts, cheeses, lunch meats with preservatives, ingredients added to keep them safe, stable, and appealing.
But what if some of these preservatives are quietly influencing our metabolism in ways we never recognized?
That’s the question Rajesh K. Garg, MD, an endocrinologist and researcher at The Lundquist Institute and his colleagues, have been working to answer. His research focuses on propionic acid (PA), a widely used food additive found in many baked and processed foods. What he and collaborators have uncovered so far is raising critical new questions about how processed foods interact with our bodies.
Why Look at Propionic Acid?
Propionic acid and its salts have been used in packaged foods for decades. They’re considered safe, and their role is simple: help keep food fresh. But as processed food consumption has increased over recent generations, so has the prevalence of obesity, insulin resistance, and type 2 diabetes.
Dr. Garg’s team wondered: could even small, routine exposures to PA influence the hormones that govern our blood sugar?
Their earlier work in mice suggested the answer might be yes. Over time, animals that consumed PA levels similar to those in human diets gained more weight, accumulated more fat, and developed insulin resistance. That work set the stage for carefully controlled studies to understand whether the same thing happens in humans.
A Pivotal Study of PA in Humans
In a major clinical study published in BMJ Open Diabetes Research & Care in 2021, Dr. Garg and colleagues, including Amir Tirosh, MD, PhD, investigated the effects of a single dose of propionic acid in healthy adults. The study compared PA to a placebo under different metabolic conditions. They found that PA increased glucagon, a hormone that raises blood sugar, and activated the sympathetic nervous system, elevating levels of norepinephrine and epinephrine, signals typically associated with “fight or flight” responses.
While these changes weren’t enormous, they were consistent, and, notably, they occurred at doses similar to those people might easily consume in an ordinary processed meal. Dr. Garg’s takeaway? That propionic acid behaves in humans the same way it does in mice, activating biological pathways that induce higher blood sugar and may contribute to insulin resistance over time.
Over the years, Dr. Garg and his collaborators have continued to refine their understanding of how PA activates hormones like glucagon, norepinephrine, and FABP4, which together can raise blood glucose and alter the body’s insulin response. Their long-term studies continue to show that chronic exposure, even at low levels, can contribute to weight gain and worsening glucose control. For example, in a recent study conducted at the Lundquist Institute, they found a strong correlation between routine daily dietary PA intake and insulin resistance in Hispanic men with obesity.
With these findings in hand, the next step is clear to Dr. Garg. He firmly believes that we need more definitive human studies to establish the impact of chronic PA intake and to see whether the harmful effects of PA can be reversed by removing it from diet.
Keeping the Good in Processed Foods, Removing the Harm
It’s important to say what this research is not. It’s not an argument to eliminate processed foods or preservatives altogether.
In fact, Dr. Garg emphasizes that processed foods play a critical role in modern nutrition. They make safe, stable, affordable food accessible, especially in communities where fresh foods are out of reach. Removing processed foods without alternatives could worsen, not solve, food insecurity.
Dr. Garg also believes we can do better. His vision is simple yet transformative:
- Preserve the convenience and accessibility of processed foods
- Identify which additives may be causing metabolic harm
- Improve food processing, so we keep the benefits while reducing the risks
Investing in the Next Chapter: Building a Healthier Future for Processed Foods
The science so far offers an exciting and essential opportunity to determine whether reducing dietary propionic acid can genuinely improve insulin sensitivity and metabolic health in people who consume it daily. Answering that question requires complex, resource-intensive research, including controlled meal plans, repeated hormone and glucose measurements, microbiome and metabolomics analyses, and months of carefully supervised dietary intervention with enough participants to reveal meaningful effects.
This kind of work is both expensive and logistically demanding. It cannot advance without additional funding and support, but the potential payoff is enormous. If larger, longer-term studies confirm the early findings, the results could guide food manufacturers toward safer preservatives, inspire innovations in food processing, shape public health guidelines, and ultimately help millions of people reduce diabetes risk.
Dr. Garg’s vision is rooted in a simple truth: nutrition science must evolve alongside food technology, and that evolution requires bold investment from public and philanthropic leaders. As processed foods remain central to how much of the world eats, now is the time to ensure they support long-term health rather than undermine it. Strategic funding is needed to propel Dr. Garg’s research to fully understand preservatives like propionic acid and guide the innovation necessary to reimagine processed foods for the well-being of communities everywhere.